Studies on bacteria in fish species of commercial importance at the Aquaculture Unit in Nigeria

Abstract

Bacteria diseases are widespread and can be of particular importance in fish farming. Bacteria exist as micro
flora in water until certain environmental conditions such as poor water quality occur, which could impose a
stress on fish, thereby making them vulnerable to infection, most especially by pathogenic bacteria. This
study was carried out to assess and compare the bacteria diversities and population in Clarias gariepinus,
Sarotherodon melanotheron and Oreochromis niloticus, in the three grow out ponds of the aquaculture unit
of the Department of Marine Science and Lagoon Front of the University of Lagos. It also aims at determining
their public health significance. The experiment was carried out between May-September 2013. Water
samples were collected from the three grows out ponds in the Department of Marine Sciences and from
Lagos lagoon Front of the University of Lagos. In each case, water samples were analysed for the possible
indicator organisms of faecal and industrial pollutions such as Escherichia coli, Staphylococcus aureus,
Salmonella spp., feacal streptococcus, Vibrio spp., and Clostridium spp. From the result obtained, all the
bacteria listed above were first seen as common bacteria in all the samples of water analysed. Further
studies (biochemical tests) also reveal bacteria such as Klebsiella spp., Proteus spp., Enterobacter
aerogenes, Citrobacter spp. and Pseudomonas aeroginosa. Moreover, the same indicator bacteria seen in
water samples were also detected in the different body parts (flesh, mouth, gill and gut) of each of the fish
species analysed, both from the Departmental ponds and Lagoon front, except Clostridium perfringes (C.
welchii), Vibrio cholera and Salmonella typii which were found in the gut of those fish species from the
departmental ponds A-C and in the mouth, gill and gut of the fishes from lagoon front. The population of
each of these bacteria was found to be highest in the gut region, followed by the gill, the mouth and least in
the flesh. There was no significant difference in the population of each of the bacterial across pond water
(P>0.05). Same is the case with each bacteria analysed across body parts of the fish species (skin, mouth, gill
and gut) in the Departmental ponds, that is, no significant difference (P>0.05). But, when compared with the
lagoon front (both for water and fish samples) the difference was highly significant (P<0.05). None of the
population of the bacteria in the ponds exceeds the limit for human consumption. The bacteria load in the
lagoon fish (skin, mouth, gill and gut) was higher than the recommended limit for human consumption.
Therefore, they are not fit for consumption most especially samples from the mouth, gill and gut, except
effective processing treatment is employed before consumption. Due policy should also be taken by the
government to curtail the tradition of indiscriminate discharge of untreated effluent into the lagoon.