Juvenile Red Sea Bream Research Articles

Seagrass habitat reduces vulnerability of red sea bream Pagrus major juveniles to piscivorous fish predator

Predation experiments were conducted in mesocosms to test the hypothesis that habitat complexity affects vulnerability of red sea bream Pagrus major juveniles to piscivorous fish predators. Juvenile behavior was video-recorded for 6 h in two structurally different habitats: vegetated with sea grass Zostera marina, and unvegetated 0.5-t tanks. Association behavior with seagrass was observed in the vegetated tank throughout the trials. Predation experiments were conducted with 30 red sea bream juveniles (29.9 mm body length) exposed to two individuals of the piscivorous fish predator Chinese sea bass Lateolabrax sp. (261.6 mm), for 6 h in 1.0-t tanks. Predation rate (no. of fish predated on per predator per h) was significantly lower in the vegetated tank (0.02/predator per h) than in the unvegetated tank (0.27/predator per h). Present experiments indicate that habitat complexity reduces vulnerability of juvenile red sea bream to predation by piscivorous fish by serving as physical and/or visual barriers and limiting the predator’s ability to pursue and capture prey. Seagrass beds in the shallow coastal waters around Japan are suggested to be an important nursery for red sea bream since they provide the juveniles with habitat complexity as well as serve as a feeding ground.

Effect of dietary canola oil level on the growth performance and fatty acid composition of juvenile red sea bream, Pagrus major

This study was undertaken to evaluate the suitability of using refined canola oil as a source of supplemental dietary lipid for juvenile red sea bream ( Pagrus major). Triplicate groups of 25 red sea bream fingerlings held under identical culture conditions (25 °C, aerated, re-circulated artificial seawater, 30 g/L; 12-h light/12-h dark photoperiod) were fed three times daily to satiation one of four diets with equivalent protein (∼ 46%), energy (∼ 21.9 MJ/kg) and lipid (∼ 15%) content on a dry weight basis for 12 weeks. The diets were identical in composition except refined canola oil (CO) replaced either 0%, 33%, 67%, or 100% of the supplemental dietary lipid content with the remainder originating from pollock liver oil (FO). Thus CO comprised either 0% (diet FO), 25% (CO25), 48% (CO48), or 70% (CO70) of total dietary lipid content. Fish weight gain, specific growth rate, feed intake, feed efficiency, protein and gross energy utilization, and percent survival were not affected by diet treatment. Except for percent moisture which was depressed in CO48 and CO70-fed fish, concentrations of terminal whole body proximate constituents were similarly uninfluenced by diet treatment. Dietary lipid compositions reflected the proportions of CO and FO in supplemental lipid and their respective fatty acid compositions. Whole body fatty acid compositions mirrored those of diet treatments. However, liver polar lipids of the fish suggested, some essential fatty acids such as eicosapentaenoic acid, docosahexaenoic acid and arachidonic acid were preferentially incorporated and regulated, which resulted in a relatively lower degree of difference between diet treatments compared to what was found in whole body lipid. Our findings suggest that refined canola oil is a suitable dietary lipid source for juvenile red sea bream under our test conditions. However, chronic assessments of CO as a supplemental dietary lipid source for red sea bream are warranted to ensure that similar results are obtained without adverse effects on fish health.

Dietary medicinal herbs improve growth and some non-specific immunity of red sea bream Pagrus major

The effects of dietary medicinal herbs on growth and some non-specific immunity were investigated in juvenile red sea bream Pagrus major. The fish (mean body weight 24.0±0.2g) were fed fishmeal diets supplemented with either Massa medicata (Mm), Crataegi fructus (Cf), Artemisia capillaries (Ac), Cnidium officinale (Co), or a mixture of all the herbs (HM), and a control diet without medicinal herbs, for 12 weeks. Survival, specific growth rate, feed efficiency, condition factor and hemoglobin levels were higher in fish given herbal diets than fish given the control diet without herbs. Significantly higher serum high density lipoprotein-cholesterol level and lysozyme activity were detected in HM and Co diet groups, and alternative complement pathway activity was detected in the HM diet group. However, significantly lower serum alanine aminotransferase and aspartate aminotransferase activities were obtained in all herbal diet groups compared with the control diet group. Pathogen challenge test by intraperitoneal injection of Vibrio anguillarum indicated that highest survival was obtained in the HM diet group followed by Ac, Co, Cf, and Mm diet groups. The lowest survival was obtained in the control group. These results reveal that medicinal herbs in diets enhance growth and some non-specific immunity of red sea bream.

Effect of photoperiod manipulation on the growth performance and stress response of juvenile red sea bream ( Pagrus major)

Juvenile of red sea bream ( Pagrus major, body weight 1∼30 g) were reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) with constant light intensity 1500 lx on the water surface to investigate their growth performance and stress response. Fish were fed a commercial diet to apparent satiation for 8 weeks of the experiment. Significantly higher weight gain and specific growth rates (SGR) were observed in fish exposed to a 24L:0D photoperiod followed by 16L:8D, 6L:6D and 12L:12D photoperiods ( P < 0.05). Food intake was significantly higher in fish exposed to 24L:0D followed by 6L:6D, 16L:8D and 12L:12D photoperiods ( P < 0.05). There was no significant difference in the feed conversion efficiency (FCE) between fish exposed to 24L:0D and 16L:8D photoperiods, but the FCE in both photoperiods was significantly higher than that of 6L:6D and 12L:12D photoperiods. There were no significant differences in hematocrit levels and plasma levels of cortisol and glucose among the treatments at the end of experiment. The results demonstrated that the growth performance of juvenile red sea bream reared from 1 to 30 g can be stimulated significantly by using a continuous (24L:0D) photoperiod without any measurable significant stress response in fish.

Genetic vaccines protect red seabream, Pagrus major, upon challenge with red seabream iridovirus (RSIV)

We have investigated the protective effect of immunization of juvenile red seabream, Pagrus major, with DNA plasmids encoding the viral major capsid protein (MCP) and an open reading frame (ORF) containing a transmembrane domain against red seabream iridovirus (RSIV). The expression of the MHC class I transcript in the DNA-vaccinated fish was significantly upregulated at the 15th day post-vaccination and the relative level of expression was maintained until the 30th day post-vaccination. This pattern of expression was similar in fish vaccinated with a commercially prepared formalin-inactivated RSIV vaccine. In vaccine efficiency tests, the relative percentage survival (RPS) of fish receiving the DNA vaccines and their combination ranged from 42.8 to 71.4% in two experimental runs, and these were significantly different from the control groups. Our results clearly demonstrate that DNA vaccines are able to induce robust protection in fish against RSIV infection, and a cellular immune response as shown by the upregulation of the MHC class I transcript after vaccination, which may be associated with such protection.

Assessment of reference dietary amino acid pattern for juvenile red sea bream, Pagrus major

Four semi-purified diets, containing crystalline amino acids (CAAs), were fed to juvenile red sea bream, Pagrus major in order to ascertain the ideal dietary amino acid pattern for this species. A control diet containing 50% casein–gelatin as protein sources, but no CAAs were fed to the fish. The other diets contained 30% casein–gelatin and 20% CAAs. CAAs were added to diets to simulate with amino acid pattern of the red sea bream eggs protein (REP), red sea bream larvae whole body protein (RLP), red sea bream juvenile whole body protein (RJP), and brown fishmeal protein (BFP). The juveniles (average initial body weight, 1.58 ± 0.01 g) were maintained in triplicate tanks and fed twice daily for 30 days. The highest weight gain was observed in juveniles fed the RJP diet. No significant difference was observed in juveniles fed the RLP and BFP diet. Feed efficiency ratio, protein efficiency ratio and amino acid retention in the whole body were significantly (p < 0.05) affected by the simulated dietary amino acid patterns. The essential amino acid profile and A/E ratios of the whole body after the growth trial showed little difference among the dietary treatments. The results suggest that red sea bream juveniles are able to utilize high amounts of CAA in coated form. The amino acid pattern of RJP could be used as an appropriate of reference dietary amino acid for this species.

Comparison of the spectral sensitivity of juvenile red sea bream investigated by the physiological technique and by the behavioral technique

The optomotor reaction of the red sea bream Pagrus major was utilized in order to measure its spectral sensitivity. The high spectral sensitivity of this species in twilight conditions was estimated to be from 480 to 560 nm, whereas it was observed to be also on longer wavelengths in the probable photopic vision. This result was compared with the sensitivity curve obtained by the physiological technique of the induction of electroretinogram. The form of both sensitivity curves did not show similar tendencies. It will be necessary to investigate the adjustment of a physiological phenomenon and a behavioral phenomenon concerned with various stimulus-reaction systems.

Ontogeny of tolerance to hypoxia and oxygen consumption of larval and juvenile red sea bream, Pagrus major

Changes in tolerance to hypoxic stress and oxygen consumption were studied in the red sea bream, Pagrus major, from its early life stage until 42 days post-hatch. In the experiments, metamorphosis was observed mainly from days 15 to 30, and the morphological shift from larva to juvenile was completed at around 9.5 mm total length (TL). During the larval stage, lethally low dissolved oxygen (DO) levels and mass-specific metabolic rates increased with growth from 2.6 to 5 mm TL ( P<0.01). Subsequently, the levels remained high and decreased until about 9.5 mm TL around the flexion stage and post flexion stage. Finally, beginning in the juvenile stage, lethal DO levels and mass-specific metabolic rates decreased as TL increased up to about 30 mm ( P<0.01). The relationship between lethal DO levels and mass-specific metabolic rates was significantly linear ( r=0.59, p<0.001, n=207) in fish larvae and juveniles. These results indicated that, around the stage of flexion and post flexion larvae in red sea bream, metabolic rates were highest during metamorphosis, and consequently hypoxia tolerance was lowest. It was presumed that the increasing metabolic rate during metamorphosis induced a decrease in the metabolic scope of activity and thereby induced the decrease of the tolerance to some environmental stressors in the background.

Effects of Dietary Vitamin A on Juvenile Red Sea Bream Chrysophrys major

AbstractA 55‐d feeding experiment was conducted to evaluate the effects of dietary vitamin A on growth of juvenile red sea bream Chrysophrys major. Nine semi‐purified diets with supplemental retinol palmitate at levels of 0, 300, 600, 1,500, 3,000, 4,500, 6,000, 15,000 and 30,000 retinol eq/kg diet, were fed twice daily to triplicate groups of 10 juveniles per tank with an initial weight of 1.178 ± 0.001 g. Weight gain and specific growth rate increased with the increase of supplemental retinol palmitate in the diet up to a level of 6,000 retinol eq/kg diet, beyond which those indices tended to decrease slightly or to plateau. Significantly lower weight gain and specific growth rate were observed in fish fed with 0 and 300 retinol eq/kg diet. No significant differences were found in survival rates among the different levels of supplementation. The crude protein, lipid, moisture and ash contents in the whole body were not affected by the different vitamin A supplemental levels. Besides the reduced growth, fish fed with low levels of vitamin A supplement showed no other signs of deficiency. No hypervitaminosis A symptoms were observed in fish fed on high levels of supplementation. Fish fed on diets with 0 and 300 retinol eq/kg diet showed a significantly lower content of vitamin A (as a total retinol) in the liver than those in groups fed with higher levels of supplementation. Vitamin A was stored in the liver mainly as retinyl esters. Total retinal content of the eye showed no significant differences among the treatments; however, fish fed with 0 and 300 retinol eq/kg of diet had slightly higher concentrations. According to the results of the mean weight gain, specific growth rate and liver retinol content, the requirement of dietary vitamin A for juvenile red sea bream was estimated to be between 1,500 and 6,000 retinol eq/kg.

Silicone implants for delivery of estradiol-17β and 11-ketotestosterone to red seabream Pagrus major

To develop effective methods for delivering steroid hormones to red seabream, we investigated the utility of dimethyl sulfoxide (DMSO) as a solvent for steroid hormones by examining the in vitro and in vivo release of estradiol-17β (E2) and 11-ketotestosterone (11-KT) from silicone capsules. In vitro E2 and 11-KT release rates from capsules containing steroid hormones in castor oil were proportional to the concentration of steroids within capsules. Increasing the proportion of DMSO to castor oil increased sex steroid hormone release from the capsules. The in vivo implantation of a single capsule containing 400 μg of E2 in 50% DMSO or 11-KT in 25% DMSO effectively increased serum levels of each steroid hormone in juvenile red seabream for a month. These results demonstrate that use of silicone capsules containing steroids in DMSO provides a useful method for delivering controlled and easily manipulated physiological doses of E2 and 11-KT to large fish such as red seabream.

Territorial behavior in juvenile red sea bream Pagrus major and crimson sea bream Evynnis japonica

: The territorial behavior of juvenile red sea bream Pagrus major and crimson sea bream Evynnis japonica was examined at Morode Cove, Ehime Prefecture. Four exclusive types of behavior (attack, mutual attack, head down threat and mutual display) and one escaping behavior (fleeing) were observed in both species. Juvenile of the two sea bream could discriminate between each other and change their territorial behavior depending on the presence of conspecifics or heterospecifics. The territorial behavior toward conspecifics was more aggressive than toward heterospecifics. Interrelationships between the two sea bream were more aggressive than in other heterospecific cases. The two sea breams performed following behaviors toward solo and schooled mullid species. E. japonica ascended the water column more frequently than P. major in high frequency. The former joined conspecific aggregations foraging for planktonic animals around their territories. These observations suggest that territorial individuals of the two sea bream could discriminate intruders utilizing similar food resources in order to maintain their territories.

Nutritional assessment of Australian canola meals. II. Evaluation of the influence of the canola oil extraction method on the protein value of canola meals fed to the red seabream (Pagrus auratus, Paulin)

This study examined the biological value of expeller- and solvent-extracted canola meals when included in the diets of juvenile red seabream. Notably, the test and reference diets in this study were prepared to be protein (300 g kg−1 DM) and energy (16.5 MJ kg−1 DM) limiting. Test diets were prepared, in which canola meal provided either 20%, 40% or 60% of the total dietary digestible protein. To minimize the influence of compensatory feed intake, all diets were pair-fed to the fish on restricted basis. Positive and negative controls were also included as treatments in the study to demonstrate that the diets were protein limiting and also to demonstrate the relative value of the highest inclusion levels of each test ingredient. The canola meals, either expeller- or solvent-extracted, were found to be nutritionally useful in diets for red seabream. Both ingredients were of similar value to that of the soybean meal when included on an equivalent digestible protein basis. No significant differences in weight gain, survival, FCR, N retention, energy retention or the apparent biological value of the N content were observed among any of the groups receiving the test or reference diets. A few significant differences were observed among some of the test and reference diets with regard to the apparent biological value of their energy content, although no consistent pattern was evident. The positive control treatment supported significantly superior growth and food utilization by the fish relative to all other treatments. The negative control treatment resulted in significantly poorer growth and food utilization by the fish relative to all other treatments. On a relative basis, there were no declines in fish performance between the highest inclusion levels of the expeller- and solvent-extracted canola meals or the soybean meal. Hence, the fish in this study obtained equivalent nutritional value from these ingredients, on a digestible basis, to that of the fishmeal in the reference diet.

Restoration of the fatty acid composition of red seabream (Pagrus auratus) using a fish oil finishing diet after grow-out on plant oil based diets

This study evaluated the potential for manipulating the fatty acid composition of juvenile red seabream, Pagrus auratus. Prior to the start of the study, three groups of fish had been reared for 3 months on a fish oil based diet or diets where the added fish oil had been replaced with either canola or soybean oil. In the present study, fish that had previously been fed either the canola or soybean oil diets were fed a fish oil based diet. Three additional treatments included fish being maintained on their original diets of fish oil, canola oil or soybean oil. Fish were fed their respective diets twice daily to apparent satiety for 32 days. Samples of fish from each treatment were collected after 0, 1, 2, 4, 8, 16 and 32 days. Composition and growth of the fish were determined at each sample point. Most treatments showed no differences in growth performance, although fish fed a fish oil diet after previously being fed a soybean oil diet showed slightly better growth. No significant differences among treatments were observed in proximate composition of the fish, although there was a significant increase in total fat and individual fatty acid (g kg−1 live-weight) content of the fish from all treatments over the period of the study. No significant changes in the relative fatty acid composition (% of total fatty acids) over time were observed in the three treatments where fish were maintained on their original diets. In contrast, fish that were previously fed either the canola or soybean oil diets and were then fed a fish oil diet had significant changes in both the relative (% of total fatty acids) and absolute (g kg−1 live-weight) fatty acid content. Key changes observed included a decrease in the relative levels of polyunsaturated fatty acids (PUFA) such as 18 : 2n − 6 and 18 : 3n − 3. Increases in the relative levels of the long-chain polyunsaturated fatty acids (lcPUFA) 20 : 5n − 3 and 22 : 6n − 3 were also observed in both treatments. The rates of absolute (g kg−1 live-weight) change/accumulation of these fatty acids followed an exponential equation that differed for each fatty acid in each treatment. Examination of the retention efficiency of specific fatty acids also showed marked differences between fatty acids within treatments and also differences between treatments. Biologically important fatty acids such as 20 : 5n − 3 and 22 : 6n − 3 had only moderate retention efficiencies and these were unaffected by treatment. In contrast, the retention efficiencies of 18 : 2n − 6 and 18 : 3n − 3 suggested selective retention of these fatty acids when fed fish oil diets, but moderate catabolism when fed the plant oil diets. There were also high retention efficiencies of most saturated and monounsaturated fatty acids suggestive of active retention and/or active synthesis of these fatty acids by the fish. The results of this study, particularly the increases in lcPUFA, support the usefulness of a fish oil based finisher diet for fish raised predominantly on plant oil based diets.

Evaluation of canola oils as alternative lipid resources in diets for juvenile red seabream,Pagrus auratus

This study examined three potential oil resources, crude and refined canola oil and refined soybean oil as replacements for added dietary fish oil in diets for juvenile red seabream. These oil resources were evaluated for their potential to replace added fish oil (40 g kg−1) in fishmeal based (600 g kg−1) diets, with 100 g kg−1 of total lipids. Each of the three plant oils was used to replace 25%, 50%, 75% or 100% of the added dietary fish oil. Each of the three plant oils showed potential as a replacement for dietary fish oil, although a significant reduction in growth and feed utilisation was observed with the complete (100%) replacement of added fish oil by crude canola oil. No other significant effects of oil type or inclusion level on growth were apparent. A negative control (no added fish oil or plant oil, 60 g kg−1 of total lipid) yielded poorer growth than all treatments except the diet containing 40 g kg−1 of added crude canola oil (100% replacement). This observation confirmed that the added oils were utilized by the fish. A positive control diet containing 80 g kg−1 of added fish oil (140 g kg−1 total dietary lipid) sustained the best growth in the study, confirming that the 13 experimental diets were energy limiting as planned. Notably, few effects of the alternative oils were seen on the proximate composition of the fish. However, the influence of the alternative oils on the tissue fatty acid composition was considerable, irrespective of plant oil type or processing grade. Particularly notable was the overall increase in the level of polyunsaturated fatty acids in the tissues of the fish fed the plant oil diets, with these trends becoming more apparent with the greater levels of fish oil replacement. Minimal reductions in the levels of the long-chain polyunsaturated fatty acids of eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acid were observed from any of the plant oil treatments. Sensory assessment, by an Australian taste panel, of the fish fed the fish oil reference, or the 100% replacement by refined canola or refined soybean diets showed a preference in order of canola oil > soybean oil > fish oil fed fish. Clearly, both canola and soybean oils have considerable potential as replacements of fish oils in diets for this species.

Evaluation of the feed value of a transgenic strain of the narrow-leaf lupin (Lupinus angustifolius) in the diet of the marine fish,Pagrus auratus

This study assessed the nutritional and biological value of a noncommercial, transgenic line of the Australian sweet lupin, Lupinus angustifolius, (cv. Warrah), produced to increase the methionine content of the seed. An initial experiment demonstrated that differences in the methionine content of the transgenic and nontransgenic control lupins had no apparent influence on the growth of juvenile red seabream fed practical diets. Re-evaluation of the nutritional characteristics of the lupin meals with subsequent digestibility studies allowed the determination of the digestible value of the protein and energy content of each of the varieties. The digestible protein content of either variety was similar, however significant differences in the digestible energy value of each variety existed (56.3% cf. 64.0%). This re-evaluation of the nutritional value of the genetically manipulated (GM) and non-GM lupin varieties enabled the reformulation of diets on a digestible protein and energy basis. A second growth trial was undertaken using sub-satietal pair-feeding regimes, with the experiment also involving protein-restrictive diets to allow expression of the differences in the methionine content of the transgenic and nontransgenic lupin meals. A significant benefit of the enhanced methionine level in the transgenic lupin was observed. It is argued that in the high-protein fish diets used, the importance of amino acid composition is relatively limited. Economic modelling of the potential value of the increased methionine in the transgenic lupin suggests that this will have limited benefit for aquaculture industries, and that greater value would be attributable to higher protein and energy levels in ingredients.

Development of a Real-time PCR Assay for the Detection and Quantification of Red Seabream Iridovirus (RSIV).

A novel real-time PCR detection and quantification method for the red seabream iridovirus (RSIV) was developed using the major capsid protein (MCP) gene. A linear relationship was observed between the amount of input DNA and the threshold cycle (CT) values over a range of 1 to 109 viral copies. The real-time PCR was 2 orders of magnitude more sensitive than the conventional PCR. It was also shown to be specific to RSIV, i.e., it did not react with either hirame rhabdovirus (HIRRV), viral hemorrhagic septicemia virus (VHSV) or a DNA sample from apparently healthy red seabream Pagrus major. The viral load of dead juvenile red seabream (1 g average body weight) experimentally challenged with RSIV was in the range of 2.4 × 105 - 5.4 × 107 MCP gene copy number. To determine the target tissues of RSIV in the infected fish, 2 red seabream with average body weight of 50 g were experimentally challenged with RSIV and DNA was extracted from the various tissues and organs at 3rd day post-infection. Highest viral load was obtained in the heart with a mean MCP gene copy number of 2.7 × 105, while the blood had the lowest viral load at 8.8 × 103 mean MCP gene copy number. After the viral challenge, the real-time PCR assay was still able to detect RSIV from vaccinated survivors, which otherwise tested negative for RSIV by conventional PCR.

Effects of water temperature on the gonadal development and expression of steroidogenic enzymes in the gonad of juvenile red seabream, Pagrus major

The effects of water temperature on the development of hermaphroditic gonads in red seabream (Pagrus major) and on mRNA expression of cytochrome P450 aromatase (P450arom) and 11β-hydroxylase were examined. High water temperature suppressed both expression of P450arom and 11β-hydroxylase and the development of oocytes in ovarian portion of hermaphroditic gonads.

Effect of dietary fatty acids on lipoprotein lipase gene expression in the liver and visceral adipose tissue of fed and starved red sea bream Pagrus major

Juvenile red sea bream Pagrus major were fed either a commercial diet (diet 1) or diets supplemented with 10% oleate (diet 2), 5% oleate+5% linoleate (diet 3) or 5% oleate+5% n-3 polyunsaturated fatty acid mixture (diet 4) for 4 weeks. Following the conditioning period, the effects of dietary fatty acids on lipoprotein lipase (LPL) gene expression in the liver and visceral adipose tissue of fed (5 h post-feeding) and starved (48 h post-feeding) fish were investigated by competitive polymerase chain reaction. Fish liver showed substantial LPL mRNA expression that is not found in adult rat liver. When compared with diet 1, diets 2–4 tended to increase the LPL mRNA level in the liver, but tended to decrease it in the visceral adipose tissue under the fed condition. The reciprocal regulation of the liver and visceral adipose LPL mRNA abundance by dietary fatty acids was comparable to that of rat brown and white adipose tissue, respectively. The change in the LPL mRNA level by fatty acids was not completely consistent with the degree of fatty acid unsaturation. Our results indicate that the regulatory effect of dietary fatty acids on LPL gene expression was tissue-specific and related to feeding conditions, but was not solely dependent on the degree of unsaturation of fatty acids.

Population of olfactory sensory cells and olfactory sensitivity in juveniles of red sea bream &lt;i&gt;Pagrus major&lt;/i&gt; and black sea bream &lt;i&gt;Acanthopagrus schlegeli&lt;/i&gt; from wild and cultured stocks

Population of olfactory sensory cells and olfactory sensitivity in juveniles of red sea bream &lt;i&gt;Pagrus major&lt;/i&gt; and black sea bream &lt;i&gt;Acanthopagrus schlegeli&lt;/i&gt; from wild and cultured stocks

Lordosis induction in juvenile red sea bream, Pagrus major, by high swimming activity

Lordosis is correlated with absence or malfunction of the swimbladder. However, swimbladder abnormalities do not completely explain the occurrence of lordosis. We examined whether muscle activities from vigorous tail beat induced by removal of the caudal fin could induce lordotic malformation in juvenile red sea bream. We also attempted to determine the minimal current velocity for inducing lordosis in relation to total length (TL). For this purpose, we employed relative current velocity in terms of “move of water in times of total body length per second (TL s −1)”. We compared effects of different water current (2 vs. 4 TL s −1) for 10 days on bone malformation using juvenile of 25-mm TL. Exposure to 4 TL s −1 current velocity, but not 2 TL s −1, induced lordosis. Lordotic juvenile red sea bream had a cuneiform centrum mainly at the 15th vertebra. Lordosis was observed in fish with normal swimbladders as well. Thus, swimbladder abnormalities alone cannot completely explain the occurrence of lordosis. We removed part or all of the caudal fins of fish of 40-mm TL and exposed these fish to 2 TL s −1 current for 10 days. Control fish did not show deformations in the vertebrae. Fish with complete removal of the caudal fin swam with vigorous tail beats. However, fish with complete, upper or lower caudal fin removal (36%, 29% or 7%, respectively) displayed lordosis even at the current velocity of 2 TL s −1. These findings suggested that the muscle activities from excess beat of the tail against excessive current, but not the mechanical action of the caudal fin, induced lordosis.