Comparison of stress responses in wild and captive winter flounder (Pseudopleuronectes americanus Walbaum) broodstock

Chronic stress is responsible for many problems occurring in fish holding facilities, such as increased susceptibility to disease, reduced growth rate and suppression of the immune response. The goal of this study was to verify if wild winter flounder (Pseudopleuronectes americanus Walbaum) suffer from chronic stress when kept several months in captivity. We hypothesized that winter flounder not subjected to chronic stress in captivity would have similar or higher condition indices and similar stress response compared to fish from the wild. Our results showed that the condition index of winter flounder kept in captivity was higher (1.50) than those from the wild (1.33) even after one year of captivity. The intensity of the acute stress response following short‐term exposure to air was similar between wild and captive fish (no significant interaction between the factors ‘stress’ and ‘origin of the fish’). Body water content (an indicator of energy reserves) was lower (76.1%) compared to wild fish (79.8%) after one year of captivity, suggesting that the winter fast had been less energetically demanding in captive fish. These results indicate that no chronic stress was present in captive fish. On the other hand, the mortality during captivity was around 30%, which is high for the aquaculture industry. Further work to address this problem is required.     

Influence of gonadotropic hormone-releasing hormone analog (GnRH-A) on plasma sex steroid profiles and milt production in male winter flounder,Pseudopleuronectes americanus (Walbaum)

The effects of gonadotropic hormone-releasing hormone analog (GnRH-A) treatment on the onset and duration of increases in plasma sex steroids and milt production (milt volume and number of spermatozoa) were investigated in prespawning male winter flounder. After treatment of maturing males during the winter with a single injection of either 20 or 200 g/kg [D-Ala⁶, Pro⁹-NHEt]LHRH (GnRH-A), plasma levels of testosterone and 11-ketotestosterone were increased within 12h and the steroid hormone levels remained elevated for long periods lasting several days. The androgenic steroid response of males was delayed after the administration of a lower dose of GnRH-A (2 g/kg). Although a single GnRH-A injection in December or January advanced the onset of spermiation in some males, only small amounts (<50 l) of milt could be collected. By March, all males were in spermiating condition following GnRH-A treatment; however, significant increases in sperm production, particularly increases in milt volume, occurred in fish twice treated with GnRH-A.Part of this work presented at the First Symposium of Fish Endocrinology, Edmonton, Alberta, Canada June 1988 and the Satellite Symposium on Applications of Comparative Endocrinology to Fish Culture, Almuñecar, Granada, Spain May 1989     

Bacterial colonization of winter flounder Pseudopleuronectes americanus fed live feed enriched with three different commercial diets

The proliferation of bacteria in intensive aquaculture systems may be responsible for poor growth and mass mortality of marine fish larvae. Essential fatty acids provided in the diet could protect larvae by modulation of the immune response via arachidonic acid (AA) and eicosapentaenoic acid (EPA). Winter flounder Pseudopleuronectes americanus larvae were fed rotifers Brachionus plicatilis enriched with three commercial diets containing different fatty acid profiles. Bacterial colonization on the gills and skin and in the intestinal lumen was evaluated at the end of the rotifer feeding period (day 26), and growth was surveyed until metamorphosis. At 26 days post hatching, larvae fed rotifers containing the higher AA content and with a higher docosahexaenoic acid (DHA) to EPA ratio showed better growth and the lowest bacterial colonization of the intestinal lumen compared to larvae fed rotifers with the lowest AA and DHA : EPA levels. AA had been selectively incorporated into the polar lipids of larvae fed the rotifers enriched with the three diets. This is the first study in winter flounder larvae to report a link between different commercial rotifer enrichments and bacterial density in intestinal lumen.     

Early weaning of winter flounder (Pseudopleuronectes americanus Walbaum) larvae on a commercial microencapsulated diet

Like most small marine fish larvae, the stomachs of winter flounder Pseudopleuronectes americanus are undeveloped at first feeding and have relatively reduced digestive capacity. This work was undertaken to test whether larvae at the onset of stomach differentiation (larval size about 5.5 mm) could be early weaned onto a commercial microencapsulated diet. We assessed the effect of early weaning by first comparing growth performance (standard length, total protein content and age at metamorphosis) of larvae fed enriched live prey from first feeding to a size of 5.5 mm and then reared on three different feeding regimes until metamorphosis: (1) live prey (LP) as a control group; (2) mixed feeding of live prey and microencapsulated diet (LP‐ME); (3) exclusively microencapsulated diet (ME) after fast weaning over 4 days (to a larval size of 6.2 mm). No differences were observed between larval development in the two first groups, which began metamorphosis at 40 days old. The larvae of the third group showed significantly slower growth that resulted in a delay of 4 days in the onset of metamorphosis. Differences in live prey availability between the treatments and the short transition period to allow the larvae to adapt to the new diet were identified as possible contributing factors to the slower growth and to the delay in metamorphosis of early weaned larvae. In a second experiment, the transitional weaning period was increased until the larvae were 6.6 mm in length. Weaning at that size resulted in no slowing of growth or delay in metamorphosis, suggesting that the feeding schedule was adequate.     

The development of a sperm cryopreservation protocol for winter flounder Pseudopleuronectes americanus (Walbaum): evaluation of cryoprotectants and diluents

Three cryoprotectants (dimethyl sulphoxide, propylene glycol and glycerol) and two diluents (sucrose based and saline based) were mixed (9 parts diluent–1 part cryoprotectant) factorially to produce six extenders that were tested to develop an effective sperm cryopreservation protocol for winter flounder Pseudopleuronectes americanus (Walbaum). Sperm were diluted 1:3 with each extender and frozen by flotation on liquid nitrogen before being submerged and stored for 30 days. Sperm left unfrozen in each extender for 20 min showed no toxic effects on motility. Extenders containing propylene glycol (PG) as cryoprotectant yielded higher post‐thaw sperm motilities than those containing dimethyl sulphoxide (DMSO) or glycerol. The sucrose‐based diluent performed better than the saline‐based diluent when DMSO was used as cryoprotectant, but there were no differences in post‐thaw motility between diluents for the other cryoprotectants. Activating sperm with ovarian fluid and sea water instead of sea water alone had no effect on post‐thaw motility. In fertilization trials, no differences were observed between any of the extenders and fresh milt when milt, eggs and sea water were left in contact for 1 h. When sperm were forced to compete for eggs by reducing contact time to 20 s, fertilization results followed those of sperm motility rates. Percentage hatch and morphology of larvae at hatching did not differ for eggs fertilized by cryopreserved and fresh sperm. This study represents the first reported successful attempt at cryopreserving winter flounder sperm and should improve gamete and broodstock management protocols for this species.     

Evidence for the presence of a viral non-lymphocystis type disease in winter flounder, Pseudopleuronectes americanus (Walbaum), from the north-west Atlantic

Abstract. A non-lymphocystis type disease associated with virus particles has been documented in winter flounder, Pseudopleuronectes americanus (Walbaum), taken from a small estuary in Conception Bay, Newfoundland. The papillomatosis-type lesions found on the dorsal surface of the fish contained numerous electron-dense particles, approximately 30 nm in diameter. A number of lines of evidence, including cytochemical studies, indicated that the particles were not glycogen but virions. Sensitivity to deoxyribonuclease enzyme treatment and the presence of crystalline viral'factories' in the nuclei of infected cells further suggested that the particles were small DNA virions. Characteristics including nucleic acid composition, particle size, site of multiplication and the lack of an envelope indicate that this fish virus is similar to the Papovaviridae and Parvoviridae families of mammalian viruses. Lymphocystis is common in flatfish populations along the Newfoundland and Labrador coasts of the N.W. Atlantic, but this is the first record of flatfish infection with a small DNA virus.     

Trichodina murmanica (Ciliophora) and Gyrodactylus pleuronecti (Monogenea) parasitizing hatchery-reared winter flounder, Pseudopleuronectes americanus (Walbaum): effects on host growth and assessment of parasite interaction

Winter flounder, Pseudopleuronectes americanus, caught in Passamaquoddy Bay, New Brunswick, Canada, and held captive under crowded conditions, developed mixed infections of Trichodina murmanica Polyanski, 1955 (Ciliophora) and Gyrodactylus pleuronecti Cone, 1981 (Monogenea). A protocol involving sequential sieving was used to separate the two species of parasites and produce viable experimental baths. Replicate groups of juvenile, hatchery-reared flounder received one of the following treatments: mixed bath of G. pleuronecti and T. murmanica , bath of G. pleuronecti, bath of T. murmanica or parasite-free (controls). The abundance of both parasites correlated negatively with condition factor of the flounder ( r =−0.354, P  < 0.001 for Trichodina ; r =–0.205, P  < 0.05 for Gyrodactylus ). During the periods of peak parasite abundance (1–2 weeks postinfection), the effect of the two parasite species was additive, as mean condition factor and the percentage change in weight were significantly lower (ANOVA, P  < 0.05) among fish with mixed infections compared to single infections or controls. The most common signs of tissue pathology were increased density of epidermal mucous cells on the fins and macrovesicular lipidosis of the hepatocytes. After a significant decline in parasite infrapopulations (3 weeks postinfection), infected fish resumed normal growth, indicating the observed effects were somewhat reversible.     

Survival of larval summer flounder Paralichthys dentatus on formulated diets and failure of thyroid hormone treatment to improve performance

Summer flounder is a new aquaculture species, the culture of which could be made simpler by the replacement, to the greatest extent possible, of live feed with formulated diets. Previous work has shown that development of the summer flounder stomach can be accelerated by treatment of the larvae with thyroid hormone. Two series of experiments were conducted. In the first experiment, 2-week feeding trials were conducted beginning with fish (which were not treated with thyroid hormone) 14, 21, 28, 35, or 42 days after hatch (DAH) to determine when they could begin to utilize commercially available formulated diets. In the second experiment, two groups of sibling larvae, one treated with thyroid hormone, the other not, were placed in similar 2-week feeding trials at 25, 30 or 35 DAH to test whether survival of thyroid hormone-treated larvae would surpass those of untreated larvae. The first series of experiments demonstrated that the larvae could not effectively utilize the formulated diets until 35 DAH. The second series of experiments indicated that thyroid hormone-treated larvae do not exhibit significantly greater survival than untreated larvae.     

Optimal dietary taurine level for growth of juvenile Japanese flounder Paralichthys olivaceus

The requirement for taurine in juvenile Japanese flounder Paralichthys olivaceus was determined by feeding diets containing various levels of taurine and cystine. Test diets supplemented with 0.5, 1.0 and 1.5% of taurine or with 0.5, 1.0 and 1.5% of L -cystine were prepared. The basal diet contained 55% protein from white fish meal. These diets were fed to juvenile Japanese flounder with an initial mean bodyweight of 0.9 g (total length (TL) 48 mm) for 5 weeks. Approximately 1.4% taurine content in the diet was required for optimum growth of juvenile flounder. A positive linear relationship was noted between the content of taurine accumulated in the muscle, liver and brain and the level of taurine in the diet. However, there was no increased taurine content in tissues of fish fed the cystine-supplemented diet. In contrast, the fish fed control and cystine-supplemented diets showed higher contents of cystathionine in the tissues. The concentration of cystathionine in tissues rapidly decreased with an increase of taurine in the diet. It was also observed that for each of the dietary groups, a trace amount of taurine was excreted. These results suggest that the taurine content in the diet affects the sulfur amino acid metabolism of juvenile Japanese flounder, and indicate that juvenile flounder are unable to biosynthesize taurine from cystine.     

Genetic characterization, morphometrics and gonad development of induced interspecific hybrids between yellowtail flounder, Pleuronectes ferrugineus (Storer) and winter flounder, Pleuronectes americanus (Walbaum)

Viable interspecific hybrids between yellowtail flounder (Pleuronectes ferrugineus, Storer) and winter flounder (Pleuronectes americanus, Walbaum) were produced by artificial insemination of yellowtail flounder eggs with winter flounder sperm. However, mean fertilization rate, hatching success and early survival up to 3 weeks post hatch were significantly lower than those of parental pure cross controls (P < 0.01). Overall, cytogenetic traits (karyological analysis and estimation of cellular DNA contents using flow cytometry) of hybrid flounder were intermediate between the two parental species. Microsatellite assay was used to distinguish the parental genomes in the hybrids; in most cases, one allele was specific to each of the parents. Morphometrics assessed by body proportions indicated that hybrids generally displayed a morphology intermediate between the maternal and paternal species. Interspecific hybrids exhibited abnormal and retarded gonad development in both sexes based on histological analysis of gonads from adult fish. The sterility of the hybrids presents a significant advantage for their use in aquaculture, as potential escapees would not be capable of reproducing in the wild and contaminating natural stocks.     

Effects of different dietary levels of L-ascorbyl-2-polyphosphate on growth and tissue vitamin C concentrations in juvenile olive flounder, Paralichthys olivaceus (Temminck et Schlegel)

This experiment was conducted to study the effects of different dietary levels of vitamin C, L‐ascorbyl‐2‐polyphosphate (ASPP), on growth and tissue vitamin C concentrations in juvenile olive flounder, Paralichthys olivaceus (Temminck et Schlegel). Fish were fed one of six semi‐purified diets containing an equivalent of 0, 25, 50, 75, 150, or 1500 mg ascorbic acid (AA) kg^?1 diet (C₀, C₂₅, C₅₀, C₇₅, C₁₅₀ or C₁₅₀₀) in the form of ASPP for 12 weeks. Weight gain (WG) and protein efficiency ratio (PER) of fish fed the C₀ diet were significantly lower than those of fish fed the other diets (P < 0.05), and WG and PER of fish fed the C₂₅, C₅₀ and C₇₅ diets were significantly lower than those of fish fed the C₁₅₀₀ diet (P < 0.05). Fish fed the C₀ diet exhibited vitamin C deficiency symptoms such as anorexia, scoliosis, cataract, exophthalmia and fin hemorrhage at the end of the 12‐week test. After 12 weeks of the feeding trial, AA concentrations from gill, kidney, and liver of fish fed the C₀, C₂₅, C₅₀ and C₇₅ diets were significantly lower than those of fish fed the C₁₅₀ and C₁₅₀₀ diets (P < 0.05). Based on broken line analyses for WG and PER, the optimum dietary levels of vitamin C were 91 and 93 mg AA kg^?1 diet respectively. These findings suggest that the dietary vitamin C requirement could be 93 mg AA kg^?1 diet to support reasonable growth, and greater than 150 mg AA kg^?1 diet may be required for AA saturation of major tissues for juvenile olive flounder under experimental conditions.     

Optimum dietary phosphorus level of juvenile Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> reared in the recirculating system

ABSTRACT:   An 8-week feeding trial was conducted to determine the optimum dietary phosphorus level of juvenile Japanese flounder Paralichthys olivaceus reared in the recirculating system. The basal diet containing 0.33% total phosphorus (TP) was supplemented with NaH₂PO₄·H₂O to provide 0.33, 0.51, 0.71, 0.94, 1.10 and 2.12% TP for the experimental diets. Fish averaging 2.0 ± 0.04 g (mean ± SD) were fed in triplicate groups with the experimental diets for 8 weeks. After 8 weeks, fish fed the 0.51% TP diet showed significantly higher weight gain (WG), feed efficiency (FE), specific growth rate (SGR), and protein efficiency ratio (PER) than those fed the 0.33% and 2.12% TP diets ( P  < 0.05). Meanwhile, no difference was observed in WG, FE, SGR and PER of fish fed the 0.51, 0.71, 0.94 and 1.10% TP diets. Fish fed the 0.33% TP diet showed phosphorus deficiency symptoms such as poor growth and a deformed head by the end of 8 weeks. Ash and phosphorus contents of bone increased with the increase of dietary phosphorus concentrations. anova test, the quadratic regression analysis, and the broken line analysis suggested that the optimum dietary phosphorus level could be between 0.45 and 0.51% TP for maximum WG in juvenile Japanese flounder.     

几种工业废水对牙鲆仔稚鱼的急性毒性及联合毒性作用

印染废水、电镀废水、农药废水都是常见的、易进入近岸海域的工业废水。本文通过室内实验,研究了这3种工业废水及其混合物对牙鲆仔稚鱼的急性毒性作用。结果表明,印染废水、电镀废水、农药废水及其混合物对牙鲆初孵仔鱼48hLC50(95％置信区间）和96h LC50（95％置信区间）分别为2．28％（1．39％－3．74％）、0．21％（0．18％－0．27％）、0．47％（0．37％－0．60％）及0．42％（0．07％－2．54％）和0．58％（0．15％－0．76％）、0．10％（0．04％－0．25％）、0．23％（0．18％－0．29％）及0．17％（0．12％－0．23％）;对牙鲆后期仔稚鱼48h LC50(95%置信区间）和96h LC50（95％置信区间）分别为2．95％（1．65％－5．29％）、0．22％（0．15％－0．31％）、0．71％（0．50％－1．01％）及0．77％（0．50％－1．19％）和0．69％（0．51％－0．93％）、0．14％（0．10％－0．20％）、0．38％（0．23％－0．61％及0．24％（0．16％－0．35％）。以对牙鲆仔稚鱼半致死浓度为指标,这几种工业废水的毒性顺序为电镀废水＞农药废水＞印染废水,初孵仔鱼较后期仔稚鱼对这些废水更为敏感。这些废水以等体积混合时,对初孵仔鱼和后期稚鱼的联合毒性作用表现为相加作用。     

Evaluation of optimum dietary protein-to-energy ratio in juvenile olive flounder Paralichthys olivaceus (Temminck et Schlegel)

An 8‐week feeding trial was conducted to estimate the optimum dietary protein to energy (P/E) ratio in juvenile olive flounder Paralichthys olivaceus. Eight experimental diets were formulated with two energy levels and four protein levels at each energy level. Two energy levels of 12.5 and 16.7 kJ g^?1 diets were included at crude protein (CP) levels of 25%, 30%, 35% and 45% with 12.5 kJ g^?1, and CP levels of 35%, 45%, 50% and 60% with 16.7 kJ g^?1. After 1 week of the conditioning period, fish initially averaging 8.1±0.08 g (mean±SD) were randomly distributed into the aquarium as groups of 15 fish. Each diet was fed on a dry‐matter basis to fish in three randomly selected aquariums at a rate of 3–5% of total wet body weight per day for 8 weeks. After 8 weeks of the feeding trial, weight gain (WG), feed efficiency ratio and specific growth rate of fish fed 45% CP with 16.7 kJ g^?1 energy diet were significantly higher than those from the other dietary treatments (P<0.05). WG of fish fed 12.5 kJ g^?1 energy diets increased with the increase of dietary protein levels. However, WG of fish fed 16.7 kJ g^?1 energy diets increased with the increase of dietary protein levels up to 45% CP and then decreased when fish fed 50% and 60% CP diets. Both dietary protein and energy affected protein retention efficiency and energy retention efficiency. Haemoglobin (Hb) of fish fed 35% and 45% CP diets with 12.5 kJ g^?1 energy were significantly high and not different from Hb of fish fed 45% and 50% CP diets with 16.7 kJ g^?1 energy. Haematocrit of fish fed 45% CP diet with 16.7 kJ g^?1 energy was significantly higher than those from fish fed 25% and 30% CP diets with 12.5 kJ g^?1 energy (P< 0.05). Based on the results of this experiment, we concluded that the optimum dietary P/E ratio was 27.5 mg protein kJ^?1 with diet containing 45% CP and 16.7 kJ g^?1 energy in juvenile olive flounder.     

Diurnal stream habitat use of juvenile Atlantic salmon, brown trout and rainbow trout in winter

Abstract  The diurnal winter habitat of three species of juvenile salmonids was examined in a tributary of Skaneateles Lake, NY to compare habitat differences among species and to determine if species/age classes were selecting specific habitats. A total of 792 observations were made on the depth, velocity, substrate and cover (amount and type) used by sympatric subyearling Atlantic salmon, subyearling brown trout and subyearling and yearling rainbow trout. Subyearling Atlantic salmon occurred in shallower areas with faster velocities and less cover than the other salmonid groups. Subyearling salmon was also the only group associated with substrate of a size larger than the average size substrate in the study reach during both winters. Subyearling brown trout exhibited a preference for vegetative cover. Compared with available habitat, yearling rainbow trout were the most selective in their habitat use. All salmonid groups were associated with more substrate cover in 2002 under high flow conditions. Differences in the winter habitat use of these salmonid groups have important management implications in terms of both habitat protection and habitat enhancement.     

Effects of dietary testosterone on growth and sex ratio in juvenile Atlantic salmon (Salmo salar)

Diets to which testosterone (1 or 10 ng/g diet) had been added were fed to juvenile Atlantic salmon (Salmo salar) for nine months beginning for months after hatching (Experiment 1) and upon completion of yolk absorption (Experiment 2) to determine the effects on growth, gonadal development, and sex ratio. Dietary testosterone at 10 ng/g fed to juvenile salmon at four months after hatching (Exp. 1) induced significant changes in condition factor (0.69±0.01) compared to controls (0.79±0.01) at the end of the test period. In both experiments, salmon treated with 10 ng/g diet induced a significantly higher percentage of male fish compared to controls. Dietary testosterone at 1 ng/g fed to juvenile salmon beginning four months after hatching induced significant increases in weight (18.95±0.99) and length (13.58±0.23) compared to controls (14.55±1.50 and 11.94±0.43, respectively). In Experiment 1 or 2, there was no apparent influence of dietary testosterone on precocious male sexual development. Dietary testosterone at 1 or 10 ng/g fed to juvenile salmon upon completion of yolk absorption (Exp. 2) induced no consistent changes in growth in juvenile Atlantic salmon. These studies indicate that low levels of dietary testosterone may influence physiological responses in juvenile Atlantic salmon dependent upon timing of treatment.