Tuna Euthynnus Affinis Research Articles

The Small-Scale Tuna Fishery in Leyte, Philippines: Fishing Gears, Practices, Catch Rate and Composition

The Philippines is a significant tuna producer globally and ranks among the major tuna-fishing nations. One of the various areas where tuna fishery occurs in the country is the province of Leyte in Eastern Visayas. However, available information on the fishery in the province is limited. Thus, this study aimed to provide comprehensive information on the current status of small-scale tuna fishery in selected municipalities in Leyte, particularly on the types of fishing gears used, practices employed by fishers, and the catch rate and composition of the gears. This study used a purposive sampling method, and data were gathered through face-to-face interviews with a total of 68 small-scale tuna fishers, and actual catch sampling. The respondents’ involvement in tuna fishing ranged from 3 to 60 years with a mean of 26±13 years. A total of three different types of hook and line gear used in the fishery were recorded, namely: 1) paired troll line, 2) single troll line, and 3) single hook and line with float. The paired troll line is the most commonly used gear among tuna fishers. The mean catch per unit effort varies depending on the fishing gear type. The catch composition of the three gears based on the actual catch sampling was comprised of four tuna species including longtail tuna Thunnus tonggol (50.48%), big-eye tuna T. obesus (21.90%), eastern little tuna Euthynnus affinis (18.10%), frigate tuna Auxis thazard (3.81%), and two other species including Megalapis cordyla (3.81%) and Scomberomorus commerson (1.90%). The current major issues in the fishery include catch seasonality, illegal fishing, and border restriction.

A Possible Mixing Genetic Pool of Eastern Little Tuna Euthynnus affinis Cantor (1849) from the Western and Southern Part of Indonesian Waters

Eastern little tuna (Euthynnus affinis) is a commercially important species for coastal communities in the western and southern part of Indonesia. However, little is known about its characteristics. Therefore, a comprehensive and broader research of its population structure is imminent in response to conserve and manage the fishery sustainably. This study aimed to fill the gap of the lacking information on the stock separation of eastern little tuna within the Indonesian archipelagic waters and its Economic Exclusive Zone (EEZ). Population genetic approaches were used to examine population structure using the mitochondrial DNA (mtDNA) control region marker. A total of 94 samples were collected from nine landing sites between January to September 2020. Polymerase chain reaction (PCR) was used to amplify the samples, and Sanger sequencing was used to sequence them. The findings showed a mean value of 0.922 for genetic diversity (Hd) and 0.009 for nucleotide diversity (π). Both of these numbers pointed to a high level of genetic diversity. A further population analyses using Analysis of Molecular Variance (AMOVA) and Discriminant Analysis of Principal Component (DAPC) confirmed a mixing gene pool with no distinct population structure detected (ΦST value of 0.097 and p-value>0.05).

Evaluating Kenya’s coastal gillnet fishery: trade-offs in recommended mesh-size regulations

Gillnets are a widely used fishing gear in Kenya’s artisanal fisheries, yet their mesh sizes are inadequately monitored or regulated. This study evaluated the impacts of gillnets of seven stretched-mesh sizes, through comparative analysis of species-related metrics and catch per unit effort (CPUE), to inform Kenya’s small-scale fisheries regulations. Data were collected from June 2014 to May 2015. Three mesh-size groups were identified from catch composition data using non-metric multidimensional scaling and comprised small (1.3, 5.1 and 7.6 cm), medium (10.2 and 15.2 cm) and large (20.3 and 25.4 cm) mesh. The dominant species (and their mean lengths) that were caught in the small, medium and large mesh sizes, respectively, were whitespotted rabbitfish Siganus sutor (21.7 cm [SD 5.3]), mackerel tuna Euthynnus affinis (40.8 cm [SD 9.1]) and honeycomb stingray Himantura uarnak (87.3 cm [SD 37.4]). Values of length at first capture (L 50) for S. sutor and E. affinis caught with the small and medium mesh sizes were below length at maturity (L m). Catches of juveniles were proportionately high in the small meshes (61.3–74.2%) and lower in the medium (38.3–50.9%) and large (9.1–36.2%) mesh sizes. Catches with small mesh tended to be species categorised as Least Concern on the IUCN Red List, in contrast to catches with large mesh which tended to be Near Threatened or Vulnerable species. Biomass CPUE differed between mesh-size groups, with the small sizes recording low CPUE. The medium sizes caught mid- to high-trophic-level species with high-income returns, displayed moderate CPUE, and had the lowest juvenile retention and capture of threatened species. Medium mesh sizes are therefore recommended for artisanal fisheries, given low trade-offs between ecological impact and fishery returns.

Establishment of a tracing technique for transplanted bluefin tuna germ cells in recipient’s gonads using monoclonal antibodies specifically recognizing bluefin tuna spermatogenic cells

Our ultimate aim is to establish a small-bodied surrogate broodstock (e.g., mackerel) that produces functional gametes of the Pacific bluefin tuna Thunnus orientalis using xenogeneic germ cell transplantation. To accomplish this goal, we need to be able to sequentially trace transplanted donor cells in recipients. Here we succeeded in identifying two monoclonal antibodies that could specifically recognize the germ cells of bluefin tuna but not of the chub mackerel Scomber japonicus or the eastern little tuna Euthynnus affinis, which are promising recipient species. Using these antibodies, we developed a method to detect transplanted bluefin tuna germ cells in the gonads of xenogenic recipients. Since all stages of testicular germ cells can be recognized by these antibodies, donor germ cells can be observed throughout gametogenesis in the recipient’s gonads. Thus, the antibodies established in this study could be a powerful tool to observe survival, proliferation, and differentiation of the transplanted bluefin tuna germ cells in the gonads of small Scombridae recipients, and evaluate transplantation efficiency.

Spawning induction of blue mackerel Scomber australasicus and eastern little tuna Euthynnus affinis by oral administration of a crude gonadotropin-releasing hormone analogue

Scombridae species, such as tunas and mackerels, often do not spawn in land-based fish tanks without hormone treatment. To induce spawning in various fishes, a gonadotropin-releasing hormone analogue (GnRHa) is often administered by pellet implantation. Noninvasive administration is desired to induce spawning in scombrids that are sensitive to handling stress. Spawning induction by oral administration has been reported in several fishes, yet this method has not been put into practice in the aquaculture industry since a considerable amount of GnRHa is needed. Utilization of peptide synthesizers is widespread, and antigen-grade GnRHa (AgGnRHa) produced by a custom-peptide supplier is approximately 100-fold cheaper than conventional reagent-grade GnRHa (RgGnRHa), although the purity of AgGnRHa is lower. Here, we confirmed that the spawning induction potency of AgGnRHa was similar to that of RgGnRHa by pellet implantation in blue mackerel Scomber australasicus. Oral administration of AgGnRHa [6.0 mg/kg body weight (BW) per day] showed an equivalent ability to induce spawning of the mackerel as pellet implantation (0.1 mg/kg BW). We could also induce spawning of eastern little tuna Euthynnus affinis by oral administration of the AgGnRHa. Further, the obtained eggs showed higher survival. Thus, the oral delivery of AgGnRHa could be a powerful tool to induce spawning in Scombridae.

Spawning induction of blue mackerel Scomber australasicus and eastern little tuna Euthynnus affinis by oral administration of a crude gonadotropin-releasing hormone analogue

Scombridae species, such as tunas and mackerels, often do not spawn in land-based fish tanks without hormone treatment. To induce spawning in various fishes, a gonadotropin-releasing hormone analogue (GnRHa) is often administered by pellet implantation. Noninvasive administration is desired to induce spawning in scombrids that are sensitive to handling stress. Spawning induction by oral administration has been reported in several fishes, yet this method has not been put into practice in the aquaculture industry since a considerable amount of GnRHa is needed. Utilization of peptide synthesizers is widespread, and antigen-grade GnRHa (AgGnRHa) produced by a custom-peptide supplier is approximately 100-fold cheaper than conventional reagent-grade GnRHa (RgGnRHa), although the purity of AgGnRHa is lower. Here, we confirmed that the spawning induction potency of AgGnRHa was similar to that of RgGnRHa by pellet implantation in blue mackerel Scomber australasicus. Oral administration of AgGnRHa [6.0 mg/kg body weight (BW) per day] showed an equivalent ability to induce spawning of the mackerel as pellet implantation (0.1 mg/kg BW). We could also induce spawning of eastern little tuna Euthynnus affinis by oral administration of the AgGnRHa. Further, the obtained eggs showed higher survival. Thus, the oral delivery of AgGnRHa could be a powerful tool to induce spawning in Scombridae.

Baseline concentration of Polonium-210 (210Po) in tuna fish

Several species of tuna fish were analyzed for 210Po content in their edible muscle tissues. This study was carried out as a part of baseline data generation around a large nuclear power plant situated at Kudankulam, southeast coast of India. The concentration of 210Po in the muscle tissue ranged from 40.9±5.2 to 92.5±7.9Bq/kg of fresh fish, and the highest activity was recorded for the tuna Euthynnus affinis and the lowest for Auxis thazard. The committed effective dose to the local residents was calculated to be 62.7–141.8μSvyear−1.

Complete mitochondrial genome of the kawakawa tuna Euthynnus affinis

The present study represents the first report on the complete mitochondrial genome (mitogenome) of the kawakawa tuna Euthynnus affinis. Illumina next-generation sequencing generated a total of 38,428 reads with an average sequencing depth of 232.83×. The mitogenome of E. affinis was 16,513 bp in length and contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a 849 bp control region, as found in other typical teleosts. With the exception of ND6 and eight tRNA genes, all other mitochondrial genes were encoded on the heavy strand, whose nucleotide composition is 28.11% A, 24.77% T, 17.16% G and 29.96% C. All the protein-coding genes shared the start codon ATG except for COXI gene (start with GTG), and appeared to be terminated with four types of stop codons including two complete codons (TAA and TAG) and two incomplete codons (T and TA).

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature-controlled, Brett-type swimming-tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L(F) ), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U(crit)) was 102·5 ± 13·7 cm s⁻¹ or 4·6 ± 0·9 L(F) s⁻¹. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U(max,c)) was 99·4 ± 14·4 cm s⁻¹ or 4·5 ± 0·9 L(F) s⁻¹. Oxygen consumption rate (M in mg O₂ min⁻¹) increased with swimming speed and with fish mass, but mass-specific M (mg O₂ kg⁻¹ h⁻¹) as a function of relative speed (L(F) s⁻¹) did not vary significantly with fish size. Mean standard metabolic rate (R(S) ) was 170 ± 38 mg O₂ kg⁻¹ h⁻¹, and the mean ratio of M at U(max,c) to R(S) , an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U(opt) ), at which the gross cost of transport was a minimum of 2·14 J kg⁻¹ m⁻¹, was 3·8 L(F) s⁻¹. In a subset of the fish studied (19·7-22·7 cm L(F) , 106-164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L(F) . The mean propulsive wavelength was 86·7 ± 5·6 %L(F) or 73·7 ± 5·2 %L(T) . Mean ±s.d. yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L(F) ; 23·4, 25·3 and 26·4 cm L(T) ), were 4·6 ± 0·1 and 17·1 ± 2·2 %L(T) , respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.

Monogenea of Arabian Gulf fishes: 1. Descriptions of three Capsala spp. (Capsalidae) including Capsala naffari n. sp. infecting mackerel tuna Euthynnus affinis from coasts of Emirates

Three species of the genus Capsala including Capsala naffari n. sp., C. neothunni (Yamaguti, 1968) and C. nozawae (Goto, 1894) are recorded and described from the buccal cavity of mackerel tuna Euthynnus affinis caught from Emirate coasts. Capsala naffari can be differentiated by its lateral spiniform teeth, which extend posteriorly, small measurements compared with the closely resembled C. gotoi and relatively large testes. This is the first record of the genus Capsala from Arabian Gulf fishes and E. affinis is a new host record.

Community structure of helminth parasites of the tuna, Euthynnus affinis, from the Visakhapatnam coast, Bay of Bengal

AbstractAn analysis is made of the community structure of the helminth parasites of the tuna Euthynnus affinis collected off the coast of Visakhapatnam, Bay of Bengal. The helminth fauna comprised 23 species, consisting of two monogeneans, 18 digeneans, one larval cestode, one nematode and one acanthocephalan. Didymozoids, represented by 14 species, were the dominant members of the parasite spectrum. The parasite assemblage is characterized by species richness as well as a high diversity. Most of the parasites found, the didymozoids in particular, were host specialists, exhibiting a high degree of host specificity. The fauna comprised three core species, four satellite species and many secondary species, with no potential for interaction among them but the degree of predictability is high in that each infracommunity comprised two or three core species superimposed by a few secondary species. Many host factors such as the varied diet, high vagility, long life span and endothermy appear to have contributed to the development of the species rich and diverse parasite communities in the tuna. There was evidence for a decrease in parasite density and an increase in diversity with increase in host size, indicating that host size has a profound influence on the component community structure.

Community structure of helminth parasites of the tuna, Euthynnus affinis, from the Visakhapatnam coast, Bay of Bengal

An analysis is made of the community structure of the helminth parasites of the tuna Euthynnus affinis collected off the coast of Visakhapatnam, Bay of Bengal. The helminth fauna comprised 23 species, consisting of two monogeneans, 18 digeneans, one larval cestode, one nematode and one acanthocephalan. Didymozoids, represented by 14 species, were the dominant members of the parasite spectrum. The parasite assemblage is characterized by species richness as well as a high diversity. Most of the parasites found, the didymozoids in particular, were host specialists, exhibiting a high degree of host specificity. The fauna comprised three core species, four satellite species and many secondary species, with no potential for interaction among them but the degree of predictability is high in that each infracommunity comprised two or three core species superimposed by a few secondary species. Many host factors such as the varied diet, high vagility, long life span and endothermy appear to have contributed to the development of the species rich and diverse parasite communities in the tuna. There was evidence for a decrease in parasite density and an increase in diversity with increase in host size, indicating that host size has a profound influence on the component community structure.

Acanthocephala of Marine Fishes off Fiji Islands, with Descriptions of Filisoma longcementglandatus n. sp., Neorhadinorhynchus macrospinosus n. sp. (Cavisomidae), and Gravid Females of Rhadinorhynchus johnstoni (Rhadinorhynchidae); And Keys to Species of the Genera Filisoma and Neorhadinorhynchus

A parasitological collection from marine fishes off the Fiji Islands yielded 5 species of acanthocephalans from 4 species of fish as follows: Filisoma longcementglandatus n. sp. from scat Scatophagus argus; Neorhadinorhynchus macrospinosus n. sp. from vermiculated rabbit fish Siganus vermicularis; Neorhadinorhynchus nudum (Harada, 1938) Yamaguti, 1939 (Cavisomidae) from mackerel tuna Euthynnus affinis; Rhadinorhynchus johnstoni Golvan, 1969 (Rhadinorhynchidae) from E. affinis; and Neoechinorhynchus agilis (Rudolphi, 1819) Van Cleave, 1916 (Neoechinorhynchidae) from striped mullet Mugil cephalus. All are new locality records and, except for N. agilis, new host records. Filisoma longcementglandatus is distinguished from all other species of the genus by its very long cement glands and size and armature of its proboscis. Neorhadinorhynchus macrospinosus has distinctly larger proboscis hooks than all other members of the genus. Keys to species of the genera Filisoma and Neorhadinorhynchus are included. Gravid females of the inadequately described R. johnstoni are described for the first time. Taxonomic notes on the other acanthocephalan species are also included.