## 4 Discussion  
Soybean meal-induced enteritis was not observed in juvenile Atlantic salmon, despite the high dietary SBM inclusion level of 30%. Nevertheless, intestinal health impairment was characterized by mild changes in distal intestine morphology (i.e., changes in length, shape, and number of mucosal folds, changes in thickness of lamina propria and changes in number of goblet cells), indicating enteritis progression. Speciality soybean types lacking 11 sA4 and A5 globulins of Glycinin, lipoxygenases and oligosaccharides did not further reduce the intestinal inflammatory process compared to STD SBM, although inflammation was mild overall. Similarly, a recent thorough study removing three proteinaceous antinutrients, namely trypsin inhibitor, lectin and the allergen P34/Gly m Bd 30 k, from soybean meal did not mitigate enteritis in Atlantic salmon [9]. The authors suggested extrusion technology inactivated these compounds during feed manufacturing. Although soybean agglutinin, a type of lectin, has been reported to bind to Atlantic salmon intestinal epithelium contributing to pathological changes in gut health, the study did not describe the feed manufacturing procedure [19]. It is unlikely that extrusion technology inactivated the compounds investigated in the present study due to their chemical compositions and exposure to lower mechanical energy during extrusion conditions compared to those reported by [9] (specific mechanical energy69-80 vs. 1872-3060 kJ/kg, respectively). Soybean-induced enteritis in Atlantic salmon has been widely reported. However, the main drivers of enteritis and their positive and negative interactions with other compounds present in feed formulations remain unclear. A summary of seventeen studies around soybean-induced enteritis in Atlantic salmon is provided in Tables 7-9. Due to the complexity of the matter, there is a wide breadth of experimental designs with different stocking densities, fish size, duration, water temperature, salinity, feeding ration and experimental systems. For example, most literature is focused on smaller fish ranging from 41-442 g and some on larger fish 500-927 g. Similarly, soybean type and pre-processing and dietary composition varies throughout the literature. Soybeans are from different parts of the globe and are under several pre-processing conditions such as dehulled, toasted, defatted, and solvent-extracted, included at various levels 8-34% in feeds containing crude protein of 35-47%, total lipids 23-31%, and gross energy 15-24 MJ/kg. Regardless of this variation in the experimental design, most histology analyses are focused on the distal intestine describing morphological changes of standardized parameters including mucosal folds, supranuclear vacuoles, lamina propria, eosinophilic granulocytes, sub-epithelial mucosa, and connective tissue, and continue to be one of the most reliable tools to detect this histopathological condition. Other parameters such as reduced feed intake and growth commonly used as indicators of enteritis are not as reliable with contradicting findings throughout the literature. Most studies highlight the inflammatory process in the intestine of Atlantic salmon fed soybean-based feeds leading to enteritis; however, there are exceptions where only minor to mild intestinal damage were reported, including the present findings. Collectively, these studies illustrate the challenge and high complexity in tackling this issue in fish nutrition. Understandably, the aquafeed industry does not prioritize this research topic and adopt a more conservative approach of using moderate inclusion levels of plant ingredients avoiding any potential intestinal health impairments caused by antinutritional factors. It is likely extremely difficult to identify the key antinutritional factors in the major plant ingredients and their interactions with compounds from other components of the formulations having the effect.