Comparative assessment of acute toxicity and histological changes in liver of African catfish Clarias gariepinus exposed to cotton insecticides.

This study investigated the acute toxicity in Clarias gariepinus to insecticides currently used in Benin cotton fields, including Thalis 112 EC (Emamectin benzoate 48 g L-1, Acetamiprid 64 g L-1), Vizir C 92 EC (Cypermethrin 72 g L-1, Abamectin 20 g L-1), Pyrinex Quick 212 EC (Deltamethrin 12 g L-1, Chlorpyrifos 200 g L-1) and Pyro FTE 472 EC (Cypermethrin 72 g L-1, Chlorpyrifos 400 g L-1) with emphasis on liver histopathological effects. A set of 180 juveniles of C. gariepinus (5.21 ± 3.22 g) was exposed for 96 h to increasing concentrations of each pesticide. The values of 96-hLC50 were 4.778, 0.002, 0.004, and 0.012 µL L-1 for Thalis, Vizir, Pyrinex, and Pyro, respectively, indicating that Vizir, Pyrinex, and Pyro were very highly toxic to C. gariepinus juveniles. During the experiments, the morphological and behavioral responses (discoloration, hyperactivity, lethargy, etc.) were observed in exposed fish, hypothesizing the neurotoxicity of these pesticides. Histopathological alterations observed in liver of contaminated fish were regressive changes, such as necrosis, vacuolation, bleeding, nuclear degeneration, hepatocytes degeneration, sinusoids dilatation, etc. Vizir induced the highest histological alteration indices while the lowest were induced by Thalis, confirming the highest toxicity of Vizir. These results indicate that acute concentrations of these insecticidal molecules have destructive effects on the liver of C. gariepinus.

Intestinal histopathology and immune responses following Escherichia coli lipopolysaccharide challenge in Nile tilapia fed enriched black soldier fly larval (BSF) meal supplemented with chitinase.

This study aimed to determine to what extend the addition of chitinase to black soldier fly larvae (BSF) meals enriched with either PUFA or LC-PUFA could improve the gut health of Nile tilapia and increase its immune status. Two types of BSF meals enriched with either α-linolenic acid (ALA) or ALA + eicosapentaenoic acid (EPA) + docosahexaenoic acid (DHA) were produced using BSF larvae cultured on vegetable substrates (VGS) or fish offal substrates (FOS), respectively. Seven diets were formulated: a control FMFO diet and two other control diets VGD0 vs FOD0 containing the meals of each type of BSF meal as total replacement for fishmeal (FM) and fish oil (FO), as well as four diets supplemented with chitinase. Two doses of commercial chitinase from Aspergillus niger (2 g/kg and 5 g/kg of feed) were supplemented to the other diets VGD0 and FOD0 to formulate VGD2, VGD5, FOD2 and FOD5. After 53 days of feeding, FOD5 diet induced a similar growth performance as the FMFO control diet, while a significant decrease of growth was observed for the other BSF larval-based diets. BSF/FOS meal led to higher SGR of fish than BSF/VGS, as for the FOD5 compared to VGD5. At day 53, lysozyme values showed an increasing trend in fish fed all the BSF-based diets, especially those fed the VGD5. After the Escherichia coli lipopolysaccharide (LPS) injection (day 54), the same increasing trend was observed in lysozyme activity, and modulation was observed only in the VGD5 fish. ACH50 activity was reduced by the BSF-based diets except for the FOD5 diet at day 53, and LPS modulation was only observed for the VGS-chitinase-based diets at day 54. Peroxidase activity and total immunoglobulin (Igs) blood level were not affected by substrate, chitinase dose or LPS injection. At day 53, the low or high dose of chitinase increased the expressions of tlr2, il-1ß and il-6 genes in the head kidney of fish fed the BSF/VGS diets compared to those fed the VGD0 or FMFO control diets. At day 54 after LPS injection, the high dose of chitinase decreased the expressions of tlr5 gene in the spleen and mhcII-α gene in the head kidney of fish fed FOD5 diets compared to those fed FOD0 diets. BSF/VGS but not BSF/FOS based diets increased fish sub-epithelial mucosa (SM) and lamina propria (LP) thickness and the number of goblet cells (GC) in fish, but dietary chitinase seemed to prevent some of these effects, especially at low dose. Results showed that chitinase supplementation of 5 g/kg of chitinase to a BSF-based diet enriched with LC-PUFA improved growth, prevented histological changes in the proximal intestine and enhanced some innate immune functions of Nile tilapia without any clear booster effect after challenge with E. coli LPS.

Comparative study on accuracy of mucosal estradiol-17ß, testosterone and 11-ketotestosterone, for maturity, and cutaneous vitellogenin gene expression in goldfish (Carassius auratus).

Providing a non-invasive procedure to track fish maturity remains a priority in broodstocks' management. In the present study, the main goal was to assess reproduction status by measuring sex steroids and vitellogenin (VTG) in the skin mucosa, as a non-invasive method. For this purpose, the present study compared the levels of estradiol-17ß (E2 ), testosterone (T), 11-ketotestosterone (11-KT), VTG and calcium (Ca) in skin mucosa and blood plasma of goldfish (Carassius auratus). Skin mucosal and blood samples were collected, as well as gonad tissues, from goldfish, as a seasonal spawner. Histological analysis confirmed the gender and maturity status from females' ovaries (as primary-growth, cortical-alveoli, initial and late-vitellogenesis) and males' testes (as spermatogenesis and spermiation). Furthermore, vitellogenin (vtg) expression was observed in skin, liver and gonads. The results indicate that mucosal E2 concentrations were significantly higher during initial and late vitellogenesis than the other stages. Mucosal 11-KT concentrations significantly increased at spermiation (P < 0.05). E2 /T and 11-KT/E2 ratios significantly increased at early vitellogenesis and spermatogenesis, respectively (P < 0.05). Females' mucosal VTG levels were significantly fluctuated according to the maturity stage. Ca showed a similar trend, but Ca was more accurate for sex identification than the VTG. Although mucus showed high levels of VTG, ovarian vtg expression was strongest while liver and skin had the similar results. These results show that measuring the mucosal androgens could be considered as an accurate, non-invasive method to monitor fish maturity.

Ex vivo approach supports both direct and indirect actions of melatonin on immunity in pike-perch Sander lucioperca.

The melatonin hormone, which is a multifunctional molecule in vertebrates, has been shown to exert complex actions on the immune system of mammals. In teleosts, the immunomodulatory capacity of this hormone has seldom been investigated. In the present experiment, we exposed ex vivo spleen and head kidney tissues of pike-perch to melatonin (Mel) and cortisol (Cort). We applied three concentrations of both hormones, alone and in combination, namely (1) Mel (10, 100 or 1000 pg mL-1) (2) Cort (50, 500 or 5000 ng mL-1) (3) Mel + Cort (10 + 50, 100 + 500 or 1000 pg mL-1+5000 ng mL-1). Pure medium without Mel or Cort served as control. After 15 h of incubation, we assessed the expression of a set of immunity-related genes, including genes encoding for pro-inflammatory proteins (il-1ß, cxcl8 and tnf-α), acute-phase proteins (fgl2, fth1, hepc, hp and saa1) and key factors of the adaptive immune system (fκbp4 and tcrg). Both Mel and Cort, when used alone or combined at physiological concentrations, significantly influenced immune gene expressions that may lead to a global immune stimulation. Our results support both, an indirect action of the Mel hormone on the immune system through the regulation of intermediates such as Cort, as well as a direct action on immune targets through specific receptors.

Impact of downstream passage through hydropower plants on the physiological and health status of a critically endangered species: The European eel Anguilla anguilla.

Hydropower plants (HPPs) are a source of "green" energy but also a threat to migrating fish such as the European eel (Anguilla anguilla) owing to the disruption of river connectivity and the obstruction of downstream migration. The impact of HPP are well-documented in terms of fish survival and damages but there is no available information concerning the condition of surviving and unharmed fish. The aim of this study is to assess the impact of the passage through HPP on the survival, the physiological and health status of adult eels. Two trials were carried with variants of the Kaplan turbine - one of the most common types in Europe. After a deliberate passage through the turbines, we studied direct mortality, external and internal damages, stress and immune biomarkers such as plasma cortisol and glucose levels, alternative complement (ACH50), lysozyme and peroxidase activities, and total immunoglobulin (Ig) content. Our results showed a lower survival and a higher external and internal damages rates in the HPP groups. Glucose levels, ACH50, lysozyme and peroxidase activities and TIgc were also affected by the passage depending on HPP characteristics. Those findings suggest a greater energy expenditure and a disruption in innate immunity due to this passage. HPPs can not only have an impact in terms of direct mortality and injuries but also affect the physiological and health condition of the surviving eels. This impact may explain the delayed mortality observed in telemetric studies and the passage through many HPPs may compromise the ability of adult eels to migrate successfully to the ocean.

Integrated multi-biomarker responses of juvenile rainbow trout (Oncorhynchus mykiss) to an environmentally relevant pharmaceutical mixture.

Pharmaceuticals are emerging pollutants of concern for aquatic ecosystems where they are occurring in complex mixtures. In the present study, the chronic toxicity of an environmentally relevant pharmaceutical mixture on juvenile rainbow trout (Oncorhynchus mykiss) was investigated. Five pharmaceuticals (paracetamol, carbamazepine, diclofenac, naproxen and irbesartan) were selected based on their detection frequency and concentration levels in the Meuse river (Belgium). Fish were exposed for 42 days to three different concentrations of the mixture, the median one detected in the Meuse river, 10-times and 100-times this concentration. Effects on the nervous, immune, antioxidant, and detoxification systems were evaluated throughout the exposure period and their response standardized using the Integrated Biomarker Response (IBRv2) index. IBRv2 scores increased over time in the fish exposed to the highest concentration. After 42 days, fish exposed to the highest concentration displayed significantly higher levels in lysozyme activity (p < 0.01). The mixture also caused significant changes in brain serotonin turnover (p < 0.05). In short, our results indicate that the subchronic waterborne exposure to a pharmaceutical mixture commonly occurring in freshwater ecosystems may affect the neuroendocrine and immune systems of juvenile rainbow trout.

Modulations of lipid metabolism and development of the Atlantic salmon (Salmo salar) fry in response to egg-to-fry rearing conditions.

In stocking program, the use of artificial incubation conditions in hatcheries from the fertilisation of eggs to the release of unfed fry could reduce their ability to adapt to the natural environment. This study evaluates the effects of three factors on the fitness and physiology of salmon fry at their emergence, the origin of water (river vs drilling), the type of support in the incubator (support matrix vs plastic sheets) and the type of incubators (Californian vs vertical trays), and compares them to a semi-natural incubation method in river. Key biological functions including nutritional and immune status were compared among experimental conditions using biometric parameters, lipid composition and gene expression analyses. Our findings demonstrated that fry incubated in vertical trays supplied with river water had no significant difference in growth and lipid composition compared to those in semi-natural incubators. Besides, fry incubated on a substrate matrix in Californian trays exhibited phenotypic characteristics closest to those incubated in river. This support matrix improved fish growth, lipid consumption and distribution compared to fry on plastic sheets. Moreover, the large amounts of several PUFAs in these fry could allow a better membrane fluidity ensuring a better adaptation to temperature variation under cold conditions. In addition, drilling water improved the survival rate compared to river water due to lower numbers of fine particles, known to be responsible for the clogging of eggs. To conclude, using a substrate combined with drilling water in artificial incubators could increase fry fitness and its adaption to wild life.

Repeated hormonal induction of spermiation affects the stress but not the immune response in pikeperch (Sander lucioperca).

Hormonal induction of spermiation, previously reported to be immunogenic in fishes, is a common hatchery practice in pikeperch, Sander lucioperca. The aim of the present study was to investigate the effects of repeated induction of spermiation in pikeperch, following application of either human chorionic gonadotropin (hCG) or salmon gonadoliberine analogue (sGnRHa) on sperm quality indices as well as on immune and stress response. Mature males of pikeperch (n = 7 per group) were stimulated twice with five days between injections of either hCG (hCG; 500 IU kg-1), sGnRHa (sGnRHa; 50 µg kg-1) or NaCl (control group; 1 ml kg-1) to assess spermatozoa motility with a computer-assisted sperm analysis (CASA) system. During second sampling, blood plasma was sampled for humoral innate immune (peroxidase and lysozyme activities, ACH50), stress (cortisol, glucose) and endocrine (testosterone) markers. In addition, the head kidney was dissected to assay the expression of several immune genes (such as il1, c3, hamp, tnf-α and lys genes). The results indicate that hormonal treatment significantly increased sperm production. Sperm sampled after the hormonal treatment maintained its quality throughout the study, regardless of the sampling time. However, it appears that the application of hCG induced elevated cortisol and glucose plasma levels compared to the control group. Almost all immune markers, except the relative expression of hepcidin (hamp gene), were unaffected by the two hormones applied. The results showed that the induction treatment of spermiation processes in pikeperch resulted in an important physiological stress response for which the intensity varied according to the hormonal agent used. However, this stress response (more profound following application of hCG) was weakly associated with innate immune functions. On the other hand, a significant negative correlation between the expression of several important immune markers (peroxidase activity, relative expression of c3 and il1 genes) and sperm quality indices indicates significant involvement of immune status on sperm quality. The results obtained shed light on immune-system-induced modifications to sperm quality. The data presented here highlight the need for careful revision of broodstock management and selection practices where welfare status as well as individual predispositions of fish to cope with the stress should be taken under the consideration.

Impact of temperature shift on gill physiology during smoltification of Atlantic salmon smolts (Salmo salar L.).

Exposure to a temperature increase may disrupt smoltification and delay or stop the downstream migration of smolts. Thermal regimes are often different between a river and its tributaries, but the effects of a relative temperature shift are not well described. We used expression of smoltification genes coupled with gill Na+/K+-ATPase activity (NKA) and plasma cortisol and growth hormone (GH) levels to investigate the impact of a 5 °C difference between tributary and river on salmon juveniles. Responses to a temperature challenge were examined at four time points during the smoltification period, with juveniles reared under three regimes including control, early and late temperature increase. The temperature shifts reduced gill NKA, plasma GH and cortisol levels which indicate hypo-osmoregulation impairment and may reduce the survival of smolts. Out of the 22 genes examined, the expression of six genes was influenced by the temperature treatments, while changes in further eleven genes were influenced by the date of sampling. Genes usually known to be upregulated during smoltification were downregulated after the temperature increase, notably nkaα1b, nkcc1a and igf1r. Upregulation of some genes involved in the hormonal regulation and acid-base equilibrium in early June may indicate a switch towards desmoltification. This study gives further insights about the impact of temperature increase on the molecular processes underlying smoltification and possible responses to human-related water temperature increase. The data also suggest dual roles in the smoltification and desmoltification for GH and IGF1 and points to the implication of genes in the smoltification process, that have previously been unstudied (nbc) or with little data available (igf2).

Passage through a hydropower plant affects the physiological and health status of Atlanstic salmon smolts.

Atlantic salmon is an anadromous species migrating from upper-reach nursery areas in rivers to the oceanic feeding areas at smolt stage and inversely at adult stage requiring unimpeded migration routes. However, dams associated with hydroelectric power plants (HPP) disrupt river connectivity and affect fish movement and survival. The objective of the current study was to evaluate the short and mid-term physiological and immune response of Atlantic salmon smolts after passing through Andenne HPP (Meuse River, Belgium). Several parameters were studied after an in situ deliberate passage including direct mortality and external damages, stress and immune biomarkers as plasma cortisol and glucose levels, complement and peroxidase activities, and immune and oxidative stress related gene expression 24 h, 72 h and 120 h after passage. Survival rate was lower and external damages were more important in fish that confronted the HPP compared to the control ones. Moreover, the passage through the turbine affected plasma glucose levels, complement and peroxidase activities and the expression of some immune genes such as lysg, igm and mpo in a timely manner suggesting that this passage can lead to a great energy expenditure and a disruption of innate immunity. Our observations can partially explain the delayed mortality observed in many studies leading to a poor success of restocking programs. HPPs not only have a direct impact in terms of mortalities and injuries but also an indirect one in terms of physiological and immune changes that can compromise Atlantic salmon smolts ability to escape successfully to the ocean.

Joint toxicity of two phytosanitary molecules, lambda-cyhalothrin and acetamiprid, on African catfish (Clarias gariepinus) juveniles.

This study was designed to evaluate the acute toxicity of acetamiprid (neonicotinoid) and lambda-cyhalothrin (pyrethroid), individually and mixtures (Act-LCh mixture and Acer 35 EC®, 15 g/L of acetamiprid and 20 g/L of lambda-cyhalothrin) in African catfish juveniles (3.35 ± 0.75 g). The tests were conducted in the laboratory under semi-static conditions according to OECD Guideline 203. Mixture toxicity effects as a function of lethal concentrations were assessed using the additive index (AI) method. Acetamiprid with 96 h-LC50 = 265.7 ppm can be considered to be nontoxic for this species. However, lambda-cyhalothrin was highly toxic to C. gariepinus with 96 h-LC50 = 0.00083 ppm. Acer 35 EC® was less toxic (96 h-LC50 = 0.21 ppm) than the Act-LCh mixture (96 h-LC50 = 0.043 ppm). Marked changes indicating nervous system damage were also recorded. An antagonistic effect was shown for lethal concentrations leading to 5 to 15% mortality in 96 hours (96 h-LC5-15) while an additive effect was obtained for the 96 h-LC20-50. The results indicate that ecological risk assessment of these molecules in aquatic environments should consider their contamination levels. Moreover, particular attention to behavior changes related to their neurotoxicity is recommended for additional monitoring of the negative effects of these insecticides.

Are cortisol and melatonin involved in the immune modulation by the light environment in pike perch Sander lucioperca?

The pineal gland is the main organ involved in the transduction process converting environmental light information into a melatonin response. Since light environment was described as an important factor that could affect physiology of teleosts, and because melatonin is a crucial hormone regulating numerous physiological processes, we hypothesized that environmental light may act on both stress and circadian axes which in turn could influence the immune status of pike perch. Therefore, we investigated the effects of two light spectra (red and white) and two light intensities (10 and 100 lx) with a constant photoperiod 12L(8:00-20:00) /12D on pike perch physiological and immune responses. Samples were collected at 04:00 and 16:00 at days 1 and 30 of the experiment. Stress markers, plasma melatonin levels, humoral innate immune markers, and expression of key immune genes in the head kidney were assessed. Light intensity clearly affected pike perch physiology. This included negative growth performances, increase in stress status, decrease in plasma melatonin levels, and immune depression. Light spectrum had only little influences. These results demonstrate that high stress status may have impacted melatonin production and secretion by the pineal organ. The drop in circulating melatonin and the increase in stress status may both be involved in the immune suppression.

Growth performance and immune status in common carp Cyprinus carpio as affected by plant oil-based diets complemented with ß-glucan.

Omnivorous fish species such as the common carp (Cyprinus carpio) are able to biosynthesise long chain polyunsaturated fatty acids (LC-PUFAs) from plant oil PUFA precursors, but the influence of the amount and quality of the LC-PUFAs biosynthesised from these oils on the immunocompetence status of the fish has received little attention. This study aims to evaluate whether the conversion of PUFA by carp induces a sufficient biosynthesis of LC-PUFA to maintain a good immunocompetence status in this species. Six iso-nitrogenous (crude protein = 39.1%) and iso-lipidic (crude lipids = 10%) diets containing three different lipid sources (cod liver oil (CLO) as fish oil; linseed oil (LO) and sunflower oil (SFO) as plant oils) were formulated with or without ß-glucan supplementation at 0.25 g/kg diet. Juvenile carp (16.3 ±â€¯0.6 g initial body weight) were fed a daily ration of 4% body weight for 9 weeks and then infected at day 64 with the bacteria Aeromonas hydrophyla. No significant differences in survival rate, final body weight, specific growth rate and feed conversion rate were observed between diets. After bacterial infection, mortality rate did not differ between fish fed CLO and plant oil-based diets, indicating that the latter oils did not affect the overall immunocompetence status of common carp. Plant oil-based diets did not alter lysozyme activity in healthy and infected fish. No negative effects of plant oils on complement activity (ACH50) were observed in healthy fish, even if both plant oil-based diets induced a decrease in stimulated fish two days after infection. Furthermore, the levels of various immune genes (nk, lys, il-8, pla, pge, alox) were not affected by plant oil-based diets. The expression of pla and pge genes were higher in SFO-fed fish than in CLO ones, indicating that this plant oil rich in linoleic acid (LA) better stimulated the eicosanoid metabolism process than fish oil. In response to ß-glucan supplementation, some innate immune functions seemed differentially affected by plant oil-based diets. LO and SFO induced substantial LC-PUFA production, even if fish fed CLO displayed the highest EPA and DHA levels in tissues. SFO rich in LA induced the highest ARA levels in fish muscle while LO rich in α-linolenic acid (ALA) sustained higher EPA production than SFO. A significantly higher fads-6a expression level was observed in SFO fish than in LO ones, but this was not observed for elovl5 expression. In conclusion, the results show that common carp fed plant oil-based diets are able to produce substantial amounts of LC-PUFA for sustaining growth rate, immune status and disease resistance similar to fish fed a fish oil-based diet. The differences in the production capacity of LC-PUFAs by the two plant oil-based diets were associated to a differential activation of some immune pathways, explaining how the use of these oils did not affect the overall immunocompetence of fish challenged with bacterial infection. Moreover, plant oil-based diets did not induce substantial negative effects on the immunomodulatory action of ß-glucans, confirming that these oils are suitable for sustaining a good immunocompetence status in common carp.

A temperature shift on the migratory route similarly impairs hypo-osmoregulatory capacities in two strains of Atlantic salmon (Salmo salar L.) smolts.

Anthropogenic use of water systems may cause temperature fluctuations between tributaries and large rivers for which physiological population related-effects on osmoregulatory capacity of Atlantic salmon are not well described. We simulated the downstream route in the case of the River Meuse basin to investigate the impact of a 5 °C temperature shift during smoltification on hypo-osmoregulatory capacities of smolts. Three temperature regimes were tested: control temperature-treatment (T1) without temperature shift, early (T2) or late (T3) temperature shift-treatment. Moreover, fish were subjected to seawater challenge during and after the downstream migration peak time. Two allochtonous strains were used: Loire-Allier (LA) and Cong (CG). Without temperature shift (T1), significant differences between the strains were noticed in the peak date and maximum activity of gill Na+/K+ATPase as well as in plasma sodium and potassium concentrations. For early (T2) and late (T3) temperature shift-treatments, gill Na+/K+ATPase activity, plasma osmolality and ion concentrations were negatively influenced in both strains. After salinity challenge, the highest osmolality was measured in smolts subjected to the temperature shift. Predictably circulating levels of GH and IGF-1 changed over the smolting period but they did not explain the observed modifications in hypo-osmoregulatory abilities whatever the population. The results show a negative impact of a temperature shift on hypo-osmoregulatory capacities of smolts regardless of population differences in smoltification timing under conditions without temperature shift. The resilience of such physiological impact was sustained at least for 1 week, comforting the role of high temperature in influencing the rate of changes occurring during smoltification. Therefore, favouring the downstream migration to help smolts reach the sea faster may mitigate the impact of a rapid temperature increase.

Comparative acute toxicity of two phytosanitary molecules, lambda-cyhalothrin and acetamiprid, on Nile Tilapia (Oreochromis Niloticus) juveniles.

This study aimed to compare the toxicity for fish of two active ingredients (lambda-cyhalothrin-20 g L-1, a pyrethroid, and acetamiprid-15 g L-1, a neonicotinoid) which are components of a commercial insecticide (Acer 35 EC) used in cotton crop in many West African countries. The juveniles of Oreochromis niloticus (4.01 ± 0.34 g, mean body weight) were exposed for 96 h to increasing concentrations of active ingredients (lambda-cyhalothrin and acetamiprid) or a mixture similar to Acer 35 EC (composed by 20 g of chemical compound lambda-cyhalothrin and 15 g of acetamiprid dissolved in 1 L of acetone). The experiments were carried out under controlled conditions in aquaria according to OECD Guidelines. During the experiments, the behavioral responses (loss of balance, color change, hyperactivity, etc.) that usually precede death were observed in exposed fish. Mortalities were recorded in each aquarium and the LC50-96h of each chemical was determined. The LC50-96h obtained were respectively 0.1268, 0.0029, 182.9 and 0.5685 ppm for Acer 35 EC, lambda-cyhalothrin, acetamiprid and mixture. All insecticides used in this study had profound impact on Nile tilapia behavior which may confirm the neurotoxicity of each single active compound as well as of their mixture.

Influence of strain origin on osmoregulatory and endocrine parameters of two non-native strains of Atlantic salmon (Salmo salar L.).

Non-native strains of Atlantic salmon are used in reinstatement trials where populations are extinct. Environmental cues like photoperiod and temperature are known to influence the smolting process and there is evidence of strain-, stock- or population-specific differences associated with seaward migration or smoltification. The objective of this study was to compare morphological, osmoregulatory and endorcrine features between two strains, one originating from a cold and short river in Ireland (Cong) and another from a long and warm river in France (Loire-Allier), reared under Belgian conditions in order to highlight major differences in restocking adaptability. Comprehensive endocrine profiles, consistent with their interactive role of mediating changes associated with smolting, have been observed. Na+/K+ATPase activity (1.3-10.5 µmol ADP∗mg prot.-1∗h-1) and hormone plasma levels (e.g. 55-122 ng∗mL-1 of cortisol and 4.5-6.4 ng∗mL-1 of GH) were consistent with reported values. We observed strain-related differences of the influence of temperature and daylength on cortisol, GH and sodium plasma levels. These may be related to the respective environmental conditions prevailing in the river of origin, which have impacted the genetic background for smoltification. Using Na+/K+ATPase activity as an indicator, both strains smoltified successfully and simultaneously testifying a prevailing influence of environmental cues over genetic factors for smoltification.

Multifactorial analyses revealed optimal aquaculture modalities improving husbandry fitness without clear effect on stress and immune status of pikeperch Sander lucioperca.

High mortality and impairment in growth rate during pikeperch (Sander lucioperca) ongrowing are among the major bottlenecks for its development in aquaculture. These failures may be related to high stress responsiveness since the rearing conditions are not yet optimized for this species. The objectives were to characterize the stress and immunological responses of pikeperch to major aquaculture modalities, and to identify the optimal aquaculture conditions for improving its welfare status. In a screening experiment, eight factors considered as relevant for the welfare of pikeperch were compared in two modalities using a fractional multifactorial design (28-4). Each experimental unit represented a combination of 8 factors in two modalities including grading, stocking density (15 vs 30kg·m-3), feed type (sinking vs mid-floating), light intensity (10 vs 100 lux), light spectrum (red vs white), photoperiod (long vs short), dissolved oxygen (60 vs 90%) and temperature (21 vs 26°C). Fish sampling occurred on days 36 and 63. Stress markers (glucose, cortisol and brain serotonergic activity), innate immune parameters (plasma lysozyme and complement activities) and expression of some immune genes were assessed. Light intensity and the type of feed clearly appeared as directive factors for pikeperch culture. A strong effect of the feed type was observed on growth parameters while survival was impacted by high light intensity. Light characteristics (intensity, spectrum and photoperiod) and temperature were identified as determining factors for physiological and immune markers. No obvious relation was established between stress status and growth parameters and further investigations are needed to improve management strategies of pikeperch culture and knowledge on the relations between environmental conditions, stress and immunity in percid fish.

Physiological and immune response of juvenile rainbow trout to dietary bovine lactoferrin.

Lactoferrin, a large multifunctional glycoprotein, is involved in many physiological functions but its immunomodulatory pathways are not well characterized in fish. The objective of the present study was to investigate the temporal effect of dietary bovine lactoferrin (BLf) at low (0.1%) and high (1%) on immunological organs of rainbow trout juveniles. BLf diets did not affect specific growth rate, haematocrit, splenic index, spleen respiratory burst activity as well as humoral (mIgM) and neutrophils (MPO) gene expressions after short term - 35 days (D35) and long term nutrient test - 51 days (D51) of feeding. Both low and high BLf doses induced enhanced level of plasma alternative complement activity, plasma total immunoglobulin on D35 and D51, lymphocyte plus thrombocyte cell proportion on D35 and monocyte cell proportion in total blood leukocyte cells on D51. On D51 but not on D35, BLf diets upregulated the expression of inflammatory genes in kidney for il-1 at the low BLf dose, il-8 at both BLf doses and il-6 at the high BLf dose in spleen, and il-10 at both BLf doses in kidney. Moreover, the expression of T helper (cd4-2α; cd4-2ß) genes was significantly upregulated only on D51 by both BLf doses in both spleen and kidney tissues. On D51, controls and BLf treated fish were intraperitoneally injected with A. salmonicida achromogenes. The expression of 13 immune genes was evaluated at 44 h post-injection (D54). The expression of lysozyme gene was upregulated by both BLf doses after bacterial infection both in spleen and kidney. The expression of mcsfrα (spleen) and tgf-ß1 (kidney) was also modulated by both BLf doses. Low and high BLf doses enhanced disease resistance of rainbow trout juveniles with the cumulative survival rate of 36% and 38% respectively while those of the control was 19% after 14 days challenged with bacteria. The results indicate that BLf diets activated the humoral immunity, associated to blood leukocyte cells of rainbow trout after short term BLf administration, and the long term BLf administration was necessary for sensitizing other lymphoid organs such as in spleen and kidney. Only after long term test, BLf diets induced significantly higher levels of innate and adaptive immune gene expressions than those of the control. Dietary BLf activated more markedly the expression of innate immune genes than the adaptive ones; this upregulation of some immune genes could explain the high disease resistance observed in rainbow trout juveniles fed BLf.

Osmoregulatory and immunological status of the pond-raised striped catfish (Pangasianodon hypophthalmus S.) as affected by seasonal runoff and salinity changes in the Mekong Delta, Vietnam.

In Vietnam, the production of striped catfish Pangasianodon hypophthalmus S. reached more than 1.2 millions of tons in 2014 and is mainly gathered in the Mekong Delta (South Vietnam). A survey was carried out during the dry season 2013 (March-April) and rainy season 2014 (July-August) in 12 fish farms of the lower (Tra Vinh Province) and higher (Can Tho Province) Mekong River Delta. This study allowed drawing up current key osmoregulatory and innate immune parameters of striped catfish in aquaculture depending on the geographical location, particularly the proximity to the River Mekong Estuary and the seasonal surface runoff. In the dry season, plasma osmolality was positively correlated with salinity. Gill Na+K+ ATPase dropped in the rainy season, while kidney Na+K+ ATPase remained stable. Abundance of immune blood cells, especially thrombocytes and monocytes, tended to increase in farms located in tidal area. Production of reactive oxygen species in the spleen, kidney lysozyme activity and plasma complement activity did not vary whatever the season or the proximity to the estuary. Plasma lysozyme activity was 50-fold higher than in kidney and increased in the rainy season as well as in tidal sites. Kidney complement activity decreased in the dry season, especially in tidal sites. In conclusion, regarding key osmoregulatory and immune factors, striped catfish farms located in the Mekong Delta may be affected by seasonal and regional salinity and runoff fluctuations.

Chronic hyperosmotic stress interferes with immune homeostasis in striped catfish (Pangasianodon hypophthalmus, S.) and leads to excessive inflammatory response during bacterial infection.

Hyperosmotic stress has often been investigated from osmoregulation perspectives while the effects of such stress on the immune capacity remain largely unexplored. In this study, striped catfish were submitted to three salinity profiles (freshwater, low saline water, saline water) during 20 days, followed by infection with a virulent bacteria, Edwardsiella ictaluri, responsible for the enteric septicaemia of catfish. Osmoregulatory (plasma osmolality, gill Na(+)K(+)ATPase), immune (blood cells, lysozyme activity, complement activity, respiratory burst) parameters and mortality rate were investigated. In addition, abundances of heat shock protein 70 and high mobility group box 1 were explored. With elevated salinity, plasma osmolality severely increased while gill Na(+)K(+)ATPase slightly increased. Salinity alone stimulated the number of granulocytes, lysozyme activity and respiratory burst but depleted the number of thrombocytes. Salinity in combination with infection stimulated the number of monocytes and ACH50. On the contrary, erythrocytes, hematocrit, heat shock protein 70 and high mobility group box 1 did not significantly vary with salinity profiles. Then, salinity induced earlier onset on mortalities after E. ictaluri inoculation whereas cumulative mortality reach 79.2%, 67.0% and 91.7% respectively in freshwater, low saline water and saline water. In conclusion, salinity stimulates several immune functions in striped catfish but prolonged exposure to excessive hyperosmotic condition may lead to excessive inflammatory response and death.