Microalgal Size, density and salinity gradients influence filter feeding of <i>Pinctada margaritifera</i> (Linnaeus 1758) spat

Abstract

Present study has revealed the feeding performance of pearl oyster <i>P. margaritifera</i> spat was comparatively better in salinities ranging from 28 to 37 ppt among the tested salinities. But a perfect feeding performance was noticed with a salinity between 31 to 34 ppt. Clearance rate, ingestion rate and retention efficiency of different sized algae showed that in these salinities spat can able to do a normal feeding activities in all the tested seston concentrations. these parameters were better in the optimal algal concentration of 50 x 10³ cells.ml^-1. Clearance rate and ingestion rate lower with diatoms than flagellates. Salinity, size of the food particle and its concentrations are also important factors influence the ingestion rate. The ingestion rate was proportionally increased with food concentration but the retention efficiency was inversely proportional. The smaller sized <i>Chlorella marina</i> and <i>Nanochloropsis oculata </i> showed a less retention than that of the other larger algal species, <i>Pavlova salina,</i> <i>Isochrysis galbana</i> and <i>Chaetoceros calcitrans</i>. The study has revealed that the best live feed for the blacklip pearl oyster spat should have a size of above 3 µm with cell concentration of 25 to 50 x10³ cells.ml^-1 required for nursery rearing.