Ostracoda is a diverse group of aquatic crustacean and often infest the fishes and cause huge economic losses. In the present study, the infestation of Ostracoda Vargula tsuji in major food fishes Lethrinus ornatus and Carangoides gymnostethus was studied. A detailed investigation by using biotechnological and molecular tools, it was identified that Ostracoda present in these fishes was Vargula tsujii and the sample was deposited with GeneBank (NCBI MN889442).  An attempt was also made to study the abundance and degree of infestation for different seasonality viz post-monsoon, monsoon, presmonson and summer during 2019.  Weekly samples were made from Pamban (9.27°N, 79.22°E), Gulf of Mannar, fish landing center and reported the monthly average values.  Total 1405 ± 296.5 of L. ornatus were examined during Jan-Dec 2019, of which 285.5 ±70.2 (20.31%) were found infested with Ostracoda  and in the case of Carangoides gymnostethus, out of total 1235.9 ± 205.2 fishes examined, 201.4 ± 47.2 fishes were found with infestation i.e. 16.30% but varying with seasonality.  Both L. ornatus and C.  gymnostethuse fishes had V. tsujii attacked to their gills at a significant level (p < 0.05),  was an incidence of occurrence of infestation of V. tsujii in their buccal cavity of the intestinal track but not to the significant level.  The infestation of V. tsujii in fishes from Indian water is reported for the first time and its prevalence and abundance level for seasonality are presented in this study.

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Marine fisheries and biodiversity in the Gulf of Mannar, Tamil Nadu, were severely impacted by the blooms of dinoflagellate Noctiluca scintillans, on 10th October 2021. The bloom affected the marine biodiversity in a 15 km2 area between Keelarai to Mudal in the Gulf of Mannar, Tamil Nadu, India. Post bloom observations showed mass mortality of a variety of finfish, ornamental fish, bivalves, shellfish, sea anemones, sea slugs, sea cucumbers, sea horses, polychaete worms, and seaweed that washed ashore. Two damselfish species Dascyllus reticulatus and D. trimaculatus were deleteriously affected. The intense N. scintillans bloom killed 0.83 tons of damselfish, equivalent to approximately 9 million fish, and 1.67 tons of commercially important fish valued at US$ 11.5 M.