TEMPERATURE SELECTION 

 BY YOUNG TOPSMELT: 

 LABORATORY AND FIELD 

 INVESTIGATIONS 



KARL F. EHRLICH,* G. E. McGOWEN, and G. MUSZYNSKI* 

 Biology Department, Occidental College, Los Angeles, California 



ABSTRACT 



Topsmelt (Atherinops affinis) were reared from eggs for 6.5 months. Their 

 laboratory preferred-temperature range throughout this period (3 to 198 days 

 post-hatching) was 19 to 23 C, and they avoided water temperatures warmer 

 than 27 C. Selected temperatures were independent of acclimation temperatures, 

 which were 10 to 21 C. Temperature did not act as a strong directing force for 

 these fish (which have a wide thermal preference) until their lethal temperature 

 was approached. Their behavior resulted in a frequency distribution significantly 

 skewed toward the lower temperatures. Our ichthyoplankton survey found that 

 the peak occurrence of young atherines was associated with their laboratory- 

 determined preferred-temperature range. 



Topsmelt [Atherinops affinis (Ayres)] occur from the Gulf of 

 California to Vancouver Island, British Columbia, and are common in 

 bays, sloughs, and kelp beds (Miller and Lea, 1972). These inshore 

 areas are often heavily impacted by man; e.g., warm effluents from 

 power plants are one source of environmental change. Little is 

 known of the thermal ecology of topsmelt; however, Doudoroff 

 (1938) observed a wide temperature preference (20 to 28° C) for a 

 group of unidentified atherines and determined (Doudoroff, 1945) 

 the 96-hr LT50 to be ~31°C for juvenile topsmelt. Embryonic 

 development of topsmelt occurs from 12.8 to 26.8°C (Hubbs, 

 1965). Stephens (1977) reported that atherines (unidentified species) 

 showed a positive orientation to warm water in King Harbor, 



*Present address: Lockheed Center for Marine Research, Carlsbad, California. 



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