Plasma levels of Gonadotropin-II and gonadal sex steroids in triploid catfish, Heteropneustes fossilis (Bloch)

Triploid fish have under-developed gonads due to altered reproductive endocrinology. Triploids of Indian catfish (H. fossilis) showed significantly reduced plasma levels of gonadotropin (GtH-II), testosterone (T) and estradiol-17 (E₂) than that of diploids throughout the year, except for the resting phase, irrespective of sex. Plasma levels of GtH-II were significantly different (p<0.001) between diploid and triploid fish during preparatory, prespawning and spawning phase. The plasma testosterone contents in triploids were significantly less (p<0.001) than that of diploids, except during the resting phase. Triploid females showed very low titres of estradiol-17 (<1 ng ml^–1) throughout the annual reproductive cycle in contrast to highly fluctuating levels in diploid females. Thus, this study for the first time provides information on reduced levels of GtH-II and sex steroids in plasma of male triploid fish and additional information on species-specific alteration of sex hormones in female triploids.     

Induction of meiotic gynogenesis in the stinging catfish Heteropneustes fossilis (Bloch) and evidence for female homogamety

This study reports the results on induced meiotic diploid gynogenesis and female homogametic nature in the Indian catfish, Heteropneustes fossilis. The eggs of H. fossilis were inseminated with conspecific sperm. The sperm suspension was diluted to 1 × 10⁷ sperm mL⁻¹ in Hanks balanced salt solution. Sperm were irradiated under UV light, with the exposure time ranging from 15 to 360 s (7500 ergs mm⁻² for 60 s). The genetic inactivation of paternal chromosomes was confirmed by chromosome counting from the larval cells and the larvae also had a characteristic haploid syndrome. A typical ‘Hertwig effect’ in the yield of hatched larvae was observed with doses of UV exposure >75 s (9375 ergs mm²). Larvae resulting from sperm UV irradiated above 120 s (15 000 ergs mm²) were 100% haploids. Application of heat shock to the activated eggs was effective in suppressing the release of the second polar body (meiotic gynogenesis) and resulted in diploid gynogenetic larvae morphologically identical to those of the control. The best yield of diploid gynogens (49.3% with respect to the control) was found to be at 6 min after egg activation and the heat shock at 41 °C for a 1-min duration, at an ambient water temperature of 27 °C. A total of 113 diploid gynogenetic fry from seven different female fish were reared and subjected to sexing. All gynogenetic fish were female in contrast to the control, which had a mean sex ratio of 56.7% females (which was not significantly different from 50% female). From these results, the sex determination mechanism in H. fossilis was presumed to be female homogamety.     

Effects of photoperiod alterations on day-night variations in hypothalamic serotonin content and turnover,and monoamine oxidase activity in the female catfish,Heteropneustes fossilis (Bloch)

The effects of different photoperiod regimes, and total darkness on day-night variations in hypothalamic serotonin (5-HT) content and turnover index (TI), and monoamine oxidase (MAO) activity that occur exclusively during the gonadal preparatory phase (February–March) were investigated in female Heteropneustes fossilis. Exposure of the fish to long photoperiods (16L:8D; light between 06.00–22.00h, for 40 days elevated both the midphotophase and midscotophase values of 5-HT content and MAO, and abolished their day-night differences. The daily variations of 5-HT-TI was further intensified by the treatment. Under short photoperiods (4L:20D; light between 18.00–22.00h for 40 days), there was a significant decrease in both 5-HT content and TI, a reversal of the day-night variations of 5-HT content and MAO activity, and loss of the 5-HT-TI pattern. In fish maintained in total darkness the day-night variations were not found and there was a significant inhibition of 5-HT. Exposure of the fish to continuous light abolished the day-night variations of these correlates and elevated their values at both intervals. When the LD cycle was reversed, there was a corresponding shift in the day-night patterns. The gonadosomatic index (GSI) was significantly elevated in the long photoperiod and continuous illumination groups, significantly decreased in the short photoperiod and total darkness groups, and unchanged in the reversed LD cycle regime. The results indicate that the day-night variations of 5-HT and MAO are photoperiod-dependent and are controlled by the prevailing LD cycle during the gonadal preparatory phase of the annual reproductive cycle. The photoperiod effects on the gonadal activity may be mediated through the hypothalamic serotonergic system.     

Annual cyclic,and castration and cyproterone acetate-induced,changes in sialic acid content of the seminal vesicle of the catfish,Heteropneustes fossilis (Bloch)

In this study, the presence of sialic acid is demonstrated in the seminal vesicle (SV) of Heteropneustes fossilis. Sialic acid levels show an annual variation that was correlated with the secretory activity of the SV (expressed as the SV somatic index (SV-SI)) with the index being lowest in resting phase (January) and highest in spawning phase (July). Sialic acid was not detectable from November to March (resting to mid-preparatory phases). Castration (3 weeks) induced a significant rise in both SV-SI and SV sialic acid content possibly due to an elevated local production of androgens under the influence of increased gonadotropin secretion. Cyproterone acetate treatment caused a significant decrease in both SV-SI and SV sialic acid content. The results suggest that secretion of sialic acid in the SV is influenced by androgens and its measurement can be used as a simple and reliable index for quantitative assessment of the functional testicular state.     

Response of fingerling stinging catfish,Heteropneustes fossilis (Bloch) to varying levels of dietary l‐leucine in relation to growth,feed conversion,protein utilization,leucine retention and blood parameters

Growth response of fingerling Heteropneustes fossilis (6.8 ± 0.2 g; 11.2 ± 0.3 cm) to dietary l ‐leucine levels was assessed by conducting 8‐week feeding trial in a flow‐through system (1–1.5 L min^?1) at 28 °C water temperature. Casein–gelatin‐based isonitrogenous (380 g kg^?1; crude protein) and isoenergetic [17.9 MJ kg^?1; gross energy (GE)] basal diet was supplemented with different levels of l ‐leucine to achieve desired leucine levels ranging between 10 and 22.5 g kg^?1 dry diet. Analysed values were 9.9 (Lc_9.9), 12.4 (Lc_12.4), 15.1 (Lc_15.1), 17.4 (Lc_17.4), 20.1 (Lc_20.1) and 22.4 (Lc_22.4) g leucine kg^?1 diet. Fishes were stocked randomly in quadruplicates and fed to satiation at 07:00 and 17:30 h. Maximum absolute weight gain (AWG g fish^?1), feed conversion ratio (FCR), protein utilization efficiency (PUE%), leucine retention efficiency (LRE%) and haematological parameters were found in fish fed diet Lc_17.4. For precise determination of dietary leucine requirement of Singhi, AWG g fish^?1, FCR, PUE% and LRE% were subjected to broken‐line and second‐degree polynomial regression analysis. Second‐degree polynomial regression analysis fitted the data more accurately (P > 0.05) exhibiting high R² values. Hence, based on this analysis, dietary leucine requirement of fingerling H. fossilis is recommended to be 16.5 g kg^?1 of the diet, corresponding to 43.4 g kg^?1 protein for developing leucine‐balanced commercial feeds.