THE ROLE OF GUT AND SEDIMENT BACTERIAL-FLORA IN THE NUTRITION OF CULTURED PEARL SPOT (ETROPLUS-SURATENSIS, BLOCH)

The heterotrophic bacterial flora in a brackishwater culture system in which the pearl spot Etroplus suratensis was reared on three differen t pelleted supplementary feeds was studied simultaneously with growth through a 9-month culture period. Three ponds designated P1, P2 and P3 were provided with isoproteinaeceous feeds, each of a different compo sition viz, ORT (containing groundnut oil cake, rice bran and tapioca) , P-ORT (ORT plus prawn waste) and oil P-ORT (P-ORT sprayed with an oi l mixture of 4:1 crude palm oil:fish liver oil). Growth was best with the supplementary feed ORT followed by P-ORT and then oil P-ORT. Total heterotrophic bacteria (THB) in the sediment and gut showed monthly f luctuations. The mean THB count in sediment from P1, P2 and P3 was 46. 67, 39.36 and 34.38 x 10(4) per g respectively. The THB count in the g ut was relatively higher than in the sediment, recording mean monthly counts of 191.25, 221.16 and 288.62 x 10(4) per g in P1, P2 and P3, re spectively. The gut bacterial flora were predominated by amylolytic fo rms. Protein hydrolyzers were highest in Pl (50.85%), followed by P2 ( 32.56%) and then P3 (24.53%). Sediment bacteria also showed a predomin ance of amylase producers, except in P3 where lipolytic forms dominate d. Coccal forms dominated the microflora and gram positive cocci were more abundant than gram negative cooci in both sediment and gut sample s. Fluctuations in temperature, salinity, dissolved oxygen and sedimen t organic carbon were reflected in the gut and sediment THB counts, on ly at extreme values.