Spawning performance and egg quality of wild-caught and first generation southern flounder Paralichthys lethostigma broodstock induced with piscine and mammalian GnRH analogs

Abstract

Spawning performance and egg quality were compared in wild-caught and F1 generation southern flounder broodstock following induction with mammalian mLHRHa or piscine sGnRHa at different doses. Forty F1 and 33 wild vitellogenic females (mean oocyte diameter ≥ 0.385 mm) were implanted with an 80% cholesterol-20% cellulose pellet at doses (μg/kg bw) of 0 (control), 5 (low), 25 (mid) and 50 (high) mLHRHa, or with similar doses of sGnRHa. Ovulated females (N = 5–8 per treatment) were strip-spawned and eggs were fertilized in vitro with sperm from two males. Egg quality was categorized according to fertilization and hatching success: 75–100% (high), 50–75% (medium-high), 25–50% (medium-low), and 0–25% (low). Egg production (number of eggs/kg female bw × 103) was highest at the low dose of mLHRHa in F1 females (146.4) and sGnRHa in wild females (128) and was lowest at the intermediate dose sGnRHa in F1 females (61.9) and the high dose sGnRHa in wild females (40.6). Number of fertilized eggs produced per kg bw (× 103) was highest at the low dose mLHRHa in F1 females (113.5) and sGnRHa in wild females (95.4) and lowest at the high dose sGnRHa in F1 females (18.7) and sGnRHa in wild females (7.8). Number of yolksac larvae produced per kg bw (× 103) was highest at the low dose of mLHRHa in F1 females (74) and sGnRHa in wild females (73.5) and was lowest at the high dose of sGnRHa in F1 females (2.0) and in wild females (1.2). Number of larvae per kg bw (× 103) surviving to 96 h post-hatching was highest at the low dose mLHRHa in F1 females (67.5) and sGnRHa in wild females (66.5) and was lowest at the high dose sGnRHa in F1 (0.72) and sGnRHa in wild females (0.68). In F1 females, larval production was significantly greater (P < .01) at lower doses and greater (P < .01) for mLHRHa than for sGnRHa at all doses. For wild females, larval production was greater at lower doses of sGnRHa, with the inverse trend observed for mLHRHa (hormone dose × type interaction, P < .05). Taurine concentrations (nmol/mg dw) were higher (P < .05) in ovulated eggs of high quality (27.4) than in eggs of med-low (14.8) and low (17.5) quality, supporting an important role in broodstock nutrition and in early development. The results help standardize GnRHa therapies for spawning of wild and F1 southern flounder.