Innate immune response, intestinal morphology and microbiota changes in Senegalese sole fed plant protein diets with probiotics or autolysed yeast.

The effects of using plant ingredients in Senegalese sole (Solea senegalensis) diet on immune competence and intestine morphology and microbial ecology are still controversial. Probiotics or immunostimulants can potentially alter the intestinal microbiota in a way that protects fish against pathogens. The current study aimed to examine the intestine histology and microbiota and humoral innate immune response in juvenile sole fed diets with low (35 %) or high (72 %) content of plant protein (PP) ingredients supplemented with a multispecies probiotic bacteria or autolysed yeast. Fish fed the probiotic diet had lower growth performance. Lysozyme and complement activities were significantly higher in fish fed PP72 diets than in their counterparts fed PP35 diets after 17 and 38 days of feeding. At 2 days of feeding, fish fed unsupplemented PP72 showed larger intestine section area and longer villus than fish fed unsupplemented PP35. At 17 days of feeding, fish fed unsupplemented PP72 showed more goblet cells than the other dietary groups, except the group fed yeast supplemented PP35 diet. High dietary PP level, acutely stimulate fish innate immune defence of the fish after 2 and 17 days of feeding. However, this effect does not occur after 73 days of feeding, suggesting a habituation to dietary treatments and/or immunosuppression, with a reduction in the number of the goblet cells. Fish fed for 38 days with diets supplemented with autolysed yeast showed longer intestinal villus. The predominant bacteria found in sole intestine were Vibrio sp. and dietary probiotic supplementation caused a reduction in Vibrio content, regardless of the PP level.

Novel application of nitrifying bacterial consortia to ease ammonia toxicity in ornamental fish transport units: trials with zebrafish.

AIMS: To evaluate whether two commercial nitrifying bacterial consortia can function as biocontrol agents in ornamental fish transporting systems. METHODS AND RESULTS: The consortia were applied in a simulated set-up using zebrafish as the model organism in three trials. The efficacy of the bacterial consortia in controlling the ammonia level was validated by measuring water quality parameters such as total ammonia, nitrate and pH of the transport water. The bacterial community structure in the transport unit was studied using denaturing gradient gel electrophoresis. The consortia tested improved the nitrifying activity that in turn facilitated the reduction of ammonia that had accumulated during the transport. Bacterial profiles revealed the presence of both ammonia-oxidizing and nitrite-oxidizing bacteria in the transport bags. CONCLUSIONS: The application of the consortia during the transportation of zebrafish could profoundly improve the water quality by curbing ammonia accumulation. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential of applying nitrifying bacteria as a bioremediation practice during the transport of ornamental fish has been demonstrated and this innovative approach contributes to the amelioration of current fish welfare in ornamental fish trade.

Dietary lipid levels have a remarkable impact on the expression of growth-related genes in Senegalese sole (Solea senegalensis Kaup).

In Senegalese sole (Solea senegalensis Kaup), growth is negatively correlated to dietary lipid levels. To understand the molecular basis of this effect a molecular toolbox of 12 genes, including fgf6, fst, mstn1, myf5, mrf4, myod1, myod2, myog, myHC, mylc2, igf1r and insr, was developed. The expression profiles of these genes were investigated in white muscle and liver of fish fed with three dietary lipid levels (4%, 12% and 20%). The expression of igf-I and igf-II was also examined. MRFs and myosins were only expressed in the muscle and, except for myf5, the general trend was a decrease in expression with an increase in dietary lipids. Fgf6 was identified for the first time in liver and its expression augmented in hepatic tissues with increasing dietary lipid levels. A similar tendency was observed for mstn1 and igf-I. The opposite was observed for igf1r expression in muscle and liver. Myog, mrf4, mylc2 and igf1r were highly correlated with growth and nutrient utilisation indices. In addition to its practical implications, this work provides a valuable contribution towards our understanding of the genetic networks controlling growth in teleosts.

Two novel muramidases from skin mucosa of rainbow trout (Oncorhynchus mykiss).

Two novel antibacterial muramidases were purified to homogeneity from skin exudates of rainbow trout (Oncorhynchus mykiss). Unusually, one has an acidic isoelectric point and it is the first anionic muramidase to be reported for fish. Its molecular mass is 14,268 Da, as determined by mass spectrometry. The other muramidase is cationic with a mass of 14,252 Da. Partial N-terminal amino acid sequencing and peptide mapping strongly point to it being a c-type lysozyme, the first to be purified and characterised from skin of a salmonid. Its optimum pH ranges from 4.5 to 5.5 and its optimum temperature, at pH 5.0, is 33-49 degrees C, although it still exhibits activity at 5 degrees C. It is strongly bactericidal to the Gram-(+) bacterium Planococcus citreus, with a minimum bactericidal concentration of 100 U ml(-1), but is neither chitinolytic nor haemolytic. These two muramidases probably contribute to epithelial defence of the fish against microbes, either alone or in synergism with antibacterial peptides.

Expression of vasa and nanos3 during primordial germ cell formation and migration in Atlantic cod (Gadus morhua L.).

Primordial germ cells (PGCs), progenitors of gametes, are specified very early in embryonic development and undergo an active migration to the site where the future gonads will form. While the developmental pattern of PGCs during embryogenesis has been documented in few model teleost fishes, there is currently no information available for any representative of Superorder Paracanthopterygii. This includes Atlantic cod (Gadus morhua), which is a historically important food fish in both fisheries and aquaculture industries. In the present study, we cloned and characterized vasa and nanos3 and used them as germ cell markers in Atlantic cod. Sequencing results showed prospective vasa and nanos3 mRNA contained the domains used to describe their respective protein family. Furthermore, phylogenetic analysis using the amino acid sequence placed Atlantic cod Vasa distinct from representatives of three other taxonomic Superorders. Atlantic cod Nanos3 was placed with other homologues from the Nanos3 subfamily. Expression of both genes was detected from the first cleavage division; both were specifically expressed in Atlantic cod PGCs from the 32-cell stage. While nanos3 expression ceased during early somitogenesis, vasa was strongly expressed throughout embryonic development. Using vasa as a marker, we described the Atlantic cod PGC migration pattern. We demonstrated that Atlantic cod PGCs migrate ventral to the trunk mesoderm. With the exception of Pacific herring (Clupea pallasii), PGCs in other described teleost fishes migrate lateral to the trunk. The results from this study are the first step toward understanding germ line formation in Atlantic cod.

Profiling of key apoptotic, stress, and immune-related transcripts during embryonic and postembryonic development of Atlantic cod (Gadus morhua L.).

We investigated the profiles of 25 genes involved in apoptosis (bcl-x2, casp3, casp8, ccar1, mcl1, and tpt1), immunity (bty, cathl, ifng, il1b, il6, il8, il10, lyzg, and tfa), oxidative stress (cat, gpx4, gsh-px, hsp70, hsp90a, and sod1), and stress axis (crh, pomc, grl1, and mlr) during Atlantic cod development and compared the mRNA transcript levels between samples from farmed (FB) and wild broodstock (WB) using real-time polymerase chain reaction. The suitability of nine endogenous housekeeping genes and an external standard (luciferase) as reference genes was also evaluated. The cycle threshold values of all housekeeping genes differed significantly throughout Atlantic cod development. Fertilization and hatching rates were significantly higher in WB group (95 ± 1.8% and 89 ± 2.8%, respectively) compared with FB (75 ± 3.4% and 66 ± 3.2%, respectively). Eleven target genes, namely, ccar1, casp3, bcl-x2, mcl-1, cat, gsh-px, hsp70, sod1, lyzg, il8, and grl were expressed in both groups at fertilization stage, indicating their maternal transfer. Among them, transcripts of gsh-px were more abundant in WB eggs, while the expression of hsp70 was significantly higher in FB eggs. In FB larvae, expression of cat, hsp70, hsp90a, pomc, mlr, grl1, bclx2, and il6 was significantly higher at hatching and the expression of cat, gpx4, casp3 and ccar1 was significantly higher at first feeding stages, than in WB group. These findings give an insight into the expressional changes in certain category of genes involved in the embryonic development of Atlantic cod, which may eventually determine the ultimate quality of the larvae.

Sex-biased miRNA expression in Atlantic halibut (Hippoglossus hippoglossus) brain and gonads.

The role of miRNA in fish sexual development is not elucidated yet. We profiled miRNAs in gonads and brains of Atlantic halibut using SOLiD sequencing technology. We found tissue- and sexually dimorphic expression of several miRNAs, including miR-29a, miR-34, miR-143, miR-145, miR-202-3p, miR-451, and miR-2188. miR-9 and miR-202 were abundant in brain and gonads, respectively. In the next step, we selected some miRNAs showing differential expression patterns between sexes and performed RT-qPCR on 3 age groups: juveniles, 3-year-, and 5-year-olds. In brains, miR-451 was significantly down-regulated in juveniles compared to adults. let-7a, miR-143, and miR-202-3p were up-regulated in gonads of mature males compared to immature females at the same age. We investigated the effect of suppressing aromatase cytochrome P450 enzyme on miRNA expression at the onset of sex differentiation through masculinization with Fadrozole or 17-α-methyltestosterone. We found significant differences in miRNA expression between masculinized individuals and untreated controls. miR-202-3p was significantly down-regulated in female juveniles compared to male juveniles. The expression levels of let-7a and miR-451 were restored after termination of the masculinization treatment. Our data give a first insight into miRNA involvement in sexual development in teleosts.