Re: Why do fish gills slow down when the temperature drops?

Most fish are cold-blooded (ectothermic), which means that their bodies 
stay at the temperatre of their environment.  This is contrast to mamals, 
including humans, who are warm-blooded and maintain a constant body 
temperature despite the environmental conditions.  Most fish are therefore 
able to survive at diferent temperatures, as you may have already observed 
in your project.  However, growing at higher temperatures causes fish to 
speed up their metabolism and consequently grow faster.  Conversely, fish 
growing at lower temperatures grow slower.  It is possible that the opening 
and closing of the gills (called gilling) follow a similar pattern, 
speeding up at higher temperatures and slowing down at colder ones.  While 
temperature is proven to have an effect on growth rate, the relationship 
with gilling may not be as direct. for instance, maybe increased gilling at 
higher temperatures is just a response to the general stress of being hot.  
If that is true, then other types of stress might have similar results.  
I'm sure you can come up with other ways to stress fish!  

In a related topic, there are some frogs that can withstand being frozen 
while their respiration stops completely.  This suggests that decreasing 
temperature simply causes a slowing in all body functions.  Think about 
water and ice - as it freezes, it slows until it is a static crystal.

As for other resources, I can't be of any help.