FISHERY BULLETIN: VOL. 74, NO. 2 



perature and photoperiod controlled, flow- 

 through sea water system. The system delivered 

 filtered, ultraviolet-sterilized seawater from the 

 Los Angeles-Long Beach Harbor to five round, 

 950-liter, fiber glass aquaria (L5 m in diameter, 

 0.6 m high) and a single 400-liter rectangular wa- 

 ter table, all housed in a light-tight aluminum 

 cargo container (Figure 1). An exchange rate of 

 2-6 liters/min was maintained in each aquarium, 

 with overflow drainage provided by standpipes. 

 Wastewater was not recirculated. Temperatures 

 were maintained within ±0.5°C. 



Above each aquarium were two incandescent 

 light bulbs controlled by separate dimmer controls 

 and regulated by a 7-day timer to simulate photo- 

 periods. The "day" bulb provided 700 Ix and the 

 "night" bulb provided 16 Ix to the surface of each 

 aquarium. Oxygen was maintained at or near sat- 

 uration levels in all acclimation and test tanks by 

 splashing incoming water at the surface and by 

 bubbling air stones in the aquaria. Salinity varied 

 between 31.4 and 33.81. (mean 33. ID during the 

 study period. 



Juveniles and Adults 



Juvenile and adult E. mordax were obtained 

 from a live-bait dealer. The initial transfer from 

 the bait boat to the 950-liter acclimation tanks 

 caused 20-30^^ mortality during the first 2-3 days 

 of confinement. Within 2-4 days, healthy fish be- 

 gan to feed and were offered a daily ration, equiv- 

 alent to approximately 4% of the fish's wet weight, 



of Trout Chow.^ This ration was supplemented 

 with chopped anchovy, chopped squid, brine 

 shrimp, or wild plankton equal to approximately 

 1% of the fish's wet weight. Adjusted fish ate vora- 

 ciously and mortality became insignificant in ac- 

 climation tanks within 1 wk. Acclimation tanks 

 were stocked with between 3 and 7 kg of anchovy. 

 The food ration was withheld for a period of 24 h 

 prior to all thermal tests on juvenile and adult fish. 



Ninety-six Hour Tolerance 



Standardized techniques for the determination 

 of lethal temperatures (Fry et al. 1942; Brett 1944; 

 Fry 1947) call for a series of experiments in which 

 the animals are acclimated to several different 

 constant temperatures. Acclimated fish are then 

 abruptly transferred to test aquaria previously 

 equilibrated to various high and low temperature 

 extremes. Mortality is monitored and recorded. 



This procedure extends the concept of lethal 

 temperatures from two extreme end points, to a 

 family of upper and lower (incipient) lethal levels. 

 The ultimate upper and lower lethal tempera- 

 tures, which circumscribe the extreme tolerance 

 limits, may be determined by graphic 

 extrapolation — that is, by drawing a line through 

 those high and low test temperatures that proved 

 lethal to 50*7^ of the test animals for each acclima- 

 tion temperature. The extrapolated line will then 



^Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



Figure l. — Diagram of the flow-through seawater system used for experiments on Engraulis mordax. 



434 



