Effects of capture-related stress and pre-freezing holding in refrigerated sea water (RSW) on the muscle quality and storage stability of Atlantic mackerel (Scomber scombrus) during subsequent frozen storage

Crowded (stressed) and unstressed Atlantic mackerel with or without pre-freezing holding in refrigerated sea water (RSW) were stored at -19 °C for ∼12 months and analysed for nucleotide degradation (K value), muscle pH, water holding capacity (WHC), fillet firmness, cathepsin B/L like activity, lipid oxidation and fillet colour. The frozen storage showed the largest and most consistent direct effects on the quality metrics leading to increased lipid oxidation, discolouration (yellowing) and reduction on WHC and cathepsin activity. RSW treatment promoted nucleotide degradation and reduced WHC and fillet firmness in interaction with frozen storage and affected fillet colour lightness and saturation. Although showing only marginal main effects, crowding stress modified WHC, cathepsin activity and fillet firmness and colour through significant interactions with the frozen storage and RSW treatment. Further studies with larger sample sizes would be needed to elucidate their complex effects and interactions on the quality and storage stability of mackerel.

Effects of crowding stress on the hypothalamo-pituitary-interrenal axis of the self-fertilizing fish, Kryptolebias marmoratus

We tested whether crowding stress affects the hypothalamo-pituitary-interrenal (HPI) axis of the self-fertilizing fish, Kryptolebias marmoratus, which is known to be aggressive in the laboratory conditions but sometimes found as a group from a single land crab burrow in the wild. The projection of corticotropin-releasing hormone (CRH) neurons to the adrenocorticotropic hormone (ACTH) cells in the pituitary was confirmed by dual-label immunohistochemistry; CRH-immunoreactive (ir) fibers originating from cell bodies located in the lateral tuberal nucleus (NLT) of the hypothalamus were observed to project to ACTH-ir cells in the rostral pars distalis of the pituitary. Then, fish were reared solitary or in pairs for 14 days, and the number of CRH-ir cell bodies in the NLT of the hypothalamus and cortisol levels in the body without head region were compared. The number of CRH-ir cell bodies and cortisol levels were significantly higher in paired fish. These results indicate that crowding stress affects the HPI axis in K. marmoratus which thrive in small burrows with limited water volume.

High stocking density alters growth performance, blood biochemical profiles, and hepatic antioxidative capacity in gibel carp (Carassius gibelio)

This study investigated the effect of stocking density on growth performance, blood biochemical profiles, antioxidative capacity, and muscle quality of gibel carp (Carassius gibelio). Gibel carps (initial body weight 57.04 ± 1.89 g) were reared at high stocking density (HSD, 10.85 kg m^-3), medium stocking density (MSD, 5.06 kg m^-3), and low stocking density (LSD, 1.47 kg m^-3) for 60 days. The LSD group exhibited the highest growth rate, while HSD significantly inhibited fish growth. The muscular compositions of crude fat, crude ash, and moisture were significantly changed by stocking density, but crude protein content did not differ significantly. The stocking density altered the muscular texture profiles of gibel carp. Compared to either the HSD group or the MSD group, the highest levels of resilience and springiness occurred in the LSD group. Significant differences were observed in the levels of plasma glucose, alanine aminotransferase, aspartate aminotransferase, cholesterol, and creatinine among three groups. The fish exhibited the highest level of plasma cortisol as well as the lowest levels of triiodothyronine and thyroxine in the HSD group. The fish stocked in the LSD group showed the highest activities of superoxide dismutase, glutathione peroxidase, and catalase as well as the highest content of glutathione in liver. The significant highest total antioxidant capacity occurred in the fish stocked in the LSD group. The results showed that HSD resulted in chronic crowding stress, and exerted negative impact on growth performance, muscle quality, and antioxidative capacity of gibel carp.

Stocking density induces differential expression of immune-related genes in skeletal muscle and head kidney of fine flounder (Paralichthys adspersus)

Immunity can be modulated by different internal and external factors, being stress one of the most important. However, the stress effects on the immunocompetence of the skeletal muscle has not been studied in detail in earlier vertebrates. Here, we examine the effect of chronic (4 and 7 weeks) crowding stress on the immunocompetence of skeletal muscle and head kidney in the fine flounder (Paralichthys adspersus). Corticosteroid receptor transcript levels and their target genes; pro-inflammatory cytokines, and Toll-, NOD-, and RIG-like receptors were quantified by qPCR. The results indicate that chronic stress down-regulates the expression of these genes in muscle, compromising skeletal muscle immunocompetence, while the expression of these genes is upregulated in head kidney after seven weeks of crowding stress. The data suggests that chronic stress modulates the expression of these immune-related genes in a tissue-specific manner.

Effects of l-tryptophan on the growth, intestinal enzyme activities and non-specific immune response of sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress

In order to reveal the effects of l-tryptophan (Trp) on the physiology and immune response of sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress, four density groups of sea cucumbers (i.e. 4, 8, 16 and 32 individuals per 40 L water, represented as L, ML, MH and H) were fed with diets containing 0, 1, 3 and 5% l-tryptophan respectively for 75 days. The results showed that the specific growth rates (SGR) of the sea cucumber fed with diet with 3% Trp (L, 2.1; ML, 1.76; MH, 1.2; H, 0.7) were significantly higher than those fed with basal diet without Trp supplementation (P < .05). Peak amylase activity occurred at H stress density at 3% dietary Trp. Trypsin activity was higher in diet 3% in ML and MH densities than the controls, which increased by 66.4% and 53.8%. However, the lipase activity first increased and then decreased from the stocking density L to H, with highest values of 3% Trp group showed the highest value than other groups. Compared to those fed with the basal diet, sea cucumber fed diets with Trp (3%) had significantly higher phagocytic activities (0.28 OD540/10⁶ cells, H) in coelomic fluid and respiratory burst activities (0.105 OD630/10⁶ cells, MH) (P < .05). The results suggested that Trp cannot improve superoxide dismutase (SOD) activity at L, ML and MH densities. The alkaline phosphatase activity (AKP) significantly decreased at H stress density. Under the experimental conditions, the present results confirmed that a diet supplemented with 3% Trp was able to enhance intestinal enzyme activities, non-specific immune response and higher growth performance of A. japonicus.

Effect of yeast (Xanthophyllomyces dendrorhous) and plant (Saint John's wort, lemon balm, and rosemary) extract based functional diets on antioxidant and immune status of Atlantic salmon (Salmo salar) subjected to crowding stress

Salmon farming may face stress due to the intensive culture conditions with negative impacts on overall performance. In this aspect, functional feed improves not only the basic nutritional requirements but also the health status and fish growth. However, to date no studies have been carried out to evaluate the effect of functional diets in salmon subjected to crowding stress. Thus, the aim of this study was to evaluate the effect of yeast extract (Xanthophyllomyces dendrorhous; diet A) and the combination of plant extracts (common Saint John's wort, lemon balm, and rosemary; diet B) on the antioxidant and immune status of Atlantic salmon grown under normal cultured conditions and then subjected to crowding stress. Fish were fed with functional diets during 30 days (12 kg/m³) and then subjected to crowding stress (20 kg/m³) for 10 days. The lipid peroxidation in gut showed that both diets induced a marked decrease on oxidative damage when fish were subjected to crowding stress. The protein carbonylation in muscle displayed at day 30 a marked decrease in both functional diets that was more marked on the stress condition. The expression of immune markers (IFNγ, CD4, IL-10, TGF-β, IgM_mb, IgM_sec, T-Bet, and GATA-3) indicated the upregulation of those associated to humoral-like response (CD4, IL-10, GATA-3) when fish were subjected to crowding stress. These results were confirmed with the expression of secreted IgM. Altogether, these functional diets improved the antioxidant status and increased the expression of genes related to Th2-like response suggesting a protective role on fish subjected to crowding stress.

Effect of crowding stress on the immune response in turbot (Scophthalmus maximus) vaccinated with attenuated Edwardsiella tarda

The aim of this study was to evaluate the immune responses in turbot, Scophthalmus maximus, treated with 1 × 10⁷ cfu/ml attenuated Edwardsiella tarda (0.1 ml/fish) under low density (LD; ∼5.25-5.13 kg/m², initial to final density), medium density (MD; ∼10.41-13.95 kg/m²), and high density (HD; ∼20.53-30.77 kg/m²) conditions for 8 weeks. The results showed that there was a peak value in the percentage of sIg+ (surface immunoglobulin-positive) cells in blood leucocytes (BL), spleen leucocytes (SL), and pronephros leucocytes (PL) during the sixth week in the HD, which was delayed by week compared with the other groups. The specific immunoglobulin M (IgM) antibody levels increased from the first week in all groups and reached a peak in the fifth week in the LD and MD groups, but in the sixth week in the HD group. The serum cortisol levels were greater in the HD group compared with the other groups in the last 3 or 4 weeks. These results show that stocking turbot at a LD obtained the most effective immunization, and thus we conclude that crowding stress may reduce the ability to deal with immune challenge.

Psychosocial stress inhibits additional stress-induced hyperexpression of NO synthases and IL-1β in brain structures

BACKGROUND

The aim of this study was to compare the expression of interleukin-1β (IL-1β), neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in the prefrontal cortex (PFC), hippocampus (HIP) and hypothalamus (HT) during chronic crowding (CS) (psychosocial) and restraint (RS) (physico-psychological) stress. Adaptational changes of these stress mediators to a subsequent acute RS, in two models of chronic stress were investigated.

METHODS

Rats were crowded (24 in one cage) or restrained in metal tubes for 10min twice a day for 3, 7, and 14 consecutive days and decapitated. For determination of adaptational changes the chronically crowded and restrained rats 24h after the last stress session were subjected to a single 10min RS. The IL-1β, nNOS and iNOS protein levels in brain structures samples were analyzed by Western blot procedure.

RESULTS

Chronic CS for 3days did not markedly change the subsequent acute stress induced expression of nNOS, iNOS and IL-1β protein level in PFC and iNOS protein level in HT. CS markedly decreased the expression of nNOS, iNOS and IL-1β in HIP. By contrast, parallel chronic RS, significantly increased the subsequent acute stress-induced expression of iNOS and IL-1β in PFC and considerably increased iNOS level in HT.

CONCLUSION

Chronic psychosocial stress, may protect against possible harmful action of hyperproduction of iNOS and iNOS derived nitric oxide (NO) mainly in PFC and HIP. By contrast, chronic physico-psychosocial stress may strongly potentiate additional stress-induced harmful effects of NOS and IL-1β hyperproduction.

Jian

The present study was conducted to evaluate the effects of different L-alanyl-l-glutamine (Ala-Gln) feeding strategies on the growth performance, metabolism and crowding stress resistance related parameters in juvenile Jian carp (Cyprinus carpio var. Jian) under crowded condition (80 g/L). Juvenile Jian carp (initial weight 26.1 ± 0.6 g) were distributed into five groups which fed with graded concentrations (0% or 1.0%) of Ala-Gln for eight weeks. Control group (I, 0/0) fed with control diet (0% Ala-Gln) throughout the feeding trial. The other four groups employed different control and experimental diet feeding strategies ranging from two weeks control diet fed and two weeks experimental diet (1% Ala-Gln) fed (II, 0/2) to eight weeks experimental diet fed (V, 4/4). Results revealed that Mean weight gain (MEG) under all different feeding strategies of Ala-Gln were significantly higher than that of the control group (p < 0.05), and MEG of group II (201.90%) was even higher than that of group IV (184.70%). Liver glycogen and blood total protein of groups II, III and V were significantly higher than that in groups I and IV (p < 0.05). The highest level of serum thyroxine (10.07 ng/ml), insulin-like growth factor-I (52.40 ng/ml) and insulin (9.73 μ IU/mL) were observed in group V. However, diet supplemented with Ala-Gln did not affect the levels of serum glucose, cortisol and catecholamine in fish. The mRNA expression of GR1a, GR1b and GR2 were also significantly changed in Ala-Gln supplementation groups compared with control group (p < 0.05). After fish intraperitoneally injected with virulent Aeromonas hydrophila, the fish survival rates were significantly increased in all Ala-Gln supplementation groups compared with control group (p < 0.05). Results from the present experiment showed the importance of dietary supplementation of Ala-Gln in benefaction of the growth performance, metabolism and crowding stress resistance in Jian carp breeding. The optimal feeding strategy was alternatively fed with control diet and then experimental diet at an interval of two weeks for juvenile Jian carp under crowded condition.

Effects of emodin and vitamin E on the growth and crowding stress of Wuchang bream (Megalobrama amblycephala)

This study aimed to investigate the effects of dietary emodin, high-dose vitamin E and their combination on the growth of Megalobrama amblycephala and its resistance to acute crowding stress. The fish were randomly divided into four groups: a control group fed with basal diet, and three treatment groups fed with basal diet supplemented with 60 mg/kg emodin (the emodin group), 500 mg/kg vitamin E (the vit E group), and 60 mg/kg emodin together with 500 mg/kg vitamin E (the combination group). After 60 days, the fish were exposed to acute crowding stress for 24 h. The results showed that the weight gain of the vit E group, specific growth rate of the vit E group, total serum protein concentration (TP) of the vit E group, serum lysozyme activity of the emodin group, serum superoxide dismutase (SOD) activity of the emodin group, hepatic heat shock protein 70 (HSP70) levels of the vit E group and the emodin group, and serum alanine aminotransferase (ALT) activity of the combination group significantly increased while the weight gain and specific growth rate of the combination group significantly decreased compared with the control group before stress. After crowding stress, the vit E group had improved serum TP 12 h post-stress, hepatic SOD activity 24 h post-stress, and hepatic HSP70 mRNA levels 12 and 24 h post-stress while the emodin group had enhanced serum SOD activity 12 and 24 h post-stress and hepatic HSP70 mRNA levels 12 and 24 h post-stress, as compared with the control. However, the serum cortisol content of the three treatment groups 12 and 24 h post-stress, ALT activity in the vit E group and emodin group 24 h post-stress, and serum alkaline phosphatase and liver catalase activity in the combination group 24 h post-stress were lower than those in the control group. The cumulative mortality was lower in the emodin, vit E, and combination group after Aeromonas hydrophila infection compared with the control group. Therefore, dietary supplementation with 60 mg/kg emodin or 500 mg/kg vitamin E can improve HSP70 mRNA levels and antioxidant capabilities, resistance to crowding stress, and growth in M. amblycephala. However, the combination of emodin and vit E does not have a synergistic effect in M. amblycephala.