Others have found oral administration to be superior to immersion Nikl et al

Others have found oral administration to be superior

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(Anderson and Siwicki, 1994). Others have found oral administration to be superior to immersion (Nikl et al., 1993). Nikl et al. (1991) reported success at preventing infection by Ren. salmoninarum. Similarly, Matsuyama et al. (1992) used the glucans schizophyllan and scleroglucan to protect against streptococci. Thus, 2-1 Omg of glucans/kg offish, when administered by i.p. injection, enhanced resistance of yellow- tail to streptococcicosis. In particular, there was an elevation of serum complement and lysozyme, and an increase in phagocytic activity of pronephros cells. Initially, success only appeared to result from injection of the glucans into fish. Yet, claims have now been made that application via food also meets with success (Onarheim, 1992). Also, resistance to streptococcicosis and vibriosis has been enhanced following the oral administration of peptidoglycan from Bifidobacterium (Itami et al., 1996) and CI. butyricum (Sakai et al., 1995), respectively. Peptidoglycan, derived from Bifidobacterium thermophilus, was administered in
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Control 379 feed (fed at 3% of body weight daily) at 0.2 and 2mg/kg to rainbow trout of 0.12g average weight for 56 days (Matsuo and Miyazono, 1993). These doses were the equivalent of 6 or 60 |ig of peptidoglycan/kg body weight offish/day. Sub-groups of the fish were challenged on day 26 and 56 by immersion in V. anguillarum, with mortalities monitored over a 21 day period. At the half-way point of the feeding trial, survival following challenge with V. anguillarum was markedly higher than among the controls. Yet, at day 56 there was not any apparent difference in survival between the experimental groups and controls. So, it would appear that the benefits of this approach were short-lived, and in the long term were not beneficial (Matsuo and Miyazono, 1993). Vitamin E and iron sulphate, dosed at 2,500 mg/kg and 60mg/kg, respectively, have been reported to be beneficial in enhancing the immune response of channel catfish, especially by improved phagocytosis, to Edw. ictaluri (Wise et ai, 1993; Lim et al, 1996; Sealey et al, 1997). Certainly, this aspect of research looks promising, and it is envisaged that other immunostimulatory compounds will be identified in the future. Feeding with 3,3',5-triiodo-L-thyronine at 5 mg/kg of feed for 60 days to rohu (Labeo rohita) led to enhanced growth, serum protein and globulin levels, superoxide production of the neutrophils and antibodies against Aer. hydrophila. Moreover, there was a reduction in mortalities after challenge with Aer. hydrophila compared with the controls (Sahoo, 2003). Injection of 0.25 or 0.5 |ig/fish of synthetic cytidine-phosphate-guanosine (CpG) oligodeoxynucleotide (ODN) with olive flounder led to higher chemiluminescence by phagocytes; supernatants from leucocytes, which received CpG ODN as a pulse, induced much higher respiratory burst activity after 3-7 days. Additionally, the fish which received CpG ODN were better protected against challenge with Edw. tarda (mortality = 17%) compared with the controls (mortality = 92%) (Lee et ai, 2003).
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