The effect of rearing conditions on development of saddleback syndrome and caudal fin deformities in Dentex dentex (L.)

The development of saddleback syndrome and of caudal fin deformities in Dentex dentex (Linnaeus, 1758) was compared under two rearing methods, extensive (E) and semi-extensive (S). The osteological appearance and the meristic characters of the reared fish were compared to that of D. dentex juveniles, collected from the natural environment. All the wild juveniles were normal in respect to their osteological appearance, while the reared specimens presented skeletal deformities resulting from different rearing methods applied. Saddleback syndrome (4.0–4.4%) and severe external deformities of the caudal fin (14.3–15.0%) characterised exclusively the semi-extensive populations, while the extensive populations presented severe abnormalities of the pre-ural centra (25.0–25.6%) with significantly higher frequency than the S reared fish (5.8%). Saddleback syndrome was expressed as a lack of one to all the hard spines of the dorsal fin, accompanied by shape, number and position abnormalities of the related pterygiophores. Caudal fin deformities were mainly characterised by the lack of the upper lepidotrichia or/and dermatotrichia, accompanied by severe deformities of the supporting elements of the upper lobe. The saddleback syndrome and severe caudal fin deformities were anatomically and ontogenetically related to each other, originating at the early larval stage as a result of abnormalities of the primordial marginal finfold and of the posterior tip of the notochord. In respect to the dominant phenotypes, the meristic characters of the normal reared fish were not differentiated from those of the wild, but they presented higher variability.

The results are discussed in view of the aetiology, applications and research targets for the erasure of skeletal malformations.     

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.     

Changes in amino acids and essential fatty acids during early larval rearing of dentex

Samples of fertilized dentex, Dentex dentex, eggs and larvae fed enriched rotifers and Artemia according to standard hatchery procedures were analysed for free, total amino acid and fatty acid contents. Egg free amino acids (53 nmol ind-1) and total lipids (13.5 (g ind-1) levels were considerably reduced in the newly hatched larvae (6.0 nmol and 5.7 (g ind-1 respectively) while the amount of -3 PUFA (Polyunsaturated fatty acid) and 20:4-6 remained unchanged suggesting their possible role as essential fatty acids (EFA) in this species. In general, the changes in pattern of the major biochemical components during early development of dentex was similar to that outlined for other Sparidae species investigated to date. The essential amino acid profile of enriched live food did not show major imbalances when compared to that of dentex larvae. In contrast, the level of docosahexaenoic acid (22:63, DHA) and the DHA:EPA (eicosapentaenoic acid, 20:5-3) ratio in larvae given rotifers and Artemia were significantly lower relative to the corresponding values in the unfed larvae.     

The effect of light intensity on early life development of common dentex Dentex dentex (L. 1758) larvae

The effects of different levels of illumination on common dentex Dentex dentex (L.) larvae have been examined. Illumination affected the relationships between total length and digestive tube length, total length and oil globule volume, and total length and yolk sac. The relationship between total length development and yolk sac utilization in dark and light conditions was found to be significant (P<0.05). However, it was determined that the relationship between digestive tube development and oil globule absorption was not significant (P>0.05). Besides, there is no effect of different light intensities on absorption of yolk sac and oil globule and digestive tube development (P>0.05). In addition, total length development was not significant (P>0.05). Survival rate was found to be not significantly different in dark conditions (P>0.05).     

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.     

Egg quality determination based on the shape of the lipid vesicle in common dentex, Dentex dentex

The shape of the lipid vesicle (the ratio between the maximal and the minimal diameter and the shape coefficient) of the eggs of Diplodus puntazzo and Sparus aurata is correlated with larval survival rate (%) and can be used as an egg quality marker as reported previously by Lahnsteiner and Patarnello (2005) . In the present study, this method for egg quality determination has also been validated for common dentex, Dentex dentex, after introducing several modifications in the calculation and evaluation procedure in order to obtain higher sensitivity. In the present study, it could be demonstrated that the shape of the lipid vesicle is not only correlated with the hatching rate but also with the survival rate of 1, 2 and 3 days post hatch larvae and therefore it can also be used as an indicator of larval viability at early stages of development.     

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.     

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.     

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.     

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.     

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.     

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.     

Ontogeny of the digestive tract in shi drum (Umbrina cirrosa L.) reared using the mesocosm larval rearing system

Histological changes of the digestive tract were studied in shi drum (Umbrina cirrosa) from hatching until 41 days post hatching (dph), when the fry had a mean (±S.D.) total length (TL) of 32 ± 2 mm and wet weight (WW) of 0.42 ± 0.07 g. Larvae were reared using the mesocosm technique, the most natural among commercially employed rearing methods for marine larvae. Shi drum opened their mouth at 2 dph (2.78 ± 0.09 mm TL), at which time 90% of the larvae already had an inflated swim bladder. The differentiation of the digestive tract into buccopharynx, esophagus, and anterior and posterior intestine was completed by 3 dph (2.82 ± 0.07 mm TL), 1 day after the onset of exogenous feeding. The alimentary canal started coiling and formed its first loop at 2 dph, while the pancreas and liver were differentiated at 3 dph. Yolk sac reserves lasted until 7 dph (4.3 ± 0.1 mm TL), suggesting a brief period of endogenous and exogenous feeding. The first esophageal goblet cells appeared at 7 dph containing acid mucins and at 8 dph taste buds appeared on the buccopharyngeal epithelium. The stomach was morphologically differentiated at 9 dph (5.5 ± 0.1 mm TL) when gastric glands became abundant in the cardiac region, and the first pyloric caeca appeared at 14 dph (10.1 ± 0.9 mm TL). Supranuclear eosinophilic vacuoles were observed in the posterior intestine between 3 and 11 dph (6.3 ± 0.9 mm TL). Their number decreased as the stomach differentiated, suggesting a change in the protein digestion mechanism. The results of the study suggest a rapid development of shi drum and its digestive system and underline the possibility of weaning larvae to artificial feed even earlier than the 12 dph employed in the present study.     

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.     

Migration performance of wild and hatchery sea trout (Salmo trutta L.) smolts—Implications for compensatory hatchery programs

Migration success of hatchery-reared and wild sea trout smolts through the lower stretches and the estuary of a Baltic Sea river were studied. During 3 years, wild and hatchery trout smolts were implanted with acoustic transmitters and released 14 km upstream from the river mouth. In order to monitor their out-migration pattern, acoustic receivers were deployed along the migratory route. Data on number of fish detected and date and time of detections were analysed and the migratory performance of wild and hatchery-reared fish was compared. A significantly higher proportion of wild fish (80%) successfully migrated to the coast compared to fish of hatchery origin (27.5%) and migration was faster in wild smolts. Hatchery fish were larger and had a higher condition factor and lipid concentrations, which are proposed as possible reasons for the poorer migratory performance of the hatchery-reared fish.     

The influence of rearing density on stress response and disease susceptibility of ayu (Plecoglossus altivelis)

The impact of coldwater disease caused by Flavobacterium psychrophilum is a recent important problem in the farming of ayu (Plecoglossus altivelis). We hypothesized that stress from high-rearing densities predisposes fish to disease by reducing their immunocompetence, and we sought to reduce fish losses by introducing an alternative culture regime. Fish enclosed at three densities (1250 fish or 8.0 kg, 400 fish or 2.6 kg and 100 fish or 0.6 kg/m³) were examined. Fish in the high-density treatment exhibited more elevated serum cortisol concentrations and more suppressed serum immunoglobulin M (IgM) concentrations accompanied by higher mortality, possibly caused by coldwater disease, than those in the medium- and low-density treatments. These results indicate that high-rearing densities stress fish and evoke subsequent physiological responses which have maladaptive effects. We propose that coldwater disease may be prevented by improving the disease resistance of fish by using moderate stocking densities.     

Response and condition of larvae of the scallops Nodipecten subnodosus and Argopecten ventricosus reared at the hatchery with different seawater sources

Larvae of the scallops Nodipecten subnodosus and Argopecten ventricosus were reared at a hatchery under five seawater sources: (1) filtered seawater, as the control group; (2) pasteurized seawater; (3) seawater taken from a well; (4) synthetic seawater, and (5) seawater containing a commercial probiotic (Epicin). The quality of each seawater source was measured in terms of counts of Vibrio pathogenic bacteria, levels of nitrites, nitrates, and ammonium, and content of suspended and organic matter. Overall response of larvae under each treatment was measured in terms of growth, survival, biochemical composition, and recruitment rate of spat. Differences in all these parameters, as a function of the seawater source, were analyzed with one-way ANOVA. Larvae survived more, grew faster and larger, had higher protein levels, and recruited more in filtered seawater (in N. subnodosus) and pasteurized seawater (in A. ventricosus), but significant differences between treatments were slight. In A. ventricosus cultures, filtered seawater favored significantly higher Vibrio counts than pasteurized seawater, but this result did not affect the response and condition of larvae. The well seawater treatment ranked third in terms of low bacterial counts, high nitrate levels, larvae showing relatively high survival and growth rates, and spat reaching the settlement stage (only in A. ventricosus). The synthetic seawater and Epicin treatments did not yield satisfactory results for any of the indicators measured. In fact, in the Epicin treatment, larvae survived only the first days of hatchery cultivation and settlement occurred only in A. ventricosus. The results from these first set of trials are useful for planning additional experiments aimed to improve the protocol of seawater use at our research hatchery.     

Utilization of lipids by Dentex dentex L. (Osteichthyes, Sparidae) larvae during lecitotrophia and subsequent starvation

Total lipids, lipid classes and their associated fatty acids were measured in developing eggs, yolksac larvae and starving larvae (from fertilized egg to day 9 after hatch) of the common dentex Dentex dentex (L., 1758). The larvae of common dentex during lecitotrophia and subsequent starvation consumed 1.6 g of total lipid per larvae per day. The overall decrease was mainly due to utilization of the major neutral lipids, TAG and SE (0.5 and 0.6 g larvae^–1 day^–1, respectively) which was 3.4-fold greater than that of the the major phosphoglycerides (primarily PC by 0.2 g larvae^–1 day^–1). There was net synthesis/conservation of PE during the first half of the study period before it decreased rapidly (0.2 g larvae^–1 day^–1) during the second half. PUFAs were principally catabolized (468.6 ng larvae^–1 day^–1), primarily 22:6(n-3), 20:5(n-3) and 20:4(n-6) (221.8, 58.5 and 12.1 ng larvae^–1 day^–1, respectively). Saturated and monounsaturated fatty acids were also utilized (227.2 and 256.7 ng larvae^–1 day^–1, respectively), principally 16:0 and 18:1(n-9) that were both consumed at 149.8 and 156.7 ng larvae^–1 day^–1, respectively. The rank order of utilization of fatty acids (ng larvae^–1 day^–1) by D. dentex larvae from total lipids, PC and TAG coincided with the order of abundance of the different fatty acids in the respective lipid fractions. However, in PE, the most abundant fatty acid, DHA, was relatively conserved and 16:0, the second most abundant fatty acid, was catabolized to the greatest extent. D. dentex showed a pattern of lipid metabolism during early development similar to that of marine larval fish from temperate waters whose eggs contain high levels of total lipids, including an oil globule, and which preferentially utilize neutral lipids as the primary energy source.     

Effects of a peroxide-based commercial product on bacterial load of larval rearing water and on larval survival of two species of Sparidae under intensive culture: preliminary study

Larvae of two Mediterranean Sparidae species, Sparus aurata and Dentex dentex , were used to test the efficacy of a peroxide-based product (Ox-Aquaculture^©) on the reduction in bacterial load in larval rearing water and its effects on larval survival. Eleven-day-old S. aurata larvae and 15-day-old D. dentex larvae were exposed to different concentrations of Ox-Aquaculture^© (50, 100 and 200 mg L⁻¹, and 20 and 50 mg L⁻¹ respectively) for 1 h. Results indicated that 50 and 20 mg L⁻¹ were the most effective concentrations for the reduction in bacterial load (at least one order of magnitude) after 1 h treatment, without affecting larval survival and/or vitality in 11 dph S. aurata and 15 dph D. dentex larvae respectively. Ox-Aquaculture^© concentrations of 200 and 50 mg L⁻¹ during 1 h affected negatively final survival rate of the larvae of S. aurata and D. dentex respectively.