Bacteria associated with winter mortalities in laboratory-reared common dentex (Dentex dentex L.)

A pathological study was conducted on laboratory‐reared juvenile common dentex (Dentex dentex) suffering trickling and continuous mortalities. During a 3‐month period (October–December), water temperature, clinical signs and mortalities were recorded. Moribund or dead fish were examined for bacteria and parasites. Bacteria were isolated from head kidney and external ulcers, and samples from the gills, intestine, stomach, trunk kidney, gall bladder and liver were taken for histology. Cumulative mortality reached 73%, and 80% of fish examined were positive for bacteria (102 isolates). Vibrio splendidus was the most prevalent in head kidney (59.7%) and ulcers (88.9%), and it was frequently isolated as pure culture (74.7% and 100% respectively). This is the first report of this bacterium in association with mortality in common dentex. Vibrio scophthalmi was the second most prevalent bacterium (29.2%) and accounted for 63.6% of the mixed infections with V. splendidus, V. harveyi, Pseudoalteromonas spp. and other species were rarely isolated. No parasites were found in histological sections. Bacteria were frequently observed in the lumen of the intestine and stomach, destroying the epithelium. A cellular reaction was suggested by the high numbers of rodlet cells (RC) in the intestinal epithelium, and the abundance of eosinophilic granular cells (EGC) in the intestinal lamina propria. In the stomach, vacuolized cells containing unidentified debris, sometimes of crystalloid appearance, were very common. The high prevalence of V. splendidus in pure cultures and the absence of other aetiological agents suggest that V. splendidus is substantially involved in the registered mortalities, although the implication of V. scophthalmi and even of some nutritional factors cannot be discounted.     

Stress-related physiological responses to handling in common dentex (Dentex dentex Linnaeus, 1758)

The effects of handling on haematocrit, haemoglobin, plasma glucose, lactate and total amino acids, liver glycogen and hepatic activity of fructose 1,6‐bisphosphatase (FBPase) and alanine aminotransferase (AAT) were investigated in common dentex (Dentex dentex Linnaeus, 1758). A total of 42 fish (50‐g weight) were subjected to handling (netting and shaking in the air for 45 s). Six fish were sampled at 0, 0.5, 1, 2, 4, 8 and 12 h after handling. Six unstressed fish were also sacrificed at each time and used as controls. Handling resulted in a rise in plasma glucose and lactate levels, as well as in enhanced hepatic FBPase and AAT activities. In most cases values returned to control levels 8 h after handling. There were no significant changes in haematocrit, haemoglobin, plasma total amino acids and liver glycogen levels as a consequence of handling. The results suggest that dentex is rather tolerant to handling; apparently, sensitivity to handling is not the main factor responsible for the low survival exhibited by this species in aquaculture.     

Dietary intake of probiotics and maslinic acid in juvenile dentex (Dentex dentex L.): effects on growth performance, survival and liver proteolytic activities

Two feeding trials were carried out to evaluate the efficiency of probiotics and maslinic acid, on growth and survival of juvenile dentex; liver proteolytic activities were also investigated in the second trial. For experiment 1, triplicate groups were fed six diets with two probiotics (Bacillus toyoi, T, and B. cereus, E) at increasing levels (0.5, 1 and 2 g kg^?1 diet) and a control diet. Growth and feed conversion were not significantly influenced by the probiotics. The diet T1 produced the lower mortality, whereas diet E1 rendered the higher mortality. It was concluded that no significant effects on growth and survival were found following the addition of two kinds of probiotics to dentex diets. However, the diet E0.5 showed a tendency to ameliorate the growth and feed utilization of the diet. In a second trial, triplicate groups were fed four diets with increasing levels of maslinic acid (0, 20, 40 and 80 mg kg^?1 diet). Growth of fish given diets with the highest level of maslinic acid (D80) was slightly but not significantly lower than those from the other groups. Furthemore, mortality of fish fed diet D40 was the lowest. Changes in liver proteasome and endoprotease activities measured on sodium dodecyl sulphate (SDS)/gelatin gels were also detected in a dose‐dependent manner. It was concluded that a dietary maslinic acid at a level of 80 mg kg^?1 diet seems to be too high for juvenile dentex to maintain a maximal growth and survival rate.     

Protein sparing effect of dietary lipids in common dentex (Dentex dentex): A comparative study with sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)

The common dentex (Dentex dentex) is a sparid fish which is considered a suitable candidate for Mediterranean aqua-culture. A seven-weeks feeding trial was conducted over the summer period with common dentex, sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). All three species were fed to visual satiety with two practical diets with varying crude protein and crude fat levels (55 % protein, 9 % lipids; 46 % protein, 17 % lipids). The initial body weights were 8.2, 11.6 and 17.3 g for common dentex, sea bass and sea bream, respectively. In all cases, specific growth rates were not significantly affected by dietary treatment, but they varied among species (sea bass 1.7–1.8 %; sea bream 2.1–2.3 %; common dentex 3.1–3.2 %). When comparisons between fish species were made, we observed that the increase in growth rates was linked to a decrease of the whole body fat content, as a consequence of a greater utilisation of dietary lipids as energy substrates. Furthermore, in common dentex, the 17 % lipid diet was able to improve protein retention, but this diet effect was less significant in sea bream and sea bass. In contrast to sea bream, the 17 % lipid diet did not up-regulate plasma GH levels in common dentex, which provides additional evidence for a more efficient utilisation of dietary lipids.     

黄带拟鲹染色体核型特征分析

鱼类染色体核型分析在种质资源保护、遗传图谱构建、鱼类分类和育种等方面发挥着重要作用.黄带拟鲹(Pseudocaranx dentex,Bloch&Schneider,1801)是具有较高经济价值和遗传育种价值的水产资源物种,目前与该物种遗传背景相关的研究尚属空白.本研究采用热滴片法制备了黄带拟鲹鳃和鳍条组织的染色体标本...     

Exophiala xenobiotica infection in cultured striped jack, Pseudocaranx dentex (Bloch & Schneider), in Japan

This report describes Exophiala infection in cultured striped jack, Pseudocaranx dentex , in Japan in 2005. One hundred out of 35 000 fish died per day and mortalities continued for 1 month. Diseased fish showed swelling of the abdomen and kidney distension. Numerous septate hyphae, pale brown in colour, were seen in kidney in squash preparations. Histology revealed abundant fungal hyphae and conidia in gill, heart and kidney. Fungal hyphae were accompanied by cell necrosis and influx of inflammatory, mainly mononuclear cells. The fungus isolated from the diseased fish had septate hyphae, pale brown in colour and 1.8–3.0 μm in diameter. Conidiogenous cells were conspicuous annellides, short or cylindrical or fusiform in shape. Conidia were one-celled, ellipsoidal with smooth walls, accumulated in balls at the apices of annellides that tended to slide down, 1.5–2.0 μm in width and 3.0–5.0 μm in length. The fungus was classified into the genus Exophiala based on its morphology and as Exophiala xenobiotica based on the sequences of the ITS 1–5.8S–ITS 2 regions of rDNA. This is the first record of this fungus in a marine fish.     

Development of the common dentex (Dentex dentex) eggs in relation to temperature

Embryonic development of common dentex (Dentex dentex) was investigated at nine different constant water temperatures (8°C, 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C and 24°C). The observed effects were compared using of regression analysis. Constant water temperatures between 12°C and 18°C were found to support successful embryonic development. A negative relationship between the rate of embryonic development and incubation temperature was observed. While embryonic development was completed within this range (12°C–18°C), there was no cell division at water temperatures of 8°C and 24°C. Total mortalities were observed at the 128 cleavage stage at a temperature of 10°C, and after the beginning of gastrulation at 20°C and 22°C.     

Effects of dietary arachidonic and eicosapentaenoic acids on common dentex (Dentex dentex Linnaeus 1758) larval performance

Oily emulsions containing constant levels of total fatty acids (FAs) and varying eicosapentaenoic acid (EPA) and arachidonic acid (ARA) levels were used to enrich rotifers. Common dentex larval survival and growth were compared between groups fed different enriched live prey. Growth, survival rate, and lipid composition of larvae suggest that feeding common dentex in the first 15 days posthatching with 2.5–3% EPA, 6–8% docosahexaenoic acid (DHA), and DHA/EPA ratio of 2.0–2.5 is sufficient to fulfill their EPA requirements. Higher amounts of dietary EPA did not result in any significant improvement in growth or survival. EPA requirement during this period of larval development does not seem to be as critical as other FAs during the first 15 days of common dentex larval development, but it does not exclude its essentiality later in development. In the case of ARA, nutritional requirements are low compared to other marine finfish species, with the upper limit of this essential FA being around 2% of total FAs provided in the live prey composition.     

Effect of squid meal in dry pellets on the spawning performance of striped jack Pseudocaranx dentex

SUMMARY: This study was carried out to investigate the effects of dietary squid meal or a combination of squid meal and krill meal as part of the protein source in dry pellets on the spawning of striped jack Pseudocaranx dentex . Five months prior to spawning, 7-year-old fish were divided into three groups of 10 fish each (male : female ratio, 5 : 5). The control group was fed a raw fish mix (RF) and the other two groups were fed either steam-dry pellets with squid meal replacing 50% of their fish meal (fs-DP) or steam-dry pellets containing equal proportions of fish, squid and krill meals (fsk-DP). Feeding was carried out once every other day in 5 × 5 × 5 m floating net cages and the fish were transferred to 65 m³ indoor tanks for spawning. Eggs and yolksac larvae produced were evaluated for their quality and those obtained during the first 2 weeks of spawning were sampled for chemical analysis. The fish had an average bodyweight of 3.5 ± 0.4 kg at spawning. Although egg production of the RF group was significantly higher ( P < 0.05) than that of the dry pellet groups, the fs-DP group produced the best quality eggs with higher fertilization and hatching rates. The fsk-DP group had the lowest egg production and quality. Lipid classes and fatty acid compositions of eggs and yolksac larvae were dependent on the broodstock diets. These results show that the combination of fish meal and squid meal in dry pellets for striped jack improved egg quality but not production whereas the combination of fish meal, squid meal and krill meal was not effective.     

Characterization and functional properties of digestive proteases in two sparids; gilthead seabream (Sparus aurata) and common dentex (Dentex dentex)

Digestive proteases present in two sparids, seabream (Sparus aurata) and common dentex (Dentex dentex), have been characterized using both biochemical and electrophoretic techniques. Although optimum pH and temperature for maximum activity of both acid and alkaline proteases were similar in the two species, important differences in total activity, as well as in thermal and pH stability were found. Specific inhibitors and SDS-PAGE zymograms were used to clarify such differences. Evidences support the existence of a more active and complex protease set in dentex. Results are discussed from the perspective of their application to the formulation of feeds for each species.     

Metabolic adjustments of Dentex dentex to prolonged starvation and refeeding

The particular metabolic strategies of the common dentex (Dentex dentex) to face a period of prolonged starvation and subsequent refeeding were assessed. Plasma metabolites, endogenous reserves, and the activity of key enzymes of intermediary metabolism in liver, white muscle, and heart were evaluated. Plasma glucose, total lipid, triglycerides, total-, HDL- and LDL-cholesterol, and protein levels, liver, and white muscle glycogen, and perivisceral, and muscle fat were significantly reduced by starvation, whereas liver lipid content was surprisingly increased. Those enzymes involved in phosphorylation and oxidation of glucose and lipid synthesis, as well as alanine aminotransferase activity, were significantly depressed in liver of starved fish. The increase in β-hydroxyacyl-CoA dehydrogenase (HOAD) indicated an enhanced fatty acid oxidation during starvation. Part of the acetyl-CoA generated by β-oxidation was oxidized in the hepatic Krebs cycle, as reflected the increased citrate synthase (CS) activity. The oxaloacetate required for the reaction catalized by CS activity would be supplied by aspartate aminotransferase (ASAT) activity whose activity was also enhanced. Glutamate dehydrogenase also increased to deaminate the glutamate produced by transaminases, especially by the increased ASAT activity. Liver gluconeogenesis of starved fish was maintained at the same rate that in controls, with glycerol playing an important role as glucogenic substrate. The increased hepatic β-hydroxybutyrate dehydrogenase (β-OHBDH) activity indicates that part of the acetyl-CoA arriving from β-oxidation was being diverted for ketone bodies production with dentex liver playing an important role in providing ketone bodies as fuels for other tissues under such circumstances. Most enzyme activities in white muscle of starved dentex were significantly depressed. In heart, starvation induced an important inhibition of those enzymes involved in glucose and protein metabolism, whereas CS, HOAD, and β-OHBDH activities were maintained at control levels. Although several biomarkers assayed returned to control values after refeeding, many others did not, which indicate that after 3 weeks of refeeding, pre-starved dentex is still experiencing a transient period of metabolic adjustments directed toward the restoration of body mass.     

Comparative analysis of artisanal and recreational fisheries for Dentex dentex in a Marine Protected Area

The common dentex, Dentex dentex (L.), is an iconic marine coastal fish in the Mediterranean Sea. This study was performed in the Bonifacio Strait Natural Reserve (BSNR), (NW Mediterranean Sea). The aims were to: (1) evaluate temporal variation of the artisanal fishing of common dentex (2000–2012); (2) compare and quantify catch rates, fishing techniques and catch composition for artisanal and recreational fisheries, and determine the influence of management measures by both activities; and (3) estimate the production of both artisanal and recreational fisheries. Fishery data were collected from different artisanal fishing surveys (onboard fishing vessels and landings) and recreational fishing surveys (roving). The gears with the highest rates of exploitation were longline (3554 g per 100 hooks) and Trolling (351 g boat^?1 h^?1 ±SE), respectively, for artisanal and recreational fishing. This study showed that catches by both activities were quantitatively higher in partially protected areas than outside them. Production estimations suggest that the recreational fishery contributes significantly to fishing mortality and that it can magnify the negative effects of artisanal fisheries. Specific measures are needed for the sustainable fishery management of common dentex.     

Reproductive performance of common dentex, Dentex dentex, broodstock held under different photoperiod and constant temperature conditions

The effect of photoperiod and temperature on the timing and the quality of spawning, and on associated endocrine changes in circulating 17β-oestradiol, 11-ketotestoserone (11-KT) and vitellogenin (Vtg) were investigated in common dentex, Dentex dentex, undergoing their second reproductive cycle. The possibility was also explored of using the measurement of steroids in the culture water of broodstock tanks, rather than in individual blood plasma samples, as a potentially useful tool for assessing the physiological state of a fish without disturbing them. One group of fish was exposed to a simulated natural seasonal cycle and ambient temperature (CONTROL). The other two groups were exposed to simulated seasonal photoperiod cycles (12 month-long) but which were phase-shifted either three months before (ADVANCED) or after (DELAYED) the natural cycle. Temperature was kept at 19.4±0.9 °C all-year-round. In the CONTROL, spawning started in mid-April and lasted until mid-June, while in the ADVANCED group, spawning started 4 months earlier and in the DELAYED group 2 months later than the CONTROL. The total egg production, egg quality, hatching rate, relative fecundity, and spawning index of the experimental groups were similar to the controls. The differences in spawning time induced by photothermal manipulation were associated with a difference in the timing of peak concentrations of plasma E₂, 11-KT and Vtg. In all three groups, the amounts of conjugated 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and free and sulfated 11-KT which could be extracted from the water during the spawning period were significantly higher than those found in the preovulatory period. However, the differences were mostly less than 2-fold suggesting that, at least under the conditions employed in this study, the method was of limited use for non-intrusive detection of gonadogenesis and spawning (as had been hoped). The observed differences in spawning time and in the seasonal changes of sex steroids and Vtg confirm and extend the findings on marine fish. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes in lipid content, fatty acid composition and lipid class composition of eggs and developing larvae (0–40 days old) of cultured common dentex (Dentex dentex Linnaeus 1758)

Total lipid content, fatty acid (FA) composition and lipid class composition of common dentex eggs spawned at different times and larvae reared under different culture conditions until 40 days posthatch (dph) were analysed to get a general pattern of lipid composition during larval development. Two groups of larvae were kept under starvation to compare their FA composition with that obtained from normally fed larvae. To compare FA use or accumulation during larval development, results were grouped according to the developmental stage of the larvae instead of age in days posthatch. Saturated and monounsaturated FAs decreased along larval development, while polyunsaturated fatty acid (PUFA) content increased. The ratio of docosahexaenoic acid (DHA)/eicosapentaenoic acid shifted from 4 to 5 in early developmental stages to lower than 1 after metamorphosis. Arachidonic acid levels remained constant along larval development. Larvae kept 6 days under starvation consumed most of their n-3 PUFA while conserving the DHA to values at day 0. The results presented here are useful for the design of nutritional experiments, because there were differences detected in terms of lipid and FA composition between developmental stages with higher differences mainly found in first-feeding larvae and early developmental stages.     

Development of a reproducible infectious pancreatic necrosis virus challenge model for Atlantic salmon, Salmo salar L.

Atlantic salmon smolts, previously unexposed to infectious pancreatic necrosis virus (IPNV), were placed into tanks of sea water at 10 °C. After 4 weeks, 40 fish were injected intraperitoneally (i.p.) with homogenized and filter‐sterilized kidney material obtained from salmon with clinical IPN in a marine farm in Shetland. The injected fish were cohabited with 40 untreated fish. Mortalities began in the injected fish on day 7 and reached a peak of 48% on day 14. In the cohabitation group, mortalities began on day 14 and reached a peak of 70% on day 27. The IPNV in the Shetland kidney homogenate was cultured in Chinook salmon embryo (CHSE) cells and passed twice. This cultured virus was injected i.p. into fish at various doses ranging from 10 to 10⁷ TCID₅₀ fish^?1 4 weeks after seawater transfer. Challenge tanks contained 30 injected fish and 30 cohabitees. Mortality rates and levels were dose‐dependent. The highest dose used resulted in a similar mortality pattern as obtained with a similar dose of the Shetland kidney homogenate, indicating that virulence was retained after two passes in tissue culture. Even with the lowest dose, mortality reached 12% in the injected group and 23% in the cohabitees. The IPNV titres were high (10⁶?10⁹ i.u. g^?1 kidney) in fish which died during the experiment and low (<10⁵ i.u. g^?1 kidney) or undetectable in surviving fish. The cultured virus (pass 3) was used in a challenge model where the population density of fish in the tanks was high (50 injected and 50 cohabitees) or low (15 injected and 15 cohabitees). In the high stocking density tank, mortalities peaked at about 35% in the injected group and at 52% in the cohabitees. In the low stocking density tank, mortalities peaked at about 40% in the injected fish but no mortality occurred in the cohabitees. However, IPNV was detected (up to 10⁴ i.u. g^?1 kidney) in 82% of cohabitees sampled on day 30. These data suggest that lethal lateral transmission of the virus is dependent on the infectious pressure from the injected group. A further trial was conducted to investigate the effect of time post‐seawater transfer on the susceptibility of post‐smolts to IPN. Groups of fish were challenged every 2 weeks from week 0–10. Few mortalities occurred at week 0 and virus titres were high in these fish. Most survivors became carriers, some with titres >10⁶ i.u. IPNV g^?1 kidney. From 2 to 10 weeks after seawater transfer, mortalities in both injected and cohabitees were substantial with viral titres >10⁷ i.u. g^?1 kidney. Survivors had lower titres and in many virus was undetectable. Throughout the experiments, moribund fish were sampled for histology and all showed typical IPN histopathology.     

Assessing the spawning season in common dentex (Dentex dentex) using microsatellites

A set of five variable microsatellite markers was used for the genetic characterization of two common dentex ( Dentex dentex ) broodstocks from an experimental hatchery and for the screening of the egg batches spawned during the complete spawn season in 2006. After parentage assignment, simulations were performed for the hatchery 1 broodstocks; the microsatellite set correctly assigned over 93% of descendants to parents when one parent was known and 80% when neither parent was known. Of the 261 eggs that the DNA was correctly amplified from, 254 were successfully assigned to a parental couple. More than one female or male took part (at the same point in time) in the spawning season. However, we observed 'dominant' individuals that produced high proportions of the descendants (unequal reproductive success) in all the sampling periods, although the contributions of these dominant individuals could change over time. This phenomenon reduces the effective breeding numbers, and could lead to inbreeding if this factor is not taken into account when the next parental generation is obtained. This factor should also be considered in aquaculture selection programmes because the dominant breeders may not be the most interesting individuals for commercial or productive schemes.     

Effect of larval and prey density, prey dose and light conditions on first feeding common dentex (Dentex dentex L.) larvae

Initial larval stocking density, prey density, daily prey ration and light conditions (light intensity and photoperiod) were tested for common dentex larval rearing under experimental conditions. Experiments continued until the first peak of larval mortality. The best results in larval survival were obtained with an initial stocking density of between 10 and 40 larvae L^?1, fed with at least 10 rotifers mL^?1, maintaining ratios of 500–1000 rotifers larva^?1, with one or two adjustments of prey density per day. The use of more than 2000 rotifers larva^?1 or three daily adjustments of live prey density had negative effects on larval survival. The best light conditions for common dentex larval rearing were found using a photoperiod of 24 h L:0 h D and an intensity of at least 3.4 μmol m^?2 s^?1.     

Effect of dietary water on growth of dentex <Emphasis Type="Italic">Dentex dentex</Emphasis>

ABSTRACT:   This study is concerned with the effect of hyrdated diets on growth and feed performance of Dentex dentex . Three levels of dietary water were tested: 7%, 20% and 40%. For the 7% level a commercial feed was used and the 20% and 40% water levels were obtained after adding an appropriate amount of deionized water to the commercial feed and mixing the pellets well. The diets were offered to fish by self-feeders, by which fish were allowed continuous access to diets after activating the self-feeders; by belt feeders, by which the diets were fed continuously and in excess over a 12 h interval; and by hand to apparent satiation two times a day. After 151 days of feeding, the group fed on the 20%-water diet showed significantly ( P  < 0.05) higher growth rate than the 7 and 40% groups, while no significant differences were observed in feed conversion rate or daily feed consumption. The means of feed delivery did not influence growth rate. Self-feeder, belt and hand feeding all gave comparable growth. Fish fed the more condensed 7%-water diet had smaller stomachs than fish fed the larger volume 40%-water diet. In the stomach, all groups of fish hydrated their digesta within 2 h after feeding to a moisture content of around 60%. Apparently no difference in digestive process was observed between groups. It was concluded that the addition of water in diet at the level of 20% has a beneficial effect on dentex growth.     

Egg quality criteria in common dentex (Dentex dentex)

The spawning quality, in terms of hatching rate, larval mortality at 3 and 5 days post-hatching (dph) and day of total mortality of two broodstock groups of common dentex was evaluated for 1 month in 2005. Several biochemical parameters including total lipid content, lipid class and fatty acid composition, carbohydrate content and metabolic enzyme activities were analysed in all the egg batches collected. Comparison was carried out between low- (mortality at 3 dph higher than 35%) and high-quality (mortality at 3 dph lower than 10%) batches. No differences were observed in lipid content and/or lipid class and fatty acid composition although a slightly higher content of neutral lipids was detected in high-quality batches. However, significant differences were obtained regarding carbohydrate composition and the activity of enzymes such as alkaline phosphatase and pyruvate kinase being higher in low-quality egg batches.     

A Lactobacillus sp. from diseased female rainbow trout, Salmo gairdneri Richardson, in Newfoundland, Canada

Abstract. Post-spawning mortalities of 2- to 3-year old female rainbow trout, Salmo gairdneri Richardson, at a Newfoundland hatchery were studied. The fish were found to have a mixed bacterial infection involving primarily a Lactobacillus sp. (a Gram-positive, chain-forming coccobacillus) and to a lesser degree Enterobacteriaceae, Aeromonas hydrophila and Pseudomonas fluorescens. The bacteria were isolated from the visceral organs, kidney, and ascitic fluid present in the coelomic cavity. The fish had extensive degeneration and necrosis of the liver, spleen and kidney, and sloughing of intestinal epithelium, but whether these were caused directly by the bacterial infection was not established because the fish appeared to have received substantial stress from the mechanical stripping and from the retention of dead, unshed eggs in the coelomic cavity. Tissue sections suggested that substantial growth of the Lactobacillus sp. was occurring within these unshed eggs. The present study describes this unusual observation and compares the Lactobacillus sp. to two other Lactobacillus isolates from cultured trout.