Contents Introduction Gonads in fishes - PowerPoint Presentation

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Contents

Introduction

Gonads in fishes

Origin

Position

Anatomy

Ovaries

Testes

Testes in different groups

Structure of ovary

Structure of testes

Cyclic changes in gonads

Intermittent organs

Reproductive strategies

Acknowledgements

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Fish

 reproductive organs include 

testes

 and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.[1] There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish often can be determined by the shape of its papilla. The most predominating process is bisexual reproduction. In such fishes the sexes are separate, e.g., the individuals are dioecious. In a few fishes, both sexes are present in same individual, i.e., such fishes are hermaphrodite. The reproduction in fishes is bisexual, hermaphrodite or parthenogenic.

Introduction

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The gonads of

elasmobranchs

developed by the migration of primordial germ cells from the extra-embryonic endoderm which originate from peritoneal epithelium and inter-renal

analoge. In teleosts also the primordial germ cells originate from the genital ridge (as swelling). The primordial germ cell is quite large and slightly oval in shape with a large spheroidal nucleus containing one large nucleolus.The genital ridge develops into cortex and medulla in vertebrates. But gonads in teleosts and cyclostomes consist only cortex and lack medullary tissue. In elasmobranch it develops into medulla, but in females they develop into the cortex. Later the primordial germ cells undergo meiosis and proliferate and ultimately differentiate into male and female gonads.Origin of Gonads

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The fishes have one pair of bilateral gonad. They are generally symmetrical. They are suspended from the dorsal portion of the body cavity by mesenteries across the roof of the body cavity in close association with kidneys.

The

mesentery in female is called

mesovarium. While in male it is known as mesorchium. It is richly supported with blood vessels and nerve fibres.Position of Gonads in Fishes

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Anatomy

hagfish, lamprey

: single gonads

no ducts; release gametes into body cavity

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Anatomy

hagfish, lamprey

: single gonads

no ducts; release gametes into body cavitysharks: paired gonads internal fertilization sperm emitted through cloaca, along grooves in claspers

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Anatomy

hagfish, lamprey

: single gonads

no ducts; release gametes into body cavitysharks: paired gonads internal fertilization sperm emitted through cloaca, along grooves in clasperschimaeras, bony fishes: paired gonads external and internal fertilization sperm released through separate opening

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Female reproductive system is comprised of ovaries oviducts and in some fishes

pseudocopulatory

papilla (Fig 26.8 d).

In cystorian type ovary is connected with oviduct and ova is released outside in water through genital pore. In semicytovarian type, the oocytes in place of oviduct pass through a funnel shaped transparent groove, which opens into genital pore. Such condition is present in Notopteridae, Osteoglassidae, etc., where oviduct degenerate partially or completely and, therefore, ova are shed into the coelomic cavity and then carried through pores or funnel.Gymnovarian type of ovary is not continuous with the oviduct. The ovary hangs down like curtain and the oocytes are ovulated into the coelomic or peritoneal cavity and carried to oviduct by cilia.Normally ovary are sac like and paired and symmetrical structure both in teleosts and elasmobranchs and are functional. However, in some elasmobranchs, the right ovary become becomes functional while in some cases the left ovary only develops.Ovaries

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The testes in fishes, generally, are paired structures situated on either side somewhat lateral to and below the kidneys.

The

testis has two major functions, the production of spermatozoa (spermatogenesis) and another function is the production of steroids (

Steroidogenesis). The size of testes in the breeding season, become enormous. They are suspended from the dorsal body-wall by mesentery known as mesorchia, which is vascularized and contain nerve fibres. In dipnoi fishes e.g. in Neoceratodus and Protopterus the right testis is attached anteriorly to the tip of the liver, while the left gonad extends forward to the region of the ductus Cuvieri (Fig. 3).Testes :

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The testis may be elongated, sac-like or

lobulated

, may be rounded or triangular in cross sections.

Testes in Teleost: In mature gobies, Acanthogobius fluviatilis the testis is small and thread-like. In Notopterus and Amphipnous testis is unpaired. In Syngnathids the testis is a simple tube. The testes occupy different position in the abdominal cavity.The right is usually larger to the left. In teleosts the sperm duct or vas deferens is a modified nephric duct and may be from one or several ureters carrying the excretory fluid to the cloaca (Fig. 1c-d).Lung Fishes:The testis of Protopterus extends the entire length of the body as a thick band closely and broadly bound to the kidney. The testis of Lepidosiren is an elongated mass and embedded in fatty tissue. In lungfishes many efferent ducts extend from the central canal into the kidney and connected with the capsules of the nephric tubules (Fig. 3)

Testes in different

groups of fishes

Continue….

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Crossopterigeans

:

In

Latimaria the right testis is two to three times larger than the left but both produce sperms. The right testis extends through the middle of quarter of the body cavity ventrolateral to the swim bladder.In Chondrichthyes the position of testis varies from far anterior back to about the middle. In some sharks the testis is associated with an epigonal organ which is lymphoid in nature.From each testis a sperm duct or vas deferens originates. In some fishes mesonephric ducts unite with testis to form vas deferens and vasa efferentia (epidydimous).In some fishes the sperm duct is shared with kidney and often called nephric duct (Wolffian duct) (Fig.1a,b).Testes in different groups of fishes

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Fig

1

Vasdeferens a)Galeus sp.; b) Raja sp.;c) Acipenser sp; d) Wallago attu

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Gonads in

Labeo

sp.

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Fig. 2 Gonads in a) Female

Lepisosteus

;

b) male Lepisosteus

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Fig.3 Lung Fish

Ganads

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The ovary contains supporting tissue known as

stroma

, which contains

oogonia and oocytes. The oogonium (germ cell) after multiplication develops into primary oocyte. The oogonium cell in the early stages of development is a large cell with a large nucleus having prominent nucleolus with chromo-phobic cytoplasm. The size of the cell becomes smaller after multiplication, but is not important.The important difference is in the chromosomes. The chromosome becomes thread like in the nucleus (leptotene stage). The chromosomes undergo zygotene stage followed by pachytene and ultimately diplotene stage. At this stage of development to oocyte is surrounded by follicle cells. The follicle cells are multilayer in elasmobranch and amniota but single layer in teleosts.In elasmobranch, the theca interna lies immediately below the externa and consists of 4 to 6 rows of flattened and elongated cells, the walls of which are extended outward into processes (Dodd, 1983). Theca externa cells are secretary in function and contain organelles such as ER and mitochon­dria.

Structure

of Ovary

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Idealized anatomy of a fish ovary. This diagram shows anatomy of a mature female containing each of four

oocyte

stages. 

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Each testis is enclosed in a connective tissue sheath.

The tunica

propria

of the connective tissue projected into the lumen forming tubes. The blind end is the site of primary spermatocytes. The tubular structure consists of two parts, the interstitial and lobular. The interstitial part consists of interstitial cells, fibroblasts, and blood and lymph vessels.The lobular part is distinguished into germ cells and somatic cells. The somatic cells are positive for lipid and cholesterol and are homologous with the mammalian Leydig cells. Strucure of Testis:

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The Scientific World Journal

 / 

2012

 / Article / Fig 3Fig. Female and male gonads of Prochilodus brevis, where (a) and (b) represent immature; (c) and (d) maturing; (e) and (f) mature; (g) and (h) spent gonads.Cyclic changes in Fish Gonads

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Male 

cartilaginous fishes

 (sharks and rays), as well as the males of some live-bearing 

ray finned fishes, have fins that have been modified to function as intromittent organs, reproductive appendages which allow internal fertilization. In ray finned fish they are called gonopodiums or andropodiums, and in cartilaginous fish they are called claspers.1. Gonopodia are found on the males of some species in the Anablepidae and Poeciliidae families. They are anal fins that have been modified to function as movable intromittent organs and are used to impregnate females with milt during mating.2. Claspers are found on the males of cartilaginous fishes. They are the posterior part of the pelvic fins that have also been modified to function as intromittent organs, and are used to channel semen into the female's cloaca during copulation.. 

intromittent

organs

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Reproduction

onset of reproduction

males typically mature earlier and smaller than females mature earlier if survival and growth are low stable environment – delayed reproductionsurvivorship high if egg production is low, and vice versa high fecundity fish respond more rapidly to change

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Anatomy

in general

:

gametes produced only during spawning season gonads reduced during non-reproductive season

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Alternative reproductive strategies

parthenogenesis

:

females produce diploid eggs, no sperm used premeiotic endomitosis - mitotic division without cytokinesisgynogenesis: females produce diploid eggs, use sperm to stimulate development male genome not used congeneric species are used for sperm example: Poecilia formosa (Amazon molly)

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Alternative reproductive strategies

parthenogenesis

:

females produce diploid eggs, no sperm used premeiotic endomitosis - mitotic division without cytokinesisgynogenesis: females produce diploid eggs, use sperm to stimulate development male genome not used congeneric species are used for spermandrogenesis – does not exist (why?)

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Alternative reproductive strategies

parthenogenesis

:

females produce diploid eggs, no sperm used premeiotic endomitosis - mitotic division without cytokinesisgynogenesis: females produce diploid eggs, use sperm to stimulate development male genome not used congeneric species are used for spermhybridogenesis: one genome from female in egg, male genome discarded - then uses sperm to restore ploidy - no crossing over example: Poeciliopsis monacha-lucida

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THANKS!!!

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Reproductive

System in Fish | Fish Anatomy and Physiology

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Saraswati Jhahttp://www.y  ourarticlelibrary.com/fish/anatomy-and-physiology/reproductive-system-in-fish-fish-anatomy-and-physiology/88457https://en.wikipedia.org/wiki/Fish_reproductionREFERENCES