To be sure, Eric, higher temperatures can only support faster growth up to a point. And then there is the temperature where it's so hot that fish die. The highest consumption and gain occur at temperatures just a few degrees below lethal temps.
The best I have seen in the literature was at 30 C (86 F). But to get the better gain, consumption is significantly higher, as are the metabolic costs. LMB can handle 86 F water, but it needs to have enough O2 to support the respiration of metabolism. Their metabolism is running hotter and they need to eat more just to maintain weight. Based on what I have gleaned from the literature, at 86 F, an LMB will lose 1.3% of its body weight daily if it doesn't eat. An LMB must eat 3% of its body weight in BG at that temperature to maintain its weight and it must eat more than that if it is to grow. Many ponds are unable to support this level of consumption being forage limited (or there being too many LMB). I guess what is causing the consumption shortfall depends on the person and their perspective (like whether a glass is half-empty or half-full). In any case, it's the consumption that matters at 86 F (along with good O2, low ammonia, etc.) At 86F, healthy water is necessary and plenty of forage.
The actual peak of metabolism, efficiency, consumption, and growth could occur somewhere between 77F and 86F. I've seen different numbers from different sources. One states optimum is 82F-84F. But 86F seems to be a temperature that LMB can grow remarkably at, much better than 77 degrees provided the water parameters are good. What are your thoughts on this? What is the critical temperature where gain potential is severely impacted? Or is this possibly a range of temperature depending on how poor the water quality is?
My models are lacking conversion parametrization between 77F and 86F. At temps between these nodes parameters determining conversion are interpolated by a fitted function. So, if the peak of consumption and growth occur at temps below 86F, the models underestimate consumption and growth between those two temps. I don't think they miss the mark by a lot, however. I never apply the model above 86F and in ponds with sufficient depth, there are generally depths where the temp is below this temp even in peak of Summer temps. Below, is a plot of FCR and Specific Growth (SGR) versus Temperature under constraints of Satiation Ration and LMB body mass of 1 lb. It may look like FCR varies a lot between 77F and 86F ... but that is an illusion due to the displayed scale. The interpolated variation is less than 0.3 of 1 percent. Conversion at satiation consumption rates is pretty stable between 77F and 86F. Even so the potential for gain is 33% higher at 86F than at 77F ... provided ... the LMB consumes the satiation ration which 37% greater at 86F than at 77F.
(Sorry attachment manager isn't working ... will add chart later)
What to do over 86F? I don't know. As temps increase, it breaks down because the fish are breaking down. There is not a lot out there on greater temps. One, a study at Pine Bluff, tested growth at 35C (95 F). They actually got growth there. But the model incorrectly modeled metabolic costs and consumption. At this stressful temperature, the metabolism is significantly less. They must shut down all but the most essential metabolic processes to maintain life.
Last edited by jpsdad; 09/24/25 10:38 AM. Reason: Added additional context and chart
