Discussion
Intensification of aquaculture has led to the promotion of conditions that favor the use of a wide range of chemicals, including antibiotics (Rodgers and Furones, 2009). In the present
study, the O. niloticus in G3 and G2 showed significant increase in final body weight (g), weight gain (g) and significant decrease in food conversion ratio (FCR) when compared to the
control group. A similar trend was found by Sanchez-Martinez et al. (2008) who studied the effect of supplemented Channel Catfish (I. punctatus) feeds with oxytetracycline, they observed
that oxytetracycline-treated catfish exhibited a significant increase in weight gain to values higher than those of controls,suggesting a growth promotion action of this antibiotic agent.
The attribution of improvement of growth and feed efficiency as a result of dietary antibiotic supplementation has been subjected to a wide speculation by many investigators. Jukes et al.
(1956) mentioned that, the reduction in the gut wall and villus lamina propria has been used to explain the enhanced nutrient digestibility observed with antimicrobial growth promoters.
Waibel et al. (1991), Caston and Leeson (1992) reported that
Figure 1
Effect of oxytetracycline and florfenicol on O. niloticus growth performance (A) Bars indicate initial body weight, final body,weight gain (g) and (B) Bars indicate food conversion ratio (FCR). Data presented as mean ± SD. Different letters stand for statistically significant differences at P < 0.05
Figure 2
Effect of oxytetracycline and florofenicol on O. niloticus immunological status (A) Serum IgM and phagocytic activity, (B)serum lysozyme activity. Data presented as mean ± SD. Different letters stand for statistically significant differences at P <0.05.
antibiotics limit microbial population numbers and their production of toxins and by-products which reduce the competition with the host for vital nutrients, and they enhance the
absorption and utilization of nutrients due to a thinning of the intestinal wall. Gaskins et al. (2002) demonstrated that the effect of oxytetracycline in growth promotion depends on the reduction of the gastrointestinal tract bacteria. Dibner and Richards (2005) demonstrated that the reduction in microflora,and its consequences, may be the underlying mechanism for the beneficial effect of antibiotics.
Herein the immunological study showed insignificant differences between G3 and a control group in the immunoglobulin M (IgM) total level while there was a significant decrease in G2. The phagocytic activity of G3 had an insignificant decrease than the control group. Lysozyme activities of all treated groups significantly increased compared to the control group. Other works emphasized the same results and found that OTC suppresses the antibody production, the level of circulating leukocytes as well as phagocytic activity in rainbow trout, sea bream and Koi carp (Lunden et al., 1998; Serezli
Figure 3
Effect of oxytetracycline and florofenicol on ALT and AST activity of O. niloticus. Data presented as mean ±SD.Different letters stand for statistically significant differences at
P <0.05.
Figure 4
Effect of oxytetracycline and florofenicol on (A) urea and (B) creatinine value of O. niloticus. Data presented as mean ± SD Different letters stand for statistically significant differences at P < 0.05.
การแปล กรุณารอสักครู่..