Effect of feed availability on susceptibility of Nile tilapia, Oreochromis niloticus (L.) to environmental zinc toxicity: Growth performance, biochemical response, and zinc bioaccumulation

In natural aquatic ecosystems, fish often experiences periods of poor food availability or complete starvation. The shortage in the feed for fish may ultimately interfere with pollutants toxicity. Therefore, a study based on a 3 x 2 factorial design was conducted to evaluate if feed availability may interact environmental zinc (Zn) effects on Nile tilapia, Oreochromis niloticus (L.). Fish (25.2 +/- 0.88 g) were fed with 0.0, 0.5% body weight, or fed up to satiation with and without exposure to 5.0 mg Zn/L over 6 weeks. No significant differences were observed in water quality variables due to feed rations and/or Zn exposure except unionized ammonia concentrations, which increased as feed ration increased with Zn exposure; its highest value was observed at fish fed up to satiation with Zn exposure. Fish performance was adversely affected by Zn exposure and feed unavailability. The performance was maximized when fish fed up to satiation without Zn exposure, whereas least performance was observed at starved fish with Zn exposure. Additionally, Zn exposure elevated significantly glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and creatinine values, while total protein and total lipids in fish sera were significantly lower with Zn exposure as compared to the control group. All these variables increased significantly with increasing feed ration size. The cortisol value was inversely affected by feed availability and directly proportioned to Zn exposure. It is also noticed that crude protein and total lipids contents in whole-fish body increased significantly with increasing feed ration and decreased significantly with Zn exposure. Total ash content and Zn residuals in whole-fish body were significantly highest in starved fish with Zn exposure. This study concluded that the feed availability adversely affected Zn toxicity where feed availability to appropriate ration could minimize the deleterious effect of Zn toxicity on Nile tilapia performance and health, and vice versa. Statement of relevance: This paper presents data on the effect of feed availability on growth performance of Nile tilapia and its susceptibility to waterborne zinc toxicity via evaluating growth performance, whole-body measurements, and the biochemical response of Nile tilapia. Feeding fish up to satiation improved their welfare and reduced the impact of zinc toxicity and its bioaccumulation in whole-fish body and vice versa. Zinc exposure deteriorated the welfare of fasted fish or fish fed inadequate diet. (C) 2016 Published by Elsevier B.V.