Effects of cooling rate on post-thaw motility and fertility of Japanese pearl oyster <Emphasis Type="Italic">Pinctada fucata martensii</Emphasis> spermatozoa

The post-thaw motility and fertility of Japanese pearl oyster sperm show large variances, even among sperm samples obtained from the same individuals. This study aimed to clarify the factors that cause such differences. Spermatozoa were diluted 50 times with diluent comprising 10 % methanol, 18 % fetal bovine serum, and 72 % seawater, and dispensed into 0.25 ml straws. A total of 59 straws were cooled, one by one, at 11 different heights from the surface of liquid nitrogen (LN) to −50 °C, and then immediately immersed in LN. After thawing the straws, the relationships between the cooling rate and the post-thaw motility and post-thaw fertility of the spermatozoa were examined. Both the post-thaw motility and the post-thaw fertility showed a sharp peak when the straws were cooled at around −20 °C/min. There was a strong correlation between post-thaw motility and fertility (P < 0.001). There was a large difference in the cooling rates and the post-thaw motilities and fertilities of the spermatozoa, even between straws cooled at the same height. These results indicate that the optimum range for the cooling rate of oyster spermatozoa is quite narrow, and the method of cooling straws at a fixed distance from the LN surface is unsuitable for the cryopreservation of Japanese pearl oyster spermatozoa.     

Effects of cryopreservation on sperm structure in Japanese pearl osyter <Emphasis Type="Italic">Pinctada fucata martensii</Emphasis>

To clarify factors reducing the motility and fertility of cryopreserved spermatozoa of the Japanese pearl oyster Pinctada fucata martensii, the structure of spermatozoa before and after cryopreservation was observed by scanning electron microscopy. Testicular spermatozoa were diluted with cryopreservation diluent (10% methanol+18% fetal bovine serum+72% sea water), and dispensed into 0.25-mL straws. The straws were cooled at a rate of approximately −20 °C/min to −50°C, and subsequently immersed in liquid nitrogen. Percentage motility of spermatozoa before cryopreservation was 69.9±4.2%, and that of cryopreserved spermatozoa was 24.0±1.8%, respectively. In cryopreserved spermatozoa, the percentage that lacked or had a deformed flagellum was 56.6±3.9%, while in fresh spermatozoa this was 8.7±2.0%. In cryopreserved spermatozoa, the percentage of deformed acrosomes was 76.6±5.2%, while in fresh spermatozoa this was only 0.9±0.3%. Cryopreserved spermatozoa with a normal acrosome and flagellum were only 15.4±3.5% of those in fresh spermatozoa. These results indicate that lesion of the flagellum and deformation of the acrosome occurred through the cryopreservation procedure, and both types of damage lead to loss of the motility and fertility in thawed spermatozoa.     

Evaluation of genetic characteristics of wild and cultured populations of the Japanese pearl oyster <Emphasis Type="Italic">Pinctada fucata martensii</Emphasis> by using AFLP markers

Genetic characteristics of four wild (Mie, Fukui, Shimane and Nagasaki) and five cultured populations (selectively bred for 12 years with an origin of Ehime population) of the Japanese pearl oyster, Pinctada fucata martensii, were evaluated by using AFLP markers. Six primer pairs generated 1019 loci in total, among which 45.2–55.1 % was polymorphic among populations. Although there was no significant difference in gene diversity between wild (0.170–0.174) and cultured (0.158–0.173) populations, genetic relatedness in cultured populations (0.316–0.450) was about three times higher than that in wild populations (0.110–0.165). In addition, genetic differentiation was about twenty times larger in cultured populations (Nei’s distance: 0.0111) than in wild populations (Nei’s distance: 0.0005). These results mean that selective breeding can cause marked inbreeding as well as large genetic differentiation among cultured populations in a short period. On the other hand, it was suggested that genetic homogenization in the wild, probably due to a large-scale transport of cultured oysters, had progressed in the sea around Japan. In conclusion, it is necessary to prevent inbreeding by the reconsideration of the style of selective breeding in cultured populations, while the escape of gametes or spats of cultured strains in the wild should be avoided for the preservation of genetic characteristics in native populations of P. f. martensii.     

Motility of spermatozoa obtained from testes of Japanese pearl oyster <Emphasis Type="Italic">Pinctada fucata martensii</Emphasis>

Effects of NH₃ concentration in sea water and pH of sea water on the motility of spermatozoa obtained from testes were examined in the Japanese pearl oyster Percent motility at 30 s after dilution increased with increasing NH₃ concentration in sea water from 0.75–2.0 mM. When spermatozoa were diluted with sea water containing 0.75 mM NH₃, which is widely used as the insemination fluid in the hatchery of this species, the percent motility increased with time elapsed after dilution, and peaked at 5 min. For spermatozoa diluted with sea water containing 2.0 mM NH₃, the percent motility increased rapidly and peaked at 30 s. The pH of sea water increased with increasing NH₃ concentration from 8.2 (0 mM NH₃) to 9.9 (5.0 mM NH₃). When spermatozoa were diluted with artificial sea water at various pH (buffered without NH₃ at 6.0–10.0), only spermatozoa diluted with artificial sea water of pH 10.0 were motile, and the percent was considerably lower than those in ammonical sea water. These results indicate that sea water containing 2.0 mM NH₃ is a suitable solution for evaluating sperm motility, and that NH₃ and/or ammonium ions may activate sperm motility in this species.     

Evaluation of three phytoplankton species as food for the pearl oyster <Emphasis Type="Italic">Pinctada fucata</Emphasis>

In the pearl cultivation farms of the Ehime Prefecture, Japan, mass mortalities of the pearl oyster Pinctada fucata have occurred since 1994. The occurrences of mass mortality roughly coincided with a shift of the dominant phytoplankton from Skeletonema and Chaetoceros to Chaetoceros and Nitzschia all of which belong to Bacillariophyceae. Hence, we evaluated Nitzschia, together with Chaetoceros and Isocrysis, as food for the oyster. Wet weights, lengths, widths, glycogen contents, and growth rates in terms of wet weight of the oysters in all the feeding treatments were significantly higher than those in the non-feeding treatment. The highest glycogen content (2.34%) and growth rate (2.21 g month⁻¹) were found in the Chaetoceros treatment. Growth rate in the Isocrysis treatment (1.63 g month⁻¹) was also high, although glycogen content in this treatment (0.41%) was low. In the Nitzschia treatment, growth rate of the oyster (0.94 g month⁻¹) was the lowest and glycogen content (0.83%) was also low relative to that in the Chaetoceros treatment. Chlorophyll a concentration in fecal pellets was lowest in the Nitzschia treatment (<2.7 μg mg⁻¹), suggesting more complete digestion of Nitzschia by the oyster. Thus, Nitzschia was edible and digestible but not assimilated by P. fucata. We propose the following scenario for the relationship between Nitzschia dominance and mass mortality. When Nitzschia dominates in a culture area, the physiological condition of P. fucata deteriorates due to low assimilation of Nitzschia by the oyster, followed by susceptibility of the oyster to infection by agents lethal to the oyster.     

Exploration of the antibacterial proteins in pearl oyster <Emphasis Type="Italic">Pinctada fucata</Emphasis> induced by bacterial inoculation

The aim of this research was to characterize immune-related antibacterial substances from pearl oyster Pinctada fucata induced by bacterial invasion. Bacteria inoculation was performed by injecting 0.1 ml of 1.0 × 10¹² colony-forming units/ml Vibrio parahaemolyticus into adductor muscle. Acidic extracts were prepared with 0.1% trifluoroacetic acid from different tissues after 8 h of injection, and antibacterial activity against V. parahaemolyticus was determined via the microdilution broth method. The acidic extracts from gills of inoculated oysters (AEg) showed stronger antibacterial activity than those from non-inoculated ones. Based on this result, antibacterial proteins were purified from AEg via two-step gel filtration chromatography, followed by high-performance liquid chromatography using a TSkgel G3000 column. Protein components were analyzed by both sodium dodecyl sulfate and native polyacrylamide gel electrophoresis. As a result, two antibacterial proteins, APg-1 (with a molecular mass of approximately 210 kDa) and APg-2 (of approximately 30 kDa), were obtained from AEg. Matrix-assisted laser desorption/ionization time of flight mass spectrometry analysis and partial amino acid sequences revealed that these proteins might be novel antibacterial proteins. These results indicate that antibacterial proteins are potentially upregulated in the gill of pearl oysters or released therefrom for defense against bacterial invasion.     

Growth of wild pearl oysters <Emphasis Type="Italic">Pinctada fucata,Pinctada margaritifera</Emphasis> and <Emphasis Type="Italic">Pinctada sugillata</Emphasis> (Bivalvia: Pteriidae) in Taiwan

In order to understand growth features of pearl oysters in the genus Pinctada, i.e. Pinctada fucata, Pinctada margaritifera, and Pinctada sugillata in Taiwan, a total of 3062 wild individuals of these species from juvenile to adult were collected monthyly from March 2001 to April 2002 in Jukeng, Pingtung County, south-west Taiwan. Quantitative measurements of live oysters were conducted for shell height (SH), shell length (SL), shell width (SW), hinge length (HL), and wet weight (WW). Different cohorts were identified through multiple length frequency analysis on SH of P. fucata and P. margaritifera, and growth curves with seasonal variation were estimated for these species. Pinctada fucata in Taiwan had a different seasonal growth pattern from the Japanese population, but had similar growth rates during the high growth period. The growth rate of P. margaritifera in Taiwan was slower than in French Polynesia, the Solomon Islands, and the Red Sea. Comparisons of morphological growth features among the three species show large differences in the SW-related features. Pinctada fucata in Taiwan had larger SW than in Japan and Korea. The differences in growth rates and morphological features suggested that the wild Taiwanese oysters may retain genetically pristine characteristics, thus genetic conservation might be urgently needed.     

A baseline study on lipid and fatty acid composition in the pearl oyster, <Emphasis Type="Italic">Pinctada fucata</Emphasis>

The pearl oyster Pinctada fucata is cultured for pearl production in China, but its germplasm is degenerated. Thus, lipid and fatty acids were investigated in P. fucata based on different tissues, body sizes and condition indexes using GC–MS to provide a lipidomic baseline for evaluation of breeding variety in terms of physiology. The major fatty acids over all samples included saturated (C16:0 and C18:0), monounsaturated [C16:1(n-7), C18:1(n-7) and C18:1(n-9)], and polyunsaturated fatty acids [arachidonic acid: C20:4(n-6), EPA: C20:5(n-3) and DHA: C22:6(n-3)]. Relative percentages of lipid contents of the mantle and visceral mass were, respectively, 40.75 and 42.03 %, significantly higher than adductor muscle (14.48 %) and gill (17.15 %). Fatty acid analysis showed that there were 15 types of fatty acids in adductor muscle, 17 types in mantle and gill, respectively, and 19 types in visceral mass. Meanwhile, total fatty acids, SFA, MUFA and PUFA were the highest in visceral mass (P < 0.05). Yet the lipid contents and fatty acid compositions showed no significant differences between body sizes or condition indexes based on visceral mass. The observations above suggested that visceral mass and mantle are the major tissues for P. fucata to store lipids and thus are important candidate tissues for lipidomic study.     

Monitoring of <Emphasis Type="Italic">Francisella noatunensis</Emphasis> subsp. <Emphasis Type="Italic">orientalis</Emphasis> in farmed Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>) in Brazil

Francisella noatunensis orientalis is a bacterium that causes emerging bacteriosis in Nile tilapia (Oreochromis niloticus) in many parts of the world, including Brazil. It is a non-motile, Gram-negative, strictly aerobic, facultative intracellular coccobacillus. This species of bacteria is responsible for low to high mortality in fish farms, causing economic losses for fish farmers. This study aimed to detect the presence of F. noatunensis orientalis using qPCR (real-time polymerase chain reaction) and to describe lesions caused by the bacterium in O. niloticus in Brazilian aquaculture. For this purpose, 360 fish from six fish farms (30 per farm) were sampled at two time points (n = 180 per sampling). Necropsies and histopathology were performed for lesion observation, in addition to qPCR and sequencing for detection and identification of Francisella species. Environmental data were collected using a multiparameter sonde YSI EXO2. All measured limnological variables were within the optimum range for cultivation of Nile tilapia. The major lesions present were melanization of the skin, splenomegaly, granulomas, and inflammatory cell responses. The prevalence of francisellosis varied from 0 to 86.66% between time periods and fish farms analyzed, and an outbreak was observed during the second sampling period. This study describes the prevalence of francisellosis in O. niloticus and reports that the lesions found are not exclusively associated with this bacterial disease.     

Natural hybridization between <Emphasis Type="Italic">Pinctada fucata</Emphasis> and <Emphasis Type="Italic">Pinctada maculata</Emphasis> inferred from internal transcribed spacer regions of nuclear ribosomal RNA genes

ABSTRACT:   Genetic evidence of the occurrence of natural hybridization between female Pinctada fucata and male Pinctada maculata among wild pearl oysters ( n  = 20) collected for use as the mother shell for private pearl farming in the Oshima Strait at Amami-o-shima, Kagoshima Prefecture, Japan, were obtained. A polymerase chain reaction-based species identification method for Pinctada was developed using polymorphisms in the internal transcribed spacer (ITS) region of the nuclear ribosomal RNA (rRNA) gene. This method enabled the amplification of the ITS regions using a primer set specific for P. maculata and P. fucata . However, 10 of 20 individuals morphologically identified as P. fucata had sequences specific to both P. maculata and P. fucata in the ITS region. These putative hybrids showed sequences of a maternally inherited mitochondrial 16S rRNA gene, identical to that of P. fucata . Shells of the putative hybrids were difficult to discriminate from those of P. fucata exhibiting similar taxonomic traits. Moreover, the hybrids exhibited slower growth than P. fucata but faster growth than P. maculata .     

Growth and survival of grouper <Emphasis Type="Italic">Epinephelus</Emphasis><Emphasis Type="Italic">coioides</Emphasis> (Hamilton) larvae fed free-living nematode <Emphasis Type="Italic">Panagrellus redivivus</Emphasis> at first feeding

The free-living nematode, Panagrellus redivivus, was tested as live food for grouper Epinephelus coioides larvae during the first feeding stage. A series of experiments were conducted to determine the acceptability of the free-living nematodes in grouper larvae at first feeding, the optimum nematode density and the response of the larvae to nutritionally enriched nematode. All experiments were conducted in 200-L conical tanks filled with 150-L filtered seawater and stocked at 15 larvae L⁻¹. Duration of feeding experiments was up to day 21 (experiment 1) and 14 days (experiment 2 and 3). Brachionus plicatilis and Artemia (experiment 1) and Brachionus plicatilis alone (experiment 2 & 3) was used as the control treatment. Observations indicated that the grouper larvae readily fed on free-living nematodes as early as 3 days posthatching, the start of exogenous feeding. Optimum feeding density for the larvae was 75 nematodes ml⁻¹. The enrichment of cod liver oil or sunflower oil influenced the total lipids and n-3 highly unsaturated fatty acids of P. redivivus, which in turn influenced those of the grouper larvae, however, growth and survival of the larvae were not affected (P > 0.05). The results from this investigation showed that the nematode, P. redivivus, can be used as first live food for grouper larvae from the onset of exogenous feeding until they could feed on Artemia nauplii.     

Complete mitochondrial DNA sequence of the Japanese flying fish <Emphasis Type="Italic">Cypselurus hiraii</Emphasis>

ABSTRACT:   In this study, to develop a technique that enables authentication of processed seafood, the complete nucleotide sequence of the mitochondrial genome for the Japanese flying fish Cypselurus hiraii was determined. Three segments spanning the entire genome were amplified using polymerase chain reaction, and products were subsequently used as templates for direct sequencing with 60 primers. The genome (16 528 base pairs) was found to contain the same 37 genes (two ribosomal RNA, 22 transfer RNA, and 13 protein-coding genes) as those found in other vertebrate mitochondrial genomes, with the gene order being identical to that typical of vertebrates. A major non-coding region between the tRNA^Pro and tRNA^Phe genes (868 base pairs) appears to be the control (D-loop) region, as it has several conserved blocks characteristic of control regions.     

Biomass fluctuation of two dominant lanternfish <Emphasis Type="Italic">Diaphus</Emphasis><Emphasis Type="Italic">garmani</Emphasis> and <Emphasis Type="Italic">D. chrysorhynchus</Emphasis> with environmental changes in the East China Sea

Acoustic surveys have been conducted for estimating the biomass of commercially important fish (e.g., anchovy, jack mackerel), lanternfish (Diaphus garmani and D. chrysorhynchus), and pearlside (Maurolicus japonicus) in summer in the East China Sea (ECS) since 1997. The biomass of lanternfish and pearlside was 2.26–19.16 times that of commercially important fish, and these species represented substantial biomass in the ECS. Though there were no correlations between biomass of pearlside and environmental indices, significant correlations between biomass of lanternfish and southern oscillation index (SOI) in March (positive correlation), arctic oscillation (AO) in March (negative) and October (positive), monsoon index (MOI) in February (positive), and Kuroshio flow mass in winter (positive) were observed. Weak AO and strong MOI would cool down the sea temperature and would lead to increased primary and secondary production in the ECS, thereby enhancing larval survival of lanternfish. The SOI would affect the Kuroshio meander in the ECS, and strong SOI and Kuroshio flow mass would transport larvae of lanternfish to the present survey area. This is the first report on the lanternfish standing stock and its fluctuation in the ECS.     

Effect of combination feeding of <Emphasis Type="Italic">Nannochloropsis</Emphasis> and freshwater <Emphasis Type="Italic">Chlorella</Emphasis> on the fatty acid composition of rotifer <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> in a continuous culture

ABSTRACT:   A continuous culture of rotifer was conducted to investigate the effect of combination feeding of both a high density of Nannochloropsis oculata (N) and condensed freshwater Chlorella (FC) on the fatty acid composition of L-type rotifer Brachionus plicatilis in a continuous culture system. The algal feeding of the rotifers was carried out in three successive steps: N-feeding → N+FC-feeding → FC-feeding. The culture was conducted at 24°C and 25–27 psu in a 2000 mL bottle with 50% of water exchanged daily. The combination N+FC-feeding was effective in increasing rotifer density. The rotifers fed on N+FC (N+FC-R) had more non-polar lipids than polar ones, similar to those on N (N-R), opposite to the rotifers fed on FC (FC-R). N+FC-R contained higher levels of 16:2, 18:2n-6 (linoleic acid [LA]) and 20:2n-6, but lower levels of 18:1, 20:4n-6 (arachidonic acid), 20:5n-3 (eicosapentaenoic acid [EPA]) and 22:5n-3 (docosapentaenoic acid [DPA]) compared with N-R. Whereas N+FC-R contained higher levels of 16:1n-7, EPA and DPA, but lower levels of 16:2 and LA compared with FC-R. N+FC-R had more DPA in polar lipids than in non-polar ones. The Σn-6/Σn-3 ratio in N+FC-R was 0.9–1.0, significantly different from those in N-R (0.4) and FC-R (6.6–8.4). Therefore, it is inferred that the fatty acid profile of the N+FC-R cultured in a continuous culture system was affected by both N and FC. Also, the combination N+FC-feeding may be effective in manipulating the Σn-6/Σn-3 ratio in continuously cultured rotifers.     

<Emphasis Type="Italic">Curcuma longa</Emphasis> as additive in the diet for <Emphasis Type="Italic">Astyanax aff. bimaculatus</Emphasis>

The aim of the present study was to evaluate the effect of turmeric (Curcuma longa) as additive in the diet for Astyanax aff. bimaculatus. Fish (0.83 ± 0.04 g) were fed, for 60 days, with six diets containing 0.0, 20.0, 40.0, 60.0, 80.0, and 100.0 g turmeric kg^?1 feed. There was an increasing linear effect of turmeric on the thickness of the muscular layer, and height and width of the folds of the intestine. In the liver, a quadratic effect was observed of turmeric on the percentage of hepatocyte cytoplasm and a decreasing linear effect on the percentage of sinusoid capillaries. A quadratic effect was also observed of turmeric on the liver glycogen. There was no effect of turmeric on the antioxidant activity in the liver, carcass composition or productive performance of the fish. Thus, we concluded that Curcuma longa has trophic effects on the epithelium and the muscular layer of the intestine of A. aff. bimaculatus. Additionally, low levels of Curcuma longa cause increased deposition of liver glycogen and high levels cause reduction.     

Digestive enzymes and in-vitro digestibility of different species of phytoplankton for culture of the freshwater pearl mussel, <Emphasis Type="Italic">Hyriopsis</Emphasis> (<Emphasis Type="Italic">Hyriopsis</Emphasis>) <Emphasis Type="Italic">bialatus</Emphasis>

Hyriopsis (Hyriopsis) bialatus has been cultured during the mussel life cycle from glochidia to the adult stage with a low total survival of 6% up to 130-day-old juveniles. The main digestive enzymes (amylase and proteinases) were not detectable in one-day-old juveniles, and increased during development. The stomach, including digestive glands, was the major digestive organ for both carbohydrate and protein. The optimum conditions for amylase activity were 40°C and pH 7; for acidic proteinases they were 60°C and pH 5. Two main alkaline proteinases were found in the intestine, with optimum conditions of 30°C and pH 8 and 60°C and pH 8. To improve mussel survival by finding suitable phytoplankton species and age as food for juveniles and adults, an in-vitro digestibility test was performed on ten algal species three and seven days old using amylase and proteinases in crude enzyme extracts from different mussel life stages. Among the phytoplankton selected, the three most efficiently digested by juveniles were seven-day-old Chlorella sp.2, seven-day-old Chlorococcum sp. and seven-day-old Kirchneriella incurvata, in the ratio 1:1:3 for 30-day-old juveniles and 3:1:1 for 130-day-old juveniles. For the adult mussel, three-day-old Chlorella sp.2, seven-day-old Coccomyxa sp., and seven-day-old Monoraphidium sp., in the ratio 3:1:1, were the most digestible phytoplankton. Levels of in-vitro digestibility were related to the quality (not the concentrations) of carbohydrate and protein in the phytoplankton mixtures, and protein digestibility seemed to be the key factor determining food quality for the mussel.     

Identification of <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> and <Emphasis Type="Italic">Undaria undarioides</Emphasis> Laminariales,Phaeophyceae using mitochondrial 23S ribosomal DNA sequences

ABSTRACT:   Mitochondrial 23S ribosomal (r) DNA were sequenced from two Undaria species. The 23S rDNA from seven Undaria pinnatifida individuals were 2707 bp in length, whereas the 23S rDNA from four Undaria undarioides individuals were 2708–2709 bp in length. We found 15–20 nucleotide substitutions and 1–2 gaps between U. pinnatifida (the major haplotype) and U. undarioides . Based on the differences in sequences, we carried out PCR/RFLP analyses to distinguish between U. pinnatifida and U. undarioides , which showed different PCR/RFLP patterns upon Hin fI digestion. Sequence differences and PCR/RFLP analyses of mt 23S rDNA are useful for species identification of Undaria species .     

Cloning and characterization of <Emphasis Type="Italic">Bax1</Emphasis> and <Emphasis Type="Italic">Bax2</Emphasis> genes of <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis> and evaluation of transcript expression in response to grass carp reovirus infection

Multidomain proapoptotic Bcl-2-associated X (Bax) protein is an essential effector responsible for mitochondrial outer membrane permeabilization, resulting in cell death via apoptosis. In this study, two Bax genes of grass carp (Ctenopharyngodon idellus), designated as CiBax1 and CiBax2, were isolated and analyzed. The obtained CiBax1 cDNA is 2058 bp long, with a 579 bp open reading frame (ORF) coding a protein of 192 amino acid residues. The full-length cDNA of CiBax2 is 1161 bp, with a 618 bp ORF coding 205 amino acids. Both CiBax1 and CiBax2 are typical members of Bcl-2 family containing conserved Bcl and C-terminal domains, and they share conserved synteny with zebrafish Bax genes despite the grass carp Bax mapping to different linkage groups. Phylogenetic analysis showed that CiBax1 was clustered with Bax from most teleost fish, and CiBax2 was close to Bax2 from teleost fish but far separated from that of Salmo salar. Quantitative real-time PCR analysis revealed broad expression of CiBax1 and CiBax2 in tissues from healthy grass carp, but the relative expression level differed. The mRNA expression of CiBax1 and CiBax2 was both upregulated significantly and peaked in all examined tissues at days 5 or 6 post-infection with grass carp reovirus. Subcellular localization indicated that CiBax1 protein was localized in both nucleus and cytosol, while CiBax2 protein only in cytosol. Moreover, CiBax2, but not CiBax1 was colocalized with mitochondrion under normal condition. Taken together, the findings would be helpful for further understanding of the function of Bax in teleost fish.