BENEFITS OF STARVATION IN DISEASE MANAGEMENT IN RED SEA BREAM (Pagrus major) AQUACULTURE  

Red sea bream (Pagrus major), owing to its high adaptability to captive conditions, acceptance of pellet feed and high commercial value, has good aquacultural and recreational fisheries prospect. However, multitudes of bacterial diseases, mostly by Edwardsiella tarda, have been reported to cause severe losses to the red sea bream aquaculture. Various workers have previously speculated on the effect of decreased food intake on immune enhancement and better survival capacity of the fish when challenged with several pathogenic bacteria. The present study was designed to elucidate the effect of starvation on the metabolic adaptations, transcriptional modulations and cellular degradation in the E. tarda infected red sea bream.

Four-month old red sea breams were divided into eight experimental groups with two replicates and reared for a period of 20 days. The different groups were named as fed-placebo (FP), starved-placebo (SP), fed-infected (FI), starved-infected (SI), pre-fed-placebo (PFP), pre-starved-placebo (PSP), post-fed-infected (PFI), and post-starved-infected (PSI), depending upon their feeding and infection regime. Virulent strain of E. tarda was used to infect the fish. All treatment groups were sampled immediately after 5 hrs (0 dai (days after infection)), 5^th and 10^th day after immersion (5 and 10dai, respectively).

In the present study, short-term food deprivation resulted in reduced hepatosomatic index, and drastic depletion in liver glycogen storage and vacuole formation, in a time responsive manner. Starvation decreased the transcription of several iron homeostasis related genes (Hepcidin, etc.) at later stages (10dai) in both liver and gill. Significant alteration in glucose and energy metabolism, and decreased activities of anti-oxidative enzymes was seen in starved groups. Relatively higher hemoglobin and phagocytic activity along with increased cytokines (TNFα, etc.) level was noticed in SI groups than the FI fish. Two-color immunohistochemistry showed maximum increase in P63-positive cells in the liver of SI and PSI groups. All together our data suggests that starvation, especially prior to infection, exerts multidirectional responses, which allows for better physiological adaptations during any infectious period, in red sea bream.