Genetic validation of the unexpected presence of a tropical tuna,bigeye tuna (Thunnus obesus), in the Mediterranean

Bigeye tuna (Thunnus obesus, Lowe, 1839) is one of the eight recognized species of the genus Thunnus. It is considered a tropical species distributed in the Atlantic, Pacific and Indian Oceans. To date, no validated presence of this species has been reported inside the Mediterranean Sea. This study, however, confirms, for the first time, the presence of three young individuals of this species within the Mediterranean Sea.     

Physiological thermoregulation in bigeye tuna,Thunnus obesus

Synopsis Although a growing body of evidence has indicated that tuna can thermoregulate and have body temperatures that are decoupled from immediate changes in ambient temperature, demonstrating the extent and time-course of body temperature changes in tuna moving through their natural environments has proved to be elusive. Here we use body temperature data telemetered from free-ranging fish to demonstrate short-latency physiological thermoregulation in bigeye tuna. We used a recently developed modeling system to determine the magnitude and time-course of the whole-body thermal conductivity changes that would result in the body temperature changes observed in fish in the wild. The results indicate rapid, 100 to 1000-fold changes in whole-body thermal conductivity that occur in response to quickly changing ambient temperatures. Coupling this physiological response with behavioral thermoregulation expands the foraging space of these animals by permitting activity in wide ranges of water temperatures and depths.Paper from the International Union of Biological Societies symposium The biology of tunas and billfishes: an examination of life on the knife edge, organized by Richard W. Brill and Kim N. Holland.     

Genetic divergence between Atlantic and Indo-Pacific stocks of bigeye tuna (Thunnus obesus) and admixture around South Africa

Two mitochondrial DNA segments of the bigeye tuna (Thunnus obesus) were amplified by polymerase chain reaction (PCR), and restriction fragment length polymorphism (RFLP) analyses of these segments were used for the genetic stock study. The variation in a segment flanking the ATPase and COIII genes was low; only two genotypes (α and β) were detected by RsaI digestion. Yet a large difference in the genotype distribution was observed between ocean basin samples. The α type predominated in four Atlantic samples, where 178 of 244 individuals were the α type. In contrast, only one of 195 individuals collected in the Indo‐Pacific was the α type? The frequency of the α type varied considerably from 0 to 80% among seven samples collected off the Cape of Good Hope. The variation found in the other segment, containing the D‐loop region, was much higher; two endonucleases (DpnII and RsaI) detected five genotypes each and 15 composite genotypes. A highly significant difference in genotype frequencies was observed between the Atlantic and Indo‐Pacific samples, but no heterogeneity was observed among the four Atlantic or among four Indo‐Pacific samples. These results clearly indicate that not only gene flow, but also fish migration, between the Atlantic and Indian Oceans are severely restricted, and that fishes from these distinct stocks are intermingling around South Africa. The simple and diagnostic genetic marker found in this study can be used to estimate mixing ratios between Atlantic and Indian stocks around South Africa.     

Environmental preferences of bigeye tuna, <Emphasis Type="Italic">Thunnus obesus</Emphasis>, in the Indian Ocean: an application to a longline fishery

A survey of the fishing grounds for bigeye tuna, Thunnus obesus, in the Indian Ocean was carried out for a better understanding of the environmental preferences of bigeye tuna in a longline fishery. Catch rates of bigeye tuna were analyzed with respect to the ranges of depth, temperature, salinity, chlorophyll-a, and dissolved oxygen. The optimum capture depth, water temperature, and dissolved oxygen range of bigeye tuna were identified as 240.0 m to 279.9 m, 12.0°C to 13.9°C, and 2.00 mg·L⁻¹ to 2.99 mg·L⁻¹, respectively, in the study area of Indian Ocean. Neither salinity nor chlorophyll-a had a detectable effect on the vertical distribution of the adult bigeye tuna. The dissolved oxygen is the principal factor limiting the vertical distribution of bigeye tuna.     

Reproductive biology of female bigeye tuna Thunnus obesus in the western Pacific Ocean

The reproductive biology of female bigeye tuna Thunnus obesus was assessed by examining 888 fish (ranging from 84·9 to 174·4 cm fork length, L_F) caught by Taiwanese offshore longliners in the western Pacific Ocean from November 1997 to November 1998 and November to December 1999 and 258 gonad samples from these fish. The overall sex ratio of the catch during the sampling differed significantly from 0·5, but males were predominant in sizes >140 cm L_F. Reproductive activity (assessed by histology), a gonado‐somatic index, and the size‐frequency distributions of whole oocytes indicated that spawning occurred throughout the year and the major spawning season appeared to be from February to September. The estimated sizes at 50% maturity (L_F50) of females was 102·85 cm (95% c.i .: 90·79–110·21 cm) and the smallest mature female was 99·7 cm L_F. They are multiple spawners and oocytes develop asynchronously. The proportion of mature (0·63) and reproductively active (0·70) females with ovaries containing postovulatory follicles indicated that they spawn almost daily. Batch fecundity for 15 females with the most advanced oocytes (>730 µm) ranged from 0·84 to 8·56 million eggs (mean ± s.d . = 3·06 ± 2·09). The relationships between batch fecundity (F_B, in millions of eggs) and L_F (cm) and round mass (M_R, kg) were (r² = 0·84) and (r² = 0·80), respectively. The parameters estimated in this study are key information for stock assessments of T. obesus in the western Pacific Ocean and will contribute to the conservation and sustainable yield of this species.     

Genetic stock structure of bigeye tuna in the Indian Ocean using mitochondrial DNA and microsatellites

Genetic differentiation was minimal and overall non-significant among five collections of bigeye tuna Thunnus obesus from the Indian Ocean, examined for variation at mitochondrial DNA (mtDNA) and at seven microsatellite loci.     

Growth and mortality of bigeye tuna <Emphasis Type="Italic">Thunnus obesus</Emphasis> (Scombridae) in the eastern and central tropical Pacific Ocean

Biological parameters such as age, growth and age (or size) at maturity are vital for stock assessment and management. Aging is essential in yielding such information. However, limited aging studies have been conducted for large tropical pelagic species in the eastern and central tropical Pacific Ocean. The objective of this study is to conduct a length frequency analysis for estimating growth and mortality of bigeye tuna in the eastern and central tropical Pacific Ocean using samples from the Chinese longline fishery during February to November 2006. The von Bertalanffy growth parameters of asymptotic fork length L _∞ and growth coefficient k were estimated at L _∞ = 207.4 cm fork length, k = 0.23 year^-1, and theoretical age at zero length t ₀ = −0.40 year. The total mortality rate (Z) was estimated to be 0.60; the fishing mortality rate (F) and the natural mortality rate (M) were 0.25 year^-1 and 0.35 year^-1, respectively. The exploitation rate (E) was 0.16. This study provides the estimates of growth and mortality rate for bigeye tuna in the eastern and central tropical Pacific Ocean, which can be used as biological input parameters in further stock evaluations in this region. However, age analysis, further validation of the age composition and stock structure are needed for future studies.     

Rare occurrence of a bigeye tuna Thunnus obesus in British waters, with notes on other occurrences of sub-tropical tunas

A freshly dead bigeye tuna Thunnus obesus was washed ashore near Burry Port, Wales (51°40' N; 4°15' W) in August, 2006. This is only the third occasion that the species has been observed in British waters, and is the largest and most northerly recorded specimen.     

Large‐scale distribution of tuna species in a warming ocean

Tuna are globally distributed species of major commercial importance and some tuna species are a major source of protein in many countries. Tuna are characterized by dynamic distribution patterns that respond to climate variability and long‐term change. Here, we investigated the effect of environmental conditions on the worldwide distribution and relative abundance of six tuna species between 1958 and 2004 and estimated the expected end‐of‐the‐century changes based on a high‐greenhouse gas concentration scenario (RCP8.5). We created species distribution models using a long‐term Japanese longline fishery dataset and two‐step generalized additive models. Over the historical period, suitable habitats shifted poleward for 20 out of 22 tuna stocks, based on their gravity centre (GC) and/or one of their distribution limits. On average, tuna habitat distribution limits have shifted poleward 6.5 km per decade in the northern hemisphere and 5.5 km per decade in the southern hemisphere. Larger tuna distribution shifts and changes in abundance are expected in the future, especially by the end‐of‐the‐century (2080–2099). Temperate tunas (albacore, Atlantic bluefin, and southern bluefin) and the tropical bigeye tuna are expected to decline in the tropics and shift poleward. In contrast, skipjack and yellowfin tunas are projected to become more abundant in tropical areas as well as in most coastal countries' exclusive economic zones (EEZ). These results provide global information on the potential effects of climate change in tuna populations and can assist countries seeking to minimize these effects via adaptive management.     

Diet composition of bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares) caught on aggregated schools in the western equatorial Atlantic Ocean

The present study aims to characterize and compare the diet of bigeye and yellowfin tunas caught on aggregated schools in the western equatorial Atlantic Ocean. The samples were collected from January 2011 to June 2016. The tunas were measured on board and the stomachs were removed after evisceration. The stomachs were analyzed regarding their Index of Fullness and the importance of each prey in the diet was estimated by the Index of Relative Importance (IRI). The diet overlap was assessed by the Morisita‐Horn's Index, Non‐Metric Multidimensional Scale (NMDS), and Analysis of Similarity (ANOSIM). The feeding strategy was determined by the Costello's Diagram. The 195 bigeye and 212 yellowfin tunas ranged in fork length from 51 to 137 cm and 43 to 174 cm, respectively. The diet of bigeye tuna was composed of 10 families of fish, three cephalopod families, and four crustacean orders. The diet of yellowfin tuna was composed of 11 families of fish, three cephalopod families, and three crustacean orders. The yellowfin tuna seems to feed upon more abundant prey species near the surface like flying fish, which have the concentration enhanced by the light attractors on the boat, and occasionally on other prey from deeper habitats like lanternfish, squids, and pomfret. Bigeye tuna feed mainly at prey that commonly occurs in deeper habitats like squids, drift fish, lanternfish, and pomfret.     

Pollen, tapetum and orbicule development in Modiolastrum malvifolium (Malvaceae)

Background and Aims: Although orbicular functions are still a matter of debate, theyare considered by most authors to be exclusively formed by asecretory tapetum. However, the presence of orbicules on a peritapetalmembrane associated with a plasmodial tapetum has been describedfor Abutilon pictum (Malvaceae) in a previous study. Thus, studieson other species of Malvaceae are necessary to corroborate thepresence of such bodies in other members of the family. Pollenand microsporangium development of Modiolastrum malvifoliumhas been studied in this work. Methods: Anthers at different stages of development were processed fortransmission electron microscopy and light microscopy. Membranesand pollen walls resistant to acetolysis were isolated fromwhole anthers. Key Results: Microspore tetrads have a tetrahedral arrangement. Pollen grainsare shed at the bicellular stage. The tapetum is invasive, non-syncytialand a peritapetal membrane with orbicules is formed. Conclusions: This is the first report of the presence of orbicules on a peritapetalmembrane in a species with a tapetum of an invasive, non-syncytialtype. Taking into consideration all the information on the subject,it can be concluded that the presence of orbicules is not astable criterion to differentiate between a secretory or plasmodial,or intermediate invasive, non-syncytial tapetum.     

侧柏小孢子囊壁绒毡层和中层细胞的发育

侧柏[Platycladus orientalis (L.)Franco]小孢子囊壁包括3层细胞：表皮、中层和绒毡层。中层细胞为1层扁平的细胞。绒毡尾细胞属于分泌型。成熟的绒毡层细胞除了有单核和双核细胞外,还有三核和四核等多核细胞,细胞核有圆形和长椭圆形2种形态。绒毡层细胞的洒色质伴随着小孢子母细胞减数分裂有一个浓缩和伸展的时期,这个时期影响营养物质向小孢子囊内部转运,绒毡层细胞发育的初期就为造孢细胞提供营养,后期解体时,分泌的乌氏体不是散乱地而是有组织地向花粉粒的表面转移。中层和绒毡层细胞最终作为营养被全部吸收利用。     

Cones in the retina of the catfish, Clarias batrachus (L.)

The retina of the catfish Clarias butrachus (L.), supposed to possess an all-rod retina, is found on re-investigation to contain both rods and cones. The retina is characterized by a prominent tapetum and multiple optic papillae.     

Scale diversity in bigeye tuna (Thunnus obesus): Fat‐filled trabecular scales made of cellular bone

Tunas of the genus Thunnus possess many morphological and physiological adaptations for their high‐performance epipelagic ecology. Although Thunnus anatomy has been studied, there are no quantitative studies on the structure of their scales. We investigated the scales of bigeye tuna (Thunnus obesus) from ten regions of the body using micro computed tomography (µCT)‐scanning and histology to quantitatively and qualitatively compare regional scale morphology. We found a diversity of scale sizes and shapes across the body of bigeye tuna and discriminant function analysis on variables derived from µCT‐data showed that scales across the body differ quantitatively in shape and size. We also report the discovery of a novel scale type in corselet, tail, and cheek regions. These modified scales are ossified shells supported by internal trabeculae, filled with fat, and possessing an internal blood supply. Histological analysis showed that the outer lamellar layers of these thickened scales are composed of cellular bone, unexpected for a perciform fish in which bone is typically acellular. In the fairing region of the anterior body, these fat‐filled scales are stacked in layers up to five scales deep, forming a thickened bony casing. Cheek scales also possess a fat‐filled internal trabecular structure, while most posterior body scales are more plate‐like and similar to typical teleost scales. While the function of these novel fat‐filled scales is unknown, we explore several possible hypotheses for their function.     

Fertile Arabidopsis cyp704b1 mutant,defective in sporopollenin biosynthesis,has a normal pollen coat and lipidic organelles in the tapetum

The exine acts as a protectant of the pollen from environmental stresses, and the pollen coat plays an important role in the attachment and recognition of the pollen to the stigma. The pollen coat is made of lipidic organelles in the tapetum. The pollen coat is necessary for fertility, as pollen coat-less mutants, such as those deficient in sterol biosynthesis, show severe male sterility. In contrast, the exine is made of sporopollenin precursors that are biosynthesized in the tapetum. Some mutants involved in sporopollenin biosynthesis lose the exine but show the fertile phenotype. One of these mutants, cyp704b1, was reported to lose not only the exine but also the pollen coat. To identify the cause of the fertile phenotype of the cyp704b1 mutant, the detailed structures of the tapetum tissue and pollen surface in the mutant were analyzed. As a result, the cyp704b1 mutant completely lost the normal exine but had high-electron-density granules localized where the exine should be present. Furthermore, normal lipidic organelles in the tapetum and pollen coat embedded between high-electron-density granules on the pollen surface were observed, unlike in a previous report, and the pollen coat was attached to the stigma. Therefore, the pollen coat is necessary for fertility, and the structure that functions like the exine, such as high-electron-density granules, on the pollen surface may play important roles in retaining the pollen coat in the cyp704b1 mutant.     

Guanine-type retinal tapetum in the eye of the Pacific pomfret <Emphasis Type="Italic">Brama japonica</Emphasis> (Perciformes: Bramidae)

The eye of Brama japonica, which exhibits eyeshine, contains a retinal tapetum composed of guanine. The total amounts of guanine in the eyes of two specimens measuring 19.5 and 51.4cm in standard length were 7.4 and 70.5mg, respectively, the respective retinal surface areas being 4.9 and 39.9cm². The mean guanine content was almost identical (1.5 and 1.8mg/cm², respectively). A locus tapetalis, with guanine values exceeding 2.5mg/cm², was developed in the ventrotemporal region of the retina, where it cooccurred with the area centralis. Evidence is presented that sound functional reasons exist for both the development of the locus tapetalis and its position in the retina. A plea is made for future examination of the retinae of additional pelagic and nonpelagic species for the presence and location of a locus tapetalis.     

我国热带金枪鱼围网人工集鱼装置特征及随附鱼群行为

金枪鱼围网渔船使用人工集鱼装置(FADs)可以增加对金枪鱼随附鱼群的捕捞能力,而大规模投放FADs引起的生态问题在数十年间引起了国际社会的广泛关注。因此,开发高效集鱼能力并降低生态影响的FADs是金枪鱼围网渔业面临的挑战。由于缺乏大量试验研究,目前对FADs和捕捞物种之间相互关系的理解极其有限。本研究通过对从事金枪鱼围网捕捞生产的船长进行问卷调查,从渔民经验的角度总结了FADs的投放现状、结构设计、捕捞和生态特性,以及随附鱼群的行为特征等,并基于一致性指数(IoC)对调查内容的认知差异进行量化。结果表明: 我国金枪鱼围网船单船每年平均投放的FADs数量为(102±37),丢失数量为(72±15)。FADs的集鱼效果优于天然流木,水下悬挂结构是吸引金枪鱼的主要原因,且悬挂吸引物(如漂带)有助于诱集金枪鱼集群。FADs投放后金枪鱼的首次出现时间平均约32 d,此后的1个月内集群量趋于稳定;海龟或鲨鱼被FADs网状结构缠绕的情况偶有发生。被调查者对“生物附着对集群效果的影响”和“优化FADs隐蔽性的意愿”两个问题的反馈具有较高的一致性(IoC均为0.73),对“筏体结构类型对集群效果影响”的反馈答案分歧较大(IoC=0.34)。当前FADs的设计存在低隐蔽性和导致非目标鱼种高脆弱性的弊端。研究结果可为开发生态效应和捕捞效益兼具的生态友好型FADs提供科学依据。     

Near reef abundance and on–offshore distribution of tuna larvae around Minicoy Island in Lakshadweep Sea,India

ABSTRACT

Near reef abundance and coast–offshore distribution of tuna larvae around Minicoy Island were studied based on three cruises carried out on board FORV Sagar Sampada during 2014–15. The samples were collected by oblique tows using bongo twin nets (300 micron) for three seasons (Fall inter-monsoon (FIM), Spring inter-monsoon (SIM) and Summer monsoon (SM)) in six on–offshore stations ranging from 1 to 20?km off-shore of the Minicoy. Results indicated that the tuna larvae aggregate in the near reef waters and total tuna larvae abundance (all the species combined) shows a decreasing trend towards off-shore. Tuna larvae are found to be more abundant during SM and FIM. Comparison of the species-wise variation in tuna larvae for one season (SM) indicated that the larvae of Euthunnus affinis (32.5%) dominated among the tuna species, followed by Auxis spp. (31.6%), Thunnus spp. (3.9%) and Katsuwonus pelamis (2.7%). A pattern of highest larvae abundance in the near reef areas was observed except for Thunnus larvae. GAM indicated that mean seawater temperature and mean seawater salinity are the major environmental factors that significantly influence the larvae abundance, particularly for Thunnus followed by Katsuwonus pelamis, E. affinis and Auxis spp. The study confirms that the environmental parameters show high variation between stations and among transects as a result of the complex oceanographic characteristics around the islands. Further studies with better understanding of the larvae dynamics and their association with the environmental parameters including physical processes are essential to elucidate these relationships more clearly.