Effects of GnRH analogs on strip spawning and steroid plasma levels of Colossoma macropomum

The tambaqui ( Colossoma macropomum ) is the main native species reared in aquaculture in Brazil and in its neighboring countries. Currently, the production of fries is based on the use of carp pituitary extract (CPE), which has intrinsic disadvantages such as impurity, the presence of unknown components, and discontinuity of supply. Three GnRH analogs (GnRHa) were tested to stimulate artificial reproduction in tambaqui. A total of 28 mature females were used in the following treatments: T1: synthetic salmon GnRHa—5.0 μg/kg combined with domperidone (2.5 mg/kg); T2: gonadorelin—60 μg/kg; T3: buserelin acetate—0.7 μg/kg; and T4: CPE—5.5 mg/kg. Spawning success under strip spawning, quantity and quality of the eggs were evaluated. The plasma concentrations of 17β-estradiol, 17α-hydroxyprogesterone, and 17α,20β-dihydroxy-4-pregnen-3-one were assessed before hormonal treatment and after stripping. All CPE-treated females released eggs via stripping, as occurred in 86% of the females treated with sGnRHa, 86% released eggs with gonadorelin, and 57% released eggs with buserelin. Degree-hour (DH) for strip spawning was higher in the GnRHa groups than for CPE ( p ≤ 0.001). Total mass of the eggs, number of eggs/g of spawn, relative fecundity, fertilization index, and the rate of embryo survival were similar in all groups. There was a significant increase in steroid levels in all groups after receiving the hormones, including in the fish that did not release eggs under stripping. Although the commercial GnRHa did not stimulate the final maturation and/or ovulation in all females, they induced the ovulation of eggs in equal quality and quantity to the CPE, thus confirming the great potential of such drugs in the artificial reproduction of native neotropical fish.