Dietary protein requirement in genetically selected magur (Clarias magur) broodstock: Expression of reproduction related genes

To optimize the dietary crude protein (CP) levels on the reproductive performance of genetically selected magur (Clarius magur), a 90-day feeding trial was conducted. One hundred and fifty brooders, ranging from 95.33 to 96.16 g, in a 1:1 male-to-female ratio, to fifteen 1000 L tanks, with each treatment replicated thrice were distributed following a completely randomized design. Five semi-purified diets with differing protein levels (25 %, P25; 30 %, P30; 35 %, P35; 40 %, P40; and 45 %, P45) were prepared for the trial. The results displayed that fish fed diets comprising 35 % and 40 % dietary crude protein (CP) exhibited higher specific growth rate (SGR), respectively. Similarly, these groups had higher weight gain percent (WG%) with reduced feed conversion ratio (FCR), respectively in comparison to other groups. The gonadosomatic index (GSI) of females significantly increased (P < 0.05) up to 40 % protein levels and then decreased, while males exhibited reduced values only in the P45 group. Both male and female hepatosomatic index (HSI) increased significantly (P < 0.05) with increasing dietary CP levels. Dietary CP level increment resulted in decreased visceral fat index in females but had no effect on males. Absolute and relative fecundity significantly (P < 0.05) increased up to 40 % dietary protein level. Estradiol levels in females increased with rising protein levels up to 40 %, but decreased at the 45 % level. Conversely, 17-α,20-β di-hydroxy progesterone (DHP) increased significantly in females from 35 % to 45 % protein level, while males exhibited the highest levels at 30 % and 35 % protein levels. In males, mRNA expression of follicle-stimulating hormone receptor (FSHR) was lowest, whereas luteinising hormone receptor (LHR) and 11β hydroxysteroid dehydrogenase (11β HSD) expression increased in the P30 and P35 groups (P < 0.05). Females showed significantly increased mRNA expression of LHR and CYP19a1 (Cytochrome p450 aromatase) in P35 and P40 groups (P < 0.05). Regarding reproductive performance metrics such as fertilization rate (%), hatching rate (%), and larval survival (%), the P35 and P40 groups exhibited significantly higher values (P < 0.05). Second-order polynomial regression and broken line analysis revealed the optimum dietary CP for magur broodstock based on GSI was 36.79 %, while based on reproductive performance, it ranged between 36.1 % and 36.14 %.