# Hemp Meal (Cannabis sativa) as an Alternative Dietary Protein Source for European Perch (Perca fluviatilis)

## TL;DR

Hemp meal can replace fish meal in European perch diets without harming their health, with 20% inclusion showing the best results.

## Contribution

Hemp meal is proposed as a sustainable and cost-effective alternative to fish meal in European perch aquaculture.

## Key findings

- Hemp meal inclusion up to 30% did not negatively affect fish health or physiology.
- A 20% hemp meal diet improved growth and feed utilization in European perch.
- Hemp meal caused beneficial changes in the intestinal lining and did not harm digestive organ function.

## Abstract

The production of European perch is becoming increasingly advanced. Unfortunately, it is still associated with high costs due to the high proportion of fish meal required in the feed. We investigated whether hemp meal could replace it without harming the health of the fish. For ten weeks, the perch were fed a diet containing 0, 10, 20 or 30% hemp meal. The study revealed that there were no negative effects on growth, physical condition, muscle composition, blood parameters, or digestive organ structure. The diet containing 20% hemp meal provided the best overall growth and feed utilization. Fish receiving hemp meal also showed mainly beneficial changes in the intestinal lining, which aids digestion and nutrient absorption. Overall, hemp meal can safely replace some of the animal protein in the diet of perch, with around 20% inclusion appearing to be the most promising. The use of hemp meal can reduce feed costs, improve sustainability and reduce dependence on fish meal in fish farming.

The production of European perch (Perca fluviatilis) has become notably refined, with numerous physiological and nutritional studies conducted in recent years. However, it is still an expensive undertaking due to the high amount of animal protein required in the feed. Therefore, we investigated the possibility of using hemp meal (HM) as an alternative source of protein in extruded feed for perch reared in recirculating aquaculture systems (RASs). Perch fry (initial body weight of 68.1 g) was divided into four groups (HM0, HM10, HM20, HM30; 100 fish in each) and fed with diets containing different levels of HM (0, 10, 20 or 30%, respectively) for 10 weeks. Overall, dietary inclusion of HM did not affect body parameters, muscle composition, or blood parameters, nor did it cause any serious histopathological lesions. Nonetheless, basic production indices (SGR, FCR, PER) all peaked in the HM20 group, and predominantly positive changes in intestinal mucosa were found in all three HM-inclusion groups. Furthermore, the expression patterns of several genes in the intestine and liver were different in groups HM20-30 than in HM0-10. Lastly, hepatic activities of alkaline phosphatase (ALP) and glutathione peroxidase (GPX) diminished with increasing dietary HM inclusion levels. In summary, there were no negative effects of HM on the homeostasis of studied fish or, more specifically, the physiology of their digestive organs. When accounting for minor tendencies in the results, the dietary inclusion of hemp meal at 20% turned out to be the most promising fish meal alternative for the European perch.