Young Flounder Research Articles

Effects of food availability on growth performance and immune-related gene expression of juvenile olive flounder (Paralichthys olivaceus)

Unfavorable environmental conditions and inappropriate culture practices have increased the vulnerability of cultured fish to disease infection. Up to date many studies have aimed to determine a feeding regimen to maximize productivity; however, very little information on immune responses of cultured fish in response to underfeeding or overfeeding is available. Therefore, a preliminary study was conducted to evaluate effects of graded feeding levels (i.e., food availability) on growth performance and immune-related gene expression of juvenile olive flounder (Paralichthys olivaceus). Six different feeding rates including 1, 4, 7, 10, 13, and 16% body weight per day (BW/d) were randomly assigned to three replicate tanks stocking 150 fish (average initial body weight: 0.27 ± 0.02 g; mean ± SD) per tank. A feeding trial lasted for two weeks. Based on the results of the weight gain, nutrient gain, and whole-body compositions and energy content, the feeding rate of 10%, 13%, and 16% BW/d resulted in high nutritional status, whereas the feeding rate of 1% and 4% BW/d resulted in low nutritional status. Intermediate nutritional status was observed at the feeding rate of 7% BW/d. In the given rearing conditions the optimum feeding rate resulting in the maximum growth was estimated to be 11.9% BW/d based on the quadratic broken-line regression model, chosen as the best-fit model among the tested models. Expression of immune-related genes including IL-8 and IgM was significantly down-regulated in the flounder fed at 1% BW/d in comparison to those fed at 7% BW/d. Interestingly, expression of these genes in the flounder fed at 10%, 13%, and 16% BW/d was relatively down-regulated in comparison to that of the flounder fed at 7% BW/d. Although no statistical difference was detected, overall response patterns of other immune-related genes, including TLR3, polymeric Ig receptor, lysozyme C-type, GPx, SOD, and Trx followed what IL-8 and IgM exhibited in response to the various feeding rates. Given the current challenges in aquaculture of the flounder our findings suggest to prohibit underfeeding or overfeeding (i.e., ad-libitum feeding) when culturing the young flounder.

Nitrite Toxicity and Methemoglobin Changes in Southern Flounder, Paralichthys lethostigma, in Brackish Water

AbstractThis study was performed to estimate the nitrite toxicity to southern flounder, Paralichthys lethostigma, in brackish water (7.5 ppt of salinity). For a LC50 test, 20 fingerlings (5.7 ± 0.4 cm) in each aquarium (15 L) were exposed to the concentrations of 0, 1, 5, 10, 15, 30, 60, 120, and 240 mg NO2−‐N/L in duplication for 10 d. Median lethal concentration at 96 h (96‐h LC50) was calculated as 81.6 mg NO2−‐N/L. For a verification test, young flounder (164.2 ± 9.1 g) were exposed to a simulated culture condition in recirculating systems (1000 L). Sodium nitrite was not added to control system, whereas it was added to Treatment system 1 (TS 1) and Treatment system 2 (TS 2) to maintain nitrite concentrations of 20 and 30 mg NO2−‐N/L, respectively. The plasma nitrite concentrations of the young flounder in TS 1 and TS 2 were 4.5 and 6.6 mg NO2−‐N/L, respectively, after 2 wk. At this time, the methemoglobin percentages in TS 1 and TS 2 reached 85.8 and 89.7%, and survival rates were 37.5 and 25.0%, respectively. The results of these tests indicate that southern flounder do not concentrate nitrite in blood from the environment, but they seem to be more sensitive to nitrite compared with other species that do not concentrate nitrite.

The timing of puberty in cultured female yellowtail flounder, Limanda ferruginea (Storer): Oogenesis and sex steroid production in vivo and in vitro

This study examines puberty in female yellowtail flounder, correlating macroscopic, histological and endocrine parameters at the gonadal level. Short-term ovarian tissue incubations were used to study estradiol-17β production in relation to oogenic stage. Examining 2 year classes of young flounder demonstrated that cultured females retain phenotypic plasticity in reproductive age with pubertal onset occurring in one-year, two-year and three-year-olds. Immature ovaries were steroidogenic and capable of responding to gonadotropic stimulation. Endocrine puberty in females was detected by a peak in estradiol-17β production during the cortical alveolar oocyte stage prior to any ovarian evidence of vitellogenesis. Puberty, once initiated, proceeded to ovulation within 8 to 12 months; vitellogenic oocyte development followed the group synchronous pattern. Estradiol-17β was clearly the dominant of the two measured plasma hormones during pubertal onset and throughout vitellogenesis. Plasma testosterone was consistently detectable at low levels by mid-to late-vitellogenesis. Ovaries showed the highest sensitivity to gonadotropic stimulation in vitro during late-vitellogenesis. Variable plasma levels in both estradiol-17β and testosterone occurred in preovulatory and ovulating females during the captive spawning period. Together the results show that yellowtail flounder can mature at a young age and small size when culture conditions permit. In addition, the early sensitivity to gonadotropin by the immature ovaries may be an important physiological determinant for the timing of puberty in this species.

Effects of tributyltin on the immune system of Japanese flounder ( Paralichthys olivaceus)

Effects of tributyltin (TBT) which has been used for antifouling paint of ship's hulls and fishing nets on the immune system in Japanese flounder ( Paralichthys olivaceus) were investigated. After short-term exposure to a high level of TBT, leucocytes in the head kidney from 1-year-old flounder were examined for the proportion of neutrophils in total leucocytes. Also examined were their respiratory burst activities using flow cytometry, the reduction of nitroblue tetrazolium (NBT) and lysozyme activities. Furthermore, long-term exposures to a relatively low level of TBT using young flounder were also carried out. The proportion of neutrophils in total leucocytes prepared from head kidney in each fish exposed to TBT at 20 μg/L for 5 days and the reduction of NBT by leucocytes prepared from the same experimental conditions increase compared to the control group. The contents were 42.0 ± 6.8 and 52.5 ± 6.3%, respectively. Significant differences of the NBT reduction were observed between 0 and 20 μg/L TBT exposure groups. On the other hand, the respiratory burst activity of cells in the exposure group clearly showed a tendency to decrease compared to the control group. Furthermore, high level of TBT also inhibited lysozyme activity which plays an important role for the bacteriocidal procedures. However, similar results were not obtained in the exposure group with a relatively low level of TBT. To determine the immunotoxic effects of TBT, infection experiments using pathogens which are naturally occurring should be further investigated.

Long-term exposure of several marine benthic animals to static magnetic fields.

Electrical currents in underwater sea cables could induce magnetic fields. The sea cables lie on or within the sea bottom and this is the living area for many invertebrate and vertebrate species. North Sea prawn Crangon crangon (Crustacea, Decapoda), round crab Rhithropanopeus harrisii (Crustacea, Brachyura), glacial relict isopod Saduria entomon (Crustacea, Isopoda), blue mussel Mytilus edulis (Bivalvia), and young flounder Plathichthys flesus (Pisces) were exposed to a static magnetic field (MF) of 3.7 mT for several weeks. The results showed no differences in survival between experimental and control animals. Mussels M. edulis were kept under static magnetic field conditions for 3 months during their reproductive period in spring. The determination of gonad index and condition index revealed no significant differences to the control group.

Experimental Coinfection with Aquabirnavirus and Viral Hemorrhagic Septicemia Virus (VHSV), Edwardsiella tarda or Streptococcus iniae in Japanese Flounder Paralichthys olivaceus.

Japanese flounder Paralichthys olivaceus, farmed or wild, are ofoen infected with aquabirnavirus (ABV) but the virus does not usually exhibit pathogenicity to the fish under usual experimental conditions. The present study investigated the experimental coinfection in flounder with ABV and three flounder pathogens, i.e. viral hemorrhagic septicemia virus (VHSV), Edwardsiella tarda and Streptococcus iniae. When young flounder were injected with ABV (106.5 TCID50/fish) and subsequently (1 week later) injected with VHSV (106.7 or 104.7 TCID50/fish), higher survival rates were obtained in these flounder compared with those in fish infected with VHSV alone. In contrast, higher mortalities occurred in the flounder dually injected with ABV (106.8 TCID50/fish) and E. tarda (1.4 × 101 CFU/fish) or S. iniae (1.7 × 102 CFU/fish) at a 1 week-interval than those in fish infected with bacteria alone. These results indicate that the primary ABV infection in flounder suppresses the secondary viral infection but facilitates the secondary bacterial infections.

Metabolism, food consumption and growth of plaice ( Pleuronectes platessa) and flounder ( Platichthys flesus) in relation to fish size and temperature

Daily rates of oxygen consumption, food consumption and growth of plaice ( Pleuronectes platessa) and flounder ( Platichthys flesus) have been measured in the laboratory at various constant temperatures. Oxygen consumption was related to body weight of the fish as a power function, with a weight exponent of between 0.71 and 0.85. No significant effects of temperature or feeding on this exponent were found. Flounder showed a significantly higher metabolic rate and a higher temperature coefficient for metabolism than plaice. Maximum daily rates of food consumption and the weight increment of fish fed with excess rations of fresh mussel meat could also be related to fish weights by means of power functions. For plaice these exponents decreased from about 0.9 at low temperatures (2–6 C°) to about 0.7 at high temperatures (18–22°C). Such a temperature effect on the weight exponent indicates that small juvenile fish eat more and grow faster at higher temperatures than do large older fish, and that large fish do better at low temperatures. After scaling of daily food consumption and growth in proportion to metabolic weights of the fish (W 0.78), feeding and growth at different fish sizes and temperatures can be compared and temperature-growth rate models can be used for investigations of feeding in natural populations. Compared to plaice, young flounder ate more and grew faster at higher temperatures (> 14°C). This may partly explain the preference of flounder for the shallower parts of coastal areas and estuaries, where summer temperatures and food densities are higher. Energy budgets of young plaice and flounder fed with excess rations of mussel meat indicate that at least 29% of the food energy is used for metabolism while about 37% of the food energy is converted into growth. The net conversion efficiency was estimated at 0.45 for food and growth in units of ash-free dry weight, and at 0.53 for food and growth in energy units. Analysis of the energy budget showed that the assimilated physiologically useful food energy is divided almost equally over metabolism (42–47%) and growth (53–55%). It is suggested that flatfish spend relatively less energy in swimming and therefore convert more food energy into growth than (pelagic) roundfish.

Nitrogenous Excretion of Juvenile and Young Japanese Flounder.

Measurements of the rate of nitrogenous excretion were carried out on fed and starved Japanese flounder of 1.5 to 6.5g (juvenile), and 15 to 91g (young) in body weight at 20°C. Ammonia-N and urea-N excretion of the starved juvenile flounder were 0.76±0.20mg-N and 0.09±0.03mg-N/100g/h, and those of the young flounder were 0.23±0.05mg-N and 0.07±0.03mg-N/100g/h, respectively. Immediately after feeding, the rates of ammonia-N excretion per hour of both juvenile and young flounder became 2 to 3 times higher than those of the starved fish, and these elevated rates continued for more than 12h. In contrast to ammonia-N excretion, the rate of urea-N excretion per hour of the fed fish showed a major peak during the period of 6-12 or 12-24h after feeding. In juvenile and young Japanese flounder fed on a pelleted diet containing 7.5% nitrogen at average rations of 3.0 and 1.3%, respectively, it is estimated that 23 and 21% of the consumed nitrogen was excreted as ammonia-N, 3 and 4% as urea-N, respectively, and about 13% as faeces-N within 24h after feeding.

ヒラメ幼魚から分離されたＥｄｗａｒｄｓｉｅｌｌａ ｔａｒｄａ

In October 1982, a bacterial disease occurred among cultured young flounder, Paralichthys olivaceus, in the Kurida Bay, Kyoto Prefecture. The diseased fish showed abdominal inflation and accumulation of ascites.Bacteria isolated from the diseased fish were identified as Edwardsiella tarda.The pathogenicity of the isolate for flounder and yellowtail, Seriola quinqueradiata, was proved positive by intra-peritoneal and/or intramuscular injections.

White Spotting in the 1959 Year-Class of Georges Bank Winter Flounder, Pseudopleuronectes americanus (Walbaum)

Abstract Winter flounder with white spots on the eyed side were unusually common among fish of the 1959 year-class caught on north-central Georges Bank in 1964, 1965, and 1966. The water on eastern Georges Bank was considerably colder than normal in the spring of 1959 when young flounder were developing. A possible relationship between lowered development temperature and white-spotting is suggested.

About Fishes' Heads

About Fishes' Heads