RETORNO REPRODUTIVO DE FÊMEAS DE TAMBAQUI E QUALIDADE ESPERMÁTICA DE MACHOS ENDOGÂMICOS DE TILÁPIA-DO-NILO

Abstract

The tambaqui is a rheophilic species that must perform the piracema (swimming upstream to lay eggs) to reproduce, when in its natural environment. In fish farming, however, inducers must be used for its reproduction to occur. Compared to other fish species, Nile tilapia has reproductive advantages provided by its early sexual maturation and ability to reproduce throughout the year in favorable environmental conditions. The objective of this study was to examine the induced reproduction of Colossoma macropomum females at the beginning of the reproductive period and 75 days after the first spawning, as well as to compare the sperm characteristics of different genetic groups of Nile tilapia in three collections spaced 30 days apart. Experiment 1: eight 4-year-old females with an average weight of 6.7 kg underwent hormonal induction at the beginning of the reproductive period (October) and again 75 days after the first spawning (December). Reproductive traits of the females were evaluated on these two occasions. Of the eight females that spawned in the first reproductive induction, three (37.5%) spawned again after 75 days. All evaluated traits were similar in both spawns, except fertilization rate, which was lower (P<0.05) in the second spawn. Most females (66.7%) that spawned again (2nd time) after 75 days showed higher values than in the first hormonal induction for all evaluated traits, except fertilization rate. We concluded that return to reproduction in C. macropomum females can be achieved 75 days after the first induced spawning. Experiment 2: thirty specimens of Nile tilapia (500 g) were divided into three groups: (i) 10 inbred fish (AquaAmérica full-sibs, 25% inbreeding from parents); (ii) 10 non-inbred fish (AquaAmérica with no common ancestors up to the third generation, with inbreeding of at most 2%, without any common great-grandparent between parents); and (iii) 10 heterozygous fish (AquaAmérica × GIFT parents). Semen characteristics were evaluated in a computerized system (Sperm Class Analyzer) and membrane integrity and mitochondrial activity were analyzed. There was no significant difference in sperm characteristics between the genetic groups in the different collections, except for beat-cross frequency (BCF) in the first collection. When the collections of each genetic group were compared, only BCF in the inbred AquaAmérica group differed significantly (P<0.05), with a higher value observed in collection 3 (7.7 Hz) than in collection 2 (6.86 Hz). As regards membrane integrity and mitochondrial activity, only the percentage of damaged plasma membrane with high mitochondrial potential in the inbred AquaAmérica genetic group was lower (P<0.05) in collection 2 (0.29%) than in collections 1 (8.34%) and 3 (8.72%). Likewise, intact plasma membrane with high mitochondrial potential in the non-inbred AquaAmérica group was higher (P<0.05) in collection 2 (27.1%) than collections 1 (2.97) and 3 (1.72), whereas in the AquaAmérica × GIFT group, it was higher (P<0.05) in collection 2 (68.02%) than collections 1 (6.19%) and 3 (5.79%). In conclusion, BCF values in the non-inbred AquaAmérica variety are better in the first collection. This variable behaves differently according to the degree of inbreeding in the AquaAmérica variety throughout collections, with a marked contrast between membrane integrity and mitochondrial activity between collections.

Keywords: Colossoma macropomum, Flow cytometry, Oreochromis niloticus, Return to reproduction, Rheophilic fish, Sperm evaluation.