Retinomotor responses of juvenile bluefin tuna Thunnus thynnus

SUMMARY: In bluefin tuna culture, a high mortality of juveniles is caused by bumping into the tank and net-pen walls at dawn. This bumping can possibly be attributed to visually disoriented behavior of the fish. To examine this possibility, the authors carried out retinomotor response experiments with juvenile bluefin tuna (50.7–96.8 mm total length, at which they were transferred from a indoor tank to a sea net-pen) and measured ambient light intensity at the culture site at dawn. The light intensity at which the transition from scotopic to photopic vision takes place was 7.52 lx and the time taken by the transition was 15 min. At dawn, the ambient light intensity rapidly increased from scotopic light intensity level and attained photopic light intensity level in 10 min. This incompatibility of the retinal adaptation with the change in the ambient light intensity could cause the visual disorientation of the fish. It is therefore possible that the visually disoriented juveniles cannot control their high power swimming and thus bump into the walls at dawn.     

Inclusion of prey data improves prediction of bluefin tuna (Thunnus thynnus) distribution

We examined the distribution of Atlantic bluefin tuna ( Thunnus thynnus ) in the Gulf of Maine, Northwest Atlantic Ocean, from 17 to 23 August 1995, in relation to physical and biological parameters. Specifically, we fit a binomial GLM to the bluefin tuna presence–absence data and predictor variables that include: sea surface temperature (SST), ocean depth, distance to an SST front, time-lagged density of SST fronts, and an interpolated surface of Atlantic herring ( Clupea harengus ) density. In addition, we use simple and partial Mantel tests to examine whether bluefin tuna presence–absence data are significantly associated with these predictors, once spatial autocorrelation is accounted for. Results suggest that the distribution of bluefin tuna significantly correlated with herring density ( z  =   3.525, P  =   0.000424), and that inclusion of biological variables results in a more parsimonious model. Mantel tests results indicate that bluefin tuna abundance is significantly correlated with herring density after the effect of spatial structure is removed (Mantel r  =   0.043, P  <   0.019).     

Serum biochemical profiles of captive and wild northern bluefin tuna (Thunnus thynnus L. 1758) in the Eastern Mediterranean

Northern bluefin tuna (NBT) are a prominent marine pelagic fish species. There are few reference values for their blood chemistry and this is the first report to demonstrate blood biochemical values in the Eastern Mediterranean. The study was carried out with 60 captive (penned) and 60 wild NBTs from Ildir Bay (Izmir) and Antalya Bay in the Eastern Mediterranean, from winter to early summer 2003. The aim of this research was to determine the biochemical parameters of wild male/female and captive male/female NBTs. According to the present results, the blood biochemical values of the captive NBTs were significantly higher than those of wild NBTs ( P <0.05) except albumin, globulin, total protein and very low-density lipoprotein levels. Moreover, many of the biochemical parameters were detected at high levels in captive and wild male NBTs than those of the females. Especially, the values of glucose, lactate dehydrogenase, creatine phosphokinase, γ-glutamyl transferase, cholesterol, triglyceride, low-density lipoprotein, ferritin, transferrin and iron levels were significantly higher, although high-density lipoprotein values were significantly lower in wild and captive male samples than those of both groups of females ( P <0.05).     

Complete mitochondrial DNA sequence of the Japanese anchovy Engraulis japonicus

ABSTRACT: The complete nucleotide sequence of the mitochondrial genome for the Japanese anchovy Engraulis japonicus (Teleostei: Clupeiformes) was determined. The entire genome was purified by gene amplification using the long polymerase chain reaction (PCR) technique, and products were subsequently used as templates for PCR with 56 fish-versatile primers that amplify contiguous, overlapping segments of the entire genome. Direct sequencing of the PCR products demonstrated that the genome (16 675 base pairs [bp]) contained the same 37 mitochondrial genes (two ribosomal RNA, 22 transfer RNA and 13 protein-coding genes) as those found in other vertebrates, with the gene order being identical to that in typical vertebrates. A major non-coding region between the tRNA^Pro and tRNA^Phe genes (1024 bp) was considered to be the control (D-loop) region, as it has several conservative blocks characteristic to this region.     

In vivo total nitrogen and total phosphorous digestibility in Atlantic Bluefin Tuna (Thunnus thynnus thynnus Linnaeus, 1758) under industrially intensive fattening conditions in Southeast Spain Mediterranean coastal waters

Atlantic Bluefin Tuna (hereafter referred to as tuna) fattening has been developed quite a lot in south‐eastern Spanish Mediterranean coastal waters, but previous information about nutrition and environmental impact is scarce. Total nitrogen and total phosphorous digestibility was investigated in tuna under routine operation fattening conditions as a first step to know nutrient utilization and to provide tools for estimation of waste output. Tunas were fed ad libitum once a day with a mixture of mackerel, herring, pilchard and gilt‐sardine. Body weight of sampled tuna ranged between 150 and 350 kg. Faeces were collected by dissection of the distal intestine after slaughtering and directly with a manual sieve by scuba divers into the sea cages. Endogenous inert marker was acid insoluble ash. Apparent digestibility coefficient (ADC) for total‐N was lower when faeces were collected by dissection of the intestine (DI: 658.2 g kg^?1) than when by direct collection (DC: 937.4 g kg^?1). Total‐P ADC was lower when faeces were directly collected (DC: 481.4 g kg^?1) than when collected by intestine dissection (DI: 661.9 g kg^?1). The nitrogen digestibility in tuna was as high as in other carnivorous fish, while low phosphorous digestibility, as in many fishes, could be related with phosphorous excess in diet. DC results seem to be more consistent and appropriate for waste output estimation. Results demonstrate the need for a more accurate nutritional evaluation and development of formulated artificial diets.     

Prevalence,intensity and pathology of the nasal parasite Nasicola hogansi in Atlantic bluefin tuna (Thunnus thynnus)

Ectoparasitic flatworms of Nasicola (Monogenoidea: Capsalidae), which infect nasal epithelium of true tunas (Thunnus spp.), are not well studied, nor have their impacts on the host's olfactory organ been evaluated. Infections of Nasicola hogansi on Atlantic bluefin tuna, Thunnus thynnus, were investigated with emphasis on the relationship between infection prevalence, abundance and mean intensity with bluefin tuna size, sex, body condition and capture month, as well as histopathological effects. Commercially caught Atlantic bluefin tuna (n = 161, 185–305 cm curved fork length) from the Gulf of Maine were sampled during June through August 2009 for infections by N. hogansi. A total of 247 specimens of N. hogansi were collected, with a prevalence of 45.3%, mean abundance of 1.57 (CI: 1.21–2.03) and mean intensity of 3.45 (CI: 2.91–4.22). Neither fish sex nor landing month had a significant effect on parasite parameters. Larger and better-conditioned Atlantic bluefin tuna had a higher mean intensity of infection. Pathology associated with infection by N. hogansi included extensive necrosis, sloughing of the nasal epithelium and associated inflammation of underlying connective tissues. Further epidemiological and pathological study of this host–parasite system is warranted since impaired olfaction, if present, could adversely affect spawning and migration of this top ocean predator.     

Identification of Atlantic bluefin tuna (Thunnus thynnus) stocks from putative nurseries using otolith chemistry

Chemical signatures in the otoliths of teleost fishes represent natural tags that may reflect differences in the chemical and physical characteristics of an individuals' environment. Otolith chemistry of Atlantic bluefin tuna (Thunnus thynnus) was quantified to assess the feasibility of using these natural tags to discriminate juveniles (age 0 and age 1) from putative nurseries. A suite of six elements (Li, Mg, Ca, Mn, Sr and Ba) was measured in whole otoliths using solution‐based inductively coupled plasma mass spectrometry. Otolith chemistry of age‐1 T. thynnus collected from the two primary nurseries in the Mediterranean Sea and western Atlantic Ocean differed significantly, with a cross‐validated classification accuracy of 85%. Spatial and temporal variation in otolith chemistry was evaluated for age‐0 T. thynnus collected from three nurseries within the Mediterranean Sea: Alboran Sea (Spain), Ligurian Sea (northern Italy), and Tyrrhenian Sea (southern Italy). Distinct differences in otolith chemistry were detected among Mediterranean nurseries and classification accuracies ranged from 62 to 80%. Interannual trends in otolith chemistry were observed between year classes of age‐0 T. thynnus in the Alboran Sea; however, no differences were detected between year classes in the Tyrrhenian Sea. Age‐0 and age‐1 T. thynnus collected from the same region (Ligurian Sea) were also compared and distinct differences in otolith chemistry were observed, indicating ontogenetic shifts in habitat or elemental discrimination. Findings suggest that otolith chemistry of juvenile T. thynnus from different nurseries are distinct and chemical signatures show some degree of temporal persistence, indicating the technique has considerable potential for use in future assessments of population connectivity and stock structure of T. thynnus.     

A rapid latex agglutination test for gender identification in the Atlantic bluefin tuna,Thunnus thynnus (Linnaeus)

A rapid, one‐step agglutination assay has been developed, based on latex particles sensitized with antibodies against vitellogenin (Vtg), aimed at Atlantic bluefin tuna, Thunnus thynnus (Linnaeus) (ABFT), gender identification. The egg‐yolk precursor protein Vtg was used as a gender marker for the assay as it is a female‐specific protein synthesized during reproductive maturation. The presence of Vtg in the plasma was revealed in 60–120 s through an agglutination reaction by mixing small volumes of ABFT plasma and an anti‐Vtg antibody‐latex suspension on a microscope slide. The effectiveness of the present test was restricted to the months of May and June, concomitant with high circulating Vtg levels. Because of its rapidity and ease of performance in the field, the present gender identification assay could be useful for broodstock management in the aquaculture industry as well as in tagging studies on wild populations.     

Complete mitochondrial DNA sequence of ayu Plecoglossus altivelis

SUMMARY: We determined the complete nucleotide sequence of the mitochondrial genome for ayu, Plecoglossus altivelis . Two large DNA fragments covering the entire genome were amplified using a long polymerase chain reaction (PCR) technique, and the products subsequently used as templates for PCR with 57 fish-versatile and five species-specific primers that amplify contiguous, overlapping segments of the entire genome. Direct sequencing of the PCR products demonstrated that the genome (16 537 bp) contained the same 37 mitochondrial genes (two ribosomal RNA, 22 transfer RNA, and 13 protein-coding genes) as those found in other vertebrates, with the gene order identical to that in typical vertebrates. A major non-coding region between the tRNA^Pro and tRNA^Phe genes (857 bp) was considered to be the control region (D-loop), as it has several conservative blocks that are characteristic to this region.     

Bluefin tuna (Thunnus thynnus) distribution in relation to sea surface temperature fronts in the Gulf of Maine (1994–96)

Fishery‐linked aerial surveys for bluefin tuna (Thunnus thynnus) were conducted in the Gulf of Maine (GOM) from July through October, 1994–96. Each year, from 507 to 890 surface schools were detected and their locations examined in relation to oceanographic conditions. Correlations between bluefin tuna presence and environmental variables were explored for sea surface temperature (SST), distance to a SST front, frontal density (relative density of all SST fronts seen in a given 1 km area for 2 weeks prior to each tuna sighting), and bottom depth and slope. Mean SST associated with bluefin schools was 18.1°C (±2.8). Schools were located at a mean distance of 19.7 km (±19.6) from SST fronts, and in water masses with an average frontal density of 28.2 m km^?2 (±35.7). Mean bottom depth of detected schools was 139.0 m (±70.3), and mean bottom slope was 0.7% rise (±0.7). A binomial generalized linear model fit to these variables indicated that bluefin are seen closer to fronts than locations in which no tuna were seen. Using simple and partial Mantel tests, we investigated the spatial correlation between bluefin tuna presence and the environmental variables, controlling for spatial autocorrelation. For each day that schools were sighted, we performed 24 Mantel tests, on a combination of response and predictor variables. The spatial relationship between bluefin tuna and SST fronts was inconsistent. Our analysis identified significant spatial structure in the bluefin school locations that had no significant correlation with any of the measured environmental features, suggesting that other untested features, such as prey density, may be important predictors of bluefin distribution in the GOM.     

Liver melanomacrophage centres as indicators of Atlantic bluefin tuna,Thunnus thynnus L. well‐being

Melanomacrophage centres (MMCs), located in different organs of non‐mammalian vertebrates, play a role in the destruction, detoxification or recycling of endogenous and exogenous materials. Cytochrome P450 monoxygenase 1A (CYP1A) is involved in xenobiotics biotransformation, and its liver expression is considered as a biomarker for detecting exposure to environmental pollutants. Atlantic bluefin tuna (ABFT), Thunnus thynnus L., liver samples were collected from: wild animals caught in the eastern Atlantic; juveniles reared in the central Adriatic; juveniles reared in the northern Adriatic; adults reared in the western Mediterranean. The samples were processed for basic histology, histochemistry and for CYP1A immunodetection. An unexpected high density of MMCs, containing ferric iron and lipofuscin–ceroids, was detected in the juveniles sampled in the northern Adriatic Sea. These individuals showed also a strong anti‐CYP1A immunopositivity in hepatocytes and in the epithelium of bile ducts. This study supports the utility of MMCs as biomarkers of fish ‘health status’ and gives concern for a potential contaminant accumulation in ABFT.     

Testes maturation of reared Pacific bluefin tuna Thunnus orientalis at two-plus years old

ABSTRACT:   Stable reproduction is essential for supplying artificially hatched fish to tuna aquaculture. We observed testes maturation in reared Pacific bluefin tuna (PBT) Thunnus orientalis at 2+ years of age. The incidence of males with mature testes was 25.0%, and 40% of the males had developing testes that contain spermatozoa, while oocytes of the same aged females were not mature. These fish were wild-caught at 0+ years old in August 1997 and the gonads were examined in October 1998 and January–February 2000. Therefore, the age at examination in 2000 was estimated to be 2 years and 7–10 months old considering the spawning season of the wild PBT and the size when captured. Histological examination of the matured and developing testes showed that they contained spermatozoa, spermatids, spermatocytes, and spermatogonia. All the spermatozoa were observed to be motile in sea water under light microscopy. From the results of this and previous studies, matured males are probably fertile for at least 5 months a year in Kushimoto. The testes maturation observed at young age in captivity is considered promising to reduce the cost of broodstock maintenance for the juvenile production of PBT, especially if the sperm are cryopreserved.