EFFECTS OF PRODUCTS RELEASED BY APHANIZOMENON FLOS-AQUAE AND PURIFIEDSAXITOXIN ON THE MOVEMENTS OF DAPHNIA-CARINATA FEEDING APPENDAGES

Experiments were run to determine the effect of filtrate from incubate d Aphanizomenon flos-aquae on the thoracic appendage beat rate and fre quency of postabdominal rejections by Daphnia carinata. Comparisons we re made between the response to Aphanizomenon filtrate and to purified saxitoxin (STX). The short-term response pattern to the filtrate incl uded an immediate 30-50% depression of thoracic appendage beat rate an d elevation of postabdominal rejection rate followed by slowly decreas ing thoracic appendage beat rate and increasing postabdominal rejectio n rate during the IO-min exposure. Animals recovered to pretreatment a ctivity rates in <5 min. A similar response was observed in STX, excep t that Daphnia began to recover immediately from the thoracic appendag e beat rate inhibition. Animals recovered to similar to 60% of pretrea tment activity after 1-2 h in Aphanizomenon filtrate, whereas in STX t hey returned to pretreatment activity levels after similar to 1 h of e xposure to the neurotoxin. Water from a lake with a winter bloom of A. flos-aquae produced the same pattern of thoracic appendage beat rate and postabdominal rejection rate response as seen with the cultured Ap hanizomenon. A comparison of responses to STX and the Aphanizomenon fi ltrate indicates the effect on D. carinata is through chemosensory sti mulation rather than neuromotor inhibition.