Temperature and ph influence on bacterial pathogens infecting farmed Nile tilapia in aquaculture systems in Bungoma county, Kenya

Abstract

Protein needs in the increasing Kenyan population is getting critical particularly with the reduced land acreage for animal and poultry production. Aquaculture production, therefore, has been expanding in recent years through Governement support via financial and input subsidies in small scale farmers. However, fish farming just like other productive sectors face challenges which include fish diseases that constitute the largest cause of economic loss in aquaculture. The diseases that occur in fish are as a result of the interaction among the farmed fish, potential pathogens and the fish ponds environment. Environmental factors, temperature and pH influence bacterial infections in cultured fish. The fish bacterial infections are caused by Aeromonas, Edwardsiella, Flavobacterium, Francisella, Photobacterium, Piscirickettsia, Pseudomonas, Tenacibaculum, Vibrio, Yersinia, Lactococcus, Renibacterium, Streptococcus, Nocardia, Staphylococcus, Vagococcus and Weissella species. With this continued expansion, bacterial disease outbreaks are bound to increase. Most studies on fish diseases in Kenya have been done on fish in the wild. This study focused on characterizing pathogenic bacteria present in aquaculture systems in Bungoma County. At every fish pond, five water quality parameters namely temperature, dissolved oxygen, conductivity, pH and turbidity were assessed using a portable auto sampler. Further, fish were harvested from ponds using a seine net. Fins, scales and skin were removed from each fish and put in sterile bijou bottles. The harvested fish were opened dorso-ventrally using sterile scapels in aseptic conditions and mouth, gills, stomach, liver, kidney and intestinal contents were washed into the sterile bijou bottles where physiological saline was added and stirred with assistance of a mounted pin. The sampled fish were transferred to a microbiology laboratory in Nairobi where they were subjected to bacterial analysis including microscopy, culture methods and biochemical tests. The study showed that temperature and pH were outside the recommended levels of fish culture production. Further, pathogenic bacteria recovered were Vibrio vulnificus, Vibrio parahaemolyticus, Aeromonas hydrophila, and Pseudomonas aeruginosa from Nile tilapia. Vibrio vulnificus and Vibrio parahaemolyticus were isolated from gills and were found to be significantly different (P<0.001) across the six sub counties. In fish ponds water, Aeromonas hydrophila were isolated and found to be significantly different (P<0.016) across the sub counties. In addition, Streptococcus iniae were isolated from fish feeds. Therefore, efforts should be made to reduce the presence of bacterial pathogens in aquaculture in order to increase fish yields.