Evaluation of candidate probiotic strains for gilthead sea bream larvae (Sparus aurata) using an in vivo approach

Comparison of growth performance, oxidative stress, and intestinal microbiota of rockfish (Sebastiscus marmoratus) in different culture modes

To investigate the response of fish intestines to different culture modes, we conducted a comparative trial on rockfish in the recirculating aquaculture system (RAS) and offshore aquaculture net pen system (OAS). After the 152-day trial, we compared the differences in growth performance, antioxidant capacity, intestinal morphology, and intestinal microbiota to evaluate the health status of rockfish cultured in these two modes. Results showed that rockfish cultured in the RAS exhibited a superior growth performance and antioxidant capacity compared to those cultured in OAS. Histological examination indicated pathological lesions in the intestine of rockfish cultured in the OAS, including a disordered arrangement of epithelial cells, rupture of chorionic villi, and decreased thickness of the muscle layer, which may further cause damage to intestinal barrier function. Sequencing analysis of 16S rDNA showed that Firmicutes, Bacteroidota, and Proteobacteria were the dominant phyla in the rockfish intestines. Microbial community diversity analysis indicated that there were significant differences in intestinal bacterial richness and diversity between the two groups; however, no differences were observed in the dominant bacteria. The relative abundance of metabolic pathways (such as energy, carbohydrate, and lipid metabolism) in the OAS group was significantly enhanced. Furthermore, the relative abundance of conditional pathogenic and potentially pathogenic bacteria increased, and that of beneficial and stress-tolerant bacteria decreased in the OAS group, indicating potential inflammation in the intestine. This study accumulated basic biological information for the study of fish welfare cultured in different modes and will contribute to the understanding of the physiological and health status of the rockfish.

Dietary effects of vitamin C on antioxidant capacity, intestinal microbiota and the resistance of pathogenic bacteria in cultured Silver pomfret (Pampus argenteus)

As most teleosts are unable to synthesize vitamin C, supplemental diets containing vitamin C diets play a crucial role in fish health. The aim of this study was to investigate the effect of dietary vitamin C on the intestinal enzyme activity and intestinal microbiota of silver pomfre (Pampus argenteus). Four experimental diets were supplemented with basic diets containing 300 mg of vitamin C/kg (group tjl3), 600 mg of vitamin C/kg (group tjl6), and 1200 mg of vitamin C/kg (group tjl12), as well as vitamin C-free supplemental basic diet (group tjl0), respectively. The four diets were fed to juvenile P. argenteus (average initial weight: 4.68 ± 0.93 g) for 6 weeks. The results showed that the activity of SOD (superoxide dismutase) and CAT (catalase) increased significantly while that of MDA (malondialdehyde) decreased significantly in group tjl3 compared to vitamin group tjl0. At the genus level, groups tjl0, tjl6, and tjl12 contained the same dominant microbial community, Stenotrophomonas, Photobacterium, and Vibrio, whereas group tjl3 was dominated by Stenotrophomonas, Delftia, and Bacteroides. Among the fish fed with a basic diet containing 300 mg of vitamin C/kg, the intestines exhibited a notable abundance of probiotic bacteria, including lactic acid bacteria (Lactobacillus) and Bacillus. The abundance of Aeromonas in groups tjl3 and tjl6 was lower than that of the vitamin C-free supplemental basic diet group, whereas Aeromonas was not detected in group tjl12. In addition, a causative agent of the disease outbreak in cultured P. argenteus, Photobacterium damselae subsp. Damselae (PDD) was the dominant microbiota community in groups tjl0, tjl6 and tjl12, whereas the abundance of PDD in group tjl3 was the lowest among the diets. Taken together, the diets supplied with vitamin C could influence the composition microbial community of P. argenteus. The low level of vitamin C (300 mg of vitamin C/kg per basic diet) supplementation could not only improve the antioxidant capacity but also resist the invasion of pathogenic bacteria.

Harnessing probiotics and prebiotics as eco-friendly solution for cleaner shrimp aquaculture production: A state of the art scientific consensus

In recent years, the advancement and greater magnitude of products, which led to the intensification in shrimp aquaculture is the result of utilization of modern tools and synchronization with other fields of science like microbiology and biotechnology. This intensification led to the elevation of disorders such as the development of several diseases and complications associated with biofouling. The use of antibiotics in aquaculture is discouraged due to their certain hazardous paraphernalia. Consequently, there has been a growing interest in exploring alternative strategies, with probiotics and prebiotics emerging as environmentally friendly substitutes for antibiotic treatments in shrimp aquaculture. This review highlighted the results of probiotics and prebiotics administration in the improvement of water quality, enhancement of growth and survival rates, stress resistance, health status and disease resistance, modulation of enteric microbiota and immunomodulation of different shrimp species. Additionally, the study sheds light on the comprehensive role of prebiotics and probiotics in elucidating the mechanistic framework, contributing to a deeper understanding of shrimp physiology and immunology. Besides their role in growth and development of shrimp aquaculture, the eco-friendly behavior of prebiotics and probiotics have made them ideal to control pollution in aquaculture systems. This comprehensive exploration of prebiotics and probiotics aims to address gaps in our understanding, including the economic aspects of shrimp aquaculture in terms of benefit-cost ratio, and areas worthy of further investigation by drawing insights from previous studies on different shrimp species. Ultimately, this commentary seeks to contribute to the evolving body of knowledge surrounding prebiotics and probiotics, offering valuable perspectives that extend beyond the ecological dimensions of shrimp aquaculture.

Screening of New Potential Probiotics Strains against Photobacterium damselae Subsp. piscicida for Marine Aquaculture

On intensive fish farms, 10% of the population dies exclusively from pathogens, and Photobacterium damselae subsp. Piscicida (Ph. damselae subsp. Piscicida), the bacteria causing pasteurellosis in marine aquaculture, is one of the major pathogens involved. The objective of this study was to obtain new probiotic strains against pasteurellosis in order to limit the use of chemotherapy, avoiding the environmental repercussions generated by the abusive use of these products. In this study, 122 strains were isolated from the gills and intestines of different marine fish species and were later evaluated in vitro to demonstrate the production of antagonistic effects, the production of antibacterial substances, adhesion and growth to mucus, resistance to bile and resistance to pH gradients, as well as its harmlessness and the dynamic of expression of immune-related genes by real-time PCR after administration of the potential probiotic in the fish diet. Only 1/122 strains showed excellent results to be considered as a potential probiotic strain and continue its characterization against Ph. damselae subsp. piscicida to determine its protective effect and elucidating in future studies its use as a possible probiotic strain for marine aquaculture.

Diet, Immunity, and Microbiota Interactions: An Integrative Analysis of the Intestine Transcriptional Response and Microbiota Modulation in Gilthead Seabream (Sparus aurata) Fed an Essential Oils-Based Functional Diet

Essential oils (EOs) are promising alternatives to chemotherapeutics in animal production due to their immunostimulant, antimicrobial, and antioxidant properties, without associated environmental or hazardous side effects. In the present study, the modulation of the transcriptional immune response (microarray analysis) and microbiota [16S Ribosomal RNA (rRNA) sequencing] in the intestine of the euryhaline fish gilthead seabream (Sparus aurata) fed a dietary supplementation of garlic, carvacrol, and thymol EOs was evaluated. The transcriptomic functional analysis showed the regulation of genes related to processes of proteolysis and inflammatory modulation, immunity, transport and secretion, response to cyclic compounds, symbiosis, and RNA metabolism in fish fed the EOs-supplemented diet. Particularly, the activation of leukocytes, such as acidophilic granulocytes, was suggested to be the primary actors of the innate immune response promoted by the tested functional feed additive in the gut. Fish growth performance and gut microbiota alpha diversity indices were not affected, while dietary EOs promoted alterations in bacterial abundances in terms of phylum, class, and genus. Subtle, but significant alterations in microbiota composition, such as the decrease in Bacteroidia and Clostridia classes, were suggested to participate in the modulation of the intestine transcriptional immune profile observed in fish fed the EOs diet. Moreover, regarding microbiota functionality, increased bacterial sequences associated with glutathione and lipid metabolisms, among others, detected in fish fed the EOs supported the metabolic alterations suggested to potentially affect the observed immune-related transcriptional response. The overall results indicated that the tested dietary EOs may promote intestinal local immunity through the impact of the EOs on the host-microbial co-metabolism and consequent regulation of significant biological processes, evidencing the crosstalk between gut and microbiota in the inflammatory regulation upon administration of immunostimulant feed additives.

Molecular Taxonomic Profiling of Bacterial Communities in a Gilthead Seabream (Sparus aurata) Hatchery

As wild fish stocks decline worldwide, land-based fish rearing is likely to be of increasing relevance to feeding future human generations. Little is known about the structure and role of microbial communities in fish aquaculture, particularly at larval developmental stages where the fish microbiome develops and host animals are most susceptible to disease. We employed next-generation sequencing (NGS) of 16S rRNA gene reads amplified from total community DNA to reveal the structure of bacterial communities in a gilthead seabream (Sparus aurata) larviculture system. Early- (2 days after hatching) and late-stage (34 days after hatching) fish larvae presented remarkably divergent bacterial consortia, with the genera Pseudoalteromonas, Marinomonas, Acinetobacter, and Acidocella (besides several unclassified Alphaproteobacteria) dominating the former, and Actinobacillus, Streptococcus, Massilia, Paracoccus, and Pseudomonas being prevalent in the latter. A significant reduction in rearing-water bacterial diversity was observed during the larviculture trial, characterized by higher abundance of the Cryomorphaceae family (Bacteroidetes), known to populate microniches with high organic load, in late-stage rearing water in comparison with early-stage rearing-water. Furthermore, we observed the recruitment, into host tissues, of several bacterial phylotypes-including putative pathogens as well as mutualists-that were detected at negligible densities in rearing-water or in the live feed (i.e., rotifers and artemia). These results suggest that, besides host-driven selective forces, both the live feed and the surrounding rearing environment contribute to shaping the microbiome of farmed gilthead sea-bream larvae, and that a differential establishment of host-associated bacteria takes place during larval development.

Virgibacillus proomii and Bacillus mojavensis as probiotics in sea bass (Dicentrarchus labrax) larvae: effects on growth performance and digestive enzyme activities

This study examined the effects of two probiotics (Virgibacillus proomii and Bacillus mojavensis) on the digestive enzyme activity, survival and growth of Dicentrarchus labrax at various ontogenetic stages in three separate experiments. These probiotics were incorporated as single or mixed into fish feed for a period of 60 days. The growth parameters, proximate composition of whole body, digestive enzymes and gut microbiology were monitored at regular. The increments in length and weight and the survival were significantly higher (P < 0.05), and the values of food conversions were significantly lower (P < 0.05) in fishes fed the probiotic. The administration of V. proomii and B. mojavensis in diet resulted in an increase (P > 0.05) in body ash and protein content and in the specific activity of phosphatase alkaline and amylase in the digestive tract of all the fishes. V. proomii and B. mojavensis persisted in the fish intestine and in the feed in high numbers during the feeding period (group 1: 5.8 × 10(4) CFU/ml, group 2: 9.6 × 10(4) CFU/ml, and group 3: 9.8 × 10(4) CFU/ml day 60). The two probiotics V. proomii and B. mojavensis were adequate for improved growth performance and survival and for healthy gut microenvironment of the host.

Inactivation of Vibrio anguillarum by attached and planktonic Roseobacter cells

The purpose of the present study was to investigate the inhibition of Vibrio by Roseobacter in a combined liquid-surface system. Exposure of Vibrio anguillarum to surface-attached roseobacters (10(7) CFU/cm(2)) resulted in significant reduction or complete killing of the pathogen inoculated at 10(2) to 10(4) CFU/ml. The effect was likely associated with the production of tropodithietic acid (TDA), as a TDA-negative mutant did not affect survival or growth of V. anguillarum.

Phaeobacter and Ruegeria species of the Roseobacter clade colonize separate niches in a Danish Turbot (Scophthalmus maximus)-rearing farm and antagonize Vibrio anguillarum under different growth conditions

Members of the Roseobacter clade colonize a Spanish turbot larval unit, and one isolate (Phaeobacter strain 27-4) is capable of disease suppression in in vivo challenge trials. Here, we demonstrate that roseobacters with antagonistic activity against Vibrio anguillarum also colonize a Danish turbot larval farm that relies on a very different water source (the Danish fiord Limfjorden as opposed to the Galician Atlantic Ocean). Phylogenetic analyses based on 16S rRNA and gyrase B gene sequences revealed that different species colonized different niches in the larval unit. Phaeobacter inhibens- and Phaeobacter gallaeciensis-like strains were primarily found in the production sites, whereas strains identified as Ruegeria mobilis or Ruegeria pelagia were found only in the algal cultures. Phaeobacter spp. were more inhibitory against the general microbiota from the Danish turbot larval unit than were the Ruegeria spp. Phaeobacter spp. produced tropodithietic acid (TDA) and brown pigment and antagonized V. anguillarum when grown under shaking (200 rpm) and stagnant (0 rpm) conditions, whereas Ruegeria spp. behaved similarly to Phaeobacter strain 27-4 and expressed these three phenotypes only during stagnant growth. Both genera attached to an inert surface and grew in multicellular rosettes after stagnant growth, whereas shaking conditions led to single cells with low attachment capacity. Bacteria from the Roseobacter clade appear to be universal colonizers of marine larval rearing units, and since the Danish Phaeobacter spp. displayed antibacterial activity under a broader range of growth conditions than did Phaeobacter strain 27-4, these organisms may hold greater promise as fish probiotic organisms.

Microbial diversity of mid-stage Palinurid phyllosoma from Great Barrier Reef waters

AIMS

This study aimed to determine the bacterial community associated with wild-caught, mid-stage larvae of spiny lobsters (Palinuridae) in their native oligotrophic marine environment, and to compare their diversity and composition with communities associated with aquaculture-reared larvae of the tropical rock lobster Panulirus ornatus.

METHODS AND RESULTS

Bacterial clone libraries constructed from wild P. ornatus (two libraries) and Panulirus penicillatus (one library) larvae (phyllosoma) revealed a dominance of alpha-proteobacterial sequences, with Sulfitobacter spp.-affiliated sequences dominating both P. ornatus libraries and constituting a major portion of the P. penicillatus library. Vibrio-related sequences were rarely detected from wild phyllosoma clone libraries in contrast to similar studies of aquaculture-reared animals. Scanning electron microscopy analysis revealed low levels of bacterial colonization on the external carapace of wild phyllosoma, again in contrast to aquaculture-reared animals, which are often colonized with filamentous bacteria (mainly Thiothrix sp.) that compromise their health. Fluorescence in situ hybridization of sectioned wild phyllosoma tissue displayed low overall abundance of bacteria within the tissue and on external surfaces, with alpha-, beta-, and gamma-Proteobacteria being confirmed as members of this bacterial community.

CONCLUSIONS

The consistency in predominant clone sequences retrieved from the three libraries indicated a conserved microbiota associated with wild phyllosoma. In addition, the observed differences in the microbial composition and load of reared and wild phyllosoma are indicative of the different environments in which the animals live.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacterial disease during early larval stages is a major constraint currently hindering the development of an aquaculture industry for the ornate rock lobster P. ornatus. Knowledge of the microbial community associated with wild animals will be advantageous for the identification of bacteria that may promote animal health.

Effects of bacteria on Artemia franciscana cultured in different gnotobiotic environments

The use of probiotics is receiving considerable attention as an alternative approach to control microbiota in aquaculture farms, especially in hatching facilities. However, application with consistent results is hampered by insufficient information on their modes of action. To investigate whether dead bacteria (allowing investigation of their nutritional effect) or live bacteria (allowing evaluation of their probiotic effect) have any beneficial effect towards Artemia franciscana and, subsequently, if live bacteria have probiotic effects beyond the effects observed with dead bacteria, a model system was employed using gnotobiotic Artemia as a test organism. Nauplii were cultured in the presence of 10 bacterial strains combined with four different major axenic live feeds (two strains of Saccharomyces cerevisiae and two strains of Dunaliella tertiolecta) differing in their nutritional values. In combination with poor- and medium-quality live feeds, dead bacteria exerted a strong effect on Artemia survival but a rather weak or no effect on individual length and constituted a maximum of only 5.9% of the total ash-free dry weight supplied. These effects were reduced or even disappeared when medium- to good-quality major feed sources were used, possibly due to improvements in the health status of Artemia. Some probiotic bacteria, such as GR 8 (Cytophaga spp.), improved (not always significantly) the performance of nauplii beyond the effect observed with dead bacteria, independently of the feed supplied. The present approach can be an excellent system to study the exact mode of action of bacteria, especially if combined with challenge tests or other types of analysis (e.g., transcriptome and proteonomic analysis).