copyright Jon Wood For ordering information contact: Fishingbooksender, Caerbannog, Sarn, Powys SY16 4EX www.fishingbooksender.com or www.carpfishingscience.com Telephone 05601 972040 ISBN 978-0-9567297-1-2 The right of Jon Wood to be identified as the Author of the Work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in any retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photocopying, recording or otherwise without prior permission of the publishers and copyright holders. No re-binding or alterations to this book without written permission from the publishers and copyright holders.

Contents

Page Introduction 1 1. Water 4 What is Water? 4 The Soup 5 The Water Basin 8 The Main Characteristics of Water 9 a) pH 9 b) Dissolved solids 11 c) Hardness and alkalinity 14 d) Dissolved gases 17 e) Metals 20 f) Suspended solids 22 g) Phosphorus 25 h) Ammonia, nitrite and nitrate 27 i) Temperature 29 2. Lake Formation and Characteristics 33 Background 33 General lake information 33 Formation types 34 a) Natural processes leading to lake formation 34 b) Artificially formed lakes 37 Changing lakes 38 Light and heat 38 Stratification 39 Oxygen 40 Nutrients 40 Sedimentation 41 3. Sediments 42 Background 42 Sediment types 42 a) Silt 42 b) Clay 43 c) Gravel 43 Deposition 43

Sediment profile and benthic health 44 4. Natural Food and Food Categories 46 a) Concepts 46 b) General diet 47 c) Herbivory 48 d) Waterborne food 51 e) Animals 53 f) Other foods arriving in the aquatic environment 65 g) Abundance and diversity in the aquatic environment 65 h) Constituents and chemical composition of major food items 67 Food categories 77 a) Proteins 77 i) Classification 77 ii) Structure 77 iii) Properties 78 iv) Chemical determination 78 v) Gross protein requirements 78 vi) Amino acids 79 vii) Essential and non-essential amino acids 79 viii) Essential amino acids and protein quality 80 ix) Quantitative requirements of amino acid 80 x) Supplementing the diet with amino acids 81 b) Carbohydrates 81 i) Classification and chemistry 82 ii) Carbohydrate metabolism in fish 83 iii) Digestion, absorption and storage of carbohydrate 83 iv) Other factors affecting metabolism 84 v) Energy transformation 84 c) Lipids 85 i) Factors affecting the fatty acid composition of fish 86 ii) Body lipid composition and dietary lipid requirements 87 iii) Essential fatty acid requirements of carp 88 d) Vitamins 88 i) Water-soluble vitamins 88 ii) Fat-soluble vitamins 90 iii) Vitamin requirements of carp 90 e) Minerals 91 i) Calcium and phosphorus 92 ii) Magnesium 93 iii) Other essential inorganic elements 93

f) Energy 94 i) Energy flow in animals 95 ii) Energy loss 95 iii) Energy sources 96 a) Fats 96 b) Carbohydrates 97 c) Proteins 97 iv) Energy requirements of fish 97 a) Energy distribution in relation to feeding level 98 b) Maintenance energy 98 c) Energy cost of growth and factors that alter energy needs 98 g) Specific studies regarding natural food and food groups in carp 99 5. Climate, Water Movement and Aquatic Dispersion 101 Introduction 101 Horizontal water movement 101 Vertical water movement 103 The effect of climate and water movement on environmental conditions and carp behaviour 104 Principles of diffusion and dispersion in water 106 Oil and water-based dispersion 107 Optimizing attraction 108 6. The Carp 109 Background 109 a) Origins 109 b) Classification 110 c) Diversity, earliest carp and distribution 111 d) Habitat and general behavior 111 e) Physical appearance 111 f) Physical changes due to domestication and culture 112 g) Reproduction 114 h) Lifespan 115 i) General food and feeding habits 116 j) Predation 117

Responses to environmental changes 117 a) Temperature 117 b) Oxygen 119 c) pH 121 d) Salinity 122 e) Habitat use 123 Swimming and Maneuvering 124 Breathing 125

Osmoregulation 126 Senses 127 a) Sight 128 i) Theory of vision and sight in fishes 128 ii) Studies and information specific to carp vision 132 b) Hearing 135 i) Theory of sound in water 135 ii) Theory of hearing in fishes 136 iii) Studies and information specific to carp hearing 137 c) Smell 139 d) Taste 140 Food Location and Identification 143 Feeding 145 a) Why carp feed 145 b) The feeding mechanism 145 i) The development of the feeding mechanism in fish 145 ii) Fish-food interactions 147 iii) Functional morphology of feeding in teleosts 148 iv) Feeding structures 151 v) Food processing 152 vi) Food intake 154 vii) Feeding abilities and diet of the carp 160 viii) Conclusions 164 c) Digestion 165 i) The digestive process 165 ii) Protein digestion 166 iii) Carbohydrate digestion 166 iv) Fat digestion 166 v) Specific information relative to carp digestion 167 Growth 169 i) Specific information regarding growth in carp 171 7. Bait 177 Development of carp baits 177 Principal bait types 179 a) Standard baits 180 i) Bread 180 ii) Worms 180 iii) Corn 181 iv) Tiger nuts 182

v) Hempseed 183 vi) Luncheon meat 186 vii) Molluscs 186 viii) Insect larvae 187 ix) Summary and comparison of nutrient contents of standard baits 188 b) Elaborated baits 193 i) Boilies 193 Basics 193 Boilie theory 194 Boilie improvements 196 Factors affecting boilie effectiveness 197 ii) Pellets 198 iii) Artificial baits 200 Palatability 201 Additives and attractants 204 i) L-Amino acids 204 ii) Minamino 205 iii) Betaine 206 iv) Inosine 208 v) Corn steep liquor 208 vi) Butyric acid 209 vii) Robin Red 209 Bait density 210 Specific information and studies related to carp baits and preferences 211 i) Orientation of carp to free amino acids 211 ii) Composition and nutrient digestibility of commercial baits 211 Bait conclusions 215 8. Diseases and Carp Care 216 The stress response 216 Infection and transmission 219 a) Natural protection 219 b) Disease symptoms 220 Principal carp diseases 221 a) Spring viraemia of carp (SVC) 222 b) Fish pox 223 c) Koi herpes-virus (KHV) 224 d) Columnaris disease 225 e) Carp erythrodermatitis (CE) 226 f) Fungal diseases 226 g) Parasites 227

Carp care 228 a) Rigs 229 b) Landing 229 c) Unhooking and weighing 230 d) Mouth and body treatment 230 e) Handling 231 f) Other carp care tips 231 9. Conclusions 232 a) The Carp 232 b) The Carps Environment 235 c) Carp Location 236 d) Food and Bait 238 Bibliography 242

6. The Carp

When youre fishing for one individual fish, you have to have tunnel vision. You have to have it in your thoughts 24/7

Ritchie McDonald in Advanced Carp Fishing.

Background a) Origins The carp Cyprinus carpio is a fish native to Europe which has been introduced to every part of the world with the exception of northern Asia and the poles. The original common carp was that found in the inland delta of the Danube river about 2000 years ago, and was torpedo-shaped and golden-yellow in colour. It had two pairs of barbels and a mesh-like scale pattern (Balon, 2004). Although this fish was initially kept as an exploited captive, it was later maintained in large, specially built ponds by the Romans in south-central Europe (verified by the discovery of common carp remains in excavated settlements in the Danube delta area). As aquaculture became a profitable branch of agriculture, efforts were made to farm the animals, and the culture systems soon included spawning and growing ponds.

Figure 6.1 A wild common carp (a) and its feral form (b) from the Danube delta in 1900 (from Antipa, 1909).

Unintentional artificial selection took place, and between the twelfth and fourteenth centuries, the streamlined, fully scaled carp had transformed into a deeper-bodied, partially scaled or scaleless domesticated version. The appearance of coloured versions (aberrations) became the koi of Japan, but the common carp was not, as is often thought, originally domesticated in China. Cyprinus carpio was therefore the oldest domesticated fish, and for that reason, we have had a long relationship with the animal. Although initially the carp was a food item, in later times, and as more fish species have become readily available for the table, the importance of carp culture in Western Europe has become less important because of declining demand, partly due to the appearance of more desirable table fish such as trout and salmon through intensive farming (see the figure below), and environmental constraints. However, fish production in ponds is still a major form of aquaculture in Central/Eastern Europe, including the Russian Federation where most of the production comes from low intensity or semi-intensive ponds. In Asia, the farming of carp continues to surpass the total amount of farmed fish volume of intensively sea-farmed species such as salmon and tuna.

Figure 6.2 Inland aquaculture production of rainbow trout and common carp by volume in Europe (source FAO, in Vradi, 2001)).

b) Classification Within the animal kingdom (Animalia) and the phylum Chordata, Cyprinus carpio is in the sub-phylum Vertebrata (vertebrate), class Actinopterygii and order Cypriniformes. The cypriniformes (family cyprinidae) is traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain common features such as being found predominantly in fresh water and the fact that they possess Weberian ossicles, an anatomical structure originally made up of small pieces of bone formed from four or five of the first vertebrae; the most anterior bony pair is in contact with the extension of the labyrinth and the posterior with the swimbladder. The function is poorly understood but it is presumed that this structure takes part in the transmission of vibrations from the swimbladder to the labyrinth and in the perception of sound, which explains why the Ostariophysi have such a great capacity for hearing.

Most cypriniformes have scales and teeth on the inferior pharyngeal bones which may be modified in relation to the diet. Tribolodon is the only cyprinid genus which tolerates salt water, although there are several species which move into brackish water but which return to fresh water to spawn. All of the other cypriniformes live in continental waters and have a wide geographical range (Billard, 1995). c) Diversity, Earliest Carp and Distribution The diversity of cyprinid species is at its greatest in China and South-East Asia, but is lower in Africa and North America, where there are nevertheless 36 genera and 280 species (118 belonging to a single genus Nototropsis). Fossilized cyprinids go back to the Plaeocene era in Europe, the Eocene era in Asia and the Oligocene era in North America. The cyprinids are dispersed to the east of the Wallace line, reaching Borneo, but have not crossed the Strait of Makassar, between Borneo and Indonesia. The carp originating from Western Asia is no longer represented in the wild form other than by the sub-species Cyprinus carpio haematopterus in Eastern Asia and Cyprinus carpio carpio in Eastern Europe (Billard, 1995). d) Habitat and General Behaviour Carp exploit large and small manmade and natural reservoirs, and pools in slow or fast moving streams. They prefer larger, slower-moving bodies of water with soft sediments but they are tolerant and hardy fish that thrive in a wide variety of aquatic habitats (Page & Burr, 1991; Froese & Pauly, 2002). The attributes of carp include high environmental tolerances such as with regards to temperature (2 to 40.6C), salinity up to about 14 parts per thousand, pH from 5 to 10.5, and oxygen levels as low as 7% saturation. These, as well as being omnivorous, with a high reproductive capacity, are reasons why the fish is widely distributed and found in most types of freshwater habitat. Carp can typically be found in small schools, although larger carp often lead a solitary existence (Smith, 1991). e) Physical Appearance Carp often grow 30 to 60 cm in length and weigh 0.5 to 4 kg (Tomelleri & Eberle 1990); it is not uncommon for common carp to reach 15 to 20 kg (McCrimmon 1968). Males are usually distinguished from females by the larger ventral fin. Carp are characterized by their deep body and

serrated dorsal spine (Nelson, 1984). The mouth is terminal on the adult and subterminal on the young (Page & Burr, 1991). Color and proportions are extremely variable, but scales are always large and thick. Three sub-species with slightly different scale patterns are recognized. C. carpio communis (scale carp) has regular concentric scales, C. carpio specularis (mirror carp) has large scales running along the side of the body in several rows with the rest of the body naked, and C. carpio coiaceus (leather carp) with few or no scales on the back and a thick skin (McCrimmon, 1968). Carp usually possess 48-50 pairs of chromosomes, but some species such as the common carp and the crucian carp have sometimes more. Hybridization occurs frequently in cyprinids, resulting partly from environmental changes, in particular changes in spawning habitat: these changes can be natural or due to human activities.

Two key physical features of carp are that they possess bilateral symmetry (having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends) and the lack of sexual dimorphism (the two sexes look alike).

f) Physical changes due to domestication and culture

Mainly as a result of the addition of supplementary food to the carps environment, initially in ponds and later in tanks, the species has undergone a number of morphological changes which now result in a wide range of carp types available to the angler (see Hughes & Crow, 1997).

When the wild carp was introduced into pond systems, it naturally started to change its torpedo-shaped body into a deep, laterally compressed and hunchbacked body. Soon individuals appeared that did not have a regular, geometrical arrangement of scales, but showed severe irregularities, scale-reductions or even complete scalelessness. These variations soon became a foundation for artificial selection. Ultimately, domesticated common carp are represented by a variety of forms, such as the fully scaled carp, linear, mirror carp and leather (or naked) carps (Brylnska, 1986; Gorda et al., 1995; Pokorn et al., 1995).

The domesticated carp, which is of major importance in modern stocked fisheries, not only changed its external shape, scalation and colour, but also underwent internal and physiological changes (Balon, 1974, 1995a,b; Baru et al. 2002). Briefly, the mouth gape, the first character that Rudzisky (1961) and Steffens (1964) used for clear distinction between wild and domesticated common carp, was much smaller in the wild than in the domesticated varieties. Even more pronounced differences are encountered among the mouth-gape indices calculated by dividing ten times the mouth gape in cm2 by the length of head in cm: 4.46 to 5.57 for the wild common carp and 8.12 for domesticated fish (Steffens, 1964). Both Rudzisky (1961) and Steffens (1964) considered the enlargement of the mouth in domesticates to be caused by diet change, and possibly the result of artificial selection. Domesticated common carp selected to utilize

supplementary food, grew better in ponds when man-made food was added (Sibbling, 1988). Studies on the wild common carp in ponds (Rudzisky, 1961; Leszczysky & Biniakowski, 1967) proved that wild common carp progeny was better suited for stocking natural riverine habitats than were domesticated varieties.

Rudzisky (1961) found and Steffens (1964) confirmed that the intestine of the wild common carp was 15 to 25% shorter than that of the domesticated carp. The index calculated by dividing the length of the intestine by standard length (Ls) in cm was 2.11 for wild common carp and 2.64 for the domesticated fish. Longer intestines in domesticated fish are probably due to utilization of vegetable food not normally consumed by wild common carp. Both authors also found, when comparing the deeper body of domesticated common carp with the cylindrical one of wild common carp, that the calculated muscle mass was the same in both, although it appears to be greater in the domesticated fish. This means that the dressed mass of the domesticated fish is not larger in spite of the different body proportions. Also, the wild common carp has both chambers of the swimbladder of similar size, whereas the domesticated fish has the anterior chamber always much larger and the posterior chamber much smaller. This proportion (%) as given by Steffens (1980) is 61:39 for the wild and 90:10 for the domesticated. This may be related to the relative greater mass of the head in a domesticated carp.

Figure 6.3 The author with a stocked mirror showing the relatively larger head and body form and scale pattern which are far removed from the original wild carp stereotype.

The greater strength of the wild common carp is supported by some of its physiological attributes (Steffens, 1964). Wild common carp have 18 to 19% more erythrocytes (red blood cells) and haemoglobin (the oxygen-carrying component of the cells) than domesticated fish, and the blood

sugar level is 16 to 26% higher in the former. Also, wild common carp have a much lower water content in muscles and liver than domesticated fish, greater fat content in individual organs, more glycogen (the polysaccharide of glucose which forms the primary short-term energy source in animals) in the liver, and more vitamin A (a vitamin with importance in vision and bone growth) in the eyes, intestine and liver. In addition the muscles of the wild common carp are better vascularized (contain more blood vessels) and do not fatigue as quickly as do those of domesticated common carp (Balon, 2004). The persistence of these traits in some carp varieties may be the reason why they present the angler with better fights than others.

g) Reproduction Carp generally spawn in the spring and early summer depending upon the climate. They segregate into groups in the shallows to spawn. Carp prefer shallow waters with dense macrophyte cover. Males externally fertilize eggs, which the females scatter over macrophytes in a very active manner and the eggs stick to the substrate upon which they are scattered. A typical female (about 45 cm) may produce 300,000 eggs, with some estimates as high as one million over the breeding season. Incubation is related to water temperature and has been documented as being three days at temperatures of 25 to 32C. Fry average 5 to 5.5 mm in total length. Temperature, stocking density, and availability of food influence individual growth and by the time the fish reach 8mm, the yolk has disappeared and they begin to actively feed ( HFroese & Pauly, 2002H; HMcCrimmon, 1968H).

Carp usually reach sexual maturity when the testes (in males) and ovaries (in females) develop. Sexual maturity can occur at a very early age in carp where waters are constantly warm, but more often, it is reached when i) a male is around 2 years old, ii) a female is around 3 years old, iii) they exceed 30 cm in length and iv) weigh around 400 grams. (Swee & McCrimmon, 1966). Females facilitate attachment of fertilized eggs to the substrate. There is no further parental care, the hatching of the eggs is rapid and the newly hatched carp grow very quickly.

Because ovaries are much larger organs than the testes, females are generally easier to spot, as the stomachs of mature females are mostly plump, while males remain a sleeker 'torpedo' shape. When males are ready for spawning, they develop breeding nodules on the head and pectoral fins, principally along the bones of the fin rays. These breeding nodules appear as fine whitish raised spots. The nodules appear in abundance on the pectoral fins in regular rows and are rough to the touch. During breeding, the male nudges the female with his head and fins to encourage spawning (Swee & McCrimmon 1966).

0Bh) Lifespan

There are reports of carp living more than forty years (see table below). Other cyprinid species are included for reference, with the (+) symbol signifying that the fish was still alive when the age was assessed:

Table 6.1 Summary of cyprinid longevities according to the Max Planck Institute for Demographic Research

Scientific Name Common Name Wild Captive Reference

Abramis brama Bream 17.0 HAltman & Dittmer (1962), Flower (1935) H

Abramis brama Bream 10.0 HAltman & Dittmer (1962), Seemann (1961) H

Abramis brama Bream 23.0 Beverton & Holt (1959)

Carassius auratus Goldfish 30.0 Carlander (1969), Flower (1925), Moyle (1976)

Carassius auratus Goldfish 41.0 Bobick & Peffer (1993)

Cyprinus carassius auratus Goldfish 10.0 Flower (1925)

Leuciscus cephalus Chub 11.0 HAltman & Dittmer (1962), Flower (1935) H

Leuciscus orfus Golden orfe (+) 14.25 Flower (1925)

Rutilus rutilus Roach 12.0 HAltman & Dittmer (1962), Flower (1935) H

Scardinius erythrophthalmus Rudd 10.0 HAltman & Dittmer (1962) Flower (1925) H

Cyprinius carpio Carp 38.0 Hinton (1962)

Cyprinus carpio Common carp 47.0 Flower (1935)

Cyprinus carpio Common carp 20.0 McCrimmon (1968)

Cyprinus carpio Carp 6.0 Flower (1925)

Cyprinus carpio Common carp 38.0 Hinton (1962)

Cyprinus carpio var. Prussian carp 6.4 Flower (1925)

The two main methods for ageing fish are the counting of the rings on the scales or on the otoliths (ear bone). Otoliths are part of fishs inner ear or vestibular apparatus, and reside in the cranial cavity. They are composed of calcium carbonate and protein. They function as sound receptors and are also used for balance and orientation.

1BThere are 3 pairs of otoliths or ear stones in the inner ear of a carp. The largest pair of otoliths, the sagittae, is routinely used for aging, since the rings (annuli) can be counted in the same way as those on a cut tree trunk. So too can those of fish scales, which adopt a similar pattern. a) b)

Figures 6.4 a,b Methods of ageing; a) otolith and b) scale reading of annuli

2BThe reading of otoliths is preferred to scale reading when the fish species does not possess scales (as is the case with a leather carp) or when the scales are particularly small, for example in the case of some flatfish such as plaice.

3Bi) General Food and Feeding Habits

Carp are primarily selective benthic omnivores that specialize on invertebrates that live in the sediments (Lammens & Hoogenboezem, 1991). Newly hatched carp initially feed on zooplankton; specifically rotifers, copepods, and algae (McCrimmon, 1968). Young carp feed on a variety of macroinvertebrates including chironomids, caddis flies, molluscs, ostracods, and crustaceans (McCrimmon, 1968). Adult carp are known to eat a wide variety of organisms including, insects, crustaceans, annelids, molluscs, fish eggs, fish remains, and plant tubers and seeds (McCrimmon 1968, Lammens & Hoogenboezem, 1991). Carp feed by sucking up mud from the bottom, ejecting it, and then selectively consuming items while they are suspended (McCrimmon, 1968). The feeding areas of carp are easily recognized in shallow water as depressions in the sediment (Cahn, 1929).

4Bj) Predation

Predators on carp include large fish such as pike, birds such as herons and mammals such as otters (Britton & Shepherd, 2005). The colouration of the fish helps to camouflage it against their surroundings so it can stalk its prey or hide from predators.

Responses to environmental changes The main environmental changes to which carp can be exposed are changes in temperature and the concentration of dissolved gases which were described in chapters 1 and 5. The effects of decomposition and the addition of quantities of rain water into a lake or river, may also cause changes in pH, which has a direct effect on the species. a) Temperature Temperature is the most important environmental factor affecting the activity of poikilothermic (creatures whose internal temperatures vary, often matching the ambient temperature of their immediate environment) animals such as fish. Membranes are the first targets affected by change of temperature and their lipid (fat) components respond immediately to this challenge. Expectedly, a decrease in temperature results in a decrease in motional freedom of constituent phospholipids and vice-versa, with resulting alteration in membrane fluidity. In order to maintain structural and functional integrity of these structures, poikilotherms must counteract this affect of temperature and maintain proper fluidity in the new thermal environment. It can be hypothesized that organisms unable to adjust membrane physicochemical properties to temperature are not able to survive in a changing thermal environment. Fish use several methods in order to adapt to temperature change by adjusting the composition of membranes, and studies have shown that fish accumulate phospholipid molecules in a cold environment in order to adapt to periods of low temperature (Farkas et al., 2001). The metabolic rate of all ectothermic (creatures that control body temperature through external means, such as the sun, or flowing air/water) organisms is strongly dependent on temperature, as well as body size. This relationship tends, however, to be clearer in aquatic organisms, where the large thermal mass of water buffers the rate of change of environmental temperature experienced by organisms (Clarke & Johnston, 1999). The oxygen consumption rate of fish is directly proportional to the temperature of the water, since a fishs biological processes occur faster in warmer water. This means that the fish breathes faster, it digests food faster and therefore requires more food than it would if in water of a lower temperature.

The resting oxygen consumption of teleost (bony) fish has been found to vary significantly with temperature. The estimate of the factorial increase in resting metabolism comparing a representative tropical (30C) and polar (0C) teleost ranged from 5.9 to 6.2, which indicates that a typical tropical fish consumes roughly six times as much oxygen as does a typical polar fish and therefore must find six times as much food per unit time simply to fuel resting metabolism. One of the most contentious aspects of the evolution of teleost fish to cold temperatures, has been that of metabolic cold adaptation which was theorized by a Danish physiologist Krogh. He predicted that fish which have evolved to live at very cold temperatures should have developed or evolved some kind of compensation for the metabolic-rate depressing effect of temperature. His first experiment into metabolic cold adaptation involved a single goldfish (Carassius auratus), a species closely related to the carp, and which was exposed to a series of temperatures and its oxygen consumption rate measured (Ege & Krogh 1914). The experiment produced a roughly exponential decrease in respiration rate as the temperature was lowered, and this relationship became known as Kroghs normal curve. Initial experiments seemed to confirm the theory, but since then, a number of other trials have not been able to confirm whether metabolic cold adaptation exists. As far as differences in resting metabolic rates between different fishes, there are significant variations within the major groups. However, resting metabolism has been shown to correlate strongly with the activity of the species, with resting metabolic rate increasing from less active to more active species (Morris & North, 1984). Relatively speaking, carp are not particularly active species, and were shown to have lower metabolic rates and lower resting oxygen consumption compared with Salmoniformes (salmon and trout), Perciformes (perch) and Gadiformes (cod-like fish) (Clarke & Johnston, 1999). Food intake regulation in fish is a complex interplay between endogenous and environmental factors (Peter, 1979; Fletcher, 1984), with water temperature being viewed as one of the main environmental factors influencing feeding and growth (Brett, 1979; Elliot, 1982). For example, Rozin & Mayer (1961) demonstrated that feeding by goldfish is temperature dependent, with a 10C decrease in water temperature (from 25C to 15C) inducing a reduction in food intake. Most natural water temperature changes are not abrupt, and carp are able to adapt to a wide range of temperatures. However, the information available would suggest that temperature has an important effect on both carp biological activity and behaviour, both of which should concern the carp angler.

b) Oxygen We have already seen that there is an important relationship between temperature and dissolved oxygen concentration, and for that reason this section is somewhat of a continuation of the previous one. Dissolved oxygen is an important concern for fishery owners particularly in summer, where high temperature results in low oxygen concentrations, since the warmer water has a lower maximum saturation level than cooler water. Also, in ice-covered lakes in winter, where the water has no contact with the atmosphere because of the ice, and when the ice is covered by snow which doesnt permit photosynthesis of aquatic plants beneath it, the oxygen can be gradually consumed by the respiring fish and other animals, and as a result fall to very low levels. It is known that carp react to low levels of dissolved oxygen by increasing their activity in search of better oxygenated water (Schperclaus, 1990). In some lakes, this water is often found where the tributary or inflow enters the lake, and on frozen ponds or lakes, it is often in this area to which the carp move when oxygen levels become particularly low. In Winter, the opposite of the formation of the thermocline in Summer occurs, and it is frequently the case that the warmest water is found in the deepest areas, and shallow water may be warmest close to the lake bed. When carp congregate in Winter, in an area which displays more attractive environmental conditions, be that temperature, oxygen, or a mixture of both, then the movement of the bulk of fish causes a mixing of the lower layers with those cooler layers closer to the ice. As a result, the temperature of the higher layers increases and the ice in that area begins to melt. Radio telemetry (tracking) has been used to monitor carp movement in winter as a method of ascertaining the reaction of the carp to various stress factors, leading to a better understanding of carp behaviour (Bauer & Schlott, 2006). Work has shown that in the absence of oxygenation, carp prefer the areas closer to the inflow, due to the higher oxygen concentration to be found there. Also, carp have been shown to move towards and remain in more oxygenated areas, despite the presence in some cases of lower temperatures to be found there, for example when the oxygenation of the water has caused a mixing of warmer lower layers with those closer to the ice, resulting in a decrease in water temperature. This study was repeated the following year and the same results were found, with carp initially preferring the deeper parts of the lake in December and then moving towards the shallow part of the lake near the inflow at the end of January. The fish returned to the deeper parts of the lake in February. The carp involved in the experiment were weighed before and after overwintering, and were found to lose weight during those months (as high as 10% of body weight). In some commercial fisheries and aquaculture production units, in order to avoid problems which may result from unfavourable environmental parameters, an effort is made to ensure that carp face optimal conditions. For example, hypoxia (lack of oxygen) resulting from low dissolved oxygen, as well as low water temperature or fluctuations of ambient temperature cause a whole-body stress response (Vianen et al. 2001; Van den Burg et al. 2005). Metabolic pathways are affected as well

as the immune system and significant hormonal changes have been observed in C. carpio (Le Morvan-Roger et al. 1995; Van Raaij et al. 1996; Zhou et al. 2000). Moreover, complex interactions of environmental parameters may occur. For example, responses to hypoxia exhibit a temperature-dependant component in carp (Stecyk & Farrell, 2002). However, environmental conditions in lakes are not easy to control if at all and especially for the overwintering of carp, it is dissolved oxygen which is the most crucial parameter. Ice and snow covering the pond prevent contact with air and photosynthesis, while degradation of organic matter continues and results in decreasing dissolved oxygen. In winters with long periods of ice cover and/or ponds with a high loading of phosphorus and high degradation, dissolved oxygen may drop to a level dangerous for carp. Even though carp may withstand dissolved oxygen as low as 0.6-0.7 mg/L in winter (Haas & Menzel, 2003), they clearly try to avoid such situations, by enhanced activity as it is known from other species of fish. In summer, if dissolved oxygen drops to 3.0 3.5 mg/L, the carp stop feeding and search for better oxygenated water (Schperclaus, 1990). As one would expect, this is the same in winter. In fact, prior to the oxygen crisis event in the experiment by Bauer & Schlott (2006), the carp mostly roamed the deeper parts of the pond and avoided the shallow areas near the shore. This is consistent for findings of carp overwintering undisturbed and under good environmental conditions (Bauer & Schlott, 2004). The depletion of oxygen increased activity and carp moved to the shallow areas near the tributary. This clearly demonstrated the intensive search of the carp for better oxygenated water. As the oxygen supply improved, carp returned to the deeper parts of the pond. In fact, dissolved oxygen was highly correlated (P4C) cyprinids can still feed satisfactorily (Huet, 1986). Ziemiankowski & Cristea (1961) found that foraging is limited in winter but not completely suspended. This corresponds with the findings during the same radio tracking study that intestines of carp caught in November (4.5C) and December (4.4C) contained food. By contrast, the empty intestines of carp which had aggregated near the inflow in January (at the height of an oxygen crisis) may be interpreted as, along with low temperature of 2.1C, a result of stress caused by low dissolved oxygen leading to a cessation of feeding (Schperclaus, 1990). The investigation of the potential influence of low dissolved oxygen and temperature on the activity of overwintering carp using radio telemetry has not only given an insight into behaviour of stressed

fish in ponds and lakes, but has demonstrated the suitability of this technique for the evaluation of stressors on the activity and behaviour of carp in their environment. Beside this, other telemetry techniques have been used to evaluate the impact of stressors on common carp. Long baseline acoustic telemetry has been used by Shin et al. (2003) to evaluate the effect of dynamite explosions on the behaviour of common carp. c) pH pH in the environment is a much less variable environmental parameter than dissolved oxygen and temperature. Heavy rain can affect the pH of a shallow lake, and in some cases, nearness to the inflow of a lake experiencing relatively large input of rainwater or water at least of a different pH, could theoretically result in a pH gradient in a lake. However, studies on the avoidance of particular areas of water due to the presence of a pH difference are few and far between, but the existing information would suggest that carp may show preferences with respect to pH as they do with the other water parameters described. i) Low pH The physiological effects of acid water on fish have been studied (McDonald, 1983; Howells, 1984; Wood, 1989). From these studies, it is clear that the key toxic mechanism of acid stress is disturbance of electrolyte balance at the gills, and not internal acidosis (acidification of the blood). Ultsch et al. (1980) found, in carp, that two instant step changes in water pH (from 7.4 to 5.1 and from 5.1 to 4.0) resulted in declining plasma sodium and chloride concentrations and a progressive reduction of arterial pH. A further decrease of the pH to 3.5 finally led to the death of the animals within 24 hours. Other studies with various fish species have produced similar results (McDonald, 1983; Howells, 1984; Wood, 1989). In a study by Van Dijk et al. (1993), carp were exposed to sublethal levels of water acidity, and gradual acidification to pH 4.0 led to only minor transient changes in the measured blood parameters and did not cause any mortality in the 2-day experimental period. Thus, carp are able to survive water of pH 4.0 for 48 hours, without major physiological disturbances. In addition, in the first month after their return to the holding tanks, there was no mortality among the experimental fish. Blood pH was shown to fall during periods of hypoxia and recover once the oxygen levels were returned to normal in the study by Boeck et al. (2000b) into the effect of salt stress on the resistance of common carp to low oxygen levels.

ii) High pH Natural alkaline waters are not as common as acidic ones. In the carps environment, however, temporary high levels of pH can occur during hot summers as an effect of algal blooms, although the effects have been studied in carp ponds, where pH has reached 10.0 or even more (Alabaster & Lloyd, 1980). The effect of high pH has been studied on carp larvae, using different pH levels between 7.8 and 10.3 (Korwin-Kossakowski, 1992) where growth was shown to be retarded in alkaline water, and the results showed significant differences in growth rate for both length and weight and also reduced survival of larvae at the highest pH. These effects were attributed to pathological alterations of both anatomy and physiology, and also affected feeding behaviour due to the water conditions, since anorexia had previously been observed in alkaline waters by Witschi & Ziebell (1979). Another possible reason for the slower growth is reduction of respiration, and Jezierska (1988) reported that oxygen consumption of carp fry at pH 9.5 was 1.8 mg/O2 per hour compared with 0.7 mg/O2 at a pH of 10.3 (Korwin-Kossakowski, 1992). Respiration is reduced mainly by mucus coagulation in the gills, which is a consequence of high pH levels (Daye & Garside, 1976, 1980; Jezierska, 1988). Jezierska (1988) also found that a pH level of 10.0 was lethal to carp. d) Salinity Carp are found in tidal areas of several European rivers including the coastal areas of the Northern Caspian Sea, where large-scale attempts for extensive management of mirror carp in the brackish waters of the Baltic coast have been made successfully (Kuliyez & Agayarova, 1984; Schildhauer et al. 1992). Martemanov (1996) reported that carp can survive sodium levels of 176 mM (10.3 parts per thousand) for months and diluted seawater (0.3 to 3.0 parts per thousand) has been reported to enhance the survival, growth and development of carp larvae (Lam & Sharma, 1985). However, exposure of carp larvae to higher levels of diluted seawater (10 to 15 parts per thousand) showed unfavourable effects with lower growth rates and increased mortality (Abo Hegab & Hanke, 1982, 1984; Schildhauer, 1983). Despite the fact that freshwater fish can occur in brackish water, studies examining the physiological responses to increased salinity are performed mostly on anadromous fish, while comparatively few studies have focused on stenohaline freshwater fish such as the carp (Balment et al. 1987). A study previous to that of De Boeck et al. (2000b) by the same authors (De Boeck et al., 2000a) investigated whether the observed failures in dealing with higher salinities were due to an increased energy demand which exceeded the available energy sources and internal energy stores. Although some effects could be explained partly by the reduced food intake of the salt exposed fish, a clear additional effect was caused by the salinity itself, because extra energy was

required to survive under these conditions. The study by De Boeck et al. (2000b) assessed if these metabolic changes affect the resistance of common carp towards hypoxia and thus influence the capacity of the carp to cope with any further environmental perturbations. The capacity of fish to deal with reduced levels of oxygen in the environment differs considerably among fish species. In general, cyprinids are more tolerant towards hypoxia than salmonids (Ott et al., 1980; Ultsch et al., 1980). As with most fish, common carp are oxygen regulators, meaning that they maintain their oxygen consumption at a constant level along a gradient of environmental oxygen concentrations, until a critical oxygen concentration (Cc) is reached. Below this level, oxygen consumption becomes proportional to the ambient oxygen concentration. The metabolic responses to changes in oxygen availability vary, depending on the physiological state of the animal, level of activity and temperature (Grieshaber et al., 1988; Burggren & Roberts, 1991). Under conditions of stress, the Cc is likely to increase, reflecting the decreased capacity of the fish to cope with environmental perturbations (Ultsch et al. 1980; De Boeck et al., 1995). When challenged with decreasing environmental oxygen concentrations in their normal freshwater environment, carp can regulate their oxygen consumption down to environmental oxygen concentrations of 34 M. After 1 week in brackish water, carp are still able to maintain their Cc at 55 M but after 1 month of exposure, the Cc increases substantially to an oxygen concentration of 120 M. In conclusion, studies have showed that the usual tolerance of common carp towards low environmental oxygen concentrations is affected by long-term exposure to brackish water, and critical oxygen concentrations shift to values that could occur in the natural habitat of common carp. Ammonia excretion was also disturbed after long-term exposure to the brackish water. e) Habitat Usage Some examples of environmental factors affecting carp movement in lakes have been shown by way of radio telemetry. Some attempts have been unsuccessful (Okland et al. 2003), but the majority have shown some interesting findings regarding carp preferences and the ways in which they avoid stressful conditions. Studies related to thermal discharges from power stations have indicated that carp show a preference for warmer water and have been shown to reside there for long periods of time (Cooke & McKinley, 1999). The potential effects of residing in a thermal discharge channel include altered metabolic rates, feeding responses and reproductive potential, increased susceptibility to disease and at worst, death from cold or heat shock (Coutant, 1970; Spigarelli et al. 1974). During the winter of 1997, the behavioural response of fish exposed to fluctuating discharge temperatures in the NTGS discharge canal (Lake Erie) was examined (Cooke & McKinley, 1999). A fixed radiotelemetry system was used to continuously monitor movements of common carp, for several months in order to evaluate the distance fish penetrated and the duration of their residence

in the discharge channel, and correlate activity and residency to environmental and operational conditions. As a result of the radio-tracking, it was established that the common carp were resident in the discharge canal for the majority of the winter of 1997-1998. Compared with another species (Channel Catfish, Ictalurus punctatus), another bottom living fish, residency times within the warmer water were greater, therefore showing a selective preference for the discharge water, with carp spending almost 50% of their time in there rather than in the cooler lake itself. Another study by Yoder & Gammon (1976) showed a similar preference for carp, where they were found during the winter in much larger numbers in the heated effluent and backwater areas of another electric generating station, rather than in the ambient river reference sites. At other times of the year, carp have also been shown to prefer the warmer discharge environment. In one study (Romberg et al. 1974), carp were shown to appear in large shoals in May and routinely swim in and out of the discharge flume through temperature gradients as much as 10C. Although the carp seems to seek out more comfortable conditions, their presence in heated waters is unusual since these flows are not of a constant temperature. The water may be of a more attractive temperature than that of the lake, particularly in winter, and it appears that as long as the fish are not subjected to thermal shock, where great differences in temperature occur after acclimatizing to a particular temperature over a period of time, then they still seem to avoid stressful conditions. This same study by Cooke & McKinley (1999) suggested that carp were attracted to the discharge canal during periods of higher flow, therefore indicating that the carp knew that those flows would be associated with warmer and more advantageous living conditions. By the same reasoning, an angler may take advantage of this, since the evidence suggests that not only temperature but also oxygen and maybe additional environmental conditions affect where the carp move to at different times of the year and times of the day. This suggests to the angler that if carp are able to selectively search out, identify and then occupy areas of a lake with more appropriate environmental conditions, then identifying the areas of a lake which offer those conditions at a particular moment, will allow him to increase his or her chances of success. Swimming and Maneuvering Fish move through the water using their fins for locomotion, stability or balance, and steering. The tail, or caudal fin, helps to propel the fish forward as it is moved back and forth - the actual forward thrust coming from the pressure of the fish's tail against the surrounding water. Fish with smaller caudal fins undulate their bodies to move forward.

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