Sea Bass Fingerlings Research Articles

Dinoflagellate Alexandrium leei (Dinophyceae) from Singapore coastal waters produces a water-soluble ichthyotoxin

A strain of Alexandrium leei Balech that was isolated in October 2002 from Singapore coastal waters and identified by light and scanning electron microscopy and phylogenetic analysis using LSU rDNA sequences, is toxic to Asian sea bass fingerlings (Lates calcarifer Bloch). The ichthyotoxicity of the algal cells obtained by filtration (15 μm mesh net) and rinsed with sterile culture medium indicated that the toxicity of A. leei was probably not due to bacterial contamination, which was further supported by a negative correlation between the time to death of the fish and the dosage of algal cells applied. Paralytic shellfish toxins (PST) could not be detected indicating that PST was not the cause of fish mortality. Fish bioassays using frozen culture, heat-treated cultures, cell-free culture medium, and hexane, ethyl acetate, and water extracts of algal cells indicated that A. leei produces a heat-stable, polar ichthyotoxin(s) which can be released from the algal cells into the culture medium. Phylogenetic analysis based on the LSU rDNA sequences of A. leei confirmed its identification and indicated that the Singapore strain is more similar to isolates from Malaysia than to a geographically distant strain from Korea. This is the first evidence of icthyotoxin production by A. leei.

Effects of lipid on growth and feed utilization of white seabass (Atractoscion nobilis) fingerlings

Abstract A study was carried out to examine the effect of lipid level on growth and feed utilization of white seabass. Fingerling white seabass (27 days old, 0.65 ± 0.05 g, 32 ± 3.2 mm) were fed four formulated diets with four levels of lipid (15.5%, 18%, 19.5% and 21.5% of dry matter) at one level of protein (61% crude protein, dry matter (DM) basis) for six weeks. Survival exceeded 90% for all treatments. Weight gain (g) and specific growth rate (SGR, % day − 1 ) values indicated that fish fed diets with 15.5% and 18% lipid exhibited higher growth performance. Lowest growth was recorded for fish fed diets with 19.5% and 21.5% lipid. Feed intake (FI, g fish − 1 ) was also significantly ( P P − 1 . More work is needed to determine the precise dietary protein and carbohydrate requirements for this profitable aquaculture species.

Optimum feeding rates for European sea bass Dicentrarchus labrax L. reared in seawater and freshwater

Growth, feed conversion efficiency, fillet composition and morphological indices of European sea bass (initial weight of 2.6±0.3 g) were investigated in a 6×2 factorial designed experiment employing two salinities [seawater (SW, 40 ppt) and freshwater (FW, 0.4 ppt)] and six different feeding rates (2.0%, 2.5%, 3.0%, 3.5%, 4.0% of their body weight (bw) day −1 and to satiation) for 60 days. Twenty fish were stocked into 155-l round tanks and each treatment had three replicate tanks. Throughout the experiment, weight gain and specific growth rate (SGR) were highest at ration 4.0 bw day −1 and to satiation in SW group. Regardless of feeding rate, sea bass fingerlings grew about 20–30% more in SW than those reared in FW. There was a significant ( P<0.05) interactive effect of feeding rates and culture media (SW and FW) on weight gain and feed conversion efficiency (FCE). FCE was found to be lower in fish fed to satiation (65–66%) compared to the feeding rate of 3.5% bw day −1, which was best in both SW (89.1%) and FW (86.5%). There were no significant differences in either protein or ash contents of the fish cultured in SW or FW although lipid and moisture contents changed with increasing feeding rate. Condition factor, fillet yield and carcass/body weight were significantly increased, whereas hepatosomatic index, viscera somatic index decreased when the feeding rate was increased above 2.0% bw day −1. Feeding rate proved to be the main differentiating factor in all growth, FCE and fillet composition parameters. Values of SGR plotted against feeding rates allowed the maintenance, optimum and maximum feeding levels to be determined. Based on the calculations, the optimum feeding rate for sea bass fingerlings (3 g) reared in SW and FW is 3.0% and 3.5% bw day −1, respectively. In addition, the optimum feeding rate for FCE was calculated as 2.7% bw day −1 in SW and 3.8% bw day −1 in FW. It is concluded that growth and FCE of European sea bass can be improved by feeding them at about 3.0–3.5% bw day −1 in SW or FW.

Characterisation of a pathogenic virus isolated from marine threadfin fish ( Eleutheronema tetradactylus) during a disease outbreak

An unknown virus was isolated from massive mortality of cultured threadfin ( Eleutheronema tetradactylus) fingerlings. The virus replicated in BF-2 fish cell line and produced a plaque-like cytopathic effect. Electron micrographs revealed non-enveloped, icosahedral particles approximately 70–80 nm in diameter composed of a double capsid layer. Viroplasms and subviral particles approximately 30 nm in diameter and complete particles of 70 nm in diameter were also observed in the infected BF-2 tissue culture cells. The virus was resistant upon pH 3 to 11 and ether treatment. It is also stable to heat treatment (3 h at 56 °C). Replication was not inhibited by 5-iododeoxyuridine (5-IUdR). Acridine orange stain revealed typical reovirus-like cytoplasmic inclusion bodies. Electrophoresis of purified virus revealed 11 segments of double-stranded RNA and five major structural polypeptides of approximately 136, 132, 71, 41 and 33 kDa. Based on these findings, the virus isolated was identified to belong to the genus Aquareovirus and was designated as threadfin reovirus. This virus differed from a majority of other aquareovirus by its increase in virus infectivity upon exposure to various treatments such as high and low pH, heat (56 °C), ether and 5-IUdR. The RNA and virion protein banding pattern of the threadfin reovirus was shown to differ from another Asian isolate, the grass carp hemorrhage reovirus (GCV). Artificial injection of the threadfin reovirus into threadfin fingerlings resulted in complete mortality, whereas sea bass ( Lates calcarifer) fingerlings infected via bath route showed severe mortality within a week after exposure. These results indicate that the threadfin virus is another pathogenic Asian aquareovirus isolate that could cross-infect into another marine fish, the sea bass.

Preliminary nutritional evaluation of pea seed meal ( Pisum sativum) for juvenile European sea bass ( Dicentrarchus labrax)

An 84-day feeding and digestibility trial was conducted to evaluate the use of a pea seed derived meal in experimental diets for European sea bass fingerlings of initial weight 10 g. It was demonstrated that up to 40% pea seed meal inclusion was feasible in diets allowing for a 12% reduction in fish meal content and a 25% substitution of carbohydrate content without appreciable loss in growth performance of juvenile sea bass or diet utilization. The data showed no difference in final weight and specific growth rate measurements, and feed utilization was not compromised by the supplementation of the reference fish meal basal diet with pea seed meal. The diets were formulated to be essentially isonitrogenous and isocaloric and the results of the digestibility trial confirmed that the availability of the protein and energy was consistent between the different dietary treatments. However, carbohydrate digestibility was markedly affected by the nature of the pea seed meal starch matrix and contributed to a significant reduction in digestible energy. It was also evident that this affected carcass composition with respect to energy deposition (lipid content), but not overall growth of fish in the relatively short duration of this trial.

Growth of European sea bass fingerlings ( Dicentrarchus labrax) fed extruded diets containing varying levels of protein, lipid and carbohydrate

Sea bass fingerlings (2.78 g) were fed eight extruded diets for 90 days, in which part of the protein was replaced by lipid (Trial 1) or carbohydrate (Trial 2), so that crude protein (CP) varied between 40 and 55%, lipid from 6 to 18% and carbohydrate between 20 and 35%. The effect of protein level on growth and feed conversion was significant ( P < 0.01). The best performance was obtained with 45% CP in both experiments, with relative weight gain of 539 vs. 416, 476 and 326% in Trial 1, and 536 vs. 376, 466 and 520% in Trial 2, for 40, 50 and 55% CP, respectively. The overall results suggest that the percentage of carbohydrate in sea bass diets should not exceed 30%, and that lipid content can vary between 12 and 14%.

Arginine requirement and effect of different dietary arginine and lysine levels for fingerling sea bass (Dicentrarchus labrax)

Groups of 60 European sea bass fingerlings weighing 2.1 ± 0.05 g/fish were kept in each of 18 flow-through 65-litre tanks supplied with 2.5 l/min of brackishwater (temperature, 25 Co; salinity, 25 ppt). Duplicate tanks were fed for 9 weeks with 9 isonitrogenous (46 ± 0.2%; N × 6.25) and isolipidic (12 ± 0.2% by ether extract) semipurified diets obtained from a basal mixture formulated to be limiting in arginine (1% by weight). The basal diet contained maize gluten meal (300 g/kg), herring meal (100 g/kg) and mixtures of indispensable and dispensable amino acids to simulate, excluding arginine and lysine, the amino acid profile of sea bass muscle protein. Seven diets were used to evaluate the arginine requirement. They were obtained by adding 0, 3, 6, 9, 12, 15 and 18 g/kg of pure l-arginine to the basal mixture while maintaining the lysine level equal to the sea bass requirement (2.2 g/100 g diet). Diets 8 and 9 were prepared to contain either a 50% excess or deficiency of lysine and a constant level of arginine (1.95 g/100 g diet). By analysis of the doseresponse relationship based on growth data, the dietary requirement of arginine was found to be 1.81 ± 0.005 g/100 g diet corresponding to 3.9 g/16 g N. A similar value was obtained when the 5-h (peak) postprandial plasma urea concentrations were regressed against the dietary level of arginine (1.78 ± 0.06 g/100 g diet), suggesting the possible use of this parameter to confirm the arginine requirement estimated by conventional growth experiments. From the results of the present experiment it would seem that sea bass fingerlings, like other warmwater fish species, are apparently not sensitive to moderate disproportions of dietary arginine and lysine.

Effect of feeding pattern and dietary protein source on protein synthesis in European sea bass (Dicentrarchus labrax)

Protein synthesis was measured using the flooding dose of tritiated phenylalanine method in sea bass (Dicentrarchus labrax) fingerlings fed a fixed ration in relation to dietary amino acid balance and feeding pattern. Meal-feeding significantly enhanced growth with all diets while amino acid balance had a tendency to improve growth. Protein synthesis rate was higher in meal-fed groups and the better the amino acid balance, the lower the protein synthesis rate. The effect of amino acid balance on protein synthesis was linked to whole body RNA content, while the effect of feeding pattern was monitored by both RNA content and ribosomal activity.

Food conversion budget in sea bass, Dicentrarchus labrax, fingerlings under two different feeding frequency patterns

Four-hundred-and-eighty (480) sea bass ( Dicentrarchus labrax L.) fingerlings reared under two different feeding patterns were investigated in order to study the food conversion budget of the species. The fish under the first feeding pattern (P 1 ) were fed during day-light and those in the second one (P 2), on a full-day basis. The daily amount of food consumed was found to be affected directly by both feeding frequency and food deprivation time. The growth rate was found to be lower in fish fed once daily, while as the feeding frequency increased, the growth rates of fish in P 2 were always higher than those of fish in P 1. Both gross and net food conversion efficiency were reduced with frequency increase. The percentage of consumed food used for basic metabolism and growth increased with feeding frequency for both P 1 and P 2 and stabilized in high rations. Energy sources management was optimum when the feeding frequency was 3 meals per day, the time between two meals was 6 h and no meal took place out of daylight. Within this feeding pattern, the maximum growth rate is obtained, while a valuable energy budget occurs.

Osteological abnormalities in laboratory reared sea-bass ( Dicentrarchus labrax) fingerlings

Two groups of juvenile sea-bass, a random group and a group selected on the criteria of the appearance of macroscopically visible body deformations or anomalies in behaviour, were collected from the rearing tanks, treated for cartilage-bone staining with alizarin and alcian-blue, and examined for osteological abnormalities. The meristic characters of the stained specimens were also examined. The percentage occurrence and the interrelationship of the various abnormality types are described. The most frequently encountered abnormalities were those involving spinal column and vertebral deformities and these were often associated with swimbladder deficiencies.

Optimum Acclimation Rates from Salt to Freshwater for Juvenile Sea Bass Lates calcarifer Bloch

The rapid acclimation of 19-30 day-old sea bass (Lates calcarifer) fingerlings from seawater (28 ppt salinity) to freshwater was investigated. Sea bass reared in seawater were gradually acclimatized to freshwater over O, 3, 6 and 8 hours. There was no significant difference (P &lt;0.005) in survival between fish in the seawater control and those acclimated over 6 or 8 hours but fish placed directly into freshwater all died within 2 hours.

Cannibalism as a factor affecting the survival of intensively cultured sea bass ( Dicentrarchus labrax) fingerlings

The large percentage of intensively cultured sea bass fingerlings apparently lost to cannibalism indicates that this source of mortality probably contributes significantly to poor survival. The growth rate of ungraded fingerlings produces increasing differences in size which run parallel with increasing cannibalism, especially after the weaning period. Sea bass fingerlings, if not fed early in the morning, showed increased cannibalistic activities; 37% of the larger fish filled their stomachs with smaller siblings. The predator must be twice the length of the victim for ingestion. The extent of cannibalism is found to depend on feeding frequency.

Changes in the biochemical composition of tissues in Juvenile Sea bass during forced starvation

The effects of starvation on sea bass ( Dicentrarchus labrax) fingerlings (initial average weight 9.5 g) at 19° in sea water were studied. Fish start to die on day 19. Proximate analysis shows that water content increases with starvation time whereas protein and lipid contents decrease. After an initial decline, nitrogen excretion remains stable from day 2 to day 14. Starvation resulted in a reduction of liver, muscle and digestive tract lipids, mainly the triglycerides which are significantly reduced within the first week of starvation. The influence of water temperature on these changes is discussed.

Influence de la temperature et de la salinite sur la croissance et la composition corporelle d'alevins de Dicentrarchus labrax

Growth, food conversion, and body composition of sea bass fingerlings, Dicentrarchus labrax, exposed to different temperatures (15 and 22°C) and salinities (6, 11, 24 and 37‰) were studied. Temperature was found to have the more significant influence on these parameters. At the higher temperature, fingerlings grew faster in high and low salinities (6 and 37‰). At the lower temperature, growth was slightly faster at 11 and 24‰. Body composition was affected mainly by temperature; salinity had no significant effect. Trypsin-like activity in the digestive tract was very low at 6‰ and 15°C. Sea bass fingerlings seem to be very tolerant to changes in temperature and salinity of their environment. The results are discussed in the context of fish culture.