In addition to their use in human medicine, antimicrobials are also used in food animals and aquaculture, and their use can be categorized as therapeutic against bacterial infections. The use of antimicrobials in aquaculture may involve a broad environmental application that affects a wide variety of bacteria, promoting the spread of bacterial resistance genes. Probiotics and bacteriocins, antimicrobial peptides produced by some types of lactic acid bacteria (LAB), have been successfully tested in aquatic animals as alternatives to control bacterial infections. Supplementation might have beneficial impacts on the intestinal microbiota, immune response, development, and/or weight gain, without the issues associated with antibiotic use. Thus, probiotics and bacteriocins represent feasible alternatives to antibiotics. Here, we provide an update with respect to the relevance of aquaculture in the animal protein production sector, as well as the present and future challenges generated by outbreaks and antimicrobial resistance, while highlighting the potential role of probiotics and bacteriocins to address these challenges. In addition, we conducted data analysis using a simple linear regression model to determine whether a linear relationship exists between probiotic dose added to feed and three variables of interest selected, including specific growth rate, feed conversion ratio, and lysozyme activity.

Atlantic salmon (Salmo salar) is a carnivorous fish species whose productive performance tends to be suboptimal when fed low-cost carbohydrate rich meals. It is of interest to study the dynamics of gut microbiota communities in salmonids fed high carbohydrate diets since gut microbes are referred to as key players that influence the metabolism and physiology of the host. A study was conducted to determine the effect of feeding a high carbohydrate diet to Atlantic salmon in gut microbiota communities. A medium carbohydrate (15% wheat starch)/medium protein (MC/MP) diet or a high carbohydrate (30% wheat starch)/low protein (HC/LP) diet was fed to triplicate tanks (28 fish each) during four weeks. We conducted an in-depth characterization of the distal intestine digesta microbiota using high-throughput sequencing of the V4 region of the 16S rRNA gene. Firmicutes, Actinobacteria and Proteobacteria were the major phyla determined in either experimental group. Phylum Planctomycetes, class Planctomycetia, order Planctomycetales and genus Lactococcus were significantly more abundant in fish fed the HC/LP diet compared with fish fed the MC/MP diet. Our study suggests feeding a carbohydrate rich meal to salmon exerts a low impact on the structure of gut microbial communities, affecting mostly low-abundance bacteria capable of metabolizing anaerobically carbohydrates as a major energy-yielding substrate.

Withering syndrome (WS), an infectious disease caused by intracellular bacteria Candidatus Xenohaliotis californiensis, has provoked significant economic losses in abalone aquaculture. The pathogen infects gastroenteric epithelia, including digestive gland, disrupting the digestive system and causing a progressive wilting in abalone. Nonetheless, our knowledge about WS implications in digestive gland microbiota, and its role in diseases progress remains largely unknown. This study aims to determine whether digestive gland-associated microbiota differs between healthy red abalone (Haliotis rufescens) and red abalone affected with WS. Using high-throughput sequencing of the V4 region of the 16S rRNA gene, our results revealed differences in microbiota between groups. Bacterial genera, including Mycoplasma, Lactobacillus, Cocleimonas and Tateyamaria were significantly more abundant in healthy abalones, whilst Candidatus Xenohaliotis californiensis and Marinomonas were more abundant in WS-affected abalones. Whilst Mycoplasma was the dominant genus in the healthy group, Candidatus Xenohaliotis californiensis was dominant in the WS group. However, Candidatus Xenohaliotis californiensis was present in two healthy specimens, and thus the Mycoplasma/Candidatus Xenohaliotis californiensis ratio appears to be more determinant in specimens affected with WS. Further research to elucidate the role of digestive gland microbiota ecology in WS pathogenesis is required.

Serum proteins are essential for maintaining osmotic pressure, regulating pH, transporting metabolites, and supporting immune responses. Studying the effects of plant-based diets on these proteins is crucial to understanding their impact on fish health and immune function. Methods: This study was conducted in a recirculation system, with rainbow trout distributed across nine tanks and fed three diets: fishmeal (control), medium plant meal (MPM; 40% of fishmeal replacement), and high plant meal (HPM; 80% of fishmeal replacement). Plasma protein and plasma glucose levels were measured at the initial and final stages, under both fasting (24 h after fast) and postprandial (6 h after fed) conditions, to assess dietary impacts. Additionally, the hepatosomatic index (HSI) was calculated at the end of the experiment to evaluate potential liver adaptations to the diets. Results: The initial protein and glucose levels were similar across all groups. However, by the end of the treatment, the fishmeal-fed group showed significantly higher total protein and globulin levels, while the albumin levels remained consistent across diet types. A significant interaction between sampling time and dietary treatment in fish reduced the clarity of dietary effects on postprandial plasma glucose levels. Furthermore, the HSI was significantly lower in fish fed the high plant meal (HPM) diet compared to the fishmeal and medium plant meal (MPM) groups, suggesting potential metabolic adaptation in response to plant-based diets. Conclusions: Replacing fishmeal with plant-based proteins in rainbow trout diets reduces total globulin and protein concentrations but leaves albumin unaffected, alongside reductions in fasting and postprandial glucose levels. The low growth and different HSI in fish fed plant-based diets highlights potential liver stress, emphasizing the need for further research to optimize sustainable aquaculture feeds while maintaining fish health and performance.

Vibrio species are naturally found in estuarine and marine ecosystems, but are also recognized as significant human enteropathogens, often linked to seafood-related illnesses. In aquaculture settings, Vibrio poses a substantial risk of infectious diseases, resulting in considerable stock losses and prompting the use of antimicrobials. However, this practice contributes to the proliferation of antimicrobial-resistant (AMR) bacteria and resistance genes. Our investigation aimed to explore the potential of biological agents such as bacteriophage CH20 and endolysin LysVPp1 in reducing Vibrio bacterial loads in both rotifer and fish larvae. LysVPp1’s lytic activity was assessed by measuring absorbance reduction against various pathogenic Vibrio strains. Phage CH20 exhibited a limited host range, affecting only Vibrio alginolyticus GV09, a highly pathogenic strain. Both CH20 and LysVPp1 were evaluated for their effectiveness in reducing Vibrio load in rotifers or fish larvae through short-setting bioassays. Our results demonstrated the significant lytic effect of endolysin LysVPp1 on strains of Vibrio alginolyticus, Vibrio parahaemolyticus, and Vibrio splendidus. Furthermore, we have showcased the feasibility of reducing the load of pathogenic Vibrio in live feed and fish larvae by using a non-antibiotic-based approach, such as lytic phage and endolysin LysVPp1, thus contributing to the progress of a sustainable aquaculture from a One Health perspective.