The main objective of the study was to investigate the feasibility of the partial replacement of fish meal and fish oil by black soldier fly larvae meal (Hermetia illucens, BSFLM, produced on pre-consumer food waste) with and without supplemental algal oil in Chinook salmon (Oncorhynchus tshawytscha) diets. The impacts of the three diets, control (Diet 1), feed with BSFLM (Diet 2), and feed with BSFLM and algal oil (Diet 3), on salmon, including growth and heath, were assessed. These three diets were each fed to four random groups of female Chinook salmon (initial weight 165.0 g/fish), twice daily to apparent satiation for 52 weeks. The fish were weighed and measured every four weeks throughout the duration of the project and the daily feed intake was measured. Samples of seven tissues (gill, spleen, liver, head kidney, trunk kidney, stomach and intestine) were examined for histopathology.
Survival of the fish over the duration of the study was high (98%) and not affected by treatment. At the termination of the study, the fish fed the control diet (no BSFLM or algal oil) had grown significantly faster and had higher final mean weight than the fish fed Diet 2 (87.1% of control) or Diet 3 (90.7% of control). These differences were not statistically significant until 48 weeks on the study. Histological examination revealed some minor, but noticeable differences. In the liver, inflammation was seen in 44% of the BSFL fish, and none (0%) of the control. In the spleen, inflammation was found in 25% of BSFL samples, 17% of BSFL+algal oil samples and 9.1% of Control. The n-3 PUFA content of the muscle was highest in the fish fed the diet with the supplemental algal oil.
In conclusion, the use of BSFL meal is satisfactory as partial replacements for fish meal in diets for Chinook salmon, although with slight reduction on growth. Additionally, there were minor indicators that health could be compromised. The use of algal oil greatly enhanced the n-3 PUFA content of the fish.