Effect Crude Protein Levels on the Broodstock Spermatic Quality of Nile tilapia (Oreochromis niloticus)

Abstract

Objective: The purpose of this work was to evaluate the reproductive performance and the toxicity of DMSO cryoprotectants and methanol toward semen of Nile tilapia (Oreochromis niloticus), fed using diets containing different Crude Protein (CP) levels. Study Design:  completely randomized design. Place and Duration: The experiment was performed for 90 days, at the Hydrobiology and Fish Culture Station of Eletrobrás Furnas, in São José da Barra, State of Minas Gerais, Brazil. Methodology: 15 broodstock males with around 30 months old were used. They were stocked in ten reservoirs of storage capacity around 8 cubic meters, in which treatments consisted of five diets containing different levels of crude protein (32, 34, 36, 38 and 40%) and 9.5kcal/kg of digestible energy per gram of protein. For the in-natura semen, the statistical analyses were carried out using data obtained from a completely randomized design, while for diluted semen, the completely randomized design was also used but, in 5×2 factorial scheme, representing 5 levels of protein and 2 cryoprotectants. Results: The hepatosomatic index (HSI), gonadosomatic index (GSI), rate and duration of Nile tilapia males in-natura semen motility were not influenced (p>0.05) by the crude protein levels in the diets. After dilution, significant differences were observed for motility (p=0.053) and motility duration (p=0.021). The effects of third and fourth degree occurred for the rate (p=0.0349) and duration (p=0.0220). As these adjustments do not allow a biological interpretation, the Tukey multiple comparison test was used. The diet containing 36% of crude protein level showed mean motility rate similar (p>0.05) to those of treatments containing 32, 34 and 40% of crude protein and mean motility rate inferior (p<0.05) to treatment containing 38% of crude protein. For motility duration, fish fed using diet containing 38% and 40% of crude protein showed significant differences (p<0.05) to only the group of fish fed using diet containing 34% of crude protein. Conclusion: Diet containing 32, 38 and 40% of crude protein level does not deteriorate the semen quality, so that may be used for feeding tilapia broodstocks. As protein is an expensive input, we can infer that 32% of crude protein is sufficient to determine good quality gametes.