Evaluation of the Commercially-Available Probiotic Lymnozyme as an Effective Control of Bacterial Infections in Channel Catfish
Type of DegreeThesis
Fisheries and Allied Aquacultures
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A major problem of commercially-cultured channel catfish (Ictalurus punctatus) in the S. E. United States is disease-related mortality. Probiotics may reduce diseases. A series of pond and challenge studies were conducted to determine the effects of the commercially-available probiotic LymnoZyme® on production characteristics and survival of channel catfish exposed to Edwardsiella ictaluri, causative agent of enteric septicemia of catfish (ESC). Two pond studies were conducted in six 0.04-ha earthen ponds beginning on April 11, 2006 and on April 13, 2007 with channel catfish of mean weights of 9.8 g and 6.6 g stocked at densities of 12,350 and 4,942 fish/ha, respectively. Fish were grown for 210 and 43 days, respectively, with or without LymnoZyme®. Fish (32-d post-stocking) from the second study were used in the first challenge study. They were stocked into 18 57-L aquaria (15 fish/aquarium; n=3) with 32 L of flow-through water and exposed to 1.2 x 106 CFU/ml of E. ictaluri for 2 h under static conditions 6-h post stocking. A second challenge study (18 aquaria; 14 fish/aquarium) was conducted 43 days post-stocking using remaining fish from two control ponds. LymnoZyme® was added daily at 5 ml/aquaria (8-hr static exposure) to 12 aquaria (six from first stocking and six at the onset of mortality), with the remaining six as controls. Fish were exposed to 1.3 x 106 CFU/ml of E. ictaluri for 2 h. Both challenge studies lasted two weeks. The first study showed significant differences in mean mortalities between treatment (85%) and control (99%). In the second study, mortality rates in the continuously exposed LymnoZyme® treatment (45%) were significantly reduced compared to those from the control (80%) or those under application of LymnoZyme® after onset of ESC (75%). In the third study using specific pathogen free (SPF) channel catfish, all fish (15/aquarium; n=5) were maintained for 3 d prior to challenge with three treatments receiving LymnoZyme® daily and a control receiving none. The following treatments occurred post-challenge: control-no LymnoZyme®; 1-received no LymnoZyme®; 2-LymnoZyme® daily for the next 7 d; and 3- LymnoZyme® throughout study. Fish were challenged with 2 X 106 CFU/ml of E. ictaluri. Control fish had a mean mortality of 80%, while treatment 1, 2 and 3 had mean mortalities of 80%, 47% and 40%, respectively. A forth study using SPF fish (control) and surviving fish from treatment 3 from the third study was conducted to determine if fish had developed resistance to ESC. All fish (10 fish/aquaria; 10 aquaria; n=5) were challenged with 2 x 106 CFU/ ml of E. ictaluri. Control and LymnoZyme®-treated fish had 94% and 14% mortalities, respectively.