Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 2002
Publication Date: September 1, 2003
Citation: Lim, C.E., Klesius, P.H. 2003. Influence of feed deprivation on hematology, macrophage chemotaxis, and resistance to edwardsiella ictaluri challenge of channel catfish. Journal Of Aquatic Animal Health; Vol.15, No.1, pp.13-20. Interpretive Summary: Enteric septicemia of catfish (ESC) caused by the bacterium Edwardsiella ictaluri causes major economic losses to catfish farmers in the Southern United States. The importance of nutritional status on the susceptibility of fish to infectious diseases is a well-recognized phenomenon. Currently, some catfish farmers do not feed during ESC epizootics and believe that this practice reduces mortality due to ESC. The efficacy of this practice has not been well documented. Thus, this study was conducted to evaluate the effect of feeding regimens (non-fed, fed daily to apparent satiation, fed every other day to apparent satiation, and non-fed for three weeks followed by daily feeding during the fourth week) on growth response, hematology and resistance of channel catfish to E. ictaluri. Results obtained from two separate four- week feeding studies showed fish that were not fed lost weight, those fed daily gained the most weight, followed by the group fed every other day and fed during the fourth week. Feed efficiency ratio followed the same trend as weight gain for study I but did not differ for study II. Survival rates were not affected by feeding regimens. Fish that were not fed or fed during the fourth week became anemic (low levels of leukocyte count, erythrocyte count, hematocrit and hemoglobin). The number of white blood cells migrated in response to the substance produced by the bacteria, E. ictaluri was lowest for the non-fed fish and highest for the daily fed fish. Mortality due to ESC was highest (100%) for fish that were not fed for four weeks before and two weeks after infection challenge, and was followed by fish that were not fed for four weeks before and fed daily for two weeks after challenge (98.7%). Fish fed daily or every other day and continued on the same feeding regimens for two weeks after E. ictaluri infection had significantly reduced mortality. It is suggested that, in the environment where natural food is absent, fish should be fed at least once every other day to improve their resistance against ESC.
Technical Abstract: A series of two feeding studies was conducted to evaluate the effect of feeding regimens on growth response, hematology, immune response and resistance of channel catfish to Edwardsiella ictaluri. The first study evaluated the effect of feeding regimens on growth, hematology and immune response of channel catfish. The second study evaluated the effect of feeding regimens on the growth response and resistance of channel catfish to E. ictaluri. Juvenile channel catfish averaging 22.5 g (study I) and 18.5 g (study II) were fed the following feeding regimens for four weeks: Non fed; fed once daily to satiation; fed every other day to satiation; non fed for three weeks then fed once daily to satiation during the fourth week. Growth response and feed efficiency ratio were determined for both studies at the end of week 4. Hematology and immune response were determined at the end of week 4 for study I only. At the end of week 4, fish from three replicate aquariums of each treatment (study II) were randomly divided into six groups of 25 fish and challenged with E. ictaluri by bath immersion. Fish in three random aquariums of the same treatment stayed on the same feeding regimen, those of the other three aquariums of the non-fed treatment were changed to fed daily and whereas the remaining treatments were switched to the non fed for an additional two weeks. In both trials, fish that received no feeding lost weight, those fed daily gained the most weight, followed by the groups fed every other day and fed during the fourth weeks. Feed efficiency ratios were a reflection of weight gain and significantly differed (P < 0.05) among treatments for study I but were similar for study II. Survival rates did not differ significantly among treatments for both studies. Fish which were not fed or fed on the fourth week became anemic as indicated by reduced white blood cell count, red blood cell count, hematocrit and hemoglobin. The values of these parameters were also low for fish fed every other day but the differences were not always significant. Mean macrophage migration in response to E. ictaluri exoantigen significantly differed among treatments. The values were lowest for the non-fed group and highest for the daily-fed fish. Mortality due to ESC was highest for the non-fed/non-fed fish (100%) and was followed by the non-fed/daily fed fish (98.7%). Fish fed daily or fed every other day and continued on these feeding regimens had significantly lower mortality. These studies show that fish fed less than satiation once daily gained less weight, became anemic and had reduced macrophage chemotaxis. Fish fed daily or every other day prior to or after challenge was more resistant to ESC than were the non-fed fish.