Researchers in Canada and the UK have demonstrated the different effects that partially defatted black soldier fly larvae meal (BSFLM) and mechanically-extracted black soldier fly larvae oil (BSFLO) have in rainbow trout performance, nutrient digestibility and physiology. Among their findings, the discovery of enhanced digestibility of hydroxyproline in diets containing BSFL products has potential benefits for fish fed low fishmeal diets.

Over a three-month growth trial, researchers evaluated the effects of partially defatted black soldier fly larvae meal (BSFLM) and mechanically-extracted oil from that same insect (BSFLO) on growth, feed utilization, body composition, gut histology and blood plasma biochemistry of rainbow trout.

According to the study authors, \"there was a negative relationship between relative body protein content and dietary inclusion of BSFLM, but not BSFLO. Hydroxyproline was the sole amino acid that increased in trout fed BSFLM or BSFLO. The inclusion of BSFLM and BSFLO had no impact on the histology of the posterior intestine, but villi in the anterior intestine of trout fed Diet D (26.4% BSFLM) was significantly shorter relative to the Control. There was a negative relationship between blood glucose and BSFLO inclusion level, which suggested BSFLO had some antihyperglycemic effect in fasted rainbow trout.\"

Experiments also found that the digestibility and retention of hydroxyproline was significantly superior in diets containing BSFLM or BSFLO than in the control diet.

Based on their results, the research group recommended a maximum inclusion of 13% BSFLM in rainbow trout diets. The maximum inclusion of BSFLO could potentially be superior to 10%, but further study is needed. 

This article includes excerpts from the study abstract, published in the Journal of Aquaculture.