SWIMMING RESPONSE OF GOLDFISH, CARASSIUS-AURATUS, AND THE TETRA, HEMIGRAMMUS-CAUDOVITTATUS, LARVAE TO INDIVIDUAL FOOD ITEMS AND PATCHES

Swimming speed and swimming path of goldfish and tetra larvae were studied in aquaria containing food patches composed of decapsulated cysts and immobilized nauplii of Artemia salina or sparsely distributed prey. The mean swimming speed of starved larvae in the medium without food was about four times higher than the speed of larvae feeding in a patch. Satiated larvae swam about 1.5 times slower than hungry fish. Consumption of single prey items by starved larvae caused the following sequence of swimming responses: 'handling pause' (cessation of swimming), slow swimming in a restricted area, and fast swimming (approximately twice as fast as hungry larvae before encountering food) accompanied by a widening of the area searched ('area increased searching'). Mean swimming speed was constant over a broad range (10(1)-10(3) ind.l-1) of food density, although at extreme (high or low) values of food density it depended on swimming responses of the predator. Frequency of visits to the different parts of the aquarium strongly depended on encounters of hungry fish with food particles or patches.