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Trophic Ecology Of FishesSubmitted By;SYED AASIM HAQROLL No.A.M.U

M.Sc. ZOOLOGY

Trophic Ecology Of FishesThestudyofthefeedingrelationshipsoforganisms in communitiesandecosystems is known as trophic ecology.

Focus ontheinterplay betweenfeedingrelationships andecosystemattributessuchasnutrientcycling, physicaldisturbance,orthe rateoftissue productionbyplantsandtheaccrualof detritus.

Trophicrelationshipscanberepresented as a FoodweborasaFoodchain.

Foodwebsdepicttrophiclinksbetween allspecies sampledinahabitat,whereasfood chainssimplifythiscomplexityintolinear arraysofinteractionsamongtrophiclevels.

These trophic levels are not always simple integers, as organisms often feed at more than one trophic level.

Threefundamentalquestionsinthefieldof trophicecology are important: (1)Whatistherelationshipbetweenthe lengthoffood chainsandplant biomass

(2)Howdoresourcesupplyto producerand resourcedemandbypredatorsdeterminetherelative abundanceoforganismsateach trophiclevelin afoodchain (3)Howlongarerealfoodchains,andwhat factorslimitfoodchainlength

Trophic Level And Food ChainThetrophic levelof an organism is the position it occupies in a food chain.These are Primary producers; are principally green plants and certain bacteria. They convert solar energy into organic energy. Consumers; Above producers who ingest live plants or the prey of others. Decomposers; such as, bacteria, molds, and fungi make use of energy stored in already dead plant and animal tissues.

Further trophic levels are numbered subsequently according to how far the organism is along the food chain.

Level 1: Plants and algae make their own food and are called primary producers. Level 2: Herbivores eat plants and are called primary consumers. Level 3: Carnivores which eat herbivores are called secondary consumers. Level 4: Carnivores which eat other carnivores are called tertiary consumers. Level 5: Top Carnivore which have no predators and are at the top of the food chain

Feeding In Fishes Food eaten by various species of fishes has been divided into four categories;

Main Food; natural and preferred by the fish.Secondary Food; consumed by the fish when available.Incidental Food; enters the gut by chance with others.Emergency Food; Taken only under unfavorable conditions when basic food is not available.

Generally fishes are described as;

Herbivorous (Labeo rohita , Labeo calbasu , Ctenopharyngodon idella etc )

Carnivorous( Wallago attu , Mystus seenghala , channa marulius etc )

Omnivorous( Cirrhinus mirgala , Clarius batracus , Heteropneusts fossilis etc )

Ctenopharyngodon idella (Herbivorous )Wallago attu (Carnivorous)Heteropneusts fossilis (Omnivorous)

Other specific categories are ;

Plankton feedersInsectivorousCrustacean FeedersMollusk FeedersLarvivorousPiscivorous etc

Fresh water fishes can also be divided into three groups on the basis of their ecological zone of feedingSurface Feeders ( Catla catla , Hypophthalmichthys molitrix, Hilsa hilsa etc)

Column Feeders ( Labeo rohita , Wallago attu , tor tor etc )

Bottom Feeders ( Labeo calbasu , Labeo bata Cirrhinus mirgala etc )

Catla catlaCirrhinus mirgalaLabeo rohita(Surface Feeder) (Column Feeder )(Bottom Feeder )

Polyculture

PolycultureItis the practice of culturing more than one species of aquatic organism in the same pond.

The motivating principle is that fish production in ponds may be maximized by raising a combination of species having different food habits.

Polyculture of fish is based on the concept of total utilization of different trophic and spatial niches of a pond in order to obtain maximum fish production per unit area.

Fig; Fishes utilizing different niches in polyculture system

In India polyculture with carps (IMC) is widely being carried out.

These include Catla catla , Labeo rohita and Cirrhinus mirgala.

These are stocked at the ratio of 3:3:4 respectively.

Besides these , polyculture with Chinese carps (silver carp , grass crap and common carp) is also being carried out.

AdvantagesMaximum fish production is possible in polyculture.

More profitable and easy to maintain.More Economic.

Different fish species cultivating in a single pond.More fish can be cultivated and produced from short place.

Almost all the available niche is being utilized in a single pond. More efficient use of natural resources.

Factors Affecting Species selection

Water TemperatureMarket value of fish.

Feeding habits of fish.Pond fertilization practice.

Tolerance to pond conditions.Potential of uncontrolled swamping in grow out pond.

Food Habit Analysis

Food Habit Analysis Description of fish diets and feeding habits provides basis for understanding trophic interactions in aquatic food webs.

Diets of fishes represent an integration of many important ecological components that include the behavior, condition, habitat use and inter/intra specific interactions.

Gut AnalysisGut content analysis provides important insight into fish feeding patterns and quantitative assessment of food habits is an important aspect of fisheries management.All items in gut should be sampled. If live fish is sacrificed the stomach contents to be preserved immediately to prevent digestion (5% neutralized formalin).

Make a longitudinal cut along the stomach and transferred to a petri dish.

Remove excess formalin and keep under binocular microscope and identify.Only the immediate foregut to be sampled.

For a better understanding of diet data and for accurate interpretation of fish feeding patterns, time of day, sampling location, prey availability and even the type of collecting gear used need to be considered before initiating a diet study or analyzing existing diet data.

Gut Analysis

Methods

Qualitative ; It involves complete identification of gut contents. It needs extensive experience and good support of references.

Quantitative ; It includes Numerical ,Volumetric and Gravimetric methods.

1) Numerical Methods(Only counts of prey items are considered)

Frequency of OccurrenceNumber methodDominance methodPoints method

i) Frequency of OccurrenceThe number of stomachs in which each item occurs is recorded and expressed as a percentage of the total number of stomachs examined.

a) It provide information on how often (or not) a particular prey item was eatenb) But no indication of the relative importance of prey to overall diet

ii) Number methodThe number of individual of each food type in each stomach is counted and expressed as a percentage of the total number of food items in the sample studied, or as a percentage of the gut contents of each specimen examined, from which the total percentage composition is estimated.

a)Common method for the analysis of planktivoresb)Drawback: Small prey can represent dominant component of the diet

iii) Dominance MethodThe stomach contents comprising the main bulk of the food materials present, is determined and the number of fish in which each such dominant food material is present is expressed as a percentage of the total number of fishes examined.

a)Drawback: It yield only a rough picture of dietary of a fish.

iv) Points methodFood items are allotted a certain no. of points based on rough counts and judgments by the eye. In a more modified form, the food items are classified as very common, common, frequent, rare, etc., a)Food items are classified as common, very common, frequent, rare etcb) Personal bias.

2) Volumetric Method (Best method for herbivores and omnivores where other methods are meaningless)

1)Point method; Prey items are allotted certain points based on its volume. Very useful for Omnivores and herbivores

2) Eye estimation

3)Displacement method; Displaced volume of each prey items is measured in a graduated cylinder. Most accurate among the three and is suitable for carnivore.

3) Gravimetric methodsThe gravimetric method consists of the estimation of the weight of each of the food items, which is usually expressed as percentages of the weight of the total gut contents as in other quantitative methods.

a)Dry weight More time consumingb)Wet weight- Common method for Carnivores

Fish Deformities

Adeformity is a major abnormality in the shape of a body part or organ compared to the normal shape of that part.

Deformities in various parts of a fishs anatomy can occur in just about any part of the body, but they are mostly associated with the calcified skeletal structures. Thus, those structures which commonly exhibit defects include the vertebral column (backbone), the skull and various fins.

To a lesser degree, defects are evident in the internal organs.

Cause of DeformitiesGenetic (congenitally )

Environmental factors ; like pollution , radiations, temperature, altitude , chemical factors , pathogens , stress , nutrient deficiency etc

Skeletal AbnormalitiesSkeletal anomalies. particularly those of the spinal column are commonly observed in fishGenerally caused by effects of environmental factors such as temperature. salinity. dissolved oxygen. radiation, dietary deficiencies. and toxic chemicals.For example, increased percentages of abnormal embryos and larvae of Atlantic herring, Clupea harengus, resulted from experimental exposures to sulfuric acid waste water (Kinne and Rosenthal 19671 and to the algicides 2,4- and 2.5 dinitrophenol (Rosenthal and Stelzer 1970).

Exposure of fry to very low concentrations of DDT 1 ppb) produced anomalies in fin rays (Valentine and Soule 1973).It is seen that high chlorinated hydrocarbon and heavy metal levels are seemed to be reasons for the higher prevalence's of anomalies particularly gill raker deformities in fish from the southern California coast.Vertebral deformities in herring fish taken in waters around the British Isles showed the predominant abnormality was a cluster of two or three incomplete vertebrae located near the pelvic fins or anus (van de Kamp).

Several types of abnormalities are reported from various regions of the world by various authors. Some of the evidences of abnormalities reported are sites as;

Skeletal abnormalities in mullet and eight other species from the Inland Sea of Japan were reported by Matsusato (1973).Komada (1974) and Ueki and Sugiyama (1976) observed increasing numbers of malformed sweetfish or ayu, Plecoglossus altivelis , in rivers and culture farms of japan.Gabriel (1944) noted abnormities in vertebrae of Fundulus heteroclitus due to temperature changes

Mottley (1937) found anomalies in vertebral numbers of trout due to temperature (and possible oxygen).Hubbs (1959) found high prevalence's of vertebral abnormalities in Gambusia affinis from Texas warm springs due to high temperature.Long-term (10 wk) exposure of minnows (Phoxinus phoxinus) to sub lethal concentrations of zinc and cadmium resulted in hemorrhaging, spinal curvatures, and vertebral fractures, particularly in the caudal region, in up to 70% of individuals (Bengtsson 1975).Spinal curvatures and muscle atrophy were produced in rainbow trout by chronic exposure to lead (Bengtsoon).

In earlier studies, summarized by Bengtsson, exposure to sub lethal concentrations of Malathion, parathion, and certain other organophosphorus pesticides produced vertebral damage or spinal flexures in several fish species.Couch et al have also found that trifluralin (Treflan) induced extensive osseous hyperplasia in vertebrae of sheepshead minnows when life history stages from zygote to 28-day juveniles were exposed to 25-50 ppb trifluralin.

Brevoortia tyrannus(Skeletal Deformity)Sparus aurata(Skeletal Deformity)

(Mouth Deformity)

(Gill deformity)

(Opercular deformity)

(Fish fin erosion)

Certain Chemicals and their effectsDDT: Necrosis of hepatic cells; lymphocytic infiltration of intestinal lamina propria; possible degeneration of kidney tubules. Carbaryl (Sevin): Intramuscular hemorrhages adjacent to vertebral column: atrophy of the lateral line musculature; myxomatous degeneration of fat; vacuoles within the optic tectum of the brain. Malathion: Subcutaneous hemorrhages at the bases of pectoral fins. Endosulfan (Thiodan): Hyperemia of intestine and brain; adrenal cortical hyperplasia. 2,4-D: Striking degree of brain hyperemia; hyperemia of intestine. Atrazine: Marked edema of all tissues; changes in skin pigmentation.

ReferencePollution-Associated Diseases And Abnormalities of Fish and Shellfish: A Review CARL J. SINDERMANNTextbook ofFish BiologyandFisheries, Khanna, S S &H RSingh. Economic zoology by R.C.SOBTI.www.ncbi.nlm.nih.govwww.eprints.cmfri.org.inWikipediaComparative Physiology , Developmental Biology and Ecology by ASHOK SABHARWAl.www.fao.org