Testicular development in migrant and spawning bluefin tuna (Thunnus thynnus (L.)) from the eastern Atlantic and Mediterranean

Testis histological structure was studied in bluefin tuna (Thunnus thynnus) from the eastern Atlantic and Mediterranean during the reproductive season (from late April to early June). Testicular maturation was investigated by comparing samples from bluefin tuna caught on their eastward reproductive migration off Barbate (Strait of Gibraltar area) with samples of bluefin tuna fished in spawning grounds around the Balearic Islands. Histological evaluations of cross sections showed that the testis consists of two structurally different regions, an outer proliferative region where germ cells develop synchronously in cysts, and a central region made up of a well-developed system of ducts that convey the spermatozoa produced in the proliferative region to the main sperm duct. Ultrastructural features of the different stages of the male germ cell line are very similar to those described in other teleost species. The bluefin tuna testis is of the unrestricted spermatogonial testicular type, where primary spermatogonia are present all along the germinative portion of the lobules. All stages of spermatogenesis were present in the gonad tissue of migrant and spawning bluefin tuna, although spermatids were more abundant in spawning fish. The testis size was found to increase by a factor of four (on average) during migration to the Mediterranean spawning grounds, whereas the fat bodies (mesenteric lipid stores associated with the gonads) became reduced to half their weight, and the liver mass did not change significantly with sexual maturation. Linear regression analysis of the pooled data of migrant and spawning bluefin tuna revealed a significant negative correlation between the gonad index (IG) and the fat tissue index (IF), and a weaker positive correlation between the gonad index (IG) and the liver index (IL). Our analyses indicate that the liver does not play a significant role in the storage of lipids and that mesenteric lipid reserves constitute an important energy source for gametogenesis in bluefin tuna.

A histological study of the spermatogenesis in Ompok pabda (Hamilton-Buchanan 1822)

The present study deals with the histological analysis of testicular development in Ompok pabda. For the study, male gonads were collected month wise from January to September at Freshwater Station, BFRI, Mymensingh. From the analysis, 4 stages of sperm formation, namely, spermatogonia, spermatocytes, spermatids and spermatozoa, were distinguished. The percent distribution of spermatozoa was highest in July (about 92%). Maximum GSI value was 1.129±0.271 found in July. By analyzing the histology of spermatogenesis it was established that this species breeds once in a year.

Reproductive biology, artificial propagation and larval rearing of two freshwater eels, Monopterus cuchia and Mastacembelus armatus

Studies on reproductive biology and artificial propagation including larval rearing of freshwater mud eel, Monopterus cuchia and spiny eel, Mastacembelus armatus were attempted. The gonadosomatic index (GSI) of mud eel ranged from 0.41 (August) to 5.52 (June) in males and 0.53 (August) to 7.61 (June) in females. In both cases the GSI showed a peak in June. Fecundity ranged from 228 (TL - 396 mm; W - 78g) to 5510 (TL - 865 mm; W - 630 g). In case of spiny eel, the GSI varied from 0.65 (August) to 8.30 (July) in males and 0.70 (August) to 10.46 (July) in females. GSI showed single peak in July. Fecundity ranged from 570 (TL - 240 mm; W - 30 g) to 10870 (TL - 601; W - 350g). Histology of the testes and ovaries of the eels were carried out to investigate the gonadal development stages during the reproductive months (August to November 2003). In case of male M. cuchia, the secondary primordial germ cells, primary spermatogonium, some spermatogonia A and clone of spermatogonium B in testis were observed in September. In October-males different sized lobules having spermatogonia, spermatocytes and spermatids were observed. In the ovary of M. cuchia, polygonal shaped oocytes were seen during September. The oogonia were reduced with dense and irregular shaped during October. Numerous pycnotic cells were visible during November. In male M. armatus numerous broken lobule walls were found in testes during September. In October, abundant primary germ cells, pycnotic nests of degenerating cells, spermatogonia and spermatids were observed. In females, ovaries had distinct yolk vesicles stage and yolk granules stages in August. In September, the follicular cells of the oogonia were ruptured, shrunk forming irregular shaped in October. Oogonia were also shrunk with thin, irregular shaped structure but broken parts of the ruptured follicular cells were scattered in case of M. armatus. Experimental attempts on artificial propagation indicated that both freshwater eels were difficult to breed using inducing agents like pituitary glands (PG) of 10, 20, 50, 100 and 150 mg per kg of body weight. Same doses were used for both sexes with equal sex-ratio. In both cases, brood fish died at higher doses of injection given at 100 and 150 mg PG/kg bodyweight. However, M. cuchia breed naturally in cisterns when provided with water hyacinths and tunnel in muddy bottom. M. cuchia fed with chopped cooked fish attained a mean weight of 18.75 ± 2.3 g and cent percent survival. While in case of M. armatus best growth by weight (12.0 ± 2.48 g) and cent percent survival were achieved using chopped raw fish. Car tyre was observed as best shelter for attaining the mean weight gain 22.53 ± 2.24 g and cent percent survival of M. cuchia. While PVC pipe was found to be the best shelter for M. armatus, where it attained the mean weight of 12.73 ± 1.88 g and cent percent survival.

Study on biological characteristics, sexual maturation and reproduction of Liza abu in the water of Khozestan Province

As the most of the fish resources are known and exploited, protecting their generation is of the greatest importance. Aquaculture is one of the efficient procedures in protecting and reviving fish resources and knowing about the reproductive cycle and gonads development has an important role in approaching this aim. Liza abu belongs to the family Mugilidae that according to its resistance to the environmental condition and its fast growth , can be introduced as a fish with economical value. As there is no scientific data on the reproductive biology of this species , study on the reproductive biology and gonad development is considered as the aim of this research . For this purpose , 360 samples of this species were investigated during the period from February 2007 to January 2008 in Khozestan Province . After studing morphological and histological characteristics of gonad specimen , they were prepared through histological method. Samples were prepared through usual histological method and studied under light microscope. According to the results, the maturity stages of male and female Liza abu were separated to six different successive stages. In ovaries , these stages were as follow : In stage І, the oocytes were small , this stage was observed from July to October . In stage ІІ, considerable growth was observed in the oocytes . This stage was observed from October to January . In stage III, due to vitellogenesis, the maximum growth was observed and three layers of theca, granullosa and follicle cells were visible. This stage was observed during January and February . In stage IV, migration of germinal vesicle was observed and due to hydration of the oocytes , their diameter was increased. The ovaries were yellowish and in maximum size and ovules could be easily observed with naked-eye . This stage was observed in February and March . In stage V, spawning occured. This stage was observed in April . In stage VI, ovaries consisted of immature and atretic oocytes and also empty follicles. This stage was observed in May and June. In testes , these stages were as follow : In stage I , the testes were small in size and contained the spermatogonia which were the only cellular components.This stage was observed in August and September . In stage II (maturing virgin ) , the spermatogonia and the primary spermatocytes were visible. This stage was observed in October . In stage III (developing), intensive spermatogenesis was occured and the primary and the secondary spermatocytes were the most visible cells during this stage .This stage was observed from November to January. In stage IV(developed), cells of all stages of spermatogenesis could be seen but the secondary spermatocytes and spermatids were in large number. This stage was observed from January to March. In stage V , the testes were filled with sperms. This stage was observed in March and April .In stage VI, residual spermatozoa and the spermatogonia were visible in the testes. This stage was observed from May to August. According to cyclic changes in GSI, sexual maturation in breeding begins in January and spawning occurs in April. The ova diameter ranged from 30.75 μ in stage I to 472.19 μ in stage IV. In this study , the sex ratio was 1:2.7, and male and female percentage were 27.02% and 72.98% respectively. This means that females predominate males. In this study absolute fecundity was calculated and changing between 30805.44 to 431247.3 was observed and absolute fecundity was calculated 111275.3 in average.