FISHERY BULLETIN: VOL. 74, NO. 2 



from 6° to 32°C. Mortality was recorded after 24 h. 

 Incipient lethal levels for each acclimation level 

 were estimated as described for the juveniles and 

 adults. 



Hatching and Developmental 

 Temperature Limits 



Eggs in the blastodisc stage were transferred to 

 a series of incubation vessels, after which the 

 temperatures were gradually raised or lowered 

 from the ambient level of 16°C over a period of 60 

 min in order to avoid possible shock effects to the 

 developing embryos. Incubation temperatures 

 were then held constant (±0.5°C) between 6° and 

 12°C, and 26° and 31°C at 0.5°C intervals. A 16°C 

 temperature was used as a control. Development 

 was considered normal only if the larvae were free 

 of obvious deformities (e.g., spinal curvatures) 

 until pigmented eyes and functional jaws were 

 evident, and death had occurred only after yolk 

 reserves were exhausted. 



Resistance to Acute Temperature 

 Changes 



Embryos in the blastodisc stage (ca. 12-14 h 

 after fertilization at 16°C) and in the blastopore 

 closure stage (ca. 36-38 h after fertilization), and 

 larvae in the yolk-sac stage (vdthin 24 h after 

 hatching) were subjected to temperature shocks 

 for periods of 1, 3, 5, and 60 min. Embryos and 

 larvae were pipetted from incubation vessels 

 maintained at 16°C directly into water at high and 

 low temperature extremes. After the exposure 

 period, the embryos and larvae were returned di- 

 rectly to the incubation vessels at 16°C where they 

 remained for 48 h after hatching. Mortality and 

 developmental abnormalities were recorded. 



This procedure was an attempt to simulate what 

 the embryos and larvae might actually experience 

 if entrained by intake pipes of electrical generat- 

 ing plants or LNG (Liquified Natural Gas) vapor- 

 ization plants (or either thermal plums), subjected 

 to rapid temperature increases and decreases in 

 the heat exchange systems, and subsequently 

 flushed back into the natural environmental 

 temperatures at the outfall. 



Development and Growth 



Experiments were designed to determine the 

 temperatures required for optimal growth of an- 



chovy larvae. The tests were confined to that 

 period of larval life between hatching and starva- 

 tion following exhaustion of all stored yolk re- 

 serves. No food was offered. 



Eggs in the blastodisc stage were reared 

 through hatching in a series of constant tempera- 

 ture baths between 10° and 26°C. On the day of 

 hatching and each subsequent day, approximately 

 10 larvae were sacrificed from each rearing tem- 

 perature and measured from the tip of the snout 

 to the end of the notochord with an ocular microm- 

 eter to the nearest 0.05 mm. This procedure 

 was continued until all larvae at each rearing 

 temperature died of starvation. 



RESULTS 



Juveniles and Adults 



Ninety-six Hour Tolerance 



Experiments on juvenile and adult tolerance 

 encompassed 117 separate 96-h tests and 2,400 

 fish. Control survival ranged from lows of 81.3 and 

 87.9% at 8° and 28°C acclimation temperatures, 

 respectively, to 98.3% at the 16°C acclimation 

 temperature. 



Figure 2 graphically depicts the lethal tempera- 

 ture relations, with adjusted percent mortality 

 plotted against test temperatures for acclimation 

 levels of 8° and 28°C. Adjusted upper and lower 

 LDso temperatures were plotted against acclima- 

 tion temperatures in Figure 3 and a thermal toler- 

 ance polygon constructed (Fry 1947). Ultimate 

 upper and lower lethal temperatures are esti- 

 mated by extrapolation (line fitted by eye) to be 



TEMPEtATUIE "^ 



Figure 2.— Effects of acclimation temperatures of 8° and 28°C 

 on the upper and lower lethal temperatures ofEngraulis mordax 

 juveniles and adults (original date in Brewer 1975b). 



436 



