Effects of the natural daylight in the induced reprodution of tambaqui Colossoma macropomum (Cuvier, 1818)

Abstract

Tambaqui, Colossoma macropomum, is one of the most important fishes in the Brazilian fish culture, due to its good flavor, rusticity and rapid growth. Since it is an Amazon migrating fish, its ovulation and spawning do not occur in captivity; therefore the induced reproduction in this fish is always needed. The present work investigated the effects of the natural daylight on the ovulation of tambaqui, when it was induced with the common LHRH of veterinary use. Plasmatic levels of the hormone 17α OH-P was measured before and after hormonal injections. Seventeen mature females and sixteen males were used in the investigation. Females were induced to ovulate with the LHRH (gonadorelin), under two different photoperiodic protocols: In protocol A, the first hormonal injection started in early evening, while in the protocol B it started at early morning time. In each group, the second hormonal injection was done 12-13 after first injection. The total concentration of the LHRH applied in the female fish varied from 500-1,200 μg LHRH/fish. All male received a single dose of 50-100 μg LHRH/fish. No ovulation occurred in the females of the photoperiod A, while all females in the photoperiod B ovulated. There was statistic difference in the levels of the 17 OH-P hormone between the two groups, during the considered period of latency of the inducer hormone. The results appoint to the existence of a photoperiodic cue, which can favor the occurrence of the ovulation in tambaqui, when it is induced with the common LHRH of veterinary use.