Reproductive aspects of freshwater fishes exposed to pesticide-contamined environments: A systematic review

Fish are the predominant group of vertebrates in aquatic environments, and they are directly affected by the presence of contaminants in water bodies, which undergo changes in the structure and function of communities and dynamics of the populations. The aim of the present study was to conduct a systematic review of studies that analyze the reproductive aspects of freshwater teleosts in environments contaminated by pesticides. A systematic search for scientific articles was carried out from 2000 to 2019 using the "Web of Science" database, using the descriptors "fish reproduction", "contamination", "toxicology", "ecotoxicity" and "biomonitoring", combined with the use of boolean operators "AND" and "OR". The content analysis was performed based on the titles and the summary, with a first screening. Then, 98 articles were read in full, with 40 being selected. 24 species of fish were recorded, with a predominance of Danio rerio (17.5%). Insecticides were present in 78% of the studies, mainly Endosulfan (35%) and Cypermethrin (13%). Reproductive endocrine disorders were the most reported pathways of action (57.5%). The effects of pesticides on the reproduction of freshwater teleosts are evident, requiring studies on structural changes in gonads and a decrease in the quality of gametes.

Digestive enzyme system of larvae of different freshwater teleosts and its differentiation during the initial phase of exogenous feeding

Activities of digestive enzymes and main histological characteristics of the intestine were investigated in larvae of three salmonid species (Coregonus maraena, C. atterensis, Thymallus thymallus), of burbot (Lota lota), and pikeperch (Sander lucioperca) at the onset of exogenous feeding (0 day degrees (°d)) and at 250°d thereafter. At the onset of exogenous feeding the activities of proteolytic, lipolytic, and carbohydrate splitting enzymes were detected in the intestines of all species. The enzymatic activities showed significant species specific differences indicating specializations in functionality and digestion ability. In C. atterensis and L. lota the activities of most enzymes were low in comparison to the other investigated species and therefore their digestive system was only poorly developed. In S. lucioperca it was moderately developed and in T. thymallus and C. maraena well-developed. After 250°d, the activities of the investigated enzymes changed in a very species specific way. Histologically, the intestines of the investigated species revealed no species specific differentiations at the onset of the first feeding with the exception of the absence of goblet cells in L. lota and C. atterensis. These differentiated after 250°d.