Ecology and Genetic Structure of Zoonotic Anisakis spp. from Adriatic Commercial Fish Species

Consumption of raw or thermally inadequately treated fishery products represents a public health risk, with the possibility of propagation of live Anisakis larvae, the causative agent of the zoonotic disease anisakidosis, or anisakiasis. We investigated the population dynamics of Anisakis spp. in commercially important fish—anchovies (Anisakis), sardines (Sardina pilchardus), European hake (Merluccius merluccius), whiting (Merlangius merlangus), chub mackerel (Scomber japonicus), and Atlantic bluefin tuna (Thunnus thynnus)—captured in the main Adriatic Sea fishing ground. We observed a significant difference in the numbers of parasite larvae (1 to 32) in individual hosts and between species, with most fish showing high or very high Anisakis population indices. Phylogenetic analysis confirmed that commercial fish in the Adriatic Sea are parasitized by Anisakis pegreffii (95.95%) and Anisakis simplex sensu stricto (4.05%). The genetic structure of A. pegreffii in demersal, pelagic, and top predator hosts was unstructured, and the highest frequency of haplotype sharing (n = 10) was between demersal and pelagic fish.     

Anisakis spp. in toothed and baleen whales from Japanese waters with notes on their potential role as biological tags

In this study, Anisakis nematodes isolated from toothed and baleen whales from localities around Japan were molecularly (PCR-RFLP) identified. In Wakayama, common bottlenose dolphins (Tursiops truncatus) were infected with A. simplex sensu stricto (s.s.), A. typica and A. pegreffii, while A. typica was the only species found in pantropical spotted dolphin (Stenella attenuata) and striped dolphin (S. coeruleoalba). Offshore common minke whales (Balaenoptera acutorostrata) and sei whales (B. borealis) were almost exclusively infected with A. simplex s.s.. However, in common minke whales from two Hokkaido localities, mature worms mostly consisted of A. simplex s.s. in some individuals and of A. pegreffii in others, but immature worms were mainly A. simplex s.s.. Gross and histopathological examination on gastric mucosa attached by anisakids resulted in mild and superficial reactions by the two baleen whale species in contrast to severe inflammatory reaction associated with ulcer formations by common bottlenose dolphin. Host specificity and adaptability of Anisakis spp. in these baleen and toothed whales were discussed from the points of view of adult worm size, worm population and pathological reactions by hosts. Interestingly, most of the common minke whales predominantly harboring mature A. pegreffii adults belonged to the Yellow Sea – East China Sea stock (J stock), which migrates through the Sea of Japan, whereas most of those mainly parasitized by mature A. simplex s.s. adults were from the Okhotsk Sea – West Pacific stock (O stock), mostly inhabiting the Pacific side, suggesting that these sibling species may have utility as biological tags to differentiate whale stocks. These results represent the first definitive host records for A. pegreffi in the Northwestern Pacific Ocean.     

Anisakis pegreffii Larvae in Sea Eels (Astroconger myriaster) from the South Sea,Republic of Korea

Anisakis simplex sensu stricto (s.s.), Anisakis pegreffii, Anisakis berlandi (=A. simplex sp. C), and Anisakis typica are the 4 major species of Anisakis type I larvae. In the Republic of Korea (Korea), A. pegreffii, A. berlandi, and A. typica larvae in fish hosts has seldom been documented. In this study, molecular analysis was performed on Anisakis larvae from the sea eels (Astroconger myriaster), the major source of human anisakiasis in Korea, collected from Tongyeong City, a southern coastal area of Korea. All 20 sea eels examined were infected with Anisakis type I larvae (160 larvae; 8 per fish). Their species were analyzed using PCR-RFLP patterns and nucleotide sequences of internal transcribed spacers (ITS1, 5.8 subunit gene, and ITS2) and mitochondrial cytochrome c oxidase 2 (cox2). Most (86.8%; 112/129) of the Anisakis type I larvae were A. pegreffii, and 7.8% (10/129) were A. typica. The remaining 5.4% (7/129) was not identified. Thus, A. pegreffii is the major species of anisakid larvae in sea eels of the southern coast of Korea.     

Molecular Analysis of Anisakis Type I Larvae in Marine Fish from Three Different Sea Areas in Korea

Anisakiasis, a human infection of Anisakis L3 larvae, is one of the common foodborne parasitic diseases in Korea. Studies on the identification of anisakid larvae have been performed in the country, but most of them have been focused on morphological identification of the larvae. In this study, we analyzed the molecular characteristics of 174 Anisakis type I larvae collected from 10 species of fish caught in 3 different sea areas in Korea. PCR-RFLP and sequence analyses of rDNA ITS and mtDNA cox1 revealed that the larvae showed interesting distribution patterns depending on fish species and geographical locations. Anisakis pegreffii was predominant in fish from the Yellow Sea and the South Sea. Meanwhile, both A. pegreffii and A. simplex sensu stricto (A. simplex s.str.) larvae were identified in fish from the East Sea, depending on fish species infected. These results suggested that A. pegreffii was primarily distributed in a diverse species of fish in 3 sea areas around Korea, but A. simplex s.str. was dominantly identified in Oncorhynchus spp. in the East Sea.     

The abundance of Anisakis simplex L3 in the body-cavity and flesh of marine teleosts

Smith J. W. 1984. The abundance of Anisakis simplex L3 in the body-cavity and flesh of marine teleosts. International Journal for Parasitology14: 491–495. In experiments conducted at sea, whole (ungutted) fish of three species were stored on ice at 3–5 °C for periods from 0 to 72 h. Some Anisakis simplex L3 migrated from the body-cavity into the flesh in mackerel Scomber scombrus, but not in either blue whiting Micromesistius poutassou or whiting Merlangius merlangus. Earlier work has shown that larvae migrate into the flesh of herring Clupea harengus post mortem but not of walleye pollock Theragra chalcogramma. It seems, therefore, that larvae migrate post mortem into the flesh of ‘fatty’ species (e.g. herring, mackerel) but not of ‘non-fatty’ species (e.g. blue whiting, whiting, walleye pollock). No significant larval excapsulation occurred in isolated mackerel or whiting viscera. In vivo, most encapsulated L3 occur in the body-cavity of euphausiid-feeding fish (herring, mackerel, blue whiting, walleye pollock) but are more widely distributed throughout the tissues of piscivorous fish (whiting, cod). These observations are discussed in relation to the apparent importance of euphausiids as intermediate hosts of A. simplex.     

PERMANENT GENETIC RESOURCES: Isolation and characterization of nine microsatellite loci from the chub mackerel, Scomber japonicus (Perciformes, Scombridae)

The stock abundance of the chub mackerel Scomber japonicus - a very important species for fisheries, particularly in Japan - in the Pacific Ocean off Japan has remained at a low level. For studying the population genetics of the chub mackerel, we isolated nine polymorphic microsatellite loci (12-31 alleles/locus; expected heterozygosity, 0.762-0.983) from this species. Cross-species amplification indicated that eight of the nine microsatellite loci in the blue mackerel S. australasicus were polymorphic and functional.     

What can metazoan parasites reveal about the taxonomy of Scomber japonicus Houttuyn in the coast of South America and Madeira Islands?

The metazoan parasites of four populations of the chub mackerel Scomber japonicus were analysed from two localities in the Atlantic Ocean (Madeira Islands, Portugal, and Rio de Janeiro, Brazil) and two localities in the Pacific Ocean (Callao, Peru, and Antofagasta, Chile), collected during 2002 and 2003. A total of 373 fish specimens were studied and 34 metazoan parasite species were obtained. Parasites identified from the populations of chub mackerel studied could be separated into three categories: parasites with a wide distribution, present in the Pacific and Atlantic, parasites proper of the Pacific Ocean and parasites proper of the Atlantic Ocean. The analyses of some highly specific parasites of the genus Scomber ( i.e. monogeneans of the genus Kuhnia and didymozoid digeneans) strongly suggest the need for a revision of the taxonomic status of chub mackerels from the Atlantic and Pacific coast of America. The results demonstrated the usefulness of parasites as adequate tools to clarify the taxonomic status of their hosts.     

Calibration of a hand‐held haemoglobin analyser for use on fish blood

The HemoCue haemoglobin analyser consistently overestimated haemoglobin concentration ([Hb]) in the blood of all fish species (sockeye salmon Oncorhynchus nerka, Chinook salmon Oncorhynchus tshawytscha, Pacific bluefin tuna Thunnus orientalis and chub mackerel Scomber japonicus) by 22–50% (9·9–36·0 g l^?1) over a [Hb] range of 20–160 g l^?1. The systematic nature of the overestimation, however, allowed the formulation of an accurate calibration equation that can be used to correct values of [Hb] measured by the HemoCue in field studies.     

Anisakis simplex and Anisakis physeteris: physicochemical properties of larval and adult hemoglobins

To resolve the taxonomic relationship between two types of parasitic nematode larvae (Type I and II) and two species of parasitic nematode adults (Anisakis simplex and A. physeteris) of the aquatic ascarid genus Anisakis, collected in Japanese coastal water, a comparison was made of their hemoglobins' physicochemical properties. The larval hemoglobins were more similar to each other in electrophoretic pattern than to either adult, indeed there were few similarities whatsoever in these patterns of larval and adult hemoglobins. However, isoelectric points were 6.2 for the Type I larva and for A. simplex and 5.4 for the Type II larva and for A. physeteris. All samples showed identical patterns in spectrophotometric scanning. The circular dichroic spectra of the samples were also virtually identical, although slight differences were noted in the oxygenated hemoglobins; the Type II larva and A. physeteris exhibited a small positive peak at 575 nm but the Type I larva and A. simplex exhibited a much smaller peak (negative position). The sedimentation coefficients of the samples possessed essentially identical values (11.2–12.4). The molecular weights of the samples were estimated, roughly, to be in the range 33 to 43 × 10⁴ by thin-layer chromatography on Sephadex G-200. The evidence suggests that a relationship may exist between the Type I larva and A. simplex, and between the Type II larva and A. physeteris.     

Differential population structuring of two closely related fish species, the mackerel (Scomber scombrus) and the chub mackerel (Scomber japonicus), in the Mediterranean Sea

Population genetic structures of the mackerel (Scomber scombrus) and chub mackerel (Scomber japonicus) were studied in the Mediterranean Sea. Fragments of 272 bp (S. scomber) and 387 bp (S. japonicus) of the 5'-end of the mitochondrial control region were sequenced from spawning individuals collected off the coasts of Greece, Italy, Spain, and Portugal. High levels of mitochondrial control region haplotypic diversity (> 0.98) were found for both Scomber species. Nucleotide diversity was higher in the mackerel (0.022) than in the chub mackerel (0.017). Global F(ST) values were also higher and significant in the mackerel (0.024, P < 0.0001) as opposed to the chub mackerel (0.003, P > 0.05). Molecular variance analyses showed differential genetic structuring for these two closely related species. There is extensive gene flow between Mediterranean Sea and Atlantic Ocean populations of chub mackerel, which are organized into a larger panmictic unit. In contrast, Mediterranean Sea populations of mackerel show some degree of genetic differentiation and are structured along an east-west axis. The analysed eastern Mediterranean Sea mackerel populations (Greece, Italy) are clearly separated from that of the western Mediterranean Sea (Barcelona), which forms a panmictic unit with eastern Atlantic Ocean populations. The genetic structures of both species showed asymmetric migration patterns and indicated population expansion.     

Effects of temperature on eggs and larvae of Anisakis simplex sensu stricto and Anisakis pegreffii (Nematoda: Anisakidae) and its possible role on their geographic distributions

Effects of temperature on development of eggs, recently hatched larvae and L3 larvae of the marine parasitic nematodes Anisakis simplex sensu stricto (s.s.) and A. pegreffii were examined in vitro. The eggs of A. simplex s.s. hatched at 3–25 °C and those of A. pegreffii hatched at 3–27 °C. Days before hatching varied between 2 days at 25 °C and 35–36 days at 3 °C in A. simplex s.s. and between 2 and 3 days at 27 °C and 65 days at 3 °C in A. pegreffii. Hatching rates of A. simplex s.s. were maintained high at temperatures between 3 and 25 °C but decreased to 0% at 27 °C. In contrast, those of A. pegreffii were lowest particularly at 3 °C, but also at 27 °C. The mean 50% survivals of hatched larvae ranged from 5.3 days at 25 °C to 82.3 days at 9 °C in A. simplex s.s., while in A. pegreffii it ranged from 1.2 days at 27 °C to 77.2 days at 9 °C. L3 larvae of A. pegreffii exhibited higher survival rates and activity than those of A. simplex s.s., particularly at 20 and 25 °C. These results suggest that the early stages of A. simplex s.s. are more adapted to lower temperatures whereas those of A. pegreffii are more tolerant to warm environments, which may correspond to their distribution patterns in Japan and Europe.     

Distribution of Anisakis species larvae from fishes of the Japanese waters

Human anisakiasis is caused by the consumption of raw, marinated or undercooked fish and squid infected with nematodes of the genus Anisakis Dujardin, 1845. In view of food safety, this study was carried out to examine the distribution of Anisakis species in marine fishes within Japanese waters. Seven fish species from six localities were collected and examined for Anisakis infection. Morphological and molecular (ITS region and mtDNA cox2 gene) characterization revealed the presence of two, among the three sibling species of Anisakis simplex, viz. A. simplex sensu stricto (s.s.) and A. pegreffii. Distribution data were collated with the results from the previous researches to better understand Anisakis distribution in Japanese waters. Distributions of Anisakis species were found to be locality-specific rather than host-specific, particularly between the two major species, A. simplex s.s. and A. pegreffii. Anisakis simplex s.s. is mainly found in fishes from northern Japan to Pacific sides, whereas A. pegreffii is in fishes from the Sea of Japan to East China Sea sides.     

Effect of spawning ground location on the transport and growth of chub mackerel (Scomber japonicus) eggs and larvae in the East China Sea

Chub mackerel (Scomber japonicus) are an important pelagic fish species within the China Sea. Annual recruitment of this species is determined primarily by survival in the early life history stages. Minor changes in the physical marine environment can have a significant effect on the growth and survival of eggs and larvae, thereby affecting recruitment of population. To model this interaction, we constructed a bio-physical dynamic model of the early life history of chub mackerel in the East China Sea (ECS). The physical model was based on the unstructured grid Finite Volume Coast and Ocean Model (FVCOM) and simulated the 3-D physical fields. The biological model was based on individual-based models (IBMs) in which the early life stages of chub mackerel were divided into five stages based on age or length. The model was parameterized using functions describing spawning, growth, and survival for chub mackerel in the ECS. Using this coupled physical and biological model, driven by the March–July climatological forcing, we tracked super individuals from spawning grounds to the nursery grounds to evaluate the influence of the physical environment at each of the spawning locations (western, normal, eastern) on the transport and survival of chub mackerel. The model suggests that spawning location has a significant effect on larval transport, although the larvae were generally advected northeastward to enter the Japan/East Sea through the Tsushima/East Strait or southeastward with the Kuroshio Current which then flows along the eastern Japanese coast. Spawning to the west was highly influenced by the Taiwan Warm Current (TWC) during early transport when the larvae were advected northward and then northeastward. The speed of drifting during this period was relatively slow. The model predicted that a large number of eggs and larvae would enter and transit through China’s coastal waters (Changjiang River Estuary, Hangzhou Bay, and the Zhoushan Islands). Under this scenario, the majority of larvae were transported to the northern nursery grounds, 79% to the nursery at Jeju Island and 10% to the nursery at Tsushima Strait. In contrast, only 11% were transported to the southern nursery grounds in the Pacific Ocean and Kyushu. Larvae spawned at the eastern spawning ground were primarily influenced by the Kuroshio Current which transported the larvae southeastward. Kuroshio acts as a barrier, restricting larvae from being advected to the interior of the western Pacific Ocean. Under such circumstances, almost no eggs and larvae were retained in the coastal waters of China. Instead, the larvae were rapidly transported northeastward from the Chinese shelf towards the coast of Japan. The model predicted that a large number of larvae would be transported to the southern nursery grounds in the Pacific Ocean and Kyushu, before entering the Pacific Ocean and Japan Sea. In total, 36% of larvae were transported to the Pacific Ocean nursery, 45% to the northern nursery grounds of Jeju Island and Tsushima Strait, and 27% to the Jeju Island nursery. The three simulations assumed the same number of eggs were spawned (2.17 × 10¹²) and the survival of larvae at the western, normal, and eastern spawning grounds was 0.0306%, 0.0353%, and 0.0234%, respectively. The average length was 123.7, 126.0, and 123.5 mm, respectively. Our results suggest that larvae spawned in different regions encountered different physical environments and were subject to different transport processes. These differences explain the changes in survival and growth observed between larvae from the different areas. Survival and growth was highest for chub mackerel that were spawned at the normal spawning location and subject to suitable water depths and temperatures during transport.     

The occurrence and infection dynamics of Anisakis larvae in the black-scabbard fish,Aphanopus carbo,chub mackerel,Scomber japonicus,and oceanic horse mackerel,Trachurus picturatus from Madeira,Portugal

Larval stages of Anisakis spp. (Nematoda: Anisakidae) were found encapsulated or free in the viscera and abdominal cavity of the black-scabbard fish, Aphanopus carbo, chub mackerel, Scomber japonicus and oceanic horse mackerel, Trachurus picturatus in Madeiran waters. The prevalence of infection reached 97.2% for A. carbo, 69.5% for S. japonicus and 62.5% for T. picturatus. Considerable differences in parasite intensities between A. carbo and both S. japonicus and T. picturatus were found, with mean intensities up to 69.6 in A. carbo, while in the other two fish hosts the intensity reached only a maximum of 2.6. These differences were probably due to different feeding behaviours of the hosts. Intensities of Anisakis sp. in A. carbo were high irrespective of sex and season. No relationship between host length and prevalence of infection was observed for A. carbo, while for S. japonicus a weak positive significant relationship was found.     

Impacts per unit weight in catch by two types of fisheries on a chub mackerel population

By using data on the age-specific annual fecundity and catches-at-age by each fishery in a chub mackerel (Scomber japonicus) population in the Pacific Ocean off Japan during 1970 to 1992, we evaluated the long-term fluctuation in impacts of two types of fisheries on the chub mackerel population. The purse-seine fishery consistently had a larger impact on the population than did the dip-net fishery, mainly because the catch by the former was much larger than that by the latter. To evaluate impact per unit weight in catch, we calculated the average reproductive value per unit weight over individuals caught by each fishery as an indicator of efficient use of bioresource. Because the proportion of immature fish caught by the purse-seine fishery was usually larger than that by the dip-net fishery, the impact per unit weight in catch by the purse-seine fishery was not always less than that by the dip-net fishery.     

Seasonal and interannual variation of ichthyoplankton off Mauritania

Changes of the quantitative and qualitative composition of ichthyoplankton off Mauritania (21–16° N) in different seasons of 1997–2008 are analyzed. In this area, pelagic eggs and larvae of over 120 fish species belonging to 71 families are recorded. In warm periods, the fish of the tropical fauna intensively spawn off Mauritania; round sardinella Sardinella aurita, West-African horse mackerel Trachurus trecae, and jack mackerel Caranx rhonchus are dominant. In cold periods, active spawning of fish belonging to the tropical fauna is recorded, the most abundant are European pilchard Sardina pilchardus, European horse mackerel Trachurus trachurus, and Atlantic mackerel Scomber japonicus. The spawning biomass of principal commercial fish species is calculated on the basis of the quantity of eggs laid by females. Environmental factors control fluctuations of abundance and distribution of ichthyoplankton in the considered region.     

The parasite fauna of the chub mackerel (Scombridae: Scomber japonicus Houttuyn, 1782) in the central-eastern Atlantic (Atlantic coast of the Northern Africa and the Azores Archipelago banks)

The parasite fauna of the chub mackerel Scomber japonicus Houtuym, 1782 was studied from the neritic areas of Morocco, Western Sahara, Mauritania and from the banks of the Azores Archipelago (the Great Meteor Bank, the Hyeres Bank and the Irving Bank) in 1994-2001. Twenty eight species of parasites of following group have been were found: Coccidia (1 species), Microsporidia (1), Myxosporea (4), Monogenea (4), Cestoda (5), Trematoda (5), Acanthocephala (1) and Nematoda (6). The differences between mackerel parasite fauna in the neritic areas and from of the Azores Archipelago banks were established. Peculiarities of the mackerel parasite fauna in two areas (Morocco--Western Sahara and Mauritania) corroborate the hypothesis that two populations of chub mackerel are available: "Sahara-Moroccan" and "Senegal-Mauritanian". Ontogenetic variability of parasite fauna was related to food demands of mackerel and its feeding habits in the areas Morocco and Mauritania. Kudoa histolytica has negative influence on the commercial value of S. japonicus. These parasites were localized in the muscles of mackerel from Mauritania (40%, TL = 20-25 cm). Parasites being dangerous for human health were presented by larvae of Bolbosoma sp. (occurred on the banks of the Azores Archipelago), Anisakis simplex and Contracaecum sp. (occurred in all areas investigated).     

Morphological differences between larvae and in vitro-cultured adults of Anisakis simplex (sensu stricto) and Anisakis pegreffii (Nematoda: Anisakidae)

Proper identification of Anisakis species infecting host fishes is very important to both human health and fish disease diagnosis. The foremost problem in the identification of Anisakis larvae in fishes is that L3 larvae cannot be easily differentiated morphologically, especially between A. simplex (sensu stricto) (s.s.) (Rudolphi, 1809) and A. pegreffii Campana-Rouget et Biocca, 1955. Instead, molecular means such as allozyme, mitochondrial DNA (mtDNA) cox2 region and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses had been successfully used. In this study, morphological differences of L3 larvae collected from fishes and in vitro-cultured L4 larvae and adult A. simplex (s.s.) and A. pegreffii were evaluated. Anisakis larvae were collected from 7 different host fishes within Japan. Undamaged A. simplex (s.s.) and A. pegreffii collected from Oncorhynchus keta (Walbaum) and Scomber japonicus Houttuyn, respectively, were used for in vitro-culture in order to obtain L4 and adult stages. Species identification was confirmed by PCR-RFLP analysis of the ITS region (ITS1-5.8S-ITS2) of ribosomal DNA and by mtDNA cox2 gene sequencing. Results revealed that L3, L4 and adult stages of A. simplex (s.s.) and A. pegreffii are morphologically distinguishable based on ventriculus length, wherein the former has longer ventriculus (0.90–1.50 mm) than the latter (0.50–0.78 mm). For oesophagus/ventriculus ratio, these two species are distinguishable only during L4 and adult stages. Also, adult male A. simplex (s.s.) and A. pegreffii were found to be distinguishable by differences in the distribution pattern of the caudal papillae, particularly the 3rd pair of distal papillae.     

Gastric ulceration caused by genetically identified Anisakis simplex sensu stricto in a harbor porpoise from the Western Pacific stock

The genus Anisakis is a well-known group of nematodes that parasitize cetaceans as the final host and cause mucosal damage to their stomach. However, little has been done to precisely identify the nematodes recovered from the final hosts, especially in the Western Pacific, because of taxonomic confusion about the discrimination of sibling species and the difficulties of obtaining specimens from cetaceans. We describe the results of genetic identification and histopathological observations of specimens recovered from an ulcerated lesion and stomach contents in the forestomach of a female harbor porpoise accidentally caught by a set net fishery in Usujiri, southern Hokkaido, Japan. All the specimens arbitrarily collected from the lesion and stomach contents were identified as Anisakis simplex sensu stricto according to their ITS rDNA sequences. The size of the ulcer was approximately 6.3 mm in diameter and it was infected with 119 individual nematodes, mostly consisting of L3 and L4 stage larvae (95.0%). Histological sections were characterized by a locally extensive ulcer with the parasites penetrating into the muscularis externa that caused a thickening of the surrounding mucosa.     

Food habits of the silky shark Carcharhinus falciformis (Müller & Henle, 1839) off the western coast of Baja California Sur,Mexico

The objective of this study was to establish the trophic niche of the silky shark and to determine the ecological role of this predator in the ecosystem close to Baja California. The trophic spectrum was analyzed from samples taken during summer and autumn (2000–2002) from the fishing camps of Punta Lobos and Punta Belcher on the western coast of Baja California Sur. A total of 263 stomach contents were analyzed (143 with food; 120 empty). The index of relative importance (IRI) showed that at Punta Lobos, silky sharks fed mainly on red crabs Pleuroncodes planipes (%IRI = 83%), whereas at Punta Belcher the main food item was the jumbo squid Dosidicus gigas (%IRI = 41%), followed by chub mackerel Scomber japonicus (%IRI = 33%). According to the Levin Index (Bi), the trophic niche breadth in silky sharks is low (Bi = <0.6), which means that silky sharks are specialist predators because they mainly consume three prey types: red crab, chub mackerel, and jumbo squid. The Shannon‐Wiener Index indicated that all trophic categories at Punta Belcher (0.85–1.22) had lower diversity than at Punta Lobos (0.50–1.6), because the silky shark feeds more on tropical prey found close to Punta Lobos. The Morisita‐Horn Index (Cλ) showed an overlap in the diet between the two areas analyzed and between sexes (Cλ = >0.6). The juveniles and adult females did not show any overlap. In the caloric analysis of the main prey, the jumbo squid (D. gigas) contributed the most calories to the silky shark diet (76%).