Evaluation of the effect of autochthonous probiotics and lactobacillus divergens on rotifers brachinous plicatilis and blue-fin porgy sparidentex hasta larvae

A standard probiotic, Lactobacillus divergens (ATCC, 35677) and three autochthonous isolates, obtained from cultured yellow-fin porgy Acanthopagrus latus (SHPB), wild silver pomfret Pampus argenteus (4SQ) and wild orange-spotted grouper Epinephelus coioides (5L8) were evaluated in the present study. They were tested for their antagonism against potential bacterial pathogens of blue-fin seabream Sparidentex hasta (sobaity). Antagonism of the probiotics against Vibrio alginolyticus, V. anguillarum, V. harveyi, V. parahaemolyticus, V. vulnificus and Streptococcus agalactiae was tested along with their ability to enhance growth of rotifers and survival of sobaity larvae. The results showed that the filter paper disk overlay antagonism method was suitable to assess the effect of probiotic bacteria on pathogenic bacteria. The autochthonous SHPB showed a significant zone of inhibition against all the pathogenic bacteria with a distinctive competitive exclusion. The other probiotics showed some effect, but they were unable to inhibit the growth of all the pathogenic bacteria tested. The addition of SHPB and L. divergens increased the growth performance in respect to cell count of the rotifer population with time, while the 4SQ and 5L8 showed lower cell proliferation response compared to the control. The effects of dietary administration of either of SHPB or L. divergens and their combination on sobaity larval survival were investigated. All the probiotics tested showed significant survival rate of larvae compared to the control. The survival in L. divergens fed larvae was the highest, 11.7%, whereas it was 9.2% in the probiotic combination-fed larvae, 8.9% in SHPB and 6.3% in the control. After the challenge against vibrio harveyi (0.1 mL of 10⁹ cells ml^-1), the mortality of the fish larvae receiving the diet supplemented with the SHPB and mixture of SHPB and L. divergens was significantly lower than that observed in the control.