| Summary: | The effect of heterologous fish vitellogenin (Vg)- implantation on growth performance in the juveniles of the catfish, Clarias gariepinus, was evaluated under ambient photoperiod and temperature during February–April (experiment 1) and again at May–August (experiment 2). Compared to either unimplanted (control) or bovine serum albumin (BSA)-implanted group, juveniles (average body weight: 3.5–4 g) implanted (im) with Vg pellets (each containing 100 μg of Clarias batrachus Vg, three per fish, at one month interval), revealed significantly (P < 0.05) higher specific growth rate (SGR) at 90 days during both time frames. Congruent with accelerated somatic growth due to Vg-implantation, a trend of increase in plasma level of growth hormone (GH), estradiol-17β (E2) and testosterone (T) was recorded during expt. 1. While plasma E2 and T did not vary significantly, Vg-implantation promoted significant (P < 0.05) increase in plasma GH level in both the sexes during the course of expt. 2. Moreover, Vg-implantation could trigger significant alteration in gonadal growth; while control testis contained primarily spermatogonia (SG) and spermatocytes (SC), appearance of spermatozoa (SZ) was noticed in either Vg-implanted (expt. 1) or both BSA- and Vg-treated juveniles (expt. 2). Conversely, a robust increase in S III yolky oocytes was observed in Vg-implanted ovary during May–Aug; but not during expt. 1 (Feb–Apr). However, oocytes at earlier stages (S I and/or S II) of follicular growth and development were predominant in control ovary. Though the underlying mechanism is not yet clearly understood, present data indicate that implantation of Vg pellets in juvenile C. gariepinus may influence somatic growth indices; e.g., body weight gain and GH synthesis along with precocious gonadal growth in a manner sensitive to gonadal steroidogenesis.
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