Aquaculture has greatly contributed to the development of sustainable global animal food production and currently accounts for 57% of food fish consumed by humans. This growth has been largely credited to the changes in consumer food choices and the surge in feed-based aquaculture production. While the unprecedented growth experienced by the sector is noteworthy, the continued dependence on major ingredients commonly used in aquafeed manufacturing, especially fishmeal and fish oil, may hinder the sustainability of this growth. Thus, more effort must be made to increase the alternative ingredient portfolio for aquaculture.
Hemp (Cannabis sativa L.) is an ancient annual crop grown for its fiber, seeds, and metabolites, which are used in industrial, food or feed, and medicinal products, respectively. Industrial hemp grain and its co-products are plant-based materials traditionally known for their high-quality and easily digestible protein, health-promoting fats, and appropriate levels of micronutrients, all of which are needed for fish and shellfish growth and physiological well-being. The nutrient component of the grain shows that the whole seed contains 21%–25% protein, 30%–33.9% lipids, 28%–43% fiber, and 4%–10% ash. The protein in hemp seeds is rich in arginine, aspartic acid/asparagine, and glutamic acid/glutamine, in addition to good levels of the sulfur-containing amino acids (methionine and cysteine), which is comparable to other high-quality proteins currently used in aquafeed production. Furthermore, the oil derived from hemp grain is rich in polyunsaturated fatty acids, with linoleic acid (18:2n-6) constituting about 55% of the total fatty acid, while α-linolenic acid (18:3n-3) constitutes 13-17.4%. Moreover, hemp oil has a good level of γ-linolenic acid (18:3n-6) and stearidonic acid (18:4n-3), which are notably absent or only present in negligible amounts in the majority of plant-based oils commonly used in aquafeed manufacturing. The seed also has significant levels of macro- and trace minerals and is a rich source of tocopherols and provitamin A. Aside from the nutritional attributes, hemp seeds contain bioactive compounds with diverse biological properties that are potentially beneficial for fish and shellfish health.
As with other plant-based proteins, hemp seed meal is not without challenges in terms of the presence of anti-nutritional factors, high fiber content, and cannabinoids, especially Δ9-tetrahydrocannabinol (Δ9-THC), known for its psychoactive effect. Nevertheless, the ongoing research effort in our laboratory is geared toward understanding how fish respond to cannabinoids in feeds, their metabolism, and their potential for bioaccumulation in major organs. This study, when completed, will provide valuable information to enrich our understanding of the suitability of hemp grains and their co-products and illuminate the gray area on possible accumulation of Δ9-THC in fish fillets and other notable organs.