other physiological effects have all been demonstrated to occur following 

 thermal shock, and may cause behavioral changes (23). Laudien (18) and 

 Murray (21) both note that the lateral line system in fish is highly sensitive to 

 rapid temperature changes. It is possible that disruption of normal lateral line 

 function may potentially decrease response to a predator's attack. Blaxter (7) 

 considers the free neuromast system in larvae to play an important role in 

 avoiding predation. 



There is evidence that the lateral line may indeed be disrupted by a thermal 

 shock. Dijgraaf (10) demonstrated that tJie spontaneous discharge frequency 

 varies with temperature in the lateral line of Xenopus (Amphibia). Murray 

 (20), also working wdth Xenopus, noted that a sudden temperature increase of 

 lO^C would decrease or even completely inhibit the spontaneous discharge 

 frequency, followed by compensation back to normal levels. Sudden cooling 

 would cause a sudden increase in frequency. If free neuromast and developed 

 lateral hne receptors of fish larvae react similarly to those of Xenopus 

 following thermal shock, there are two periods when the normal receptor 

 frequency would be altered and signal information from the system possibly 

 masked or inhibited. The first would occur upon contact with water of 

 increased temperature. Thus, upon interception with a thermal discharge, and 

 if the temperature differential is high enougli, complete inliibition may occur, 

 cutting off all signals from the lateral line momentarily. Inhibition of 

 spontaneous discharge probably does not pertain to the present study, since 

 predators are absent during the initial 15-minute thermal shock period. 

 However, this initial neural inhibition could render larvae which pass through a 

 thermal discharge plume more vulnerable to predation. Next, following such a 

 thermal shock, the larvae experience rapid cooling, which could result in a 

 sudden increase in lateral line discharge frequency and possible distortion or 

 masking of near-field environmental stimuli. This latter effect may be involved 

 in the present study since cooling of larvae occurs just prior to the predation 

 interaction. 



Evaluation of Laboratory Predator-Prey Tests as Sub-lethal 

 Indicators 



Laboratory predator-prey tests, such as the one described here, can be 

 valuable as a means of observing subtle, but ecologically significant effects of 

 low pollutant levels. In developing such tests, it is important to evaluate the 

 strengths and limitations inherent in laboratory techniques utilized by other 

 investigators (2, 8, 11, 12, 16, 25, 27). One must consider which primary 

 predation factors are being measured by each method. Bams (2) states that a 

 differential predation situation is determined by three primary factors: 

 discovery rate of the prey by the predator; attack rate on the prey; and capture 

 rate of the prey. 



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