Culturing, A Method Used To Identify Algae Ingested By Tilapia

Bold's Basal and Gorham's media were used to culture algae removed from the digestive tracts of Blue Tilapia, Tilapia aurea (Steindachner). Nine fish representing three-size categories collected from Lake Parker, Florida, were used in the study. Samples extracted from three areas of the gut were introduced to the culture media within twenty-four hours after collection. Microscopic examination of the cultured materials was conducted over a four-week period to enable the completion of reproductive cycles and excystment of algal cells. Twenty-one taxa of algae were identified by sampling the culture vessels. Planktonic green algae were the dominant foods of tilapia at the time of sampling. Species of Scenedesmus, Pediastrum, A.nkistrodesmus and chlorococcoid algae appeared in all specimens. Colonial chlorophytes, pennate diatoms, flagellated unicells, and remains of filamentous algae occurred less frequently. Spirulina sp. was the only blue-green occurring in significant quantities. Two rotifers, two ostracods, and a cladoceran were the only zoplankters observed. Both, type of media used and region of gut sampled, produced slight quantitative and qualitative differences in data obtained. Maximum taxonomic diversity was encountered in the anterior samples cultured in Bold's Basal medium. Bacterial conditions in the digestive systems had no inhibitory effect on culturing algae. The method of culturing ingested materials definitely has a future in specialized fisheries research programs. It would be particularly useful in studying dietary habits of juvenile fish and other small aquatic organisms (crustaceans and mollusks).

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51796