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 the spontaneous discharge frequency 
varies with temperature in the lateral line of Xenopus (Amphibia). Murray 
(20), also working with Xenopus , noted that a sudden temperature increase of 
10°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 line 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 enough, complete inhibition 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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