Fertilizing capacity and motility of tench Tinca tinca (L., 1758) sperm following cryopreservation

Experiments were carried out to develop an optimal cryopreservation protocol for tench sperm by testing the fertilizing capacity and motility parameters including progressive motility, curvilinear velocity (VCL) and linearity (LIN) of cryopreserved sperm. Three experiments were designed to this aim: first experiment where we tested the effects of two extenders (sugar‐based Grayling and ion‐based Kurokura 180) and two cryoprotectants (DMSO and methanol) on fertilization and hatching success; second where we tested the effect of cryoprotectant type (methanol or DMSO) in different concentrations (5%, 10% and 15%) on fertilization and hatching success; and third where we tested the effect of two cryoprotectants (methanol and DMSO) on sperm motility parameters (progressive motility, VCL and LIN) after 4 h post‐thaw storage (4°C). Sperm prepared with the sugar‐based Grayling extender displayed better fertilization and hatching rates independently of the applied cryoprotectant most likely due to glucose present which acted as an external cryoprotectant. Concerning cryoprotectant concentrations, the use of 10% methanol yielded the highest fertilization (85 ± 15%) and hatching (80 ± 13%) rates, which were significantly higher than in all other groups. During the post‐thaw storage time, 5% methanol, 10% methanol and 5% DMSO groups had significantly higher motility parameters than other groups and we observed no significant decline in any of the parameters during the storage time. Overall, we found that a sugar‐based extender in combination with methanol as cryoprotectant is suitable for the cryopreservation of tench sperm and allows storage of cryopreserved sperm for up to 4 h post thaw.     

Embryonic development and larval and post‐larval growth of the tropical scallop Nodipecten (= Lyropecten) nodosus (L. 1758) (Mollusca: Pectinidae)

This work describes for the first time the embryonic development of the tropical scallop Nodipecten nodosus. Larval and post‐larval growth parameters and some characteristics of larvae shell morphology were also ascertained. The larvae were obtained from the induced spawning of a group of broodstocks under controlled laboratory conditions. After fertilization, larval cultivation was carried out in conical tanks at a temperature of 26–27 °C. Larval density was controlled as a function of larval growth to give 10, 5 and 3 larvae mL^?1 from days 1, 3 and 8 respectively. The larvae were nourished with a 1:1 mix of Isochrysis galbana (clone T‐ISO) and Chaetoceros gracilis in portions varying between 30 000 and 70 000 cells mL^?1. Expulsion of polar groups was observed 5 and 15 min after fertilization, whereas the first cellular division occurred after 30 min. The first gastrule ciliates and trocophore larvae were noted after 8 and 18 h had elapsed, respectively, whereas prodissoconch I, or D‐larvae, were discerned after 26 h. Subsequently, larvae with prodissoconch II or veliger‐conch appeared at 30 h. Larval development continued for 10–12 days, followed by metamorphosis, at an approximate length of 208–230 µm. The growth of the post‐larvae was evaluated for 9 days. Larval and post‐larval growth corresponded to the linear equations L = 71.85 + 10.85t, r² = 0.99, and L = 44.09 + 17.81t, r² = 0.94 respectively. Accordingly, larval morphology and size disparities are discussed with respect to other tropical pectinids.     

Bottom culture of the tropical scallop Lyropecten (Nodipecten) nodosus (L.) in the Golfo de Cariaco, Venezuela

Growth and survival of scallop Lyropecten nodosus were studied fromJuly to November 1997 using three bottom culture methods, (1) in corrals,(2) in pockets, and (3) in anchored sleeves. All size parameters studied (dryweight of the muscle, gonad, remaining tissues and shell, and shell length)showed significant differences due to culture method. The body componentswere larger for scallops in corrals than for those in pockets and greater forthose in pockets than in sleeves. In contrast, survival did not vary withculture method. Tissue components increased rapidly during the first 2months, when temperatures were lower and phytoplankton abundant(upwelling and transition periods). Subsequently values leveled off, or insome cases (muscle) decreased, and this coincided with stratification of thewater column and associated high temperatures and scarce food resources(and possible energetic demands for gonadal development). In contrast,shell weight and length showed no apparent affect of the environmentalchanges. The increased growth in the corrals was possibly because thecorral walls permitted the scallops to raise themselves off the bottom whichcould have provided greater access to food resources (suspendedparticles), or to better quality food.     

Growth and survival of the scallop Lyropecten (=Nodipecten) nodosus (L. 1758) in suspended culture in the Cariaco Gulf (Venezuela) during a non-upwelling period

Growth and survival of the scallop Lyropecten nodosus were studied in 1997 at two sites (inner and outer Turpialito Bay) during a non‐upwelling period normally occurring between August and November. Individuals had an initial shell height of 4.86 cm (SD=1.64 cm). Both experimental groups were held in suspended plastic baskets at the same depth (4 m). Measurements of shell height and dry weights of shell, gonad, digestive gland, remaining tissues and shell biofouling were taken at monthly intervals. Environmental parameters, including temperature, phytoplanktonic biomass, total particulate material (TPM) and associated organic (POM) and inorganic (PIM) fractions, were recorded simultaneously. At the end of the study, significant differences in growth and survival of scallops were observed between the two experimental sites. Scallops maintained inside the bay showed a 22% greater increase in shell height (7.41±0.27 cm) than those placed outside the bay (6.37±0.41 cm). Survival of scallops inside the bay was 31% higher compared with scallops outside. The greater availability of food of phytoplanktonic origin during the first two experimental months (July and August) together with greater POM throughout the whole experimental period except September, at the inner bay site, probably explained survival and growth differences observed between the two locations. Results suggest that, during the non‐upwelling period (characterized by low primary productivity and high water temperatures), POM of sedimentary origin may play an important role as an energy source required for metabolic and reproductive activities of L. nodosus.     

Reproductive performance of gilthead seabream (Sparus aurata L., 1758) fed two combined levels of carotenoids from paprika oleoresin and essential fatty acids

Despite carotenoids and essential fatty acids seem to play important roles in fish reproduction, no studies have yet been conducted to determine the effect of dietary carotenoids on gilthead seabream broodstock performance and their relation as antioxidants with dietary n‐3 highly unsaturated fatty acid (HUFA) levels. In addition, the high cost of synthetic sources of carotenoids is leading to the search for new natural carotenoid sources such as paprika oleoresin. Four experimental diets containing two combined levels of carotenoids from paprika oleoresin (40 and 60 mg kg^?1) and n‐3 HUFA (25 and 40 g kg^?1) were respectively fed to triplicate groups of gilthead seabream (Sparus aurata) broodfish. Elevation of n‐3 HUFA dietary levels from 25 to 40 g kg^?1 significantly improved gilthead seabream broodstock performance in terms of egg viability, hatching rates and fecundity. Besides, it markedly increased egg contents in HUFAs which play important energetic and structural roles and improve embryo development. Both arachidonic acid and eicosapentaenoic acid (20:5n‐3) egg contents were more readily affected by dietary n‐3 HUFA than docosahexaenoic acid. HUFA levels did not caused any negative effect suggesting an optimized content of antioxidants in broodstock diets. Increase in dietary carotenoids from 40 to 60 mg kg^?1 increased carotenoid contents in eggs and significantly improved egg fertilization rates suggesting an important sperm cell’s protective role by reducing the risk of lipid peroxidation which is detrimental for sperm motility. The increased inclusion of dietary paprika oleoresin enhanced egg carotenoid deposition and improved fish reproductive performance, denoting the high nutritional value of this product as a source of carotenoids for broodstock of this species.     

Lion's paw scallop (Nodipecten subnodosus, Sowerby 1835) aquaculture in Bahía Magdalena, Mexico: effects of population density and season on juvenile growth and mortality

This study examined the effects of density and growing season on growth and survival of juvenile lion's paw scallops (Nodipecten subnodosus) in Estero San Buto, a mangrove channel in Bahía Magdalena, Mexico. Scallops were kept in plastic mesh bags in oyster trays at three population densities (500, 1000 and 2000 organisms per tray, or low medium and high density respectively) over a period of 2 months from October to December 2001 and from February to April 2002. Growth (shell height increment) was measured every 7–12 days and mortality was evaluated at the end of the experiment (dead shell count). Overall growth was fast (0.24–0.38 mm day^?1) in comparison with other pectinids. Significant differences were found for both, density and season, with faster growth occurring at lower densities and during the fall season when the water temperature was higher. Mortality was low (0.5–3.0% 60 day^?1) except for the high‐density treatment in the fall (44% 60 day^?1). Crowding together with high water temperatures and increased metabolic oxygen demand of the scallops and possibly competition for food were the probable reasons for this high mortality. Overall, mortality was lower in the spring, when temperatures were lower, O₂ values were higher and food was more abundant.     

Influence of environmental factors,season and size at deployment on growth and retrieval of postlarval lion's paw scallop Nodipecten nodosus (Linnaeus, 1758) from a subtropical environment

The effect of seasonal variation of environmental factors on daily shell growth rates (DGR) of postlarval Nodipecten nodosus was studied at the southern distribution limit of the species in Santa Catarina State, Brazil. Five deployments of hatchery produced postlarvae (initial shell height 0.5 mm) in the sea-based nursery were carried out from August 2000 to September 2001, and DGR and percent retrievals were recorded. Chlorophyll-a, seston, salinity, dissolved oxygen and turbidity were measured weekly, and temperature was recorded hourly. Additionally, DGR and retrievals were compared for postlarvae maintained simultaneously in the sea- and land-based nurseries (initial shell height 0.5 mm), and also for post-larvae deployed in the sea-based nursery at different initial sizes (0.29–1.1 mm). Mean DGR was significantly lower in late winter–early spring 2000 (0.045 mm day⁻¹), intermediate in late winter–early spring 2001 (0.078 mm day⁻¹) and significantly higher in the other seasons (late spring–early summer, 0.152 mm day⁻¹; late summer–early autumn, 0.149 mm day⁻¹ and late–autumn early winter, 0.130 mm day⁻¹). Temperature was the best predictor of growth, which was least at temperatures below 20 °C. Growth rate was also minimal during a period of low salinity and high turbidity. Mean DGR was significantly higher in postlarvae deployed in the sea-based nursery than in those maintained in the land-based nursery. Loss of postlarvae in the sea-based nursery was initially higher in collectors transferred earlier to the sea (ca. 2–3 weeks post-set; shell height 0.5–0.8 mm), but percent retrievals were similar after postlarvae deployed to the sea ca. 4–5 weeks post-set (shell height 1.1 mm) were retrieved simultaneously with those deployed earlier. At retrieval, postlarvae deployed approximately 2 weeks post-set were larger than those deployed subsequently, but spat deployed 1 week post-set attained a similar size to those deployed 2 weeks post-set. A strategy to deploy postlarvae in the sea-based nursery at a size circa 0.5 mm is proposed as more advantageous than keeping them longer in land-based facilities. In southern Brazil, there is a wide window of opportunity to deploy post-larval scallops in the sea-based nursery in which growth is maximized, except when water temperatures drop below 20 °C.     

Sperm cryopreservation of silver barb (Barbodes gonionotus): cryoprotectants,cooling rate and storage time on sperm quality

Effectiveness and efficiency of frozen sperm on fertilization and hatching success of eggs from silver barb was examined in relation to cryoprotectants, freezing rate and storage period. Sperm was diluted in calcium‐free Hank's balanced salt solution, equilibrated with dimethylsulphoxide (DMSO), propylene glycol, sucrose or methanol at 5%, 10%, 15% or 20% final concentrations, and frozen in 250‐μL straws using a one‐step freezing procedure (1, 5 and 8°C min^?1 from 25 to ?40°C). Highest post‐thaw sperm motility was found from a treatment using 10% DMSO and 5°C min^?1 (82.2 ± 2.1%), similar to that of 10% DMSO and 8°C min^?1 (87.8 ± 3.2%). Post‐thaw motility of sperm frozen at 5 or 8°C min^?1 was significantly higher than 1°C min^?1. Relative sperm motility declined significantly after 10 months of cryostorage while viability did not change during a 12‐month cryostorage. Average fertilization rates of sperm after 1 and 4 months of storage were 64.5 ± 4.6% and 61.3 ± 3.4%, respectively, similar to those of fresh sperm (69.6–72.3%). Hatching rates of cryopreserved sperm (45.4–51.2%) were similar to those of fresh sperm (51.8–57.8%). This study developed suitable methods for cryopreservation of silver barb sperm that can be used to facilitate hatchery operation.     

Development of deformities at the vertebral column in Diplodus sargus (L., 1758) early larval stages

One of the bottleneck problems of Diplodus sargus farming is a high incidence of skeletal deformities at the vertebral column. In this study, the pattern of vertebral deformities were determined in three different larval batches from 2 to 30 days after hatching (DAH). During this period, 60 larvae per spawn were observed at 2, 8, 13, 15, 18, 21, 23, 25, 27 and 30 DAH and the different types and frequency of vertebral column malformations were registered. Deformities started from 8 to 13 DAH, when the percentage of deformed larvae rose from approximately 5% to 40%. At 15 DAH, skeletal malformations had frequencies up to 80% of the observed larvae. Serious malformations such as kyphosis, scoliosis and lordosis were observed at 18 DAH but seldom in percentages higher than 15%. Vertebral fusions and compressions especially affected the preurostyle region. Abnormal shape vertebrae were more frequent between vertebrae 15 and 21. Other malformations observed were hypertrophic vertebrae, more common in the trunk and caudal regions, reaching percentages higher than 50% in the former. This study has useful information concerning skeletal malformations at the vertebral column of D. sargus larvae, as it identifies the main deformities observed and the ages of highest incidence.     

Cryopreservation of Persian sturgeon (Acipenser persicus) sperm: effects of cryoprotectants,antioxidant, membrane stabilizer,equilibration time and dilution ratio on sperm motility and fertility

Three experiments were performed to develop protocols for cryopreservation of Persian sturgeon Acipenser persicus, sperm. In the first experiment, sperm from six males was individually split in three subsamples and cryopreserved using Modified Tsvetkova's extender (mT) supplemented with dimethyl sulfoxide (DMSO), methanol (MeOH), glycerol (Gly) and ethylene glycol (EG) at concentration of 5%, 10%, 15% and 20%. In the second set of experiments, the effects of six equilibration times (0, 5, 10, 20, 40 and 60 min) and dilution ratios (volume sperm: volume extender 1:0.5, 1:1, 1:2, 1:3, 1:5 and 1:10) and the additive advantage of bovine serum albumin (BSA; 0, 2.5, 5 and 10 mg mL^?1) and ascorbic acid (0, 2.5, 5 and 10 U mL^?1), on the post‐thaw survival of sperm (triplicate set of six fish) were evaluated. Then, sperm was diluted in 1:1 mT extender with 10 mg mL^?1 BSA with selected cryoprotectants (15% MeOH and 10% DMSO) for 5 min. After a month of storage in liquid nitrogen, post‐thawed sperm motility; fertilization and hatching rate and viability of derived larvae were measured (Exp.3). Evaluation of cryoprotectants efficiency showed that MeOH 15% and DMSO 10% were suitable for cryopreservation of Persian sturgeon sperm. Gly and EG resulted in very low post‐thaw motility rates even at lowest concentration. No significant difference was observed among the four different equilibration times (0, 5, 10, 20 min) (P > 0.05) although higher equilibration times than 20 min resulted low post‐thaw motility (P < 0.05). The motility of frozen–thawed sperm did not significantly change when dilution ratio was increased from 1:0.5 to 1:3 (P > 0.05). However, higher dilution ratios (1:5 and 1:10) reduced the percentage of motile sperm. Supplementation of the cryoprotectant solution with 10 mg mL^?1 BSA significantly improved post‐thaw motility (P < 0.05), but ascorbic acid did not improve post‐thaw motility (P > 0.05). The results of experiment 3 showed that the highest fertilization (30.2 ± 5.75) and hatching rates (28.2 ± 5.25) were observed when samples were frozen with 15% MeOH (P > 0.05). Our study indicates that the use of mT extender consisting of 10 mg mL^?1 BSA in 15% MeOH diluted with sperm at 1:1 ratio for 5 min can be recommended cryopreservation method for Persian sturgeon sperm.     

Juvenile turbot (Scophthalmus maximus L., 1758) farmed in a modern low-water exchange RAS device: Growth performance using different diets and its commercial implications

One step to improve the economics of Recirculated Aquaculture Systems (RAS) is the use of the right feed. A 12-week lasting growth trial with juvenile turbot (Scophthalmus maximus) with an average initial weight of 54.4 ± 19.3 g evaluated the economic impact of choosing the best feed. Therefore, commercially available feeds recommended for turbot culture, two floating (feed 1 and feed 3) and one sinking (feed 2), were tested in a low-water exchange RAS device. Compositions of the macronutrients for the floating diets were 56.0% (protein), 12.0% (fat), 1.1% (fiber), and 10.0% (ash) for feed 1, which will be referred to as Floating 1, and 55.0% (protein), 16.0% (fat), 0.7% (fiber), and 11.0% (ash) for feed 3, which will be referred as Floating 2. The macronutrient composition of feed 2, which will be referred to as Sinking, was 50.0% (protein), 15.0% (fat), 1.4% (fiber), and 9.9% (ash). Growth performance differed significantly between feeds; the specific growth rates (SGR) ranged between 0.92% d^?1 (Sinking) and 1.25% d^?1 (Floating 1 and 2), resulting in a significantly higher growth rate for the floating feeds. Feed conversion ratios (FCR) were also significantly different, and Sinking showed the highest FCRs during the experiment. We assume that this was caused by the different swimming characteristics of the feeds and the foraging behavior of the fish instead of the different nutritional compositions of the diets. Including retailer prices, the feed costs per kg produced fish differed between 9.3% and 20.2%, resulting in the highest production costs for the Sinking. Therefore, finding the right feed for turbot and optimizing the feeding regime according to its requirements will improve the economic feasibility of turbot culture.     

Morphological and physiological evaluation of common carp (Cyprinus carpio L., 1758) fed extruded compound feeds containing different fat levels

The study was carried out to examine morphological and physiological effects of different levels of fat in compound extruded feed for carp. A 90 days experiment was performed in tanks with water flow 0.34 L min^?1, stocked each with 29 specimens of carp, average weight 15.4 ± 4.2 g. The fish was fed 3 diets containing 38 % protein and 8, 12 or 16 % of fat (feed L8, L12, and L16, respectively). Body weight gain, specific growth rate, food conversion ratio, feed efficiency ratio, condition factor, liver and intestine histology and morphometry and some blood biochemical parameters were analysed. At the end of the experiment, a difference was established between the fish fed L8 feed compared to carp fed L12 and L16 feed for all growth parameters. For several other parameters, nuclear area of hepatocytes, nuclear/cytoplasm ratio, enterocytes height and intestinal folds’ length, a difference between carp fed feed L8 compared to feed L16 was found. The histological analysis revealed that normal structure of the liver and intestine prevailed, but changes were observed regardless of the diet type. In the hepatopancreas, more prominent changes were found around pancreatic tissue—particularly, increased number and size of adipocytes. Although blood biochemical parameters were within normal values, a difference between L8 and L16 diet-fed carp was found for plasma levels of triglycerides and total proteins. According to the results obtained in this study, the best results were achieved using a feed with 8 % fat.     

抗冻剂对日本鳗鲡精子活力及运动时间的影响

利用精子稀释液(0.5%氯化钠+0.25%氯化钾+0.25%葡萄糖)分别配制4%、8%、12%、16%、20%、24%的二甲亚砜(DMSO)、甘油(Glycerol)、1,2-丙二醇(1,2-Propanediol)、乙二醇(Ethyleneglycol)四种抗冻剂,对日本鳗鲡精子进行激活处理,观察记录精子在不同浓度抗冻剂中的活力和5种运动(激烈运动、快速运动、慢速运动、摆动、死亡)时间。结果表明:4%~24%的四种抗冻剂都可以激活日本鳗鲡精子,其中二甲亚砜浓度为12%时,精子活力最高,平均可达到78.3%;甘油浓度为8%时,精子活力最高,平均可达到72.8%;12%的1,2-丙二醇和乙二醇激活精子后,精子活力都可以达到最高,分别是47.6%和57.8%。日本鳗鲡精子在8%的二甲亚砜、8%的甘油、8%的1,2-丙二醇和8%的乙二醇中,激烈运动时间均为最长,分别为11.8 s、11.1 s、6.0 s和2.9 s;用8%的甘油、16%的二甲亚砜、16%的1,2-丙二醇和12%的乙二醇激活日本鳗鲡精子后,精子存活时间均最长,分别达到154.6 s、45 s、20 s和34 s。与其它几种抗冻剂相比,8%的甘油能显著延长日本鳗鲡精子的寿命。四种抗冻剂对日本鳗鲡精子都有一定的毒性作用,处理后精子的活力和寿命均降低。     

Sperm cryopreservation of tiete tetra Brycon insignis (Characiformes): effects of cryoprotectants,extenders, thawing temperatures and activating agents on motility features

The aim of this study was to test the effects of cryoprotectants [dimethyl sulphoxide (DMSO) and methylglycol], extenders (0.9% NaCl, 5% glucose, Beltsville Thawing Solution^? and Merck III^?), thawing temperatures (30 and 60 °C) and activating agents (0.29% NaCl and 1% NaHCO₃) on the cryopreservation process of tiete tetra Brycon insignis sperm. Sperm was loaded in 0.5 mL straws, frozen in nitrogen vapour at ?170 °C and stored in liquid nitrogen. Post‐thaw sperm quality was evaluated in terms of subjective motility rate, quality motility score (0=no movement; 5=rapidly swimming spermatozoa), duration of motility and vitality (eosin–nigrosin staining). Post‐thaw sperm motility rate was greater in methylglycol (76–88%), compared with DMSO (23–59%). In general, the highest quality motility scores were observed when sperm was thawed at 30 °C and triggered in 1% NaHCO₃ (3.5–4.3). Duration of motility was longer when triggered in 1% NaHCO₃ (95–120 s) compared with 0.29% NaCl (69–107 s). Sperm vitality was not affected by any of the parameters tested and varied from 51% to 69% intact sperm. Brycon insignis sperm frozen in methylglycol combined with any of the extenders tested and using the methods described above yields motility above 57% and that should last long enough to fertilize oocytes.     

Comparative study of the culturable microbiota present in two different rearing systems,flow‐through system (FTS) and recirculation system (RAS), in a great scallop hatchery

A comparison of the culturable microbiota present in the different compartments of a great scallop (Pecten maximus) hatchery with two experimental production systems, FTS and RAS, throughout a cycle of larval rearing was carried out. All isolates obtained from broodstock gonads, larvae, tank water, biofilm, microalgae, UV‐treated water and biofilter in both systems at three sampling times were characterized by biochemical tests and identified by sequencing of the 16S rRNA gene. Some of the genera were found to be exclusive of broodstock gonads, such as Sinobacterium, Kordia or Microbulbifer, and differences between gonad microbiota before and after spawning were detected. The number of morphotypes obtained in water, larvae and biofilm was similar in both systems, as well as the behaviour of the microbial populations in almost all hatchery compartments, in which Vibrio, Neptuniibacter, Pseudoalteromonas and Shewanella were the most common genera. The diversity obtained was analysed using the principal component analysis (PCA) and Fisher's exact test, showing that the microbial communities present in the common compartments between FTS and RAS did not significantly differ. These results suggest that, at least from a microbiological point of view, the recirculation system could be a good alternative for the production of scallop larvae.     

Effect of salinity on the rearing performance of juvenile golden pompano Trachinotus ovatus (Linnaeus 1758)

Effect of rearing salinity on the performance of juvenile golden pompano Trachinotus ovatus (Linnaeus 1758) was studied under a laboratory condition. Fish growth, survival, RNA/DNA ratio, pepsin activity, α‐amylase activity and FCR were used as evaluation criteria. The growth and RNA/DNA ratio were significantly affected by the rearing salinity. High growth rate and RNA/DNA ratio were observed when fish were reared at the salinity of 34‰. The pepsin activity of fish was not significantly affected by the rearing salinity. However, the α‐amylase activity of fish was significantly affected by the rearing salinity. The α‐amylase activity of fish reared at the salinity of 10‰ was significantly lower than fish cultured at the salinity of 34‰. Rearing salinity can significantly affect the FCR of juvenile golden pompano. The FCR of fish cultured at the salinity of 10‰ was 5‐times higher than the FCR of fish reared at 34‰. Results from the present study indicate that juvenile golden pompano can be reared above 26‰ without affecting fish performance, and the salinity of 10‰ may be too low to rear juvenile golden pompano as fish growth, RNA/DNA ratio and α‐amylase activity were reduced.     

Effects of 2-phenoxyethanol on survival of normal juveniles and malformed juveniles having lordosis or nonfunctional swimbladders of European sea bass (Dicentrarchus labrax L., 1758)

The objectives of this study were to evaluate the effects of 2‐phenoxyethanol (2‐PE), which is an anaesthetic, on survival rates of normal juveniles and malformed juveniles having lordosis or nonfunctional swim bladders of European sea bass (Dicentrarchus labrax L., 1758) and to establish the LC₅₀ (the concentration lethal to 50% of test animals at concentrations of 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4 and 4.5 mL L⁻¹) and LT₅₀ (the time lethal to 50% of test animals after 10‐, 20‐, 30‐, 40‐, 50‐ and 60‐min time periods) of 2‐PE at 19±0.5°C, salinity 38 g L⁻¹, pH 7.4–7.8 and dissolved oxygen >8 mg L⁻¹. Between concentrations of 0.05 and 0.25 mL L⁻¹, 2‐PE did not cause any mortality or toxicity on normal, lordosis and nonfunctional swimbladder juveniles of sea bass during the 60‐min exposure period. On the other hand, significance in each group fish in their mortality rates between concentrations of 0.30 and 0.45 mL L⁻¹ was observed (P<0.05). The nonfunctional swimbladder juveniles showed lower LC₅₀ than normal and lordosis juveniles respectively. Also, nonfunctional swimbladders juveniles showed lower LT₅₀ than normal and lordosis juveniles respectively. At concentrations of 0.30, 0.35, 0.40 and 0.45 mL L⁻¹, induction times were found to be significantly different among the three groups (P<0.05). Recovery times were not found to be significantly different in two groups at concentrations of 0.30 and 0.40 mL L⁻¹ (P>0.05). The toxic effect of 2‐PE on sea bass juveniles increased depending on the exposure times (P<0.05). The most suitable concentrations of 2‐PE were 0.30–0.35 mL L⁻¹ between minutes 10 and 30, although the normal juveniles can resist to 0.45 mL L⁻¹ of 2‐PE concentration for 20 min. The 2‐PE showed toxicity in relation to the concentrations and exposure time combinations among the three groups in the order; nonfunctional swimbladder fish >lordosis fish >normal fish.     

Effects of dietary L‐carnitine level on growth performance,body composition and antioxidant status in beluga (Huso huso L. 1758)

A 17‐week feeding trial was carried out to evaluate the effects of dietary L‐carnitine level in beluga, Huso huso. A total of fish averaging 1247 ± 15.6 g (mean ± SD) were randomly distributed into 18 fibreglass tanks, and each tank holding 10 fish was then randomly assigned to one of three replicates of six diets with 50, 150, 350, 650, 950 and 1250 mg L‐carnitine kg^?1 diet. At the end of 17 weeks of feeding trial, average weight gain (WG), feed efficiency (FE), protein efficiency ratio (PER) and condition factor (CF) of fish fed 350 mg kg^?1 diet were significantly (P < 0.05) higher than those of fish fed 50, 150, 950 and 1250 mg kg^?1 diets. WG, FE, PER and CF of beluga fed 650 mg kg^?1 diet were also significantly higher than those of fish fed 50, 950 and 1250 mg kg^?1 diets. Whole body and muscle protein were significantly improved by the elevation of dietary L‐carnitine level up to 350 mg kg^?1. Liver superoxide dismutase and glutathione peroxidase activities of fish fed 350 and 650 mg kg^?1 diets were significantly higher than those of fish fed 50, 950 and 1250 mg kg^?1 diets. The dietary L‐carnitine level of 350–650 mg kg^?1 diet could improve growth performance, feed utilization, protein‐sparing effects of lipid, antioxidant defence system and reproductive success. Polynomial regression of WG suggested that the optimum dietary L‐carnitine level was 480 mg kg^?1 diet. Therefore, these results may indicate that the optimum dietary L‐carnitine could be higher than 350 but <650 mg kg^?1 diet in beluga reared in intensive culture conditions.     

Exploring connectivity between spawning and nursery areas of Mullus barbatus (L., 1758) in the Mediterranean through a dispersal model

Connectivity between spawning and nursery areas plays a major role in determining the spatial structure of fish populations and the boundaries of stock units. Here, the potential effects of surface current on a red mullet population in the Central Mediterranean were simulated using a physical oceanographic model. Red mullet larvae were represented as Lagrangian drifters released in known spawning areas of the Strait of Sicily (SoS), which represents one of the most productive demersal fishing‐grounds of the Mediterranean. To consider the effect of inter‐annual variability of oceanographic patterns, numerical simulations were performed for the spawning seasons from 1999 to 2012. The main goal was to explore connectivity between population subunits, in terms of spawning and nursery areas, inhabiting the northern (Sicilian‐Maltese) and southern (African) continental shelves of the SoS. The numerical simulations revealed a certain degree of connectivity between the Sicilian–Maltese and the African sides of the SoS. Connectivity is present in both directions, but it is stronger from the Sicilian–Maltese spawning areas to the African nurseries owing to the marine circulation features of the region. However, because the majority of the larvae are transported to areas unsuitable for settlement or outside the SoS, the dispersal process is characterized by a strong loss of potential settlers born in the spawning areas. These results are in agreement with the low genetic heterogeneity reported for this species in the Mediterranean Sea and support the existence of a metapopulation structure of red mullet in the SoS and the adjacent areas.     

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu,Ethiopia

This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m^?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day^?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m^?3. The gross yield (4.5–20.55 kg cage^?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m^?3 cage for larger size fish demand in a short period and 200 fish m^?3 for higher gross production with supplementary feed.