Some observations of the effects of body weight, temperature, meal size and quality on gastric emptying time in the turbot, Scophthalmus maximus (L.) using radiography

The gastric emptying time (G.E.T.) in turbot was investigated using X-radiography and was found to decrease with temperature. Small fish processed a given ration, expressed as percent body weight, faster than large fish (G.E.T. was found to be proportional to (fish weight)^0.364). Large meals in a given fish were processed at a faster rate than small meals. Gastric emptying rate (G.E.R.) was found to be proportional to (meal size g)^0.613 at 8° C and (meal size g)^0.788 at 19° C. These exponents are in agreement with a recently proposed model relating G.E.T. and G.E.R. to meal size (Fänge & Grove, 1978). Large fish emptied a meal of given absolute size from the stomach at a faster rate (g h⁻¹) than small fish. Experimental meals diluted with kaolin were evacuated in significantly less time than a control diet, suggesting that turbot may adjust feeding rates when food quality varies.     

Immunomodulatory effects of nisin in turbot (Scophthalmus maximus L.)

In the present work, the effect of nisin on the non-specific immune response of turbot (Scophthalmus maximus L.) leukocytes has been studied both in vitro and in vivo. The head kidney macrophage chemiluminescent (CL) response was significantly increased with intermediate doses of nisin (2.5 and 0.025 micro g ml(-1)) whilst the higher dose (25 micro g ml(-1)) significantly decreased the response after 24h incubation. When the incubation time was extended to 72 h, significant differences between doses were observed and the lower nisin concentration (0.025 micro g ml(-1)) appeared to be the optimum dose for increasing the CL response. The phagocytic activity of HK macrophages was also affected by in vitro nisin treatments. Nisin at 0.25 micro g ml(-1) and 0.025 micro g ml(-1) significantly stimulated the response after 24 and 72 h incubation respectively. Nitric oxide (NO) production by HK macrophages was not influenced by any nisin concentration employed for 24 or 72 h incubationsIn vivo, one week post injection, a slightly but non-significant stimulation of the CL response was observed with the lowest nisin concentration (0.0025 micro g fish(-1)). NO in serum and serum antibacterial index were not significantly affected by nisin treatments. On the other hand, lysozyme concentration in serum was significantly augmented with the lowest nisin dose (0.0025 micro g fish(-1)).The antibacterial effect of nisin against the fish pathogenic bacteria Carnobacterium piscicola (CECT 4020) was also demonstrated in vitro.     

Double ovulatory cycles in some captive turbot, Scophthalmus maximus L.

The hypothesis that the paired ovaries of turbot, Scophthalmus maximus , ovulate alternately was tested and rejected as a possible explanation for the double ovulatory cycles found in some captive turbot. It is suggested that these double cycles are caused by variation patterns in the hormone-release cycles of individual females.     

The hepato-renal syndrome in cultured turbot (Scophthalmus maximus L.)

The histopathology of biliary hyperplasia and renal calcinosis, associated with infections of two parasites, Myxidium incurvatum and Rhabdospora thelohani , is described in turbot, Scophthalmus maximus (L.), from Scottish marine fish farms and wild populations. Liver and kidney lesions were divided into four, and parasite infections into five grades of severity. A few of the fish examined were not parasitized, but every one showed some evidence of pathological change, even the apparently normal individuals from all populations. Although there is a positive association between the parasitic and pathological data, parasitism is not considered to be the principal cause of either the hepatic or renal lesion; the evidence suggests rather a secondary opportunist role for the parasites. The general severity of the condition in captive stocks suggests that the cause may lie in the fundamentals of present techniques of turbot husbandry, but no specific agent has been identified. A case is put forward for considering Rhabdospora to be a parasite rather than a specialized host cell.     

Ontogeny of enzymatic activities in fed and fasting turbot, Scophthalmus maximus L.

The presence and localization of acid and alkaline phosphatase, non-specific proteases, aminopeptidase, amylase, non-specific esterase and lipase was investigated by histoenzymologic methods in fed and fasting turbot from day 1 to day 40 post-hatching and compared with published data. Alkaline phosphatase and aminopeptidase activities were delected at day 1 in the distal region of the developing digestive tube. At day 3 (opening of the mouth) aminopeptidase and alkaline phosphatase activities were found all along the intestine. Sites of non-specific esterase and protease activities became apparent in the digestive tract at days 2 and 3 respectively. Amylase was present in the exocrine pancreas at day 3 and in the lumen of the intestine at day 4. Acid phosphatase was active in the cellular structure surrounding the yolk stores and in the lipid droplets at day 1 and in the intestinal epithelium at day 3. Lipase was found at day 15 when the larvae metamorphose into juveniles.
All the investigated enzymes were detected in fasting animals, except for lipase. However, the intensities of the enzymatic activities were weaker in the fasting specimens relative to the fed specimens between days 7 and 10.     

Ovulatory rhythms and over-ripening of eggs in cultivated turbot, Scophthalmus maximus L.

The aim of this study was to investigate ageing of ovulated eggs retained in the ovarian lumen of captive turbot, Scophthalmus maximus L., prior to handstripping. The ovulation times of egg-batches were determined by catheterization, handstripping and plotting the percentage fertilizations and hatches of resulting eggs against time. The catheterization experiments showed that eggs age and change appearance rapidly after ovulation. The stripping method demonstrated that freshly-ovulated eggs showed greater than 90% fertilization and up to 97% hatch, but ovulated eggs retained in the ovary lumen for 1 day before stripping gave 0% hatch. The turbot showed precise ovulatory rhythms. The time between ovulations varied between individuals but was constant for any one female, making it possible to predict future ovulation times. Three of the females studied had ovulatory periods of alternating length.     

Visual cues determining prey selection by the turbot, Scophthalmus maximus L.

By presenting juvenile turbot, Scophthalmus maximus L., with models and natural prey, Crangon crangon , standardised for size, some of the visual characteristics that elicit a predatory response have been determined. By far the most important stimulus was overall body movement, but appendage movements of the crustacean and a ratio of vertical to horizontal dimensions lower than about 1:5 were also of significance. The body shape of a prey was not of great importance. Evidence was obtained for the heterogeneous summation of stimuli.     

The cellular composition of the blood and haematopoietic organs of turbot Scophthalmus maximus L.

The cellular composition of the blood, anterior kidney, spleen and thymus of turbot Scophrhalmus maximus L., aged 1 + was determined. Ninety-four per cent of blood cells belonged to the erythrocyte lineage of which 82% were mature erythrocytes. The leucocytes, which represented 4.5% of the blood cells, were mainly lymphocytes (50%). The presence of crythroblasts in the anterior kidney and the spleen demonstrated an erythropoietic activity in both organs. However, this activity appeared to be prevalent in the spleen which also appeared to act as a storage zone for erythrocytes and as the centre point for thrombopoiesis. Although 96% of the anterior kidney cells were leucocytes, the number of white cells per gram of organ was higher in the spleen.     

Gastric evacuation in horse mackerel. I. The effects of meal size, temperature and predator weight

Gastric evacuation experiments were performed on horse mackerel Trachurus trachurus. A nearly full matrix experimental design with respect to the variables predator weight (<10–400 g) meal size (up to 7·8% body weight) and temperature (10–20°) was covered with 0-group smelt Osmerus eperlanus as prey. A general evacuation model without meal size as a variable was fitted to the data on wet weights as well as on dry weights by means of non-linear regression technique. Two methods of data transformation, relative data and square root transformation, were applied to improve variance homogeneity. The most reliable model fit was achieved on dry weight data applying the square root transformation technique: where S_t=stomach content (g wet weight) at time t after ingestion, S₀=the initial meal size, W =predator (g wet weight), and T =temperature. The estimated coefficient of the exponential temperature function, δ=00·032, corresponds to a Q ₁₀ value of 1·4 which is outstandingly low in comparison with results on other species. However additional experiments to determine maximum daily food rations indicated that appetite in contrast to gastric evacuation is strongly temperature dependent.     

The ecology of young turbot, Scophthalmus maximus (L.), at Borth, Cardiganshire, Wales

The ecology of 0- and 1-group turbot was studied at Borth, Cardiganshire, during the years 1966–68. Newly-metamorphosed turbot appeared in the surf zone from July to October, Abundance during the period September 1967 to May 1968 decreased at an average rate of 25% of the sampled population per month. Fish of the 1966 year-class grew from a mean length of 4.5 cm in September 1966 to 14.4 cm in October 1967. Growth was fast in the spring and summer, slowing during the late autumn and winter. The most important food items of 0- and 1-group turbot by percentage occurrence and dry weight were polychaetes and mysids. The daily food intake of 0-group turbot in September 1967 was estimated as 2.5 % of the body weight per day.     

Gastric evacuation in plaice, Pleuronectes platessa L.: effects of temperature and meal size

The pattern of gastric evacuation in the plaice can be described by a single curve of curvilinear form, relating the amount of food remaining in the stomach and the post-prandial time. This curve can be transformed to linear form, conforming to a volume dependent model of evacuation. This allows the calculation of the time for complete evacuation of the stomach. The shape of the gastric evacuation curve is unchanged by the size of the meal fed. With increase in temperature however, the form of the curve does change, resulting in shorter times for complete evacuation.     

Quantitative and qualitative studies of the bacterial microflora of turbot, Scophthalmus maximus L., gills

Populations of aerobic heterotrophic bacteria, occurring on the gills of healthy turbot, were estimated using a dilution plate technique. From a comparison of 18 media, the highest counts, i.e. 7.0 × l0⁵ g⁻¹, were obtained after incubation at 15–25°C on a specifically formulated medium which contained low quantities of beef extract, casein, tryptone and yeast extract. These bacteria were equated with Asticacaulis sp., Hyphomicrobium sp., Janthinobacterium lividum, Prosthecomicrobium sp., Pseudomonas fluorescens and Vibrio sp. Evidence from scanning electron microscopy pointed to a general lack of intimate colonization of exposed areas of the gill. Instead, micro-organisms colonized protected niches, such as the clefts between lamellae and in secluded areas on the arches.     

Gastric evacuation in mackerel: the effects of meal size, prey type and temperature

Gastric evacuation experiments, performed with groups of Atlantic mackerel Scomber scombrus and three different prey species: sprat Sprattus sprattus , sandeel Ammodytes marinus and krill Meganectyphanes norwegicus , revealed a strong temperature effect on gastric evacuation ( Q ₁₀=4.l) and a curvilinear evacuation with a shape intermediate between the square root and the exponential model. From the experiments with krill, where no internal tagging was possible, the medians and upper quartiles of the stomach content distributions were analysed instead of individual data. From these experiments the evacuation rate of krill was 60% higher than that of sandeel. An additional simulation study confirmed that the use of medians results in more accurate estimates of the evacuation rates when compared to the arithmetic means.     

Effects of hyposmotic stress on exocytosis in isolated turbot, Scophthalmus maximus, hepatocytes

The effect of hyposmotic shock on exocytosis was examined in isolated hepatocytes of turbot, a marine flatfish, using the molecular probe FM1-43. Sudden exposure to a reduced osmolality caused an increase in cell exocytic activity related to the osmotic gradient between intra- and extracellular fluids. Cytoskeletal microtubules could contribute to this hyposmotic-induced exocytosis since colchicine inhibited the process. Protein kinase C, phosphatidylinositol-3 kinase, phospholipases A2, C and D could constitute key enzymes in the mechanism since their inhibition by specific agents altered the hyposmotic-induced exocytic activity. Moreover, arachidonic acid and derivates from the 5-lipoxygenase pathway as well as calcium could participate in the process. As regulatory volume decrease (RVD) exhibited by turbot hepatocytes following hyposmotic stimulation involves similar features, a potential role of exocytosis in volume regulation is suggested. In particular, exocytosis could serve RVD by contributing to ATP release since this latter process similarly appeared to be phospholipase D-dependent and related to the osmotic gradient. This study provides the first evidence of a volume-sensitive exocytosis that could aim at volume constancy in a marine teleost fish cell type.     

Gastric emptying and the return of appetite in juvenile turbot, Scophthalmus maximus L., fed on artificial diets

Gastric emptying time in Scophthalmus maximus , when fed friable artificial pellets based on fishmeal, is composed of two phases:
(a) a delay time (t_d) during which the meal forms a bolus and which shortens with temperature, and
(b) an emptying phase (duration t_end ) which varies with meal size ( S ), body weight ( W ) and temperature (71 according to:
(where t _end is in h, S is in g, W is in g and T is °C). During the emptying phase, stomach contents decrease curvilinearly according to:
(where S_t , & S_o is in g and t is in h) in which the instantaneous digestion rate, K , varies with fish weight and temperature as:
Food pellets were prepared which remained separate and did not form a bolus in the stomach; K increased if a given meal size was subdivided to increase surface area. If meal size was increased by ingestion of identical pellets, K decreased. After a satiation meal, appetite in young turbot returns in direct relation to the degree of stomach emptiness. When food is regularly available, young turbot feed steadily at a rate which maintains their stomachs at c. 85% maximum fullness. When trained to use demand feeders, the fish interact as a group to feed rhythmically, but feeding rate falls 33% to only two-thirds of the previous rate since stomach fullness, and hence digestion rate (g h⁻¹), is maintained at a lower level. Reduction in dietary energy density below 1 kCal g⁻¹ increases gastric emptying rate and the turbot demonstrate partial compensation by increasing food intake. On energy-rich diets, protein nitrogen and energy assimilation efficiencies remain high (97 5% and 91% respectively) irrespective of feeding rate and frequency.     

Gene diversity analysis in natural populations and cultured stocks of turbot (Scophthalmus maximus L.)

The genetic variability of eight fish-farm and three natural populations of turbot was studied by electrophoretic analysis of 35 enzymatic loci. The results showed low genetic variability in natural populations of turbot ( H _T = 0·029 ± 0·013) in comparison with other flatfish species. Great genetic similarity was revealed among the natural populations studied, which indicates high rates of gene flow in this species. The hatchery stocks showed less genetic variation than the wild populations analysed, which suggests genetic drift phenomena involved in the foundation and management of broodstocks. In addition, the heterozygosity differences detected among the hatchery stocks analysed are correlated with inverted levels of fluctuating asymmetry, which supports the existence of inbreeding depression phenomena in turbot culture.     

Acute activation of ER alpha decreases food intake, meal size, and body weight in ovariectomized rats

Estradiol exerts many of its actions by coupling with two nuclear estrogen receptor (ER) proteins, ER alpha, and ER beta. While the acute, anorexigenic effect of estradiol appears to involve such a mechanism, the relative contributions of ERalpha and ERbeta are equivocal. To address this problem, food intake was monitored in ovariectomized (OVX) rats following acute administration of a selective ER alpha agonist (4,4',4'-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol, PPT; dose range = 0-200 microg), a selective ER beta agonist (2,3-bis(4-hydroxyphenyl)-propionitrile, DPN; dose range = 0-600 microg), and a physiological (4 microg) dose of estradiol benzoate (EB). While PPT-treated rats displayed dose-dependent decreases in daily food intake and body weight, neither of these measures was influenced by any dose of DPN. In addition, DPN failed to modulate the anorexigenic effect of PPT when the two ER agonists were coadministered. Meal pattern analysis revealed that the anorexigenic effect of 75 microg PPT (a dose of PPT that produced a similar decrease in daily food intake as 4 microg EB) was mediated by a decrease in meal size, not meal number. Thus, PPT, like EB and endogenous estradiol, decreases food intake by selectively affecting the controls of meal size. The finding that acute administration of 75 microg PPT failed to induce a conditioned taste aversion suggests that the anorexigenic effect of this dose of PPT is not secondary to malaise. Taken together, our findings demonstrate that selective activation of ER alpha decreases food intake, body weight, and meal size in the ovariectomized rat.     

Genotoxic evaluation of the GH transgenic Synechocystis using mice and turbot (Scophthalmus maximus L.)

In the present paper, the genotoxicity of transgenic Synechocystis sp. PCC 6803 containing flounder (Paralichthys olivaceus) growth hormone gene has been assessed using micronucleus tests in mice and fish. No micronucleus inductions in bone marrow erythrocyte of mice were observed at three doses of transgenic Synechocystis (2.0, 5.0, and 10.0g/kg). The frequencies of micronucleus and other nuclear abnormalities in turbot (Scophthalmus maximus L.) fed with 0.2%, 0.5% and 1.0% transgenic Synechocystis were also not significantly different (P>0.05) from controls. In contrast, cyclophosphamide, used in detecting the sensitivity of the biological assays, significantly increased the frequencies of micronucleus and other nuclear abnormalities in mice and turbot. Results indicate that the flounder GH transgenic Synechocystis sp. PCC 6803 seems to have no genotoxic effects on fish.     

Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot (Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10³ ml⁻¹ and 10³ larva⁻¹. Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10² bacteria larva⁻¹ on day 3 post-hatching to approximately 10⁵ bacteria fish⁻¹ 16 days post-hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10⁴ cfu larva⁻¹ exposed to V. pelagius on days 2, 5 and 8 post-hatching. However, only 10³ of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post-hatching, the gut microbiota of 5-day old larvae was mainly colonized by Aeromonas spp. (10⁴ larva⁻¹), of which 9 × 10³ belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10⁵ Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.     

The conversion of polyunsaturated fatty acids to prostaglandins by tissue homogenates of the turbot,Scophthalmus maximus (L.)

The conversion of [¹⁴C]20:4(n?6) and [¹⁴C]20:5(n?3) to prostaglandins was measured in homogenates of gills, liver and intestine of the turbot, Scophthalmus maximus (L.). Incorporation of radioactivity into prostaglandins was similar to or greater than into phospholipids, with gills being more active than liver or intestine. When measured at equimolar concentrations, 20:4(n?6) was a better precursor of prostaglandins than 20:5(n?3). Incorporation of 20:4(n?6) into prostaglandins was decreased in the presence of an equimolar concentration of 20:5(n?3), and vice versa. Incorporation of both precursors into prostaglandins was partially inhibited by aspirin and indomethacin. The results are discussed in relation to prostaglandin formation in fish and the abundance of (n?3) polyunsaturated fatty acids in marine lipids generally.