Cortisol is the principal corticosteriod in teleost fishes and its plasma concentrations rise dramatically during stress. The relationship between this cortisol increase and its metabolic consequences are subject to extensive debate. Much of this debate arises from the different responses of the many species used, the diversity of approaches to manipulate cortisol levels, and the sampling techniques and duration. Given the extreme differences in experimental approach, it is not surprising that inconsistencies exist within the literature. This review attempts to delineate common themes on the physiological and metabolic roles of cortisol in teleost fishes and to suggest new approaches that might overcome some of the inconsistencies on the role of this multifaceted hormone. We detail the dynamics of cortisol, especially the exogenous and endogenous factors modulating production, clearance and tissue availability of the hormone. We focus on the mechanisms of action, the biochemical and physiological impact, and the interaction with other hormones so as to provide a conceptual framework for cortisol under resting and/or stressed states. Interpretation of interactions between cortisol and other glucoregulatory hormones is hampered by the absence of adequate hormone quantification, resulting in correlative rather than causal relationships.

Cortisol in teleosts: dynamics, mechanisms of action, and metabolic regulation

The innate immune system of fish is considered to be the first line of defence against a broad spectrum of pathogens and is more important for fish as compared with mammals. Lysozyme level or activity is an important index of innate immunity of fish and is ubiquitous in its distribution among living organisms. It is well documented that fish lysozyme possess lytic activity against both Gram-positive bacteria and Gram-negative bacteria. It is also known to be opsonic in nature and activates the complement system and phagocytes. It is present in mucus, lymphoid tissue, plasma and other body fluids of freshwater and marine fish. It is also expressed in a wide variety of tissues. Lysozyme activity has been shown to vary depending on the sex, age and size, season, water temperature, pH, toxicants, infections and degree of stressors. Here, we review our current understanding of different types of lysozyme and their expression and its role in fish innate immune system.

Lysozyme: an important defence molecule of fish innate immune system

Vibrios are ubiquitous and abundant in the aquatic environment. A high abundance of vibrios is also detected in tissues and/or organs of various marine algae and animals, e.g., abalones, bivalves, corals, fish, shrimp, sponges, squid, and zooplankton. Vibrios harbour a wealth of diverse genomes as revealed by different genomic techniques including amplified fragment length polymorphism, multilocus sequence typing, repetetive extragenic palindrome PCR, ribotyping, and whole-genome sequencing. The 74 species of this group are distributed among four different families, i.e., Enterovibrionaceae, Photobacteriaceae, Salinivibrionaceae, and Vibrionaceae. Two new genera, i.e., Enterovibrio norvegicus and Grimontia hollisae, and 20 novel species, i.e., Enterovibrio coralii, Photobacterium eurosenbergii, V. brasiliensis, V. chagasii, V. coralliillyticus, V. crassostreae, V. fortis, V. gallicus, V. hepatarius, V. hispanicus, V. kanaloaei, V. neonatus, V. neptunius, V. pomeroyi, V. pacinii, V. rotiferianus, V. superstes, V. tasmaniensis, V. ezurae, and V. xuii, have been described in the last few years. Comparative genome analyses have already revealed a variety of genomic events, including mutations, chromosomal rearrangements, loss of genes by decay or deletion, and gene acquisitions through duplication or horizontal transfer (e.g., in the acquisition of bacteriophages, pathogenicity islands, and super-integrons), that are probably important driving forces in the evolution and speciation of vibrios. Whole-genome sequencing and comparative genomics through the application of, e.g., microarrays will facilitate the investigation of the gene repertoire at the species level. Based on such new genomic information, the taxonomy and the species concept for vibrios will be reviewed in the next years.

Biodiversity of Vibrios

Probiotics and immunity: a fish perspective.

The current status and future focus of probiotic and prebiotic applications for salmonids

Astaxanthin, a xanthophyll carotenoid, is a secondary metabolite naturally synthesized by a number of bacteria, microalgae, and yeasts. The commercial production of this pigment has traditionally been performed by chemical synthesis, but the microalga Haematococcus pluvialis appears to be the most promising source for its industrial biological production. Due to its collective diverse functions in skin biology, there is mounting evidence that astaxanthin possesses various health benefits and important nutraceutical applications in the field of dermatology. Although still debated, a range of potential mechanisms through which astaxanthin might exert its benefits on skin homeostasis have been proposed, including photoprotective, antioxidant, and anti-inflammatory effects. This review summarizes the available data on the functional role of astaxanthin in skin physiology, outlines potential mechanisms involved in the response to astaxanthin, and highlights the potential clinical implications associated with its consumption.

https://www.mdpi.com/2072-6643/10/4/522/pdf

Astaxanthin in Skin Health, Repair, and Disease: A Comprehensive Review.

The significance of Aeromonas hydrophila in association with disease outbreaks in aquaculture production in the Zhejiang province of China was investigated. Bacteriological examination of moribund fish and crabs resulted in 95 bacterial isolates: 88 bacterial isolates from fish and 7 isolates from crabs. PCR and traditional biochemical methods were used for identification of A. hydrophila. Out of 69 motile aeromonads, 35 isolates were identified as A. hydrophila by biochemical tests. However, 6 of those were not identified as A. hydrophila by a species specific PCR method. Serotyping revealed 2 dominant serotypes (O9 and O97) among A. hydrophila isolates. The data presented show that approximately 42% of the motile aeromonads isolated from disease outbreaks among various fish species were A. hydrophila. It is noteworthy that A. hydrophila accounted for more than 50% of the isolated aeromonands isolated from crucian carp Carassius carassius and Wuchang bream Megalobrama amblycephala with haemorrhagic septicaemia. Although this species was the most frequently isolated organism from internal organs of diseased fish and crabs in the present study, other motile Aeromonas spp. were also found. The PCR assay was useful in preventing misidentification of A. hydrophila, which may occur when only phenotypic tests are employed.

/pdf/is-aeromonas-hydrophila-the-dominant-motile-aeromonas-wi72afewdq.pdf

Is Aeromonas hydrophila the dominant motile Aeromonas species that causes disease outbreaks in aquaculture production in the Zhejiang Province of China

Enhanced resistance of rainbow trout, Oncorhynchus mykiss (Walbaum), against Yersinia ruckeri challenge following oral administration of Bacillus subtilis and B. licheniformis (BioPlus2B)

We coupled multiplex PCR and a DNA microarray to construct an assay suitable for the simultaneous detection of five important marine fish pathogens (Vibrio vulnificus, Listonella anguillarum, Photobacterium damselae subsp. damselae, Aeromonas salmonicida subsp. salmonicida, and Vibrio parahaemolyticus). The array was composed of nine short oligonucleotide probes (25-mer) complementary to seven chromosomal loci (cyt, rpoN, gyrB, toxR, ureC, dly, and vapA) and two plasmid-borne loci (fatA and A.sal). Nine primer sets were designed to amplify short fragments of these loci (100 to 177 bp) in a multiplex PCR. PCR products were subsequently labeled by nick translation and hybridized to the microarray. All strains of the five target species (n = 1 to 21) hybridized to at least one species-specific probe. Assay sensitivities ranged from 100% for seven probes to 83 and 67% for the two remaining probes. Multiplex PCR did not produce any nonspecific amplification products when tested against 23 related species of bacteria (n = 40 strains; 100% specificity). Using purified genomic DNA, we were able to detect PCR products with <20 fg of genomic DNA per reaction (equivalent to four or five cells), and the array was at least fourfold more sensitive than agarose gel electrophoresis for detecting PCR products. In addition, our method allowed the tentative identification of virulent strains of L. anguillarum serotype O1 based on the presence of the fatA gene (67% sensitivity and 100% specificity). This assay is a sensitive and specific tool for the simultaneous detection of multiple pathogenic bacteria that cause disease in fish and humans.

Michael Engelbrecht Nielsen

Papers

Astaxanthin in Skin Health, Repair, and Disease: A Comprehensive Review.

Is Aeromonas hydrophila the dominant motile Aeromonas species that causes disease outbreaks in aquaculture production in the Zhejiang Province of China

Enhanced resistance of rainbow trout, Oncorhynchus mykiss (Walbaum), against Yersinia ruckeri challenge following oral administration of Bacillus subtilis and B. licheniformis (BioPlus2B)

Simultaneous Detection of Marine Fish Pathogens by Using Multiplex PCR and a DNA Microarray

Real-time gene expression analysis in carp (Cyprinus carpio L.) skin: inflammatory responses caused by the ectoparasite Ichthyophthirius multifiliis.