Methionine (Met) is an important building block and metabolite for protein biosynthesis. However, the mechanism behind its absorption in the fish gut has not been elucidated. Here, we describe the fundamental properties of Met transport along trout gut at µmol/L and mmol/L concentration. Both electrogenic and unidirectional DL‐[14C]Met flux were employed to characterize Met transporters in Ussing chambers. Exploiting the differences in gene expression between diploid (2N) and triploid (3N) and intestinal segment as tools, allowed the association between gene and methionine transport. Specifically, three intestinal segments including pyloric caeca (PC), midgut (MG), and hindgut (HG) were assessed. Results at 0–150 µmol/L concentration demonstrated that the DL‐Met was most likely transported by apical transporter ASCT2 (SLC1A5) and recycled by basolateral transporter y+LAT1 (SLC7A7) due to five lines of observation: (1) lack of Na+‐independent kinetics, (2) low expression of B0AT2‐like gene, (3) Na+‐dependent, high‐affinity (K m, µmol/L ranges) kinetics in DL‐[14C]Met flux, (4) association mRNA expression with the high‐affinity kinetics and (5) electrogenic currents induced by Met. Results at 0.2–20 mmol/L concentration suggested that the DL‐Met transport is likely transported by B0AT1‐like (SLC6A19‐like) based on gene expression, Na+‐dependence and low‐affinity kinetics (K m, mmol/L ranges). Similarly, genomic and gene expression analysis suggest that the basolateral exit of methionine was primarily through LAT4‐like transporter (SLC43A2‐like). Conclusively, DL‐Met uptake in trout gut was most likely governed by Na+‐dependent apical transporters ASCT2 and B0AT1‐like and released through basolateral LAT4‐like, with some recycling through y+LAT1. A comparatively simpler model than that previously described in mammals.

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Florida pompano perform well on soy‐based, low‐animal protein diets. These diets may be improved through the use of enzymes as a feed supplement or as pretreatment of the soy product prior to inclusion. Novel soy products produced through enzyme treatment or fermentation often have higher protein content and lower levels of indigestible carbohydrates. Two trials were conducted to evaluate the potential of enzyme supplements. The first trial evaluated the effects of carbohydrase supplementation to diets based on two different soybean meals (commodity or selectively bred meal). Pompano fed the selected soybean had significantly improved growth rates and feed efficiency, while enzymatic supplementation had no significant effect on fish performance. However, enzyme supplementation increased phosphorus and energy retention when added to diets based on commodity soybean meal. Carbohydrase supplementation improved dry matter digestibility in commodity soy‐based diets but had no significant effect on selected soybean‐based diets. The second growth trial consisted of an increasing inclusion of an enzymatically treated soybean meal product (NutriVance). Results indicate that NutriVance can replace the totality of commodity soybean without impacting fish performance. Digestibility of the commodity soy, NutriVance, and a fermented soybean meal (Pepsoygen) was also evaluated, with no detectable difference in digestibility values.

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