OFF-SEASON SPAWNING AND FACTORS INFLUENCING TOXICITY TEST DEVELOPMENTWITH TOPSMELT ATHERINOPS-AFFINIS

Three separate groups of adult topsmelt (Atherinops affinis) were spaw ned in rotation in laboratory culture over a two-year period to provid e larvae for toxicity tests. Size and viability of embryos and larvae produced during the normal summer spawning period (May-August) were co mpared to those produced during the off season (October-April). Mean e mbryo viability was relatively high throughout the study (82%), wherea s size of larvae varied. Larval size was significantly larger during t he summer spawning period than in winter. A 7-d growth and survival to xicity test protocol was developed for topsmelt larvae. Variability of the protocol was assessed over a 12-month period using copper chlorid e as a reference toxicant. Precision of 12 toxicity tests using copper was high; the intralaboratory C.V. for copper LC50s was 19%. The 7-d larval protocol also gave comparable results in two interlaboratory to xicity tests using copper and complex effluent. This study demonstrate s that topsmelt may be spawned throughout the year to provide larvae f or toxicity tests and that topsmelt larvae have comparable sensitivity to other larval fishes commonly used in toxicity testing.