Completion of the Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) life cycle

Tuna aquaculture is currently dependent on the wild capture of juveniles for production. The development of hatchery technology for bluefin and other tunas would be a major step forward in improving sustainability of their aquaculture. The present study overviews the technology in the life cycle completion of the Pacific bluefin tuna (PBT) Thunnus orientalis (Temminck et Schlegel) under aquaculture conditions in Kinki University, and the problems to be solved for the establishment of tuna hatchery technology. On 23 June 2002, broodstock of PBT that were artificially hatched and reared spontaneously spawned in captivity. The resulting eggs hatched and were subsequently reared to the juvenile stage. The spawning fish were the result of a research project started in 1987 to rear wild‐caught juvenile PBT that were several months old. Fertilized eggs were obtained from these fish in 1995 and 1996. Resulting juveniles (the artificially hatched first generation) were reared to maturity and spawned in 2002. Over the summer of 2002, 1.63 million eggs from these fish were used for a mass rearing experiment, and 17 307 juveniles were produced and transferred to an open sea net cage. Of these artificially hatched second‐generation PBT, 1100 grew to approximately 95 cm total length and 14 kg body weight in 22 months. This procedure means the completion of PBT life cycle under aquaculture conditions, which was first attained among large tuna species. The problems awaiting solution in PBT hatchery production are their unpredictable spawning in captivity, to improve survival during the first 10 days post hatch, to reduce cannibalism in larval and juvenile stages, and to solve collision problem causing high mortality during the juvenile stage.     

Effect of partial and total replacement of fish, shrimp head, and soybean meals with red crab meal Pleuroncodes planipes (Stimpson) on growth of white shrimp Litopenaeus vannamei (Boone)

Red crab meal (RCM), as a potential protein source in diets for juvenile shrimp Litopenaeus vannamei, was evaluated over a 45‐day growth trial under laboratory conditions. Eight experimental diets were tested. The basal diet contained fish (tuna by‐product), shrimp head and soybean (solvent extracted) meals as primary protein sources. Fish or soybean meals were substituted, on an equal‐protein basis, at 33%, 66% and 100% by RCM, whereas shrimp head meal (SHM) was substituted at 100%. A commercial diet was included as a reference. Final weight ranged between 2.23 and 3.36 g and growth rates (GRs) between 0.048 and 0.073 g day⁻¹. Where 66% or 100% of the protein from fish or soybean meals was substituted by RCM, the diets produced significantly higher final weights and GRs than other diets. Regression analysis showed that final weight of shrimp depended significantly on the percentage of substitution, and that the maximum weight gain would be obtained when substituting RCM for 80.2% of fish meal and 81.2% of soybean meal. Feed conversion ratio was below 1.8 for all treatments and there was no apparent relationship with other aspects of the diet. Red crab meal served as a suitable protein source for partial or total replacement of tuna by‐product, soybean and SHMs for cultivated juvenile shrimp L. vannamei.     

Comparative intestinal absorption of amino acids in rainbow trout (Oncorhynchus mykiss), totoaba (Totoaba macdonaldi) and Pacific bluefin tuna (Thunnus orientalis)

The kinetics of amino acid absorption in the proximal section of three fish species were studied using an everted intestine technique and a pancreatic digest of casein (Tryptone), as the model amino acid mixture. Fresh intestine of rainbow trout (Oncorhynchus mykiss) was used to set up the experimental system, and results were compared with those obtained using intestines from totoaba (Totoaba macdonaldi) and bluefin tuna fish (Thunnus orientalis). The kinetics of amino acid absorption was sigmoidal for all amino acids and for each species of fish tested. In general, specific absorptions of essential amino acids were higher than those of non‐essential ones. No correlation between the concentration of amino acids in the Tryptone solution and the corresponding absorptions was found. The maximum specific absorption rates of all amino acids for trout were 10 times higher than those determined for totoaba and bluefin tuna. The relative amounts of the different amino acids preferentially absorbed in all three species were different. Results obtained from the everted technique may be applicable to the design of formulated diets for large fish species with commercial value.     

Mortality processes of hatchery‐reared Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) larvae in relation to their piscivory

In mass culture of Pacific bluefin tuna Thunnus orientalis, yolk‐sac larvae of other species are fed as a major prey item to tuna larvae from 7 to 8 mm in total length. Marked growth variations in tuna larvae are frequently observed after feeding of yolk‐sac larvae, and this variation in the growth of tuna larvae is subsequently a factor leading to the prevalence of cannibalistic attacks. To elucidate details of the mortality process of hatchery‐reared tuna larvae after the initiation of yolk‐sac larvae feeding, we compared the nutritional and growth histories of the surviving (live) tuna larvae to those of the dead fish, found dead on the bottom of the tank, as direct evidence of their mortality processes. Cause of mortality of tuna larvae 3 and 5 days after the initiation of feeding of yolk‐sac larvae was assessed from nitrogen stable isotope and otolith microstructure analyses. Stable isotope analysis revealed that the live fish rapidly utilized prey fish larvae, but the dead fish had depended more on rotifers relative to the live fish 3 and 5 days after the initiation of feeding of yolk‐sac larvae. The growth histories based on otolith increments were compared between the live and dead tuna larvae and indicated that the live fish showed significantly faster growth histories than dead fish. Our results suggest that fast‐growing larvae at the onset of piscivory could survive in the mass culture tank of Pacific bluefin tuna and were characterized by growth‐selective mortality.     

In vitro amino acid absorption using hydrolysed sardine muscle or soybean meal at different intestinal regions of the Pacific bluefin tuna (Thunnus orientalis)

The amino acid (AA) absorption along the intestinal tract of the Pacific bluefin tuna (Thunnus orientalis) was evaluated using two hydrolysed protein sources (fresh sardine muscle and soybean meal) with the everted intestine technique. Pork pepsin and pancreatic enzyme extract from the bluefin tuna were used to hydrolyse the protein from fresh sardine (FSH) and soybean meal (SMH) under optimal bluefin tuna fish physiological conditions. Both of the hydrolysate solutions were tested within three intestinal sections from the bluefin tuna. The everted intestinal fractions immersed in the hydrolysate solutions were sampled at different times to analyse for AA and absorption rate calculations. Fresh sardine and SMH contained greater amounts of essential amino acids (EAA) than those of non‐essential amino acids (NEAA); however, the profiles of AA absorbed showed higher absorption of NEAA in both cases. Using a similar concentration solution, the absorption rates within the intestinal fractions showed a preferential absorption in the proximal and distal regions for Arg and His when FSH was used. However, the absorption rates for Lys resulted in a decreasing proximal‐to‐distal gradient between the different intestinal regions for FSH and SMH. The possibility of a catabolic role of certain AAs in the enterocytes being able to explain the differences in absorption is discussed.     

Comparison of the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus) tuna associated with drifting FADs in the equatorial central Pacific Ocean

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5–65.0 cm in fork length (FL)], 43 yellowfin (31.6–93.5 cm FL) and 32 bigeye tuna (33.5–85.5 cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100 m, but occasionally dived to around 150 m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow the selective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.     

Simultaneous Determination of Amino Acids and Biogenic Amines in Tuna and Mahi-Mahi by Reversed-Phase Ultra-High Performance Liquid Chromatography

Tuna and mahi-mahi are two major fish species responsible for histamine poisoning. This research developed a rapid ultra-high performance liquid chromatography (UHPLC) method to determine amino acids, histamine, and other biogenic amines that can act as co-indicators of histamine poisoning in tuna and mahi-mahi. The modified UHPLC method could simultaneously determine four biogenic amines and 10 major free amino acids in mahi-mahi (Coryphaena hippurus) and yellowfin tuna (Thunnus albacares) within 17.5 min. This UHPLC method showed good linear response, sensitivity, resolution, recovery, repeatability, and number of theoretical plates. The concentrations of detected amino acids, biogenic amines in mahi-mahi and tuna, and their relationships with fish spoilage grade were determined by this UHPLC method. The developed UHPLC method is a rapid and accurate way to monitor quality changes of mahi-mahi and tuna by inspecting the changes of amino acids and biogenic amines.     

Identification of growth‐related nucleotide polymorphism in cultured Pacific bluefin tuna,Thunnus orientalis

Pacific bluefin tuna (PBF), Thunnus orientalis, is commercially one of the most important species of tuna. In this study, amplified fragment length polymorphism (AFLP) screening was conducted to find the growth‐related polymorphic DNA in cultured PBF. Fish hatched in 2007 were harvested at an age of 818–1994 days. They were categorized into superior, average and inferior growth groups, depending on their growth score at the time of harvest. On AFLP screening of 24 fish, with eight fish from each group, 215 polymorphic DNA fragments were observed. A second amplification, with EcoRI + ACC and MseI + CCC primers, generated a polymorphic fragment of 630 bp at a rate of 80.0% (n = 15) in the superior, 56.3% (n = 16) in the average and 20.0% (n = 15) in the inferior growth groups. Polymerase chain reaction (PCR) primers, which could amplify both AFLP‐positive and AFLP‐negative loci, were developed using the consensus sequence outside the AFLP target fragment. Eleven haplotypes were obtained by sequence analysis of the PCR product at the AFLP target loci. Among those, haplotype 1 was statistically significant in the superior and average growth groups and could be used as a molecular marker for distinguishing the individuals with superior and average growth from those with inferior growth.     

Characterization and ontogenetic development of digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae

The major digestive enzymes in Pacific bluefin tuna Thunnus orientalis larvae were characterized, and the physiological characteristics of the enzymes during early ontogeny were clarified using biochemical and molecular approaches. The maximum activity of trypsin (Try), chymotrypsin (Ct) and amylase (Amy) was observed at pH 6–11, 8–11 and 6–9, respectively. Maximum activity of Try, Ct and Amy occurred at 50 °C, that of lipase (Lip) was at 60 °C and that of pepsin (Pep) was at 40–50 °C. These pH and thermal profiles were similar to those for other fish species but differed from those previously reported for adult bluefin tuna. Enzyme activity for all enzymes assayed was found to decrease at high temperatures (Try, Ct, Amy and Pep: 50 °C; Lip: 40 °C), which is similar to findings for other fish species with one marked exception—increased Try activity was observed at 40 °C. Lip activity appeared to be dependent on bile salts under our assay conditions, resulting in a significant increase in activity in the presence of bile salts. Ontogenetic changes in pancreatic digestive enzymes showed similar gene expression patterns to those of other fish species, whereas marked temporal increases in enzyme activities were observed at 10–12 days post hatching (dph), coinciding with previously reported timing of the development of the pyloric caeca in bluefin tuna larvae. However, complete development of digestive function was indicated by the high pep gene expression from 19 dph, which contradicts the profile of Pep activity and previously reported development timing of the gastric gland. These findings contribute to the general knowledge of bluefin tuna larval digestive system development.     

Peruvian fish meal has comparative potential to enzyme-treated Chilean fish meal as protein source of diet for larvae and juvenile Pacific bluefin tuna Thunnus orientalis

The present study aimed to evaluate suitable protein sources of formulated diet to replace prey fish. Regarding the test diet, the two dietary treatments (FM: Peruvian anchovy fish meal, and ETFM: enzyme-treated Chilean fish meal) were employed. Prey fish (PF; spangled emperor fish Lethrinus nebulosus) was used as a control. FM and ETFM diets are fed together with a limited amount of PF to Pacific bluefin tuna (PBT) larvae having an initial mean total length of 17.9 mm and body weight of 52.8 mg at 20 days post-hatching during the weaning period. Survival and growth were compared after 10 days of the feeding trial. Survival was significantly higher in the PF group than the FM and ETFM group. The PF group had significantly greater growth performance than the other groups. Between FM and ETFM groups, fish in the FM group showed significantly better growth than the ETFM group. Regarding the essential amino acids of the carcass, similar amino acid content was recorded in all treatments. However, carcass docosahexaenoic acid in the PF group was significantly higher than in the other groups. These results suggest that Peruvian anchovy meal without enzyme digestion can be used as the protein source in the formulated diet for juvenile PBT.

     

Dissolved nutrient release from solid wastes of southern bluefin tuna (Thunnus maccoyii, Castelnau) aquaculture

Finfish pens are point sources of dissolved nutrients released from fish metabolism or degradation of solid wastes. Nutrients leaching from uneaten feed and faeces are not usually quantified in mass budgets for these systems, leading to an overestimation of fish retention or deposition to the seabed. In this study, we investigated nutrient leaching from pellets and baitfish feed as well as faeces of southern bluefin tuna (Thunnus maccoyii) into seawater. Faeces were nitrogen depleted (51–54 mg N g⁻¹ dw) and phosphorus enriched (62–72 mg P g⁻¹ dw) compared with feeds (83–111 mg N g⁻¹ dw and 17–21 mg P g⁻¹ dw). Less phosphorus was available for leaching from pellets and faeces of pellet‐fed tuna (5–6%) than from baitfish and faeces of baitfish‐fed tuna (17–21%). The proportion of soluble nitrogen in pellets (15%) was also lower than in baitfish and faeces (35–43%). Leaching loads for a feed conversion ratio of 5 were estimated as 22 and 26 kg N tonne⁻¹ growth when baitfish or pellets were used as feed respectively. Phosphorus loads were estimated as 15 and 4 kg P tonne⁻¹ growth respectively. More than 90% of nitrogen loads, and approximately 50% of phosphorus, are likely to be released into seawater before solid wastes reach the seafloor.     

Comparison of the lipid profiles from wild caught eggs and unfed larvae of two scombroid fish: northern bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis> L., 1758) and Atlantic bonito (<Emphasis Type="Italic">Sarda sarda</Emphasis> Bloch, 1793)

Lipids and essential fatty acids are determinants of the reproductive process in marine fish, affecting fecundity, egg quality, hatching performance, pigmentation and larval malformation. We have analyzed and characterized the lipids of eggs and unfed larvae of two wild caught scombroid fish, the Atlantic northern bluefin tuna (Thunnus thynnus) and Atlantic bonito (Sarda sarda). Dry matter and total lipid contents, polar and neutral lipid classes and total lipid fatty acid contents were determined in the eggs of bluefin tuna and eggs and unfed larvae during the development of Atlantic bonito. Bluefin tuna eggs had slightly but significantly more dry mass than bonito eggs but very similar lipid content. However, bluefin tuna eggs presented a higher polar lipid content due to increased proportions of phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). Bonito eggs and larvae showed increasing dry mass and decreasing lipid content with development. The proportion of polar lipids increased due to increased PE, PS and PI, whereas choline-containing polar lipids (phosphatidylcholine and sphingomyelin) remained relatively constant. Free cholesterol also increased, whereas the levels of other neutral lipids, especially triacylglycerol and steryl ester fractions, decreased, presumably due to utilization for energy to drive development. Bluefin tuna eggs had higher levels of n − 3 and n − 6 highly unsaturated fatty acids due to higher docosahexaenoic and arachidonic acid contents, respectively, than bonito eggs. The results are discussed in relation to the lipid and fatty acid requirements of larval scombroid fish in comparison to those of other larval marine finfish species under culture conditions.     

Relationship between prey utilization and growth variation in hatchery‐reared Pacific bluefin tuna,Thunnus orientalis (Temminck et Schlegel), larvae estimated using nitrogen stable isotope analysis

In mass culture of Pacific bluefin tuna Thunnus orientalis, a marked growth variation is observed after they start feeding at 6–7 mm in body length (BL) on yolk‐sac larvae of other species, and the growth variation in tuna larvae is a factor leading to the prevalence of cannibalism. To examine the relationship between prey utilization and growth variation, nitrogen stable isotope ratios (δ¹⁵N) of individual larvae were analysed. A prey switch experiment was conducted under two different feeding regimes: a group fed rotifers (rotifer fed group), and a group fed yolk‐sac larvae of spangled emperor, Lethrinus nebulosus (fish fed group) from 15 days after hatching (6.87 mm BL). The fish fed group showed significantly higher growth than the rotifer fed group. Changes in the δ¹⁵N of the fish fed group were expressed as an exponential model and showed different patterns from those of the rotifer fed group. The δ¹⁵N of fast‐growing tuna larvae collected in an actual mass culture tank after the feeding of yolk‐sac larvae was significantly higher than those of the slow‐growing larvae, indicating that slow glowing larvae depended largely on rotifers rather than the yolk‐sac larvae.     

Using historical fisheries data to predict tuna distribution within the British Indian Ocean Territory Marine Protected Area,and implications for its management

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Purification and characterization of glutathione peroxidase 1 in the red muscle of Pacific bluefin tuna Thunnus orientalis

Glutathione peroxidase GPx1 was purified from the red muscle of Pacific bluefin tuna Thunnus orientalis and its enzymatic properties were characterized. The enzyme was optimally active at pH 7.4 with a specific activity for hydrogen peroxide and a K _m of 6.7 μM. cDNA was also isolated and it contained a predicted open reading frame (ORF) encoding a 188 amino acid protein. The phylogenetic tree shows that fish including Pacific bluefin tuna, pufferfish, and zebrafish, but not mammals, possess two genetically distinct types of GPx1, i.e., GPx1a and GPx1b. The purified enzyme was classified as a fish GPx-1b enzyme on the basis of the phylogenetic tree of the GPx1 family.     

Automated acoustic method for counting and sizing farmed fish during transfer using DIDSON

Counting and sizing large farmed fish such as tuna is often performed during their transfer from one net cage to another. Dual-frequency identification sonar (DIDSON) provides an automated fish counting and sizing tool. However, its counter and sizer are not suitable for measuring farmed fish because of net movements due to currents and subsequent frequent image breakups. This paper presents a fully automated acoustic method to count and size farmed fish during fish transfer by using DIDSON imaging. The background is subtracted from the image after being stabilized by an image phase-only correlation method. The segmentation of the fish is obtained by tracing the edges with a contour tracing method. To prevent recounting the same fish, a Kalman filter algorithm was designed and adapted to predict fish movements. Automated counting was performed by analyzing the spatiotemporal trajectory of the track. The separated fish images were searched for and body length was obtained by summing down the centerline segments from the head to the tail of the fish. The proposed system was verified using farmed yellowtail, Seriola quinqueradiata (mean total length 83.1 cm) to obtain a sizing error of mean total length within 2.4 cm.     

Substitute and complement relations among various fish species in the Japanese market: implications for fishery resource management

A demand system analysis was conducted to examine the substitute relationships between tuna and skipjack tuna in the Japanese market. Data from the Annual Report on Family Income and Expenditure Survey from 1965 to 2006 were used for the analysis using the almost ideal demand system (AIDS). Results suggest that skipjack tuna can be a strong substitute for tuna, while other fish groups are not a clear substitute. Our analysis of substitute relationships among fish species in a market indicates that this is a factor that should be considered for better fisheries resource management. For instance, even under a situation where one fish species is underexploited, proper attention to its fishery management is necessary if the fish is a strong substitute for another popular fish species in the market.     

Effect of Seasonality,Location, and Size on Lipid Content in North Pacific Troll-Caught Albacore Tuna (Thunnus alalunga)

ABSTRACT

Two hundred and thirty-nine albacore tuna (Thunnus alalunga) were troll-caught in the mid-Pacific Ocean and off the US Pacific Coast from June to November 2003. Catch location, harvest date, and sea surface temperature were recorded for individual fish, and lipid and moisture content in the white muscle were determined. The average weight of the alba-core was 6.07 kg and lipid content was highly variable (0.67–18.74%). There was an inverse correlation between the lipid and moisture content of albacore (R² = 0.93), and percent lipid increased slightly in fish caught later on in the season (R² = 0.24). Geographical Information Systems (GIS) software was used to determine correlations between lipid content and geographic location. Lipid content varied considerably among tuna caught at similar latitudes; however, most fish caught below 40°N had a lipid content of less than 10%, while the fish with the highest lipid content (13–19% lipid) were all harvested above 40°N.     

Immunochemical sexing of living yellowfin tuna, Thunnus albacares (Bonnaterre), using a vitellogeninlike protein

Sexing of living yellowfin tuna, Thunnus albacares (Bonnaterre), was carried out based on immunochemical detection of vitellogenin (VTG), a female-specific protein. Tissue samples were taken from swimming fish in a sea pen by a hand-made apparatus. Recently fertilized eggs were also collected before tissue sample trials. A double immunodiffusion pattern showed that the egg homogenate of T. albacares reacted with rabbit antibody against the purified VTG of greater amberjack, Seriola dumerili (Risso). This suggests that the VTG of T albacares has an antigenicity similar to that of S, dumerili and that this antibody can be used to detect T albacares VTG. Immunodot-blotting analysis revealed that, out of the two fish tested, the tissue sample from one, but not the other, reacted with this antibody, suggesting that the former was a mature female, and the latter a male or immature female. Examination of the fish gonads revealed an ovary and a testis, respectively. Immunological and morphological results corresponded completely. Therefore, the method used in the present study is available for discriminating the sexes of T albacares.