Intestinal microfloral synthesis has been demonstrated in common carp (Hashimoto, 1953; Kashiwada et al., 1970; Sugita et al., 1991a), channel catfish (Limsuwan and Lovell, 1981; Sugita et al., 1990, 1991a), rainbow trout (Sugita et al., 1991b), tilapia (Lovell and Limsuwan, 1982; Sugita et al., 1990; 1991a; Shiau and Lung, 1993a) and Japanese eel, ayu and goldfish (Sugita et al., 1991a).
Intestinal microfloral synthesis appeared to satisfy the B12 requirement of Nile tilapia (Lovell and Limsuwan, 1982; Shiau and Lung, 1993a). Lovell and Limsuwan (1982) estimated that 11.2 ng per g body weight per day was synthesized by intestinal bacteria in tilapia. In channel catfish the synthesis rate was only 1.4 ng per g body weight per day (Limsuwan and Lovell, 1981), and Sugita et al. (1990, 1991a) showed that the bacterial population in catfish intestine was such as to have limited B12 synthesis. Thus catfish require dietary supplementation of B12 to prevent anemia (Limsuwan and Lovell, 1981).
Intestinal synthesis of vitamin B12 is significantly reduced in catfish if the diet lacks cobalt or if an antibiotic (succinylsulfathiazole) is added to the diet (Limsuwan and Lovell, 1981). Bacterial synthesis of B12 in carp has also be shown to be influenced by cobalt supplementation (Singhal, 1995). Exposure to high levels of water-borne cadmium was shown to decrease vitamin B12 stores in sunfish (Lepomis gibbosus) by increasing the excretion rate (Merlini, 1978).
