Effects of elevated temperature and dietary additives Thermal Care™, Bio-Mos®, and GroBiotic® A on rainbow trout (Oncorhynchus mykiss) performance

Abstract

This study examined the effects of elevated temperature and dietary Thermal Care, Bio-Mos and GroBiotic A on production performance and blood chemistry parameters in rainbow trout (Oncorhynchus mykiss). Rainbow trout under supraoptimal thermal conditions (18 °C) exhibited increased growth and feed intake but no change in feed efficiency for 6 weeks. This suggests that rearing fish at 18 °C may enhance production performance during the early stages of the grow-out process. By 12 weeks, fish at 18 °C showed increased feed intake, decreased feed efficiency, but no change in growth. Additionally, fish at 18 °C had lower protein content, protein retention efficiency, and energy retention efficiency. Elevated temperature did not change relative maximum swimming speed but did increase hematological parameters, thereby increasing the fish's oxygen supply capacity. There was preliminary evidence that Thermal Care improved rainbow trout growth under optimal thermal conditions (15 °C). However, fish fed Thermal Care at 18 °C exhibited increased feed intake but one of the lowest final fish weights leading to the lowest feed efficiency. Additionally, Grobiotic A impacted acid-base balance through changes in blood pH, TCO2, and HCO3− although the relevance of these interactions remains to be determined. By the end of the experiment, there were no noticeable benefits of including Thermal Care or Bio-Mos or GroBiotic A on production performance at either culture temperature.