Effect of dietary green tea supplementation on growth, fat content, and muscle fatty acid profile of rainbow trout (Oncorhynchus mykiss)

Improved fat metabolism and reduced body fat have been observed in aquatic and terrestrial animals fed diets supplemented with green tea. Rainbow trout cultured commercially often contain high levels of body and visceral fat, which is linked to reduced yield and added difficulties in processing. Reducing fat levels is of interest to commercial trout producers. In this study, three varieties of green tea were supplemented into feed at 0, 1, 2, and 4% of diet and fed to rainbow trout (34.4 +/- 1.5 g initial weight) in triplicate tanks containing 50 fish each. At the end of 60 days, fish were sampled to determine effects on growth performance, fat content (whole body and intraperitoneal (IP)), and muscle fatty acid (FA) profile. Trout fed the highest level (4%) of green tea had an improved muscle FA profile (lower saturated FA and higher polyunsaturated FA) and reduced IP fat content (1.5 +/- 0.13% whole body weight) compared to the basal diet (2.0 +/- 0.17). However, these fish also had lower weight gain (71.9 +/- 11.3 versus 93.2 +/- 4.28 g for the basal diet). These effects did not appear to be caused by reduced feed intake, which was significantly higher for trout fed the 4% tea diet (2.21% body weight day(-1)) in contrast to the other diets (approximately 1.9% body weight day(-1)). It is unclear why the IP fat content and growth performance declined, but it may be related to lower fat digestibility in the gut or increased fat metabolism from dietary supplementation of green tea.