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.     

The rearing of common dentex Dentex dentex (L.) During the hatchery and on-growing phases

In the current paper we present the rearing methodology of common dentex (Dentex dentex), a promising candidate for Mediterranean marine aquaculture, from the larval to the on-growing phase. The results are discussed in terms of the efficiency of rearing methodology followed, for the mass production of the species.     

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.     

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.     

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.     

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.     

黄带拟鲹线粒体基因组测序及鲹科鱼类系统发育分析

摘要: 为深入开展黄带拟鲹种质鉴定、分类及遗传进化等研究,通过二代高通量测序与生物信息学分析,揭示了黄带拟鲹(Pseudocaranx dentex)线粒体基因组全序列基因结构及鲹科鱼类系统发育特征。结果显示,黄带拟鰺线粒体基因组为典型的环状DNA结构,序列全长为16 570 bp,碱基组成分别为A(27.2 %)、G(17.18%)、C(30.24%)和T(25.38%),包括13种蛋白编码基因,22个tRNA基因,2个rRNA基因,除ND6、tRNAGln、tRNAAla、tRNAAsn、tRNACys、tRNATyr、tRNASer、tRNAGlu、tRNAPro外,其余基因均在H链上编码,且基因组存在多处重叠区域。除CO Ⅰ和ND5的起始密码子分别为ATC和ATA外,其余11个蛋白编码基因的起始密码子均为ATG,以典型的TAA和TAG为终止密码子,在Cyt b中存在不完全终止密码子T;黄带拟鲹线粒体基因组全序列与蛋白编码基因的A+T含量分别为52.58%和51.55%,非编码控制区(D-loop)A+T富含61.69%,具有明显的AT偏好性。除tRNASer-(GCT)外,其余21个tRNA均含典型三叶草二级结构。为进一步研究黄带拟鲹系统进化特性,通过与18种鲹科鱼类线粒体基因组全序列及16S rRNA基因构建系统进化树显示,黄带拟鲹与高体若鲹同属一个分支,亲缘关系最近。结果可为黄带拟鲹物种鉴别、遗传多样性评价与保护提供技术依据。     

The influence of astaxanthin supplemented dry pellets on spawning of striped jack

SUMMARY: This experiment was conducted to investigate the effect of astaxanthin supplemented steam-dry pellets on the spawning of striped jack Pseudocaranx dentex . Five months before spawning, 7-year-old fish were divided into three groups, each consisting of five females and five males. The control group was fed a raw fish mix (RF) and the test diets consisted of steam-dry pellets (DP) and steam-dry pellets supplemented with 10 p.p.m. astaxanthin (a-DP). Feeding was carried out once per day, three times a week in floating net cages. The RF and the a-DP groups produced more than three times the amount of eggs produced by the DP group. The buoyancy, fertilization, and hatching rates were higher and similar for the RF and the DP groups. Total lipid contents of the diets, eggs, and larvae were similar among the groups. Highly unsaturated fatty acids (n-3 HUFA) and polar and non-polar lipids in eggs and larvae were also related to their dietary availability. These results indicate that astaxanthin, due to its various physiological functions, improved the condition of the broodstock and enhanced total egg production but not egg quality as striped jack do not incorporate carotenoids into their eggs. Therefore we confirm that the nutritional quality of diets given to striped jack prior to spawning plays a fundamental role in egg production, quality and egg composition.     

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.     

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.