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Kajikia audax, Thunnus albacares, Katsuwonus pelamis, and Auxis spp. occupy high and middle-level trophic positions in the food web. They represent important sources for fisheries in Ecuador. Despite their ecological and economic importance, studies on pelagic species in Ecuador are scarce. This study uses stable isotope analysis to assess the trophic ecology of these species, and to determine the contribution of prey to the predator tissue. Isotope data was used to test the hypothesis that medium-sized pelagic fish species have higher δ15N values than those of the prey they consumed, and that there is no overlap between their δ13C and δ15N values. Results showed higher δ15N values for K. audax, followed by T. albacares, Auxis spp. and K. pelamis, which indicates that the highest position in this food web is occupied by K. audax. The stable isotope Bayesian ellipses demonstrated that on a long time-scale, these species do not compete for food sources. Moreover, δ15N values were different between species and they decreased with a decrease in predator size. Resumo Kajikia audax, Thunnus albacares, Katsuwonus pelamis e Auxis spp. ocupam posições tróficas intermedias e/ou elevadas nas cadeias alimentares. Estas espécies representam um importante recurso pesqueiro no Ecuador. Apesar da sua importância económica e ecológica, estudos nestas espécies pelágicas no Ecuador são raras. Este estudo usa isótopos estáveis para avaliar o seu nível trófico de modo a determinar a contribuição das suas presas para os tecidos destes predadores. Dados dos isótopos foram usados para testar a hipótese de que estas espécies de peixes pelágicos possuem valores mais elevados de δ15N do que daqueles das presas consumidas, e que não existe uma sobreposição entre os valores de δ13C e δ15N. Resultados mostram que valores mais elevados de δ15N para K. audax, seguidos por T. albacares, Auxis spp. e K. pelamis, indicam que a posição mais elevada na cadeia alimentar é ocupada por K. audax. Elipses Bayesianas de isótopos estáveis demonstram que, a uma escala de longo-termo, estas espécies de peixes não competem pelos recursos. Adicionalmente, os valores de δ15N são diferentes entre espécies de peixe estudadas e estes valores decrescem com a diminuição do tamanho do predador.

Kawakawa Euthynnus affinis, also known as eastern little tuna or mackerel tuna, is a species of tuna (Thunnini tribe, subgroup Pelagiaria clade) (Sanciangco et al., 2016). Tuna includes 15 species: eight of genus Thunnus (true tuna) and seven “tuna-like” of four genera: Allothunnus, Auxis, Euthynnus, and Katsuwonus. E. affinis is widely distributed throughout the tropical and subtropical waters of the continental shelf areas of the Indo-Pacific region (Collette, 2001). The fish reaches a length of 45–60 cm and matures at approximately 3 years of age. It inhabits almost exclusively the upper layers of the ocean (Bernal et al., 2017) and feeds mainly on small pelagic fish (Griffiths et al., 2009). E. affinis makes up a substantial proportion of the commercial and artisanal fishery in many countries of the Indo-Pacific region. The meat of E. affinis is of high quality (Mukundan et al., 1979) with a comparatively high level of docosahexaenoic acid (Saito et al., 1999), but deteriorates rapidly if not properly handled (Mukundan et al., 1979). E. affinis exhibits the swimming mechanics of true tunas (Donley and Dickson, 2000) but has no swim bladder and differs from true tunas in red muscle distribution, allometry, and vascular anatomy (Bernal et al., 2017). The ability to maintain an elevated temperature in eye, brain, and red muscle has been suggested for the genus Euthynnus (Dickson et al., 2000), but reports specific to E. affinis are lacking. Compared to true tunas, E. affinis has received scant attention from researchers, and little is known about its biology and physiology. This is likely to change, as E. affinis has recently become of interest in marine aquaculture. E. affinis is the second tuna species whose full-life cycle culture in captivity has been developed so far, including spawning, egg collection, incubation, larval rearing, and grow-out to marketable size (Yazawa et al., 2015, 2016). Aquaculture in general is currently facing significant challenges to increasing production while maintaining sustainability (Bridson et al., 2020). Genetic improvement, via selective breeding and genetic engineering, is a major focus of research and can yield rapid benefits to efficient production in fish farming (Lu and Luo, 2020). To these ends, a high-quality species genome assembly is critical. Despite recent advances in sequencing technologies and genomics that, in addition to basic fish science (Lien et al., 2016; Hughes et al., 2018; Yuan et al., 2018; Du et al., 2020), have applications to aquaculture practices (Lu and Luo, 2020) and fisheries (Benestan, 2020), genomic information of tuna species is limited. To date, the genomes of only three tuna species are available in the public repositories, none of which are assembled to chromosome level. This situation exists within the entire Pelagiaria clade that, along with tuna, includes the economically important mackerel (Scombrini tribe) and bonito (Sardini tribe). Here, we report the chromosome-level genome assembly of kawakawa E. affinis (NCBI:txid8227). To our knowledge, this is the first available chromosome-level assembly within the Pelagiaria clade. The reported genome assembly is accompanied by transcriptome assembly, genetic linkage map, annotation of transposons, repetitive elements, and 23,059 genes. The dataset provides a solid genome resource not only for further study of E. affinis basic biology and genome-scale selective breeding but also for enhancing both basic and applied research within the Pelagiaria clade.

The feeding habits of Makaira nigricans, Kajikia audax, Istiophorus platypterus (Istiophoridae), and Xiphias gladius (Xiphiidae) in the southeast Pacific Ocean were examined in Manta and Santa Rosa, Ecuador. This study describes the diets of these billfish species, evaluates dietary differences between species, and assesses seasonal differences in diet. A total of 274 M. nigricans, 321 K. audax, 267 I. platypterus, and 252 X. gladius were collected between February 2014 and April 2015. The scombrid Auxis spp. was the most important prey for M. nigricans, K. audax and I. platypterus, while the squid Dosidicus gigas was the most important prey for X. gladius. The results of the ANOSIM confirmed significant differences in feeding habits between the members of the family Istiophoridae and X. gladius. Seasonal differences for I. platypterus also were observed. Billfishes are specialist consumers with a narrow niche breadth (B a: M. nigricans and K. audax=0.1, I. platypterus=0.05, and X. gladius=0.04). RESUMEN Los hábitos alimentarios de Makaira nigricans, Kajikia audax, Istiophorus platypterus (Istiophoridae) y Xiphias gladius (Xiphiidae) en el Océano Pacífico sudeste se examinaron en Manta y Santa Rosa, Ecuador. Este estudio describe las dietas de estas especies de peces de pico, evalúa las diferencias de la dieta entre especies y las diferencias estacionales en la dieta. Se obtuvo un total de 274 M. nigricans, 321 K. audax, 267 I. platypterus y 252 X. gladius entre febrero 2014 y abril 2015. El escómbrido Auxis spp. fue la presa más importante para M. nigricans, K. audax y I. platypterus, mientras que el calamar Dosidicus gigas fue la presa más importante para X. gladius. Los resultados de ANOSIM confirmaron diferencias significativas en los hábitos alimentarios entre los miembros de la familia Istiophoridae y X. gladius. También se observaron diferencias estacionales para I. platypterus. Los peces de pico son consumidores especialistas con una amplitud de nicho estrecha (B a: M. nigricans y K. audax=0.1, I. platypterus=0.05 y X.gladius=0.04).

The head region of 72 bullet tuna Auxis rochei from the western Mediterranean Sea (south-east Spain and the Strait of Gibraltar) was examined for parasites. Seven metazoan species were found in the fish from south-east Spain: three monogeneans, two trematodes and two copepods, whereas only three species were isolated in the fish from the Strait of Gibraltar. A comparison of the levels of infection of the parasites according to fish size in south-east Spain showed that the prevalence of Didymozoon auxis and the mean abundance of Allopseudaxine macrova were higher in the larger hosts (range of fork length ¼ 38–44 cm) than in the smaller ones (33–37 cm). A comparison of the parasite infections according to geographical region showed that the mean abundances of Nematobothriinae gen. sp. and Caligus bonito were higher in fish from south-east Spain than in those from the Strait of Gibraltar. A comparison of the parasite fauna of A. rochei from the Mediterranean Sea with the published data on Auxis spp. from the Atlantic, Indian and Pacific Oceans revealed the closest similarity between the Mediterranean A. rochei and the Atlantic A. thazard., SI

The aim of this study was to determine the biomagnification of mercury through the principal prey of the blue shark, Prionace glauca, off the western coast of Baja California Sur, Mexico, as well as the relationship between mercury and selenium in blue sharks. High levels of mercury were found in shark muscle tissues (1.39 ± 1.58 μg/g wet weight); these values are above the allowed 1.0 μg/g for human consumption. The mercury to selenium molar ratio was 1:0.2. We found a low correlation between mercury bioaccumulation and shark size. Juveniles have lower concentrations of mercury than adults. Regarding the analyzed prey, the main prey of the blue shark, pelagic red crab, Pleuroncodes planipes, bioaccumulated 0.04 ± 0.01 μg/g Hg wet weight, but the prey with higher bioaccumulation was the bullet fish Auxis spp. (0.20 ± 0.02 μg/g wet weight). In terms of volume, the red crab P. planipes can be the prey that provides high levels of mercury to the blue shark.

Se analiza el contenido estomacal de 52 marlines azules capturados por la flota de pesca deportiva que operó en el área de Mazatlán, Sinaloa, en el golfo de California, México, durante el periodo octubre 2002 a octubre 2004. El marlín azul se alimenta de 15 categorías alimenticias (ítemes), de las cuales las más importantes de acuerdo al índice de importancia relativa (IRI), fueron el pez melva Auxis spp. (52%) y el calamar gigante Dosidicus gigas (30%).ABSTRACTWe analyzed the stomach contents of 52 blue marlins caught between October 2002 and October 2004 by the sport-fishing fleet of Mazatlan, Sinaloa, in the gulf of California, Mexico. Blue marlin feed on 15 food items. According to the index of relative importance (IRI), the most important prey were the frigate or bullet mackerel Auxis spp. (52%) and jumbo squid Dosidicus gigas (30%).

Analysis of the stomach contents of 204 blue marlin ( Makaira mazara ) caught by the sport-fishing fleet of Cabo San Lucas in the southern Gulf of California is presented. The specimens sampled were caught during the summer and fall of 1987, 1988, and 1989 when the sea is warm (28–30°C). Blue marlin were found to feed on 35 prey species, 3 of which represented 90% of the total stomach contents by frequency of occurrence. The main prey were epipelagic organisms from the oceanic zone and demersal fishes from the neritic zone. The most important prey were bullet mackerel Auxis spp., young finescale triggerfish Balistes polylepis , and the giant squid Dosidicus gigas .