Fish farming, i.e. aquaculture, has increased about 6.2% between the years 2000-2012, according to the Food and Agriculture Organization of the United Nations. Fish farms are highly dependent on fish meal as well as fish oil as nutrients for the growing fish. Although rates of farming have increased, the supply of fish meal and oil are predicted to either not change or decrease. For this reason, researchers are exploring other nutrients, like plants, that could be used in aquaculture to make it more sustainable.
Cholesterol is an important component of cell membranes, steroid hormones and other bioactive compounds in the body. Thus, cholesterol is important for the normal growth and reproduction of animals. Dietary cholesterol is obtained from animal-based diets, which means a solely plant-based diet may result little to no dietary cholesterol intake for fish. Plants are also a rich source of phytosterols, which are known to disrupt the normal metabolism of cholesterol. For this reason, a new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology examined how a plant-based diet would affect the physiology and metabolism of cholesterol in fish – namely rainbow trout.
In addition to obtaining cholesterol from the diet, fish are able to make their own. In contrast to fish that were fed fish meal and oil for 6 months, fish that were fed only plants for the same duration weighed less and had higher expression of genes that are important for generating their own cholesterol whereas other genes responsible for digesting or eliminating cholesterol were reduced. Even though the plant-fed trout were able to increase their production of cholesterol, it should be noted that cholesterol levels in these fish were still lower when compared to animals fed fish meal and oil. This reduction in cholesterol in plant-fed fish may explain their diminished growth rates and reproductive success as cholesterol is important in cell membranes and the synthesis of steroid hormones like estrogen and testosterone.
It looks like more research is necessary to find the best alternative nutrients for the sustainability of aquaculture.
Zhu T, Corraze G, Plagnes-Juan E, Quillet E, Dupont-Nivet M, Skiba-Cassy S. Regulation of genes related to cholesterol metabolism in rainbow trout (Oncorhynchus mykiss) fed a plant-based diet. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. [Epub ahead of print].