New record of marine tube dwelling diatoms Navicula mollis and Navicula rusticensis from South Andaman, India

294-296The occurrence of two species of marine tube dwelling diatoms was reported from the water samples collected from Phoenix Bay, South Andaman. The recorded species were Navicula mollis and Navicula rusticensis. The morphometric dimensions of these two species were also given. Along with the tube dwelling diatoms, co-habitant diatoms were also observed in the present study. This was the first report of tube dwelling diatoms from Indian waters particularly from Andaman Islands

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

48-54Present study has revealed the feeding performance of pearl oyster P. margaritifera 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 Chlorella marina and Nanochloropsis oculata showed a less retention than that of the other larger algal species, Pavlova salina, Isochrysis galbana and Chaetoceros calcitrans. 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

Growth, survival and byssal attachment of the blacklip pearl oyster Pinctada margaritifera (Linnaeus 1758) spat exposed to different salinities

The influence of salinity on growth, survival and byssal fibre attachment of the blacklip pearl oyster, Pinctada margaritifera spat was assessed. P. margaritifera enjoys a coastal distribution in the intertidal reef flats of Andaman and Nicobar Islands, with maximum density at 5 -10 m depth, where drastic changes in environmental parameters such as salinity, temperature and turbidity occur. Spat showed comparatively good growth in terms of instantaneous growth rates (IGRs) of dorso-ventral measurement (DVM), antero-posterior measurement (APM) and total weight (TWT) in a wide range of test salinities from 19 to 37 psu; IGRs were drastically decreased in spat reared at lower and higher salinities outside of this range. The highlight of the present study was better growth performance and 100% survival of P. margaritifera spat at lower salinity levels (22-28 psu) than in the ambient salinity (31 psu). The study also showed that sudden exposure to a higher salinity (above 40 psu) will be helpful for detachment of P. margaritifera spat from settlement tanks in the hatchery to facilitate stress-free spat transfer to sea farming systems. This will be useful in adopting the Japanese technique on post-operative culture for producing high quality pearls from P. margaritifera. </jats:p