Is Atlantic salmon digestibility compromised by alternative raw material sources?

Recent studies showed promising results when using insect meal and alternative oil sources to replace fishmeal and fish oil.

Is Atlantic salmon digestibility compromised by alternative raw material sources?
January 23, 2020

The limited availability of sustainable feed ingredients is a significant concern in salmon aquaculture. This concern has stimulated research into alternatives to fishmeal and fish oil, in particular using insect meal and alternative oil sources. Several recent studies showed promising results in digestibility of these new sources in Atlantic salmon.

Insect meal

Insects may become an important, sustainable resource for expanding the raw material repertoire. Canadian researchers performed a study to determine the optimal dietary inclusion level of black soldier fly larvae meal (BSFM) on the digestibility and growth of Atlantic salmon. In the digestibility study, salmon were fed on diets that contained a 70:30 blend of reference diet to test ingredient, comparing BSFM, soy protein concentrate (SBM), and corn protein concentrate (CPC) as the test ingredients. In the growth study, salmon were fed diets containing 0.0 g kg−1 (control), 100 g kg−1, 200 g kg−1 and 300 g kg−1 BSFM.

Digestibility coefficients of BSFM were generally over 75%, with dry matter and gross energy showing higher coefficients in BSFM than CPC and SBM. Mineral digestibility was generally higher in BSFM compared with CPC and SBM. Salmon fed up to 200 g kg−1 showed similar growth performance to salmon fed the control diet. However, salmon fed 300 g kg−1 BSFM diet gained significantly less weight, had the lowest SGR, TGC and the highest FCR than salmon fed any other treatment. The study concluded that including BSFM at 200 g kg-1 in diets for Atlantic salmon shows promise as a complementary protein source in low fishmeal, high plant protein diets.

Norwegian researchers evaluated the salmon gut health in a 16-week feeding trial with Atlantic salmon fed on a reference diet with a combination of fishmeal, soy protein concentrate, pea protein concentrate, corn gluten and wheat gluten as protein sources, or a test diet where all the fishmeal and most of the pea protein concentrate were replaced by black soldier fly larvae meal.

Scientists found that a higher relative weight of distal intestine was found in fish fed the insect meal diet. Inflammatory morphological changes, similar to those induced in the distal intestine by standard soybean meal, were present in all the examined intestinal segments, with a higher degree of submucosa cellularity in the proximal intestine of insect meal diet fed fish, the only notable diet effect. Therefore, scientists concluded that total replacement of fishmeal with black soldier fly larvae meal did not compromise the gut health of Atlantic salmon.

A novel strain of Schizochytrium

A novel strain of Schizochytrium sp. (T18) has shown rapid growth under optimized heterotrophic cultivation, efficiently using inexpensive carbon and nitrogen feedstocks and capable of producing a high docosahexaenoic acid (DHA)-rich oil.

Canadian researchers tested for the first time its potential as a feed resource for salmonid aquaculture. The study examined the effects of partial or complete replacement of dietary marine fish oil with T18 microbial oil on apparent digestibility (AD). Four experimental diets were formulated to replace 0%, 33%, 66% and 100% of dietary fish oil with extracted Schizochytrium sp. (T18) oil. The oil used contained 50% polyunsaturated FAs (PUFA) of which 82% was comprised of the dietary n-3 long-chain PUFA (n-3 LC-PUFA) DHA and contained extremely low levels of harmful contaminants.

Partial or complete replacement of dietary fish oil had no significant effects on AD of dietary dry matter. Results suggest that conventional fish oil can be completely replaced in juvenile farmed salmon feeds by Schizochytrium sp. (T18) oil with no negative effects on digestibility of dietary proximate nutrients, energy or fatty acids.