Oxygen limitation and dietary imbalances are key aspects influencing feed intake (FI) and growth performance in cultured fish. This study investigated the combined effects of hypoxia and dietary ...electrolyte balance on the growth performance, body composition and nutrient utilization in a rainbow trout (Oncorhynchus mykiss) isogenic line. Fish were fed ad libitum two experimental diets: electrolyte-balanced or -imbalanced diets (DEB 200 or 700 mEq kg
, respectively) and exposed to normoxia or hypoxia (7.9 or 4.5 mg O
l
, respectively) for 42 days. DEB did not affect FI, growth performance or body composition. Nevertheless, hypoxia had a negative impact, reducing FI (6%), growth rate (8%), oxygen consumption (19%), energy (5%) and lipid (42%) contents. Digestible energy intake and heat production were higher in normoxic fish (40% and 23%, respectively), retaining 64% more energy in lipid or protein. Hypoxia reduced the apparent digestibility of dry matter, ash, protein, lipid, carbohydrates and energy. Trout fed DEB 700 diet were energetically less efficient, reflected in higher heat production and energy requirements for maintenance. FI was inhibited by low dissolved oxygen levels, but not by electrolyte-imbalanced diet, in spite of the higher energy requirements for maintenance. This study highlights the importance that dietary-electrolyte content and DO levels have on energy balance and growth performance when fish are fed to satiation.
In aquaculture, fish may be exposed to sub-optimal rearing conditions, which generate a stress response if full adaptation is not displayed. However, our current knowledge of several coexisting ...factors that may give rise to a stress response is limited, in particular when both chronic and acute stressors are involved. This study investigated changes in metabolic parameters, oxidative stress and innate immune markers in a rainbow trout (
) isogenic line exposed to a combination of dietary (electrolyte-imbalanced diet, DEB 700 mEq Kg
) and environmental (hypoxia, 4.5 mg O
L
) challenges and their respective controls (electrolyte-balanced diet, DEB 200 mEq Kg
and normoxia, 7.9 or mg O
L
) for 49 days. At the end of this period, fish were sampled or subjected to an acute stressor (2 min of handling/confinement) and then sampled. Feeding trout an electrolyte-imbalanced diet produced a reduction in blood pH, as well as increases in cortisol levels, hepato-somatic index (HSI) and total energy content in the liver. The ratio between the lactate dehydrogenase (LDH) and isocitrate dehydrogenase (IDH) activities decreased in the liver of trout fed the DEB 700 diet, but increased in the heart, suggesting a different modulation of metabolic capacity by the dietary challenge. Several markers of oxidative stress in the liver of trout, mainly related to the glutathione antioxidant system, were altered when fed the electrolyte-imbalanced diet. The dietary challenge was also associated with a decrease in the alternative complement pathway activity (ACH
) in plasma, suggesting an impaired innate immune status in that group. Trout subjected to the acute stressor displayed reduced blood pH values, higher plasma cortisol levels as well as increased levels of metabolic markers associated with oxidative stress in the liver. An interaction between diet and acute stressor was detected for oxidative stress markers in the liver of trout, showing that the chronic electrolyte-imbalance impairs the response of rainbow trout to handling/confinement. However, trout reared under chronic hypoxia only displayed changes in parameters related to energy use in both liver and heart. Taken together, these results suggest that trout displays an adaptative response to chronic hypoxia. Conversely, the dietary challenge profoundly affected fish homeostasis, resulting in an impaired physiological response leading to stress, which then placed constraints on a subsequent acute challenge.
European seabass (Dicentrarchus labrax) production is often hampered by bacterial infections such as photobacteriosis caused by Photobacterium damselae subsp. piscicida (Phdp). Since diet can impact ...fish immunity, this work investigated the effect of dietary supplementation of 5% Gracilaria sp. aqueous extract (GRA) on seabass antioxidant capacity and resistance against Phdp. After infection, mortality was delayed in fish fed GRA, which also revealed increased lysozyme activity levels, as well as decreased lipid peroxidation, suggesting higher antioxidant capacity than in fish fed a control diet. Dietary GRA induced a down-regulation of hepatic stress-responsive heat shock proteins (grp-78, grp-170, grp-94, grp-75), while bacterial infection caused a down-regulation in antioxidant genes (prdx4 and mn-sod). Diet and infection interaction down-regulated the transcription levels of genes associated with oxidative stress response (prdx5 and gpx4) in liver. In head-kidney, GRA led to an up-regulation of genes associated with inflammation (il34, ccr9, cd33) and a down-regulation of genes related to cytokine signalling (mif, il1b, defb, a2m, myd88). Additionally, bacterial infection up-regulated immunoglobulins production (IgMs) and down-regulated the transcription of the antimicrobial peptide leap2 in head kidney. Overall, we found that GRA supplementation modulated seabass resistance to Phdp infection.
This study aimed to evaluate the effects of dietary inclusion of plant feedstuff mixture (PFM) pre-treated by solid-state fermentation (SSF) on the physiological responses of European seabass. For ...that purpose, two diets were formulated to contain: 20% inclusion level of non-fermented plant ingredients mixture (20Mix) and 20Mix fermented by
in SSF conditions (20Mix-SSF). Seabass juveniles (initial body weight: 20.9 ± 3.3 g) were fed the experimental diets, reared at two different temperatures (21 and 26 °C) and subjected to weekly salinity oscillations for six weeks. Growth performance, digestive enzyme activities, humoral immune parameters, and oxidative stress indicators were evaluated. A reduction in weight gain, feed intake, and thermal growth coefficient was observed in fish fed the fermented diet (20Mix-SSF). Salinity oscillation led to an increase in weight gain, feed efficiency, daily growth index, and thermal growth coefficient, regardless of dietary treatment. Higher rearing temperatures also increased daily growth index. No dietary effect was observed on digestive enzymes activities, whereas rearing temperature and salinity oscillation modulated digestive enzyme activities. Oxidative stress responses were significantly affected by experimental diets, temperature, and salinity conditions. Catalase and glutathione peroxidase activities showed an interactive effect. Fish reared at 21 °C showed higher enzymatic activity when fed the 20Mix-SSF. Conversely, fish reared at 26 °C showed higher GPx activity when fed the 20Mix diet. Fish reared at 26 °C showed reduced peroxidase and lysozyme activities, while salinity fluctuation led to increased lysozyme activity and decreased ACH50 activity. ACH50 activity increased in fish fed the 20Mix-SSF. Overall, the dietary inclusion of PFM fermented by
was unable to mitigate the impact of environmental stress on physiological performance in European seabass. In fact, fermented feed caused an inhibition of growth performances and an alteration of some physiological stress indicators.
This study investigated the effects of seaweed dietary supplementation on measures of fish performance including aerobic metabolism, digestive enzymes activity, innate immune status, oxidative ...damage, and growth rate using European seabass (
Dicentrarchus labrax
). Fish were fed for 49 days with three different diets: a control diet (CTRL), a
Gracilaria-
supplemented diet (GR7.5), and a mixed diet (Mix) composed of
Gracilaria
,
Fucus
, and
Ulva
genera representatives. All diets were isoenergetic (22 kJ g
−1
adjusted for dry matter (DM)), isoproteic (47 %DM), and isolipidic (18 %DM) and tested in triplicate groups of 20 fish (initial body weight 25.5 ± 4.1 g). Final results showed similar growth rates and digestive activities between diets. Maximum and standard metabolic rates and aerobic metabolic scope revealed comparable results for the three diets. In contrast, fish fed with GR7.5 exhibited elevated routine metabolic rate (190.7 mg O
2
kg
−1
h
−1
). Fish fed with the GR7.5 and Mix diets had lower alternative complement pathway (ACH50) (62.5 and 63 units mL
−1
respectively) than CTRL (84 units mL
−1
) GR7.5 increased lipid peroxidation and cholinesterase levels, as well as glutathione s-transferase activity. Mix diet increased glutathione reductase activity when compared to CTRL. Collectively, our findings suggest that dietary seaweed supplementation may alter seabass metabolic rate, innate immune, and antioxidant responses without compromising growth parameters.
The current study evaluated the effects of two different fractions derived from the methanolic extraction of the red seaweed
Gracilaria
sp. supplemented in European seabass (
Dicentrarchus labrax
) ...diets. With that purpose, three experimental diets were prepared: a basal diet (control), a control supplemented with the methanolic extract (GE, 0.5% diet) and a control supplemented with the insoluble residue of the GE extraction (GR, 4.5%). Seabass with an average initial weight of 16.5 ± 0.6 g were fed the experimental diets for 42 days, and the following parameters were evaluated: growth indicators, digestive enzyme activities, immune and oxidative stress responses, fillet pH and color (
L
*,
a
*, and
b
* values), and skin color. The dietary supplementation of GE or GR had no effect on growth performance, digestive enzyme activities, fillet pH, and color. Skin color was significantly lighter (
L
*) in fish-fed GE (83.9 ± 1.9) and GR (84.3 ± 2.3) diets when compared with the control group (81.9 ± 3.8). The dietary treatments did not affect the oxidative stress biomarkers. Alternative complement pathway (ACH50) was significantly higher in fish-fed GE diet (168.2 ± 13.4 EU mL
−1
) than in the control diet (113.1 ± 31.4 EU mL
−1
). No dietary effect was observed on peroxidase and lysozyme activities. The current study indicates that dietary supplementation of
Gracilaria
sp. methanolic extracts may have little influence on the innate immune system and skin color in seabass.
•Tolerance limit (LD) of Aeromonas hydrophila for Arapaima gigas was determined.•For A. gigas, the LD50-96h was of 1.8×108CFU/mL.•The intradermal inoculation of 1.8×108CFU/mL A. hydrophila caused ...91.6% of mortality in fish and several clinical signs.•Fish had erratic movement, body abnormal coloration, hemorrhagic foci and abrasion of dorsal fin.•Fish had depigmentation in the tegument, body lesions, loss of balance, reduction of respiratory movements, hemorrhagic foci and necrotic hemorrhages.
Aeromonas hydrophila is causing substantial economic losses in world aquaculture. This study determined the tolerance limit (LD50-96h) of A. hydrophila in Arapaima gigas, and also investigated the clinical signs after intradermal inoculation. Arapaima gigas fingerlings were inoculated intraperitoneally with 0 (control), 1.0×105, 1.0×106, 1.0×107, 1.0×109 and 1.0×1010CFU/mL of A. hydrophila for the determination of LD50-96h, which was 1.8×108CFU/mL. In another trial with intradermal inoculation of 1.8×108CFU/mL A. hydrophila, there was a 91.6% of mortality between 8 and 23h, and several clinical signs were found. As follows: depigmentation in the tegument, lesions in the tail and fins, loss of balance, reduction of respiratory movements, hemorrhagic foci, necrotic hemorrhages in the kidney, liver and swim bladder, splenomegaly, ascites in the abdominal cavity and hyperemia, enlargement of the gall bladder, among other clinical signs observed. The results showed that A. gigas has a relative tolerance to A. hydrophila when compared to other Neotropical fish species.
The current study evaluated the effects of dietary seaweed supplementation in European seabass juveniles (
Dicentrarchus labrax
) subjected to rearing temperature and salinity oscillations, ...simulating natural variations in pond aquaculture conditions. Two experimental diets where formulated: a control diet (CTRL) with no supplementation and one supplemented with 7.5% seaweed mix (SW 2.5%
Fucus
sp., 2.5%
Gracilaria
sp. and 2.5%
Ulva
sp.). Seabass from both dietary groups (40.7 g initial body weight) was subjected to either combined salinity and temperature oscillations, or to fixed conditions. Growth performance, innate immune, and oxidative stress responses were evaluated. Results showed that seaweed supplementation had no significant effect on the analyzed parameters. However, environmental oscillations revealed significant effects on growth performance and oxidative stress response. Fish subjected to salinity and temperature oscillations had a significantly lower weight gain and daily growth index than those subjected to fixed conditions, regardless of dietary treatment. Total glutathione, oxidized glutathione, and catalase increased in fish subjected to oscillatory conditions. Lysozyme and peroxidase were not influenced by either diet or environmental conditions. In conclusion, this particular dietary seaweed mix supplementation did not mitigate the negative effects of environmental oscillations on growth performance and innate immune responses in European seabass.
The swimming activity, although an essential trait in the life cycle of fish, is still poorly understood in farmed fish. The current study aimed to investigate the impact of short-term induced ...swimming on the immune and antioxidant defence systems in European eel (Anguilla anguilla). Sixteen male yellow European eels (total length: 39.9 ± 0.7 cm; body weight: 108.8 ± 6.1 g) were individually placed in swimming flumes and divided into two groups: i) no swimming (n = 8); and ii) induced-swimming (n = 8) at 0.3 body lengths (BL)·s−1 for 7 h. Swimming resulted in a 2-fold lower cortisol concentration in plasma, whereas plasma glucose, lactate, and several immune-related parameters did not present variations between groups. Interestingly, swimming led to higher lysozyme, peroxidase, and protease activities in skin mucus, whereas bactericidal activity did not show differences among groups. Additionally, the gene expression of interleukin 1 beta showed an up-regulation in the skin of fish with induced swimming, while no differences were observed in the head-kidney or gills. Furthermore, modulation of the antioxidant status was observed in the liver and posterior skeletal muscle after induced swimming. Fish subjected to swimming showed lower lipid peroxidation and higher reduced glutathione levels, increasing the reduced/oxidized glutathione ratio. However, no variations in the antioxidant status were observed between groups in the anterior skeletal muscle. This study showed modulation of immune and oxidative stress markers in European eels upon short-term induced swimming compared to non-swimming fish.
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•Plasma cortisol levels were lower in European eels induced to swim at 0.3 BL·s−1.•Lysozyme, peroxidase, and protease activities were higher in the skin mucus of swimming eels.•Expression of il1β gene was up-regulated in the skin of fish induced to swim.•Swimming led to lower LPO and higher GSH levels and GSH/GSSG ratio in the liver and posterior skeletal muscle.•This study highlights the benefits of induced swimming in the welfare of European eel.
A fish trial was carried out to evaluate the combined effects of temperature and dietary lipid level on the body composition, growth performance, and freshness profile of the European seabass (
). ...Fish were kept for 56 days at 20 °C and 24 °C and fed on two diets, with 16% and 20% lipid. At the end of the trial, fish were euthanized at two temperature conditions (0.6 °C or -0.6 °C) and kept on ice for 10 days at 4 °C to evaluate their freshness condition. Findings demonstrated that fish reared at 24 °C presented a lower lipid level and a higher daily growth index than those at 20 °C. Additionally, sensory analysis (Quality Index Method-QIM) and microbiological analysis revealed that fish reared at 24 °C showed better freshness conditions than those at 20 °C. However, the 16S rRNA metabarcoding analyses revealed a higher proliferation of genera associated with fish-spoiling bacteria in the skin microbiome of fish reared at 24 °C, i.e., Vibrio and Acinetobacter, which was not observed in the skin microbiome of fish reared at 20 °C. Nevertheless, the dietary lipid level did not have any influence on fish freshness. Therefore, our data suggest that the increase in temperature to 24 °C is beneficial for the growth and freshness profile (lower QIM and lower CFUs/cm
) of this particular species. Additionally, the lower euthanasia temperature (-0.6 °C) seems to lead to higher fish freshness than the normal temperature (0.6 °C).
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