Environmental Benefits of Novel Nonhuman Food Inputs to Salmon Feeds.

Global population growth and changing diets increase the importance, and challenges, of reducing the environmental impacts of food production. Farmed seafood is a relatively efficient way to produce protein and has already overtaken wild fisheries. The use of protein-rich food crops, such as soy, instead of fishmeal in aquaculture feed diverts these important protein sources away from direct human consumption and creates new environmental challenges. Single cell proteins (SCPs), including bacteria and yeast, have recently emerged as replacements for plant-based proteins in salmon feeds. Attributional life cycle assessment is used to compare salmon feeds based on protein from soy, methanotrophic bacteria, and yeast ingredients. All ingredients are modeled at the industrial production scale and compared based on seven resource use and emissions indicators. Yeast protein concentrate showed drastically lower impacts in all categories compared to soy protein concentrate. Bacteria meal also had lower impacts than soy protein concentrate for five of the seven indicators. When these target meals were incorporated into complete feeds the relative trends remain fairly constant, but benefits of the novel ingredients are dampened by high impacts from the nontarget ingredients. Particularly, primary production requirements (PPR) are about equal and constant across all feeds for both analyses since PPR was driven by fishmeal and oil. The bacteria-based feed has the highest climate change impacts due to the use of methane to feed the bacteria who then release carbon dioxide. Overall, the results of this study suggest that incorporating SCP ingredients into salmon feeds can help reduce the environmental impacts of salmon production. Continued improvements in SCP production would further increase the sustainability of salmon farming.

Bile enhances glucose uptake, reduces permeability, and modulates effects of lectins, trypsin inhibitors and saponins on intestinal tissue.

Antinutritional factors (ANFs) can disrupt digestive and other intestinal functions. ANFs in soybean meal (SBM) are implicated in proliferative and inflammatory responses in the intestine of various (functionally) monogastric animals, including Atlantic salmon (Salmo salar L.). The goal of the current study was to investigate the effect of ex vivo exposure of mid and distal intestinal tissue of salmon to soybean saponins (SAP), lectin (LEC) and Kunitz' trypsin inhibitor (KTI), singly and in combination, on epithelial function, as assessed by measuring in vitro glucose uptake pathways along a glucose concentration gradient. As solubilization of SAP in the calcium-containing Ringer's solution was problematic but resolved with the addition of a physiological concentration of bile collected from the gall bladder of salmon, an evaluation of bile effects became an added element. Results indicated that bile increased baseline glucose absorption and possibly transport, and also had a protective effect on the epithelial barrier, at least partially due to taurocholate. Compared to controls, tissues exposed to LEC+bile, KTI+bile and LEC+KTI+bile exhibited increased glucose uptake at the higher glucose concentrations, apparently due to markedly increased tissue permeability. Addition of SAP, however, attenuated the response, possibly by binding bile components. SAP+bile, also in combination with LEC and/or KTI, as well as LEC, KTI and LEC+KTI without bile often reduced transcellular glucose uptake pathways, while maintaining low tissue permeability. SAP+LEC+KTI+bile, LEC and KTI caused the most marked reductions. The distal intestine was more affected, reflecting the restriction of in vivo SBM-induced inflammatory changes to this region.

Early response of gene expression in the distal intestine of Atlantic salmon (Salmo salar L.) during the development of soybean meal induced enteritis.

Plant products in general and soybeans in particular can challenge the function and health of the intestinal tract. Salmonids develop an intestinal inflammation when fed diets containing soybean meal (SBM) and certain other legume ingredients. In the present study a 44K oligonucleotide salmonid microarray, qPCR and histology were used to investigate early response mechanisms in the distal intestine of Atlantic salmon (Salmo salar L.) during the first week of oral exposure to a diet containing 20% extracted SBM. The distal intestine transcriptome was profiled on days 1, 2, 3, 5 and 7 and compared to a control group fed fishmeal as the sole protein source. Histological evaluation of the distal intestine revealed the first signs of inflammation on day 5. The most prominent gene expression changes were seen on days 3 and 5. Up-regulation in immune-related genes was observed during the first 5 days, including GTPase IMAP family members, NF-kB-related genes and regulators of T cell and B cell function. Many functional genes involved in lipid metabolism, proteolysis, transport, metabolism and detoxification were initially up-regulated on days 1-3, possibly as an attempt by the tissue to compensate for the initiating immune response. Cell repair and extracellular matrix remodeling genes were up-regulated (heparanase, collagenase) on days 3 and 5. Down regulation of genes related to endocytosis, exocytosis, detoxification, transporters and metabolic processes from day 5 indicated initiation of dysfunction of digestive and metabolic functions that may occur as a result of inflammation or as a response to the introduction of soybean meal in the diet. This is the first study conducting transcriptomic profiling to characterize early responses during the development of SBMIE. Switching Atlantic salmon from a fishmeal to a 20% SBM diet resulted in rapid changes to the intestinal transcriptome, indicating an immune reaction with subsequent impaired epithelial barrier function and other vital intestinal functions.

Ontogeny of the Digestive System of Atlantic Salmon (Salmo salar L.) and Effects of Soybean Meal from Start-Feeding.

Despite a long history of rearing Atlantic salmon in hatcheries in Norway, knowledge of molecular and physiological aspects of juvenile development is still limited. To facilitate introduction of alternative feed ingredients and feed additives during early phases, increased knowledge regarding the ontogeny of the digestive apparatus in salmon is needed. In this study, we characterized the development of the gastrointestinal tract and accessory digestive organs for five months following hatch by using histological, biochemical and molecular methods. Furthermore, the effects of a diet containing 16.7% soybean meal (SBM) introduced at start-feeding were investigated, as compared to a fishmeal based control diet. Salmon yolk sac alevins and fry were sampled at 18 time points from hatch until 144 days post hatch (dph). Histomorphological development was investigated at 7, 27, 46, 54 and 144 dph. Ontogenetic expression patterns of genes encoding key digestive enzymes, nutrient transporters, gastrointestinal peptide hormones and T-cell markers were analyzed from 13 time points by qPCR. At 7 dph, the digestive system of Atlantic salmon alevins was morphologically distinct with an early stomach, liver, pancreas, anterior and posterior intestine. About one week before the yolk sac was internalized and exogenous feeding was started, gastric glands and developing pyloric caeca were observed, which coincided with an increase in gene expression of gastric and pancreatic enzymes and nutrient transporters. Thus, the observed organs seemed ready to digest external feed well before the yolk sac was absorbed into the abdominal cavity. In contrast to post-smolt Atlantic salmon, inclusion of SBM did not induce intestinal inflammation in the juveniles. This indicates that SBM can be used in compound feeds for salmon fry from start-feeding to at least 144 dph and/or 4-5 g body weight.