Feed and Diets

The benefits of supplementing diets with fish meal have been demonstrated in a number of species. Immunity and overall health are among some of the potential positive effects.

Fish meal has historically been used as a protein source in manufactured diets for animals ranging from beef cattle to poultry to laboratory animals. Fish meal is a concentrated source of high quality protein composed of highly digestible essential amino acids. Fish meal has one of the best overall amino acid profiles of any single protein source. In addition, fish meal is also an excellent source of omega 3 fatty acids, like DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), which have been shown to improve health by preventing cardiovascular disease, lowering serum triglycerides, potentially stabilizing atherosclerotic plaques, improving tolerance to a variety of stressors, and playing important roles in the development and maintenance of neural and retinal tissues and cognitive function.^1,5,12,20,22

In recent years, fish meal has been removed from some laboratory diets. Animal proteins generally cost significantly more than plant proteins; thus, pressure to decrease ingredient costs has driven the removal of animal-derived proteins from some formulations. Concern that fish meal is contaminated with mercury and nitrosamines has led some researchers to believe experimental results could be confounded by diets. However, as detailed below, fish meal and fish oil used in animal diet production contain very low levels of this metal or N-nitroso compounds. Further, research conducted in the last twenty years has proven that nearly any ingredient in a diet can potentially alter experimental results, depending upon the nature of the experiment and the ingredient; soybean meal and casein have been the most often cited protein sources shown to influence study outcomes.

Sourcing of Fish Meal
The primary source of fish oil and fish meal in laboratory animal diets is derived from the menhaden fish. Menhaden are short-lived omnivores that feed primarily on phytoplankton, thus, they accumulate very little methylmercury or other heavy metals, unlike carnivorous predatory fish. Currently, two companies in the U.S. supply fish meal and fish oil from menhaden. Fish meal is produced from freshly harvested menhaden that are promptly delivered chilled and whole, in refrigerated vessels, to the processing facilities. Processing at the five plants in the U.S. is immediate to ensure product quality and minimize the presence of non-nutrient factors like nitrosamines.

Fish Meal in Animal Diets
Animals do not require protein per se, but instead utilize essential and non-essential amino acids. Thus, the quality of a protein source is positively correlated with the digestibility, bioavailability, and proportions of the amino acids in the protein source.6 Animal proteins are the gold standard for protein quality because they provide the closest amino acid composition relative to an animal’s requirements. Furthermore, the nutritional quality of diets combining grains and animal protein sources is greater than diets containing grains alone.^4,9

To date, very little information is available on the effects of incorporating fish meal into grain-based diets for rodents; however, the advantages have been published in other laboratory species such as dogs, poultry, and swine. Whole menhaden fish meal has been shown to increase the number of live pigs per litter at birth as well as the overall body weight of pigs at birth and two weeks post parturition.¹⁴ Similar results have been observed in laying hens fed a diet containing 3% dietary fish meal for a 12 week period. Hens receiving the fish meal diet had higher egg production rates, egg weights and egg volume (p<0.05) compared with hens fed a corn-wheat-soybean meal (SBM) diet.¹⁸ Or-Rashid et al¹³ evaluated the effects of providing fish meal to ewes during late gestation and early lactation on the proportion of DHA and EPA in colostrum and milk as well as the subsequent effect on the plasma fatty acid profile of nursing lambs. Ewes fed a fish meal supplemented diet had greater (p<0.013) percentages of EPA, DHA, total n-3-PUFA, total CLA and total very long chain n-3-PUFA in colostrum and milk compared to control ewes receiving a SBM based diet. At birth, lambs born to fish meal supplemented ewes had greater concentrations of plasma EPA, DHA, and total very long chain n-3-PUFA compared to lambs born to control ewes. Fatty acid concentrations also increased over time for lambs nursing ewes supplemented with fish meal.