Modification of Walleyes Stizostedion vitreum Tolerance to Hydrogen Peroxide Bath Treatment

Abstract— Hydrogen peroxide is being evaluated for its potential as a therapeutic compound for a variety of external disease organisms of fish. The value of hydrogen peroxide as a therapeutic compound for use in walleye Stizustedion vitreum culture has been questioned due to the high sensitivity (i.e., high mortality) of walleyes to this compound. We conducted bioassays and histopathological studies to determine if exposure of walleye to hydrogen peroxide bath treatments would result in increased tolerance to subsequent exposure. Test fish exhibited increased tolerance to hydrogen peroxide after initial exposures. This phenomenon of increased tolerance of walleyes to hydrogen peroxide may be of value in the development of management strategies for the successful treatment of fish diseases.     

Depletion of serum alternative complement pathway activity in gilthead seabream caused by α-tocopherol and n-3 HUFA dietary deficiencies

Studies on the alternative complement pathway (ACP) activity in fish have suggested the particular relevance of this pathway as a non-specific immune mechanism being its activation directly related with the availability of certain nutrients. In the present study ACP activity in gilthead seabream fed different dietary levels of a-tocopherol and n-3 HUFA deficiencies was studied under different stress conditions (overcrowding and repetitive chasing).A reduction in ACP activity was found when diets with deficiencies in -tocopherol and n-3 HUFA were assayed at any of the experimental conditions assayed. Levels of plasma cortisol were similar to those of fish after crowding stress subjected to dietary deficiencies at low stocking density, suggesting that dietary deficiencies produced a chronic elevation of cortisol. When fish were subjected to repetitive chasing, plasma cortisol from fish fed control diet showed a progressive increase whereas plasma cortisol levels from both dietary deficient groups showed a transitory peak 4 days after the beginning of the repetitive chasing. However, ACP activity levels of fish fed deficient diets remained lower than the control group and constant during chasing period. These results suggest that both a-tocopherol and n-3 HUFA nutritional deficiencies rather than stress are an important determinant of fish complement activity.     

Alteration of liver and muscle fatty acid composition in gilthead seabream (Sparus aurata) juveniles held at high stocking density and fed an essential fatty acid deficient diet

The aim of the present study was to determine the combined effect of both stress and EFA deficiency on several biological and biochemical parameters. Fish were fed during 15 weeks two isocaloric and isoproteic diets: a control diet based on fish oil and formulated to meet the n-3 HUFA requirements for this species (1.5% of n-3 HUFA) and a deficient diet containing beef tallow and formulated to be deficient in n-3 HUFA. Each experimental diet was evaluated both at high and low stocking densities (10 and 3.2 kg m^–3 of initial density, respectively).High stocking density produced a chronic stress situation with elevation of plasma cortisol levels. It also caused a reduction in hepatosomatic index and liver lipid contents, increasing the oleic acid/n-3 HUFA ratios in the polar lipids. Fish fed the EFA deficient diet at low stocking density showed common deficiency symptoms. High stocking density in fish fed the EFA deficient diet induced a higher degree of EFA deficiency symptoms leading to mortality, liver steatosis, liver lipid deposition, reduced muscle lipid and reduced n-3 HUFA contents, which particularly affected EPA, but not DHA, suggesting a preferential retention of the latter fatty acid, specially in the phosphoglycerides fraction.     

Mortality and non-specific immune response of Eurasian perch, Perca fluviatilis, during the spawning season

Perch breeders showed high mortality rates during the spawning season. This could be linked to immunosuppressive effects of environmental conditions or reproduction.     

Cortisol and haematological response in sea bream and trout subjected to the anaesthetics clove oil and 2-phenoxyethanol

Clove oil has been tested for anaesthesia induction and recovery time as well as for haematology and stress indicators in the gilthead sea bream and rainbow trout. The former parameters were compared with those generated by 2‐phenoxyethanol. The results showed only slight differences between both anaesthetics in terms of anaesthetic efficiency and physiological effects. In addition, clove oil does not block the cortisol response to stress, as happens with other anaesthetics.     

Circadian heart rate changes and light-dependence in the Mediterranean seabream Sparus aurata

Despite the abundant literature on circadian heart rate rhythms in fish, few studies have attempted to elucidate if such pattern is endogenous or if it is modulated by environmental cues. In this study, heart rates were continuously recorded in Sparus aurata acclimated to different light regimes (normal or shifted LD 12:12 cycle and a pulsed 0.75:0.75 LD cycle) to investigate the endogenous nature and the role of light on the circadian pattern of heart rate. Under LD 12:12, the daily pattern of heart rate showed higher values at night and lower rates during the day (average amplitude of the heart rate change of 10.6 ± 5.7 beats min^–1). The circadian pattern was maintained in animals under constant light but the amplitude was decreased (2.4 ± 1.1 beats min^–1). Light masks the expression of the rhythm because under a pulsed LD cycle, heart rate tracks the pulsed LD phases, increasing during the dark phase and decreasing during the light phase. Besides the ultradian pattern imposed, an underlying circadian rhythm was detected, which indicates that the rhythm is endogenous. However, the strong link between heart rate and light obtained under pulsed LD cycles suggest the timing mechanism to be mostly based on external light reception.     

Inhibition of HPI axis response to stress in gilthead sea bream (Sparus aurata) with physiological plasma levels of cortisol

This study investigates the effect of corticosteroid (cortisol) administration on the stress response of the gilthead sea bream Sparus aurata subjected to a 48 h confinement. The effect of (in-vitro and in-vivo ) cortisol administration on the in-vitro ACTH sensitivity of the interrenal tissue; the plasma levels and tissue concentration of cortisol; and the plasma levels of ACTH, -MSH, -endorphin and glucose were determined. Confinement caused a transient and concomitant increase in plasma cortisol and ACTH levels. However, in cortisol-fed fish the plasma ACTH levels were lower, indicating a suppresion of the ACTH release from the corticotropes by cortisol. In contrast to the activation of the corticotropes, the levels of plasma melanotrope derived peptides were not affected. In spite of the fact that interrenal cells of cortisol-fed gilthead sea bream released less cortisol than controls, the interrenal sensitivity to ACTH was not affected by in-vivo and in-vitro cortisol administration. This suggests that the interrenal sensitivity to ACTH in stressed (confinement) sea bream is probably not regulated by -MSH, N-ac--END, or by cortisol. Thus, in gilthead sea bream the interrenal sensitivity to ACTH could be regulated at the hypothalamus and/or pituitary and communicated via circulating ACTH levels.     

Immunomodulatory effects of <Emphasis Type="Italic">Rhodomyrtus tomentosa</Emphasis> leaf extract and its derivative compound,rhodomyrtone, on head kidney macrophages of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Rhodomyrtus tomentosa is a medicinal plant that shows biological effects including immunomodulatory activity on human and other mammals but not in fish. In this study, we evaluated the in vitro immunomodulatory effects of R. tomentosa leaf extract and its active compound, rhodomyrtone, on the immune responses, using rainbow trout (Oncorhynchus mykiss) head kidney (HK) macrophages as a model. The tested immune functions included the expression of genes involved in innate immune and inflammatory responses and the production of reactive oxygen species (ROS). Gene expression was evaluated after exposure to 10 μg mL^?1 of R. tomentosa and 1 μg mL^?1 of rhodomyrtone for 4 and 24 h. R. tomentosa and rhodomyrtone induced changes in the expression of pro-inflammatory cytokines (il1β, il8, and tnfα), anti-inflammatory cytokines (il10 and tgfβ), inducible enzymes (inos, cox2, and arginase), and an antioxidant enzyme (gpx1). Co-exposure of R. tomentosa with LPS resulted in a prominent reduction in the expression of genes related to an inflammatory process (il1β, il8, tnfα, inos, saa, hepcidin, and gpx1), suggesting anti-inflammatory effects. Similarly, co-exposure of rhodomyrtone with LPS led to a downregulation of inflammation-related genes (il1β, inos, saa, and hepcidin). In addition, exposure to both natural plant products caused a reduction in cellular ROS levels by HK macrophages. The present results indicate that R. tomentosa and rhodomyrtone exerted immunostimulatory and anti-inflammatory effects on fish macrophages, thus opening up the possibility of using these natural products to further develop immunostimulants for health management in aquaculture.     

High stocking density produces crowding stress altering some physiological and biochemical parameters in gilthead seabream, Sparus aurata, juveniles

High stocking density has been shown to produce a wide variety of effects on cultured fish populations, such as alterations in behavior and poor feed utilization, resulting in mortality and poor growth. High stocking density has also been reported to produce chronic stress and mobilization of energy sources in fish. There are few studies focusing on the effect of high stocking density on one of the most important marine fish species for Mediterranean aquaculture, gilthead seabream (Sparus aurata). Consequently, this study investigates the effect of high stocking density on juveniles of this species, focusing on effects of stocking density on growth, biochemical composition, immune status and hematology.The results of this study showed that high stocking density produced a chronic stress situation. Plasma cortisol levels increased up to 16.25 ng ml–1 in fish held at high stocking; this value was 4 fold that of fish held at low stocking; density (3.91 ng ml–1 ). As a consequenceof this stressful situation, there was both haemoconcentration and a decrease in alternative complement pathway (ACP), an important component of the immune system of fish (from 167.23 U ml–1 down to 146.37 U ml–1). Haematocrit, haemoglobin concentration and red blood cell count were significantly higher in fish held at high stocking density (43.87%, 10.76 9dl–1 and 3.36 ×106 mm–3, respectively) compared with those fish held at low stocking density (37.21%, 9.32 g/dlg–1 and 2.82 ×106 mm–3, respectively).In addition, high stocking density produced a decrease in hepatosomatic index (from 2.26 down to 2.04) and altered liver fatty acid composition. Oleic acid (18: 1n-9) decreased in liver total lipids of fish held at high stocking density and arachidonic acid (20: 4-n6) and n-3 high unsaturated fatty acids (n-3 HUFA) were reduced in liver polar lipids of those fish. These alterations reflect the effect of stocking density on lipid metabolism to help meet the increased energy demand.