SAPONINS IN EGGS AND LARVAE OF ACANTHASTER-PLANCI (L) (ASTEROIDEA) AS CHEMICAL DEFENCES AGAINST PLANKTIVOROUS FISH

The suggestion that saponins in eggs and larvae of Acanthaster planci (L.) serve as chemical defences was tested by feeding groups of planktivorous pomacentrid fish with random series of gelatin food particles, some with and some without crude saponin extract from A. planci. The four fish species discriminated at statistically significant levels against food particles with crude saponin extract at 1× 10-3 and 1× 10-5 parts of wet weight. Three species also discriminated at significant levels against particles with 1× 10-7 parts crude saponin extract per wet weight. Degree of discrimination was strongly influenced by the state of hunger of the fish. Tastiness of particles containing saponins also influenced acceptability. The lower two concentrations of saponins used in these feeding trials were respectively two and four magnitudes less than in A. planci eggs and larvae. Thus, the saponins in eggs and larvae of A. planci are at levels detectable by, and unpalatable to, planktivorous fish and they account, at least in part, for the observed rejection of these early developmental stages by planktivorous fish. © 1979.