Reproductive responses of Synodontis eupterus to different dietary melatonin levels under blue light conditions

This study evaluated Synodontis eupterus (squeaker catfish) reproductive responses maintained under blue light exposure and different melatonin dietary levels for 56 days, with dosage: 0 mg/kg (M0), 0.5 mg/kg (M0.5), and 1 mg/kg (M1). Each treatment consisted of 12 individually maintained broodstock (6 individuals of each sex), with 90.15 ± 16.66 g (males) and 89.51 ± 16.65 g (females) initial body weights. Fish were reared individually in 75 × 60 × 60 cm tanks under continuous aeration and blue LED light (550 lux; 465-467 nm). Assessments were conducted using defined subsamples: GSI, HSI, and gonadal histology from 3 fish/sex/treatment; hormone profiles from 4 fish/sex/treatment; and gamete quality, fertilization, and hatching rates from 3 spawning pairs/treatment. Dietary melatonin influenced several reproductive parameters, with the M0.5 treatment showing higher female and male GSI (10.99 ± 4.05 % and 0.51 ± 0.03 %), egg diameter (0.49 ± 0.02 mm), and fecundity (8.73 ± 2.64 eggs/g). Sperm concentration, viability, and motility were also higher in M0.5. Broodstock receiving 0.5 mg/kg melatonin exhibited earlier peaks of estradiol-17β and testosterone. Fertilization, hatching, and early larval survival and growth were highest in M0.5. Responses in the M1 group were generally lower than those in M0.5 across several parameters; however, these differences were not consistently significant, and therefore no definitive inhibitory effect is inferred. Overall, the findings suggest that a moderate melatonin dose (0.5 mg/kg) under blue light supports improvements in gonadal maturation, gamete quality, and early larval performance in S. eupterus, warranting further validation with larger experimental replication.