EFFECTS OF REPEATED EXPOSURES TO MARINE CYANOBACTERIAL SECONDARY METABOLITES ON FEEDING BY JUVENILE RABBITFISH AND PARROTFISH

Secondary metabolites isolated from marine algae and cyanobacteria can act as feeding deterrents to a variety of herbivores, but past studie s have rarely considered the responses of herbivores to these compound s over time. We examined the influence of repeated preference tests on the responses of juvenile rabbitfish Siganus spinus and juvenile parr otfish Scarus schlegeli to malyngamide A, malyngamide B, and malyngoli de, 3 secondary metabolites from the marine cyanobacterium Lyngbya maj uscula. We offered fish choices between control food and food treated singly with these compounds in series of 3 to 5 preference tests, duri ng which fish were either fed only during tests (periodic feeding) or continuously fed. Each of the 3 compounds deterred feeding by juvenile rabbitfish and parrotfish, but the magnitude of deterrence varied ove r time and between the 2 feeding protocols. In the continuous feeding protocol, rabbitfish were more discriminating in later trials with mal yngamides A and B, while parrotfish were more discriminating in later trials with malyngamide A. Levels of deterrence of malyngamides A and B did not change over time in the periodic feeding protocols, and were lower than in the continuous feeding protocols for both species. Maly ngolide generated the same amount of feeding deterrence in each feedin g protocol and the fishes showed no changes in their consumption of ma lyngolide over time. Changes in hunger level and the amount of experie nce with foods may influence whether fish learn to reject foods that c ontain feeding deterrents, though the extent of this learning varies a mong compounds and fish species. These behavioral mechanisms may lead to the consumption of broader diets when preferred foods are less abun dant.