Diets containing crude glycerin damage the sperm characteristics and modify the testis histology of Nile tilapia broodstock
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The effects of crude glycerin in the diets of male Nile tilapia (Oreochromis niloticus) on growth, seminal and spermatic characteristics, blood parameters, histological aspects of the hepatic and testicular tissue, and on the chemical composition of different organs/tissues were evaluated. For 10 months, the animals were fed diets containing 32% digestible protein (DP), 3200 kcal digestible energy (DE) . kg ration(-1) and five inclusion levels of crude glycerin (0, 4, 8, 12 and 16%). Growth, seminal and spermatic parameters were evaluated, and the plasmatic levels of calcium, triglycerides and glucose were measured. Gonadosomatic, viscerosomatic and hepatosomatic indexes were evaluated and combined with the histological parameters of the testicles and liver. Finally, the centesimal composition of the muscles, testis, liver and viscera were evaluated. The volume of semen released, fecundity, effective fecundity and plasmatic levels of glucose decreased proportionally (p < 0.05) to the increase of glycerin in the diet. The hepatosomatic index increased proportionally (p < 0.05) to the inclusion levels of crude glycerin in the diet. Fish fed on glycerin had the highest protein levels (p < 0.05) in the muscle and testicles. Histological assessment suggests that fish fed the lowest glycerin diet had the highest amounts of spermatozoids in the testicles. Other variables under analysis were not affected by diet (p > 0.05). The results show that, although crude glycerin does not impair growth, any inclusion level in the diet impairs the spermatogenesis process and damages the sperm characteristics of male Nile tilapia. Statement of relevance: Do not use the crude glycerin to the Nile tilapia males. (C) 2016 Elsevier B.V. All rights reserved.