Effects on the Growth and Digestive Enzyme Activity in Nile Tilapia Fry (Oreochromis niloticus) by Lead Exposure

Lead is a metal capable of affecting physiology and metabolism in fish, including Nile tilapia (Oreochromis niloticus). However, few studies have evaluated the effects of lead on digestive enzyme activities in fry. At that stage, independent feeding begins, and there is increased demand and consumption of food, so chronic exposure to metal during this stage of development would cause null or minimal growth in organisms. In this study, fry from Nile tilapia was used to evaluate the effects of lead acetate by chronic exposure on the growth and the activities of the digestive enzymes after 30 and 60 days exposures. Four treatment groups 0.025, 0.050, 0.075 and 0.100 mg/L of lead acetate and a lead-free control were established. The activity of enzymes decreased, in the case of acidic proteases after 30 days and lipases after 60 days of exposure, from 0.025 and 0.050 mg/L of lead acetate, respectively. The amylase activity increased in metal-treated, while the chymotrypsin decreased partially at 60 days. Lipases decreasing activity might be causing an increase of triglycerides (lipids) and body mass observed during the first 30 days of exposure. Concentrations, equal to or above 0.075 mg Pb/L, cause significant effects on size and weight of fry, with nearly 54% lower than controls. At chronic exposure and early stage of development, the enzymatic activity is partially reduced along with body weight gain, which would affect subsequent growing and aquaculture production. The digestive enzyme response is discussed as a possible limited biomarker of exposure, to be used in biomonitoring.