High plant protein diet impairs growth performance and intestinal integrity in greater amberjack (Seriola dumerili): Molecular and physiological insights

The Mediterranean aquaculture industry that produces mainly seabream and seabass is exploring alternative plant-based protein sources for fish feeds together with the diversification of fish species. Effective plant-based formulations require diverse sources and additives to maintain fish welfare and growth, which is especially important for carnivorous species. In this scenario, the objective of the present study was to evaluate the impact of a high percentage of fishmeal replacement with protein of plant origin in Seriola dumerili , a fast-growing species with a high protein requirement. Two diets were developed: MAP (marine animal protein) with a protein content of 92 % of animal origin and PPB (plant protein blend) with a 50 % replacement of protein of animal origin with plant protein. We combined electrophysiology measurements with expression analysis of claudins and members of the SLC superfamily of solute carriers to unravel and characterise putative markers of intestinal integrity and absorption. The replacement resulted in shorter and lighter fish with a reduction in growth rate (SGR) from 2.6 to 2. We simultaneously observed lower transepithelial tissue resistance (TER), lower permeability, and decreased cld12 expression in the anterior intestine. In addition, we demonstrated a strong region-dependent electrogenic transport of essential amino acids, with the mid-intestine having the highest transport capacity. The comparative study performed in the mid-intestine with fish fed the MAP or the PPB diets exposed a negative effect of dietary replacement with plant protein. No significant dietary impact on di- and tri-peptide transporters (SLC15) was found at the molecular level. However, a clear region-dependent expression pattern of slc15a1 , slc15a2 , and slc15a4 was observed, which warrants further investigation. The expression pattern of slc7a5 showed the effect of the diet, but in contrast, the diet and intestinal region affected the expression of its functionally associated slc3a1 and slc3a2 for amino acid antiport, with the strongest effects in the posterior intestine. The integrity and absorption impairments detected in response to protein source replacement will likely underlie the significant growth differences observed between the two dietary regimes. • Fishmeal replacement: plant protein based (PPB) impacts growth performance and intestinal health • Intestinal health and absorption: PPB decreased TER and cld12 expression in the anterior intestine. • Regional nutrient transport differences: The mid-intestine showed the highest amino acid transport capacity. • Gene expression under the dietary influence: PPB affected SLC transporter genes in specific intestinal regions. • Implications for aquaculture: The findings underscore the need to optimise plant- based formulations.