Reproductive strategies in fishes

Reproductive strategies in fishes

PRESENTED TO- Dr. I.J. SINGH

PRESENTED BY- MANISH KUMAR

ID NO- 40024

OVIPARITY: EGG LAYERS AND EXTERNAL FERTILIZATION

• By far the vast majority of fishes are oviparous, that is they produce eggs that are fertilized after they have been laid

• About 96 percent of all living fishes are egg-

layers. Fishes exhibit a great variety of egg types and adaptations. Morphologically and physiologically they are tremendously diverse

OVIPARITY IN MARINE FISHES

• Very generally speaking eggs come in two kinds:

• 1. Pelagic eggs: eggs that float

• 2. Demersal eggs: eggs that sink

• By far the majority of marine fishes start out life as pelagic eggs.

This includes:

• 1. Most all fishes that live over the continental slope

• 2. Nearly all those that range over surface waters of the open ocean

• 3. All pelagic deep-sea fishes

• The eggs of these kinds of fishes are made buoyant by low-density fluids acquired from the follicle cells of the ovary or they develop an oil droplet independent of ovarian tissue.

• The kinds of fishes that develop floating eggs must be able to produce large numbers of small eggs. A fair-sized hake (Merlucciusproductus) lays about 1 million eggs; fecundity in cod (Gadusmorhua)ranges from 2–9 million eggs;

• High numbers of eggs are necessary for successful recruitment because thousands of eggs and larvae are dispersed into areas far beyond the optimal conditions for survival, and thousands die long before hatching or metamorphosis to juvenile stages

Demersaleggs

• Some marine fishes lay demersale eggs, that is, eggs that are heavier than water and thus sink to the bottom after being laid, or they are laid directly on the bottom, or placed in nests, or fastened to rocks, shells, seaweed, sponges, and a whole host of other objects

OVIPARITY IN FRESHWATER FISHES

• While most marine species lay pelagic eggs, demersal or non-floating eggs are the rule in freshwater—they sink to the bottom. There are several reasons for this:

• 1.It is physiologically more difficult to produce an egg with a specific gravity less than freshwater.

• 2. Freshwater does not provide the rich food resource in its upper layers as does the marine environment.

• 3. Fast moving rivers and streams would remove nearly all eggs and larvae from a local population preventing recruitment

OVOVIVIPARITY AND VIVIPARITY: INTERNAL FERTILIZATION

• Ovoviviparous and viviparous fishes are similar in that both are live-bearing forms that require internal fertilization. However, they differ fundamentally with regard to the source of nutrition for the developing young.

• In ovoviviparous forms the eggs are retained and fertilized within the body, but the young receive no nutrients from the mother—they must rely solely on what is provided in the yolk. In viviparous forms, the young are nourished by some kind of placental connection with the mother.

Ovoviviparity and viviparity are relatively rare among fishes—they

include only about 4 percent of all living fishes, but they are among the

most interesting when it comes to reproduction.

. Representatives are found among the following taxa: Chondrichthyes

(sharks and their allies), live-bearers(i.e., guppies and their allies,

family Poeciliidae and the coelacanths(genus Latimeria).

. Internal fertilization involves the use of some kind of organ, a

structure used to pass sperm to the female. Most live-bearing fishes

have males with such an organ. They are usually modified analog

pelvic fins.

The guppy (genus Poecilia) is the best known case of

ovoviviparity in fishes—the eggs are fertilized within the egg

follicles of the ovary where they develop for some time.

• Some marine forms and many more freshwater forms retain their eggs after they are laid, that is, they practice parental care. Parental care takes on a host of different modes, from simple to highly complex

PARENTAL CARE

Forms of parental care:

A.Male parental care: sea catfishes (Ariidae), sticklebacks (Gasterosteidae), pipe fishes (Syngnathidae), and greenlings (Hexagrammidae)

B. Female parental care:

1.Oviparity with post-spawning care: the cichlidaegenus Oreochromis

2. Ovoviviparity without post-spawning care: rockfishes, genus Sebastes

3. Viviparity without post-spawning care: Elasmobranches, livebearers (e.g., Genus Poecilia), surfperches (Embiotocidae)

C.Biparental care: bullheads (Ictaluridae), several cichlid genera (e.g.,Cichlasomaand Symphysodon)

D. Juvenile helpers: some African cichlids (e.g., genus Lamprologus)

Reproductive strategies

several males to each female (Salmoniformes, lampreys)

several females to each male (Gobiidae)

single-pair matings (guppies)


non-guarders

- pelagic (broadcast) spawners

semi-buoyant eggs

high fecundity

egg and larval ‘migrations’


non-guarders - pelagic (broadcast) spawners- benthic spawners

on coarse substrates (lake trout)on vegetation (carp, perch)on fine substrates (smelt)


non-guarders - pelagic (broadcast) spawners- benthic spawners- brood hiders:

build redd on coarse substrates (salmon, lamprey)


non-guarders - pelagic (broadcast) spawners- benthic spawners- brood hiders

build redd on coarse substrates (salmon, lamprey)beach spawners (grunion)use another species (bitterling)


guarders - nest builders (largemouth bass)


guarders - nest builders (largemouth bass)

rock and gravel (like a lentic redd - sunfishes)plant material (sticklebacks)holes, crevices, cavities (gobies, sculpin, blennies)froth (bettas)anemones (clown fish)


bearers - carry eggs and/or fry with them


bearers - external bearers

transfer: Gasterosteidae, Sygnathidae (pipefishes, seahorses)

grade from attachment to skin, to open pouch, to closed pouchgill chambers, foreheadobstetrical catfish carry eggs on ventral surface


bearers - external bearers

mouth: males or females some cichlids and bony tongues


bearers

- internal bearers (viviparity)facultative - killifishes

obligate - Lake Baikal sculpins, marine rockfishes (Scorpaenidae)

livebearers - Poeciliids, many sharksgradient of nutrient supply from mother

superfetation

placental viviparity - sharks

Alternative reproductive strategies

Hermaphroditessynchronous (or simultaneous) hermaphrodites

Myctophiformes: (laternfishes) - several familiesAtheriniformes: Aplocheilidae, PoeciliidaePerciformes: Serranidae (sea basses, hamlets),

Labridae (wrasses), and others

"Egg-trading" in black hamlets Hypoplectrus nigricans (serranid)


Hermaphroditismconsecutive (sequential) hermaphrodites

first male (protandrous) – less commonStomiiformes (lightfish, dragonfish)Scorpaeniformes: PlatycephalidaePerciformes: Serranidae, Labridae, and others

blue-headed wrasse

first female (protogynous) eels Synbranchiformes (swamp– only freshwater example)

Perciformes: Serranidae, Maenidae, Labridae


parthenogenesis: females produce diploid eggs, no sperm used

premeiotic endomitosis - mitotic division without cytokinesis

gynogenesis: females produce diploid eggs, use sperm to stimulate development

male genome not usedcongeneric species are used for sperm

hybridogenesis: one genome from female in egg, male genome discarded - then uses sperm to restore ploidy - no crossing over example: Poeciliopsis monacha-lucida

Natural polyploidstriploids - Cyprinidontiformes: Poeciliid triploids

tetraploids (autotetraploids vs. allotetraploids)

hexaploids and octaploids (rare in carp)

Natural hybrids

salmonids

centrarchids

THANKYOU

Education

Reproductive strategies in fishes