Immune response of sea bass <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> to <Emphasis Type="Italic">Tenacibaculum maritimum</Emphasis> antigens

ABSTRACT:   Seawater fishes are affected by a pathology commonly called 'myxobacteriosis', caused by Tenacibaculum maritimum (formerly Flexibacter maritimus ). The disease is characterized by fin erosion and necrotic ulcers of skin and muscle, and by low but constant mortality in cultured marine fish; in Italy is one of the most important and widely spread diseases affecting sea bass Dicentrarchus labrax , gilthead seabream Sparus aurata , sharp-snouted bream Diplodus puntazzo , white bream Diplodus sargus , and six-tooted bream Dentex dentex . In order to obtain an effective vaccine against the disease, formalin killed cells (FKC), extracellular products (ECPs) and crude lipopolysaccharide (LPS) preparations were obtained from the T. maritimum strain SPVId and injected intraperitoneally twice into the sea bass. The fish immune response to the preparations was studied: agglutinating antibody titer and in vitro phagocytosis were determined after the first and second injection in order to evaluate whether the preparations are immunogenic or not and if the booster effect took place. The results show that FKC and LPS preparations increased the antibody titer after the first injection when compared to the control sea bass. Moreover, all the preparations stimulated a secondary (booster) response. In vitro phagocytosis of the total blood was significantly higher for all the preparations when compared to the controls, but the crude LPS immunized sea bass showed the highest activity.     

Olive oil by-product as a natural antioxidant in gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis>) nutrition

The aim of the study reported here was to evaluate the efficiency of a natural antioxidant substance in gilthead sea bream (Sparus aurata) feeds. An olive oil by-product, olive mill vegetation water (VW), contains polyphenols, which have a strong antioxidant activity. A 147-day growth trial was conducted (monofactorial balanced, 4 × 3) with diet as the experimental factor. Two diets [isonitrogenous (crude protein 40%) and isoenergetic (gross energy = 18MJ kg⁻¹ on a dry weight basis] were formulated with 1 and 5% of VW (VW1, VW5); the control diet did not contain VW. A total of 600 juvenile gilthead sea breams (mean body weight 114.1 ± 5.7 g) were utilised. Production parameters and somatic indexes were calculated at the end of the growth trial. Antioxidant activity in fish fillets was investigated using TBARS and DPPH assays. A number of haematological parameters and digestive enzyme patterns were measured in fish in the middle and at the end of the experiment. The TBARS values showed slight delays in the development of oxidation in the fillet of fish fed with VW. There was no statistical difference between fish fed with the experimental diet and the control group, except for maltase activity, which increased with increasing VW in the feed. We found that the use of VW in a gilthead sea bream diet did not have any detrimental effects on gilthead sea bream production and physiological parameters and slightly improved the conservation of the fish fillets.     

Stress assessment,quality indicators and shelf life of three aquaculture important marine fish,in relation to harvest practices,water temperature and slaughter method

The objective of this study was to evaluate the effect of harvest practices and slaughter method on stress, quality and shelf life of whole fish (gilthead sea bream, European sea bass and red sea bream) towards the development of a humane slaughter practice. The use of hook and line resulted in significantly lower plasma cortisol and glucose in European sea bass and gilthead sea bream. Water temperature at harvest affected significantly the concentrations of stress indicators (plasma cortisol and glucose), mainly in European sea bass and gilthead sea bream. No significant differences were observed between the harvesting methods, regarding fish appearance, microbial spoilage and sensory scoring and subsequently shelf life. However, significantly lower hardness was recorded in fish harvested using the electric stunner, compared to the fish killed with slurry ice of the same harvesting period. Shelf life ranged between 13–18 days for gilthead seabream, 10–16 days for European sea bass and 10–14 days for red sea bream, depending on harvesting period.     

Using trace elements in otoliths to discriminate between wild and farmed European sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> L.) and Gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis> L.)

Trace elements in otoliths of sea bass (Dicentrarchus labrax L.) and sea bream (Sparus aurata L.) from fish farms and coastal wild populations in the western Mediterranean Sea were analysed by inductively coupled plasma-mass spectrometry. Results showed that concentrations of Mg, K, and Mn differed significantly between wild and farmed sea bass, while concentrations of Mg, K, Mn, Fe, Zn, Sr, and Ba varied significantly between wild and farmed sea bream. Discriminate analysis and cross-validation classification showed that the trace element profile in otoliths can be used to separate farmed fish from wild stocks with high accuracy on both sea bass (individuals correctly classified: 90.7 %) and sea bream (individuals correctly classified: 96.6 %). Moreover, trace elements in otoliths resulted to be useful to discriminate among wild fish stocks within each species.     

Growth performance and metabolic utilization of diets including starch,dextrin, maltose or glucose as carbohydrate source by gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis>) juveniles

The effect of dietary carbohydrate complexity on growth, feed utilization and activity of selected key liver enzymes of intermediary metabolism were studied in gilthead sea bream juveniles. Four isonitrogenous (50% crude protein) and isolipidic (16% crude lipids) diets were formulated to contain 20% of pregelatinized maize starch, dextrin, maltose or glucose. Triplicate groups of fish (117 g initial weight) were fed each diet to near satiation during 6 weeks. No effect of dietary carbohydrate on growth was noticed. Feed efficiency was lower in fish fed the glucose diet than the maltose and dextrin diets. The lowest protein efficiency ratio was observed in fish fed the glucose diet. Six hours after feeding, glycemia was higher in fish fed the glucose diet than the maltose and starch diets. Liver glycogen content was unaffected by dietary carbohydrate complexity. Hepatic glucokinase (GK) activity was higher in fish fed the glucose and the maltose diets, while higher pyruvate kinase (PK) activity was recorded in fish fed the glucose diet than in fish fed the starch diet. Fructose-1,6-bisphosphatase (FBPase) and glucose-6-phosphate dehydrogenase (G6PD) activities were higher in fish fed the starch diet compared to dextrin and glucose diets. Data suggest that dietary glucose and maltose are more effective than complex carbohydrates in enhancing liver glycolytic activity. Dietary glucose also seems to be more effective than starch in depressing liver gluconeogenic and lipogenic activities. Overall, dietary maltose, dextrin or starch was better utilized than glucose as energy source by gilthead sea bream juveniles.     

Effects of a probiotic bacterial <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> dietary supplement on the crowding stress response of juvenile Nile tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

To test the effects of probiotic bacteria against crowding stress, juvenile Nile tilapia Oreochromis niloticus were fed commercial feed supplemented with 1 × 10¹⁰ cfu/g pellets of Lactobacillus rhamnosus for 3 weeks. The fish were confined and subjected to crowding for 7 and 14 days after which their physiological condition was investigated. The administration of probiotic prophylaxis improved growth performance even in the stressed fish. After 7 days of stress exposure, fish receiving probiotic-supplemented feed showed proactive behavior and coping responses to the stressor, as evidenced by elevated plasma glucose levels and osmolality, stabilized plasma electrolytes, and a higher RNA:DNA ratio. Fish stressed for 7 days and fed normal commercial diet showed impairment of plasma electrolytes; after 14 days, the plasma osmolality, electrolytes, glucose, and RNA:DNA ratio decreased, indicating physiological maladaptation to the stressor. The growth rate was also found to be reduced, suggesting that energy demand exceeded the energy available from metabolism and dietary uptake. This latter effect was not observed in fish fed the probiotic-supplemented diet. The results suggest that probiotic bacteria prophylaxis may increase energy availability for metabolic support of the crowding stress response and improve the stress coping capacity of fish.     

Acute effects of benzo[a]pyrene on liver phase I and II enzymes,and DNA damage on sea bream <Emphasis Type="Italic">Sparus aurata</Emphasis>

In the present study biotransformation and detoxification responses to acute exposure to the polycyclic aromatic hydrocarbons benzo[a]pyrene (B[a]P) were investigated in the liver of Sparus aurata (sea bream). Sexually immature gilthead sea bream were treated by intraperitoneal injection of B[a]P (20 mg kg⁻¹) for 6, 12, 24, and 48 h. B[a]P accumulation was quantified in sea bream liver by mean of gas phase chromatography (GPC-MS) after the various exposure periods. The following biological responses were measured: (1) ethoxyresorufin-O-deethylase (EROD) activity, as a phase I biotransformation parameter; (2) liver glutathione S-transferase (GST) activity as a phase II conjugation enzyme. DNA damage was assessed over time using the single-cell gel electrophoresis comet assay. B[a]P bioaccumulation in the liver resulted in a biphasic curve with an increasing uptake up to 5.55 ± 0.67 μg g⁻¹ dry weight after only 6 h exposure and 4.67 ± 0.68 μg g⁻¹ dry weight after 48 h exposure. EROD activity showed a nonsymmetrical bell-shaped kinetic with a maximum at 24 h and lower but significant activities at 12 and 48 h with respect to control animals. Hepatic GST activities were only significant after 48 h exposure. Comet assay showed an increase in liver cells DNA damage with a maximum after 48 h exposure reaching up to 12.17 %DNA in the tail.     

Application of non-invasive techniques to differentiate sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>, L. 1758) quality cultured under different conditions

European sea bass, Dicentrarchus labrax, is one of the main species cultured in Europe. In this study, non-invasive techniques such as visible-near infrared spectroscopy and dynamometric analysis were used to discriminate concrete tank–cultured sea bass from sea cage–cultured sea bass. A total of 198 samples were collected at six time points from 3 Italian fish farms. A partial least squares analysis was conducted on individual animals at 48 and 96 h post-mortem to determine whether textural and spectral parameters can discriminate between concrete tank– and sea cage–reared sea bass. The results of this analysis demonstrated that spectral measurements better discriminate individual animals at 48 h post-mortem (87% in the independent test) with respect to 96 h post-mortem (66.7% in the independent test). Differences in texture were observed between the two groups of fish, but the texture changed in the time. The texture in sea cage–cultured fish showed higher values of measured force (N) with respect to fish reared in concrete tanks at 48 h post-mortem. Instead, opposite results were observed at 96 h post-mortem. Fillet colour were influenced by both farm and rearing condition.     

Physiological response,blood chemistry profile and mucus secretion of red sea bream (<Emphasis Type="Italic">Pagrus major</Emphasis>) fed diets supplemented with <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> under low salinity stress

Environmental stressors caused by inadequate aquaculture management strategies suppress the immune response of fish and make them more susceptible to diseases. Therefore, efforts have been made to relieve stress in fish by using various functional feed additives in the diet, including probiotics. The present work evaluates the effects of Lactobacillus rhamnosus (LR) on physiological stress response, blood chemistry and mucus secretion of red sea bream (Pagrus major) under low salinity stress. Fish were fed four diets supplemented with LR at [0 (LR0), 1 × 10² (LR1), 1 × 10⁴ (LR2) and 1 × 10⁶ (LR3) cells g^?1] for 56 days. Before stress, blood cortisol, urea nitrogen (BUN) and total bilirubin (T-BIL) showed no significant difference (P > 0.05), whereas plasma glucose and triglyceride (TG) of fish-fed LR2 and LR3 diets were significantly lower (P < 0.05) than those of the other groups. Plasma total cholesterol (T-CHO) of fish-fed LR3 diet was significantly (P < 0.05) lower than that of the other groups. Furthermore, total plasma protein, mucus myeloperoxidase activity and the amount of mucus secretion were significantly enhanced in LR-supplemented groups when compared with the control group (P < 0.05). After the application of the low salinity stress test, plasma cortisol, glucose, T-CHO and TG contents in all groups showed an increased trend significantly (P < 0.01) compared to the fish before the stress challenge. However, plasma total protein and the amount of secreted mucus showed a decreased trend in all groups. On the other hand, BUN, T-BIL and mucus myeloperoxidase activity showed no significant difference after exposure to the low salinity stress (P > 0.05). In addition, the fish that received LR-supplemented diets showed significantly higher tolerance against low salinity stress than the fish-fed LR-free diet (P < 0.05). The physiological status and the detected immune responses, including total plasma protein and mucus myeloperoxidase activity in red sea bream, will provide a more comprehensive outlook of the effects of probiotics to relieve stress in fish.     

Effect of dietary medicinal herbs on lipid metabolism and stress recovery in red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

The effect of dietary medicinal herbs on lipid metabolism and stress recovery was investigated in red sea bream Pagrus major. Fish (mean body weight 24.0 ± 0.2 g) were fed on test fish meal diets supplemented with either Massa Medicata (Mm), Crataegi Fructus (Cf), Artemisia capillaries (Ac), or Cnidium officinale (Co), or with a mixture of the four herbs (HM) for 12 weeks. A control group was fed a diet without herbs in the same manner. A high survival rate was observed in the herbal diet groups. The final mean body weight, feed efficiency, protein efficiency ratio, and apparent protein and lipid retention in the Ac, Co, and HM groups were higher than those in the control and Mm groups. Final carcass, hepatic lipid and triglyceride contents, and plasma triglyceride and nonesterified fatty acid levels were lower in the Ac, Co, and HM groups compared to those of control and Mm groups. However, final hepatic phospholipid, plasma phospholipid, and high density lipoprotein cholesterol levels were higher in the Ac, Co, and HM diets groups than in the control and Mm groups. The Cf, Co, Ac, and HM groups showed faster recovery time in the 2-phenoxyethanol anesthesia test and a higher recovery rate in the 10-min air exposure test than those of the control and Mm groups. Moreover, the Cf, Ac, Co, and HM diet groups had a significantly lower plasma cortisol level than the control and Mm diet group, but the glucose level in the herbal diet groups was higher than that in the control group after a 1-h air exposure. These results indicate that the addition of medicinal herbs to the fish diet improved lipid utilization and stress recovery in red sea bream.     

Vessel noise pollution as a human threat to fish: assessment of the stress response in gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis>, Linnaeus 1758)

This study examined the effects of boat noise pollution on the stress indices of gilthead sea bream (Sparus aurata, Linnaeus 1758). To assess the stress response in these fish, biometric values and plasma parameters such as ACTH, cortisol, glucose, lactate, haematocrit, Hsp70, total protein, cholesterol, triglycerides and osmolarity were analysed. After acclimatization of the animals, the experiment was carried out in a tank fitted with underwater speakers where the fish were exposed to sound treatments (in duplicate) consisting of: 10 days of no sound (control treatment; the animals were only exposed to the experimental tank’s background noise) and 10 days of noise derived from original recordings of motor boats, including recreational boats, hydrofoil, fishing boat and ferry boat (vessel noise treatment). The exposure to noise produced significant variations in almost all the plasma parameters assessed, but no differences were observed in weights and fork lengths. A PERMANOVA analysis highlighted significantly increased values (p < 0.05) of ACTH, cortisol, glucose, lactate, haematocrit, Hsp70, cholesterol, triglycerides and osmolarity in the fish exposed to vessel noise for 10 days. This study clearly highlights that anthropogenic noise negatively affects fish, and they are valuable targets for detailed investigations into the effects of this global pollutant. Finally, these experimental studies could represent part of the science that is able to improve the quality of the policies related to management plans for maritime spaces (Marine Strategy Framework Directive 56/2008 CE) that are aimed at stemming this pollutant phenomenon.     

A comparative study on the composition and importance of free amino acids in semen of gilthead sea bream, <Emphasis Type="Italic">Sparus aurata</Emphasis>, and perch, <Emphasis Type="Italic">Perca fluviatilis</Emphasis>

A comparative study was conducted on the free amino acid composition of gilthead sea bream, Sparus aurata, and perch, Perca fluviatilis. Also the effect of 21 free amino acids on sperm motility was investigated. Spermatozoa were incubated in species-specific motility-inhibiting saline solution containing the different amino acids for 48 h. Thereafter, the motility was activated and investigated using computer-assisted cell motility analysis. Twelve free amino acids, respectively, were detected in S. aurata and P. fluviatilis semen. Arginine, cysteine, glutamic acid, leucine, and methionine occurred in semen of both species. In S. aurata, arginine, glycine, hydroxyproline, lysine, and phenylalanine in concentrations of 1.25 and 2.50 mmol/l, methionine in a concentration of 2.5 mmol/l, and serine in a concentration of 1.25 mmol/l had a positive effect on the motility of spermatozoa. In P. fluviatilis, alanine, asparagine, cysteine, glycine, isoleucine, lysine, methionine, serine, threonine, and valine in concentrations of 2.50 mmol/l positively affected motility. From these data, it can be concluded that the amino acid composition and the effect on motility are species specific. Possible consequences for spermatozoa functionality are discussed.     

Oxygen consumption and feeding rates of gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis>) reveal lack of acclimation to cold

Low temperature has been implicated in inducing outbreaks of winter syndrome or winter disease in farmed gilthead sea bream (Sparus aurata). The responses of gilthead sea bream to reduced temperature followed by maintenance at low temperaturewere studied. In a first experiment, oxygen consumptionwas measured when water temperature was reduced from 18°C to 8 °C at either a rate of 1 °C· day-1 or as two sharp drops (from 18 °C to 12 °C, and from 12 °C to 8 °C). In a second experiment, the water temperature was reduced from 16 °C to 8 °C or 12 °C and then maintained for 20 days to study the fish acclimation to these temperatures. In both experiments, fish stopped feeding below 13 °C and did not resume feeding when maintained at low temperatures. The decrease in metabolic activity, expressed by the oxygen consumption rate, was directly related to the fall in water temperature: the Q10(18 °C-8 °C) values were between 2.2–2.5, independently of the descend rate in water temperature. However, we observed a more reduced metabolic rate when the water temperature was below 12 °C. Fish maintained at low temperatures showed only a partial recovery in oxygen consumption (15% at 8 °C and 20% at 12 °C) after 20 days. A higher metabolic rate together with a fasting-temperature condition meant that maintenance at 12 °C was more aggressive than at 8 °C, as revealed by the condition factor and energy needs. Data suggest that 12 .C could be a threshold temperature for the metabolic activity of gilthead sea bream. The relationship between low temperatures and their possible implication in the appearance of winter disease in gilthead sea bream is also discussed.     

Genetic assessment of three gilthead sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis> L.) populations along the Spanish coast and of three broodstocks managements

The gilthead sea bream (Sparus aurata L.) is one of the most important Sparid farmed in Europe, especially in the Mediterranean area. However, efficient breeding programs for this species are scarce and very little, and it is known concerning their population structure. The present study was mainly designed to genetically characterize, by microsatellite markers, three gilthead sea bream populations sampled along the Spanish coast (Cantabrian Sea, the Atlantic Ocean and Mediterranean Sea) and their progeny with the aim of studying its genetic variability and its genetic structure. Moreover, we evaluated different strategies of broodstocks management (breeders’ number, origin and sex combination) on parental contributions and on effective breeding numbers. That number of breeders in the stock was of great importance to the maximization of contribution since the larger broodstock resulted in larger proportion of parents contributing. Variation in dam and sire spawning incidence and in number of progeny produced per dam and per sire was translated into reduced effective breeding numbers and consequently into expected increased inbreeding rates. Our results highlight the high genetic variability of the studied sea bream populations, as well as the existence of three genetically differentiated populations along the Spanish coast. These findings should be relevant for the establishment of successful breeding programs in aquaculture of the gilthead sea bream.     

Seasonality of nuclear abnormalities in gilthead sea bream <Emphasis Type="Italic">Sparus aurata</Emphasis> (L.) erythrocytes

The frequencies of erythrocyte nuclear abnormalities, such as irregularly shaped (ISN), vacuolated nuclei (VN), binucleated cells (BN), including micronuclei (MN), were monitored in the peripheral blood of cultured gilthead sea bream (Sparus aurata L.) from the southern Adriatic Sea (Croatia) and assessed for a relation to seasonality. Fish were sampled in February, April, June, and September. The lowest frequencies of ISN and MN were measured in April, and the lowest frequencies of VN and BN were found in February. The highest values of ISN and BN were detected in September. The highest values of MN and the most frequent occurrence of VN occurred in June and April, respectively. The Spearman rank order correlation test revealed a significant positive correlation between the frequencies of ISN, BN and MN; VN did not correlate with any of the measured parameters. The ISN had significantly higher nuclear surface area values than normal nuclei (P < 0.001). Our results demonstrate that the measured parameters displayed a distinct seasonality. Consequently, we conclude that seasonal variations should be taken into account when nuclear abnormalities are used as biomarkers. This variation should be well understood in order to successfully separate true contamination effects from seasonal factors that have the potential to affect the frequency and occurrence of nuclear abnormalities.     

Anesthesia induces stress in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>), Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and Atlantic halibut (<Emphasis Type="Italic">Hippoglossus hippoglossus</Emphasis>)

Stress in response to anesthesia with benzocaine, MS-222, metomidate and isoeugenol was studied in Atlantic salmon (Salmo salar), Atlantic halibut (Hippoglossus hippoglossus), and Atlantic cod (Gadus morhua) with no concomitant stress from handling or confinement in association with anesthesia or sampling. All of the anesthetics tested induced a stress response in all species, displayed by a release of cortisol to the water. MS-222 anesthesia elicited the highest cortisol release rates, reaching maximum levels 0.5 h post-exposure and returning to basal levels after 3–4 h. Benzocaine anesthesia caused a bimodal response where the initial peak in cortisol release rate was followed by a second increase lasting towards the end of the trial (6 h). This bimodality was more profound in Atlantic salmon than in Atlantic halibut and Atlantic cod. Metomidate anesthesia induced the lowest release of cortisol of the agents tested in both Atlantic halibut and Atlantic cod, but resulted in a bimodal response in Atlantic salmon where the initial increase in cortisol release was followed by a larger increase peaking at 2–2.5 h post exposure before returning to basal levels after 5 h. The stress induced in Atlantic salmon by isoeugenol anesthesia resembled that of MS-222, but did not reach the same elevated level. Overall, the cortisol release was most profound in Atlantic salmon followed by Atlantic halibut and Atlantic cod.     

Effect of <Emphasis Type="Italic">Cratoxylum formosum</Emphasis> on innate immune response and disease resistance against <Emphasis Type="Italic">Streptococcus agalactiae</Emphasis> in tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis>

The effect of aqueous extract of Cratoxylum formosum on innate immune response and disease resistance in tilapia Oreochromis niloticus was investigated. The fish were fed diets containing 0% (control), 0.5% (diet 1), 1% (diet 2), and 1.5% (diet 3) of C. formosum aqueous extract for 30 days. At the end of the experimental period, parameters of innate immune response including phagocytosis of blood leukocytes, lysozyme activity in plasma, and respiratory bust activity were examined. Feeding the fish with diet 2 and diet 3 for 20 days enhanced phagocytic activity and for 30 days stimulated lysozyme and respiratory burst activities. Diet 1 increased the phagocytic activity at 30 days, but did not affect the other measured parameters. All parameters were not significantly changed (P > 0.05) in the control group throughout the experiment. Following 30 days of feeding, fish were infected with S. agalactiae. The cumulative mortalities of bacterial-infected tilapia that were fed diet 1, diet 2, and diet 3 were 56, 12, and 10%, respectively, compared with 85% in the control group. These results indicate that the aqueous extract of C. formosum may elevate the innate immune response and enhance disease resistance in tilapia.     

Role of taurine deficiency in inducing green liver symptom and effect of dietary taurine supplementation in improving growth in juvenile red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis> fed non-fishmeal diets based on soy protein concentrate

This study was conducted to investigate the mechanism of green liver symptom induction and the effect of dietary taurine supplementation on growth performance in juvenile red sea bream fed non-fishmeal diets based on soy protein concentrate (SPC). Juvenile fish (initial BW 72 g) were fed for 20 weeks on SPC diets supplemented with taurine at levels of 0, 1.0, and 2.0%. In the taurine-unsupplemented SPC diet group, specific growth rate (SGR) and feed conversion ratio (FCR) were significantly inferior (P < 0.001), and incidence of green liver was observed in 70% of fish. In this group, hepatopancreatic and plasma taurine concentrations were lowest (P < 0.05), hepatopancreatic content of bile pigments was highest (P < 0.05), and osmotic tolerance of erythrocytes was inferior (P < 0.05) among the dietary treatment groups. Serum osmolality of all treatment groups was at similar levels. These physiological abnormalities as well as SGR and FCR were improved by dietary taurine supplementation. These results indicate that the mechanism for induction of green liver symptom is bile pigment overproduction due to increased hemolysis because erythrocytes become osmotically fragile due to dietary taurine deficiency. Taurine supplementation of SPC diets is essential for maintaining normal physiological condition and growth performance in juvenile red sea bream.     

Alterations in blood electrolytes of a freshwater catfish <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis> in response to treatment with a botanical pesticide, <Emphasis Type="Italic">Nerium indicum</Emphasis> leaf extract

The present study aimed at investigating the effects of Nerium indicum leaf extract on the blood electrolytes of Heteropneustes fossilis for short- and long term. Fish were subjected to Nerium indicum leaf extract for short term (11.27 mg/L i.e. 0.8 of 96 h LC₅₀) and long term (2.81 mg/L i.e. 0.2 of 96 h LC₅₀). Fish were killed on each time intervals from control and experimental (Nerium indicum) groups after 24, 48, 72, and 96 h in short-term exposure and after 7, 14, 21, and 28 days in long-term experiment. Blood samples were analyzed for calcium and inorganic phosphate levels. Acute exposure of Nerium indicum leaf extract caused a progressive decrease in the serum calcium levels after 48 h in fish H. fossilis, which persists till the close of the experiment (96 h). The serum inorganic phosphate levels remain unaffected till 48 h in the Nerium indicum leaf extract–exposed fish. After 72 and 96 h, the levels exhibit a decrease. Chronic Nerium indicum leaf extract treatment provoked a decrease in serum calcium levels at day 14. This decrease continues till 28 days. The serum phosphate level of the Nerium indicum leaf extract–treated fish decreases on day 14 and 21. However, on day 28, the levels become close to the normal values. We conclude that Nerium indicum leaf extract exposure alters the blood electrolytes of the fish, thus causing physiological disturbances which might affect seriously the normal vital functions, growth rate, reproduction, and their survival in nature.     

Effects of repeated crowding on the stress response and growth performance in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>)

A 64-day growth experiment was conducted in which two groups of Atlantic salmon parr were grown under either control conditions or subjected to a weekly crowding stressor. Subjecting fish to the stressor resulted in a 7.7% reduction in wet weight after 29 days, which was maintained at 7.9% by day 64. This reduction in weight was reflected in a 44% reduction in specific growth rate and 38% increase in feed conversion ratio over the first 29 days of the experiment. Elevation in plasma cortisol was observed in crowded fish on days 1, 29 and 64. Similarly, on days 1 and 29 an increase in both plasma glucose and lactate was detected. On day 64, however, no differences in plasma glucose and lactate were observed, with the magnitude of the cortisol response also significantly reduced. Overall, the relatively moderate impact on growth performance and reduction in magnitude of measured stress parameters at the end of the experiment suggests possible habituation to the applied stressor.