Rotifers feed on the nannochloropsis

Rotifers feed on the nannochloropsis concentrate, and when the larva feed on the rotifers, according to this study, it in turn enhances the larval survival rate of the fin fish. Credit: fishconsult.org

Sulogna Mehta reports for the Times of India that scientists from the Central Marine Fisheries Research Institute (CMFRI), in Vizag, the largest city in the Indian state of Andhra Pradesh, have successfully produced nannochloropsis microalgae concentrate through indoor and outdoor culture, to serve as feed for zooplanktons and as a conditioner in larval rearing tanks. Certain concentrates or paste (Chaetoceros and Isochrysis) for shrimp feed have also been produced and their experimental use in fish and shrimp hatcheries has been a big success, they say, in seed or larval production of fish and shrimps.

The one-year research on nannochloropsis cultivation for feed to rotifers and copepods (zoo planktons), in fish larval rearing tanks, is part of the project on mass scale seed production for the orange spotted grouper species, which was completed recently by CMFRI. The research team included scientists Biji Xavier, Ritesh Ranjan and Sekar Magarajan headed by CMFRI scientist-in-charge and senior scientist Subhadeep Ghosh.

Explaining about the culture of nannochloropsis, Dr. Xavier said, “The sea water is collected from which microalgae is isolated using agar plate technique to scoop the algae. The green color colonies are then cultured in test tubes for seven days, and conical flasks of various sizes for three days. A small quantity of the specific algae are added to the culture medium and, in indoor culture, the algae is finally cultured in 20-liter pet bottles.

“As the algae grows by cell division, the color of the bottled water becomes deeper green by the fifth day, when the algae has fully grown. The indoor-cultured nannochloropsis are added to the larval rearing tanks after filtration. In outdoor culture, nannochloropsis are cultured in tanks of 100 liters and larger, which is directly used for feeding rotifers.”

The scientists report that since microalgae are rich in essential fatty acid (EPA), if given to zooplankton, the zooplankton will feed on these algae and when the larva feeds on the zooplankton, it will in turn enhance the larval survival rate of the fin fish.

Another advantage of the concentrate is that the harvested algae can be stored during winter. Larval rearing is done mostly in summer, so the stored concentrate can be used for the rotifer production in the summer season. With the stored algae, continuity of the seed production can be maintained with the required zooplankton production year round, said Dr. Ghosh.

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