Microbiology of rainbow trout (Oncorhynchus mykiss) surface tissue and of the water production ponds

Abstract

Microbial quality of rainbow trout surface tissue (Oncorhynchus mykiss) and production ponds water where it is produced in northwestern Chihuahua state, Mexico, was assessed in trouts (200 fishes) and water (260 sampling) from nine fast stream, thirteen concrete and six dirt fish ponds during summer and winter seasons. Microbial quality was determined by measuring aerobic mesophiles, total coliform count, faecal coliforms and Salmonella spp., samples from the deep washing of the fish surface and the ponds. Temperature and oxygen content of water were also measured. The results for trout washing water indicated only significant differences (P<0.05) for aerobic mesophiles between seasons (398.11 CFU/mL in winter and 19,489.45 CFU/mL in summer), Salmonella spp. was not present in any fish or pond water samples. Aerobic mesophiles showed also higher numbers in water for summer season at water entrance, middle and discharge points of the different fish production ponds. Water temperature and oxygen content were always inside the normal range values considered for trout production in the three types of ponds, but water oxygen content showed significant difference (P<0.05) between the fast stream and dirt pond systems. It can be concluded, from the results obtained that surface tissue of the trout produced in the studied mexican northwestern Chihuahua State, ponds has excellent quality, having very low microbial counts and that water discharged from the production systems evaluated do not deteriorate the ecosystems, according to the government present regulations.