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Special issue: The Second International Indian Ocean Expedition (IIOE-2): Motivating New Exploration in a Poorly Understood Ocean Basin Volume 3).-- 14 pages, 7 figures, 3 tables, supplementary data https://doi.org/10.1016/j.dsr2.2020.104841, Mesopelagic fishes of the southeastern Indian Ocean are represented by a high number of lanternfish species (Myctophidae). The horizontal distribution patterns of their larvae have been previously studied; however, research on larval feeding habits is non-existent. The goal of this study was to describe the diet and trophic-based strategies of the most abundant myctophid larvae off Western Australia through stomach content analysis. Samples were collected in autumn 2007 off southwestern Australia when this oligotrophic area was under the influence of the seasonal Leeuwin Current, and in autumn 2010 on the tropical continental shelf of northwestern Australia. The species investigated during these periods were Benthosema fibulatum, B. pterotum, B. suborbitale, Dasyscopelus asper, Diaphus “deep” and “slender” morphotypes, Hygophum hygomii, Lampadena luminosa, Lampanyctus alatus, Lampanyctus spp. and Myctophum sp. Generally, myctophid larvae showed a diurnal feeding pattern. Only postflexion stages in L. alatus, L. luminosa, B. pterotum, Diaphus “slender”, and Myctophum sp. preyed at dawn or during the night. The highest feeding incidence was found in L. luminosa and the Diaphus “deep” morphotype, while the lowest, in H. hygomii. Generally, larvae were zooplankton feeders with nauplii and copepodites being the most abundant dietary groups, except for B. suborbitale and Myctophum sp. where the small non-calanoid genus Oncaea was dominant. Soft organisms such as appendicularians were frequent items in most fish diets throughout their entire larval phase, and highly abundant in Diaphus “deep” morphotype. The wide prey-size spectrum indicates that the majority of the fish species were not size-specific feeders for most of their larval life. Nevertheless, B. suborbitale, B. fibulatum, and L. alatus preferred larger prey, ignoring the smaller items as they grew. Larval feeding patterns of similar genera from other ecosystems are discussed and compared with those in Western Australia, Ainhoa Bernal was the recipient of a PhD scholarship associated with the project CTM 2008-04489-C03-02 awarded by the Spanish Ministry of Science and Innovation, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Jumbo squid, Dosidicus gigas , is a species endemic to the eastern Pacific. Its distribution ranges from the Gulf of Alaska to Chile. These squids are important components of the ecosystem, as they are prey to sharks, billfishes, and marine mammals, and active predators of myctophid fishes, other squids and crustaceans. In Ecuador, D. gigas is a potential resource for industrial and artisanal fisheries, but they are often by-catch in artisanal fisheries that use trammel net and gill-netting methods. Due to the importance of D. gigas as prey and predator, we performed this exploratory research to describe the composition of their diet and identify their most important prey. A total of 167 squids were sampled in Santa Rosa, Salinas, Ecuador from May to December 2014. Squids ranged between 17.5 and 52 cm ML, and our results showed an average size of 40 cm ML. According to the %IRI the diet was mainly composed of fish and squids. Two myctophids, Lampanyctus sp. and Myctophum sp., were important food resources. Our results showed that there was no difference between food resources, and the sex, size, and maturity of squids in our sample. Cannibalism also occurs on small to large D. gigas , and is influenced by availability of other prey in the surface waters during fishing activity.

Fishes of the order Myctophiformes (Teleostei; Scopelomorpha) comprise over half of all deep-sea biomass, and are a critical component of marine ecosystems worldwide. Members of the family Myctophidae, within Myctophiformes, form the majority of species diversity within the order (∼250 species, 33 genera, 2 subfamilies), and are further known for their diverse bioluminescent traits, comprised of distinct cranial, postcranial, and caudal luminous systems that is perhaps the most elaborate among all vertebrates. These features make myctophids particularly compelling from both economic and scientific perspectives, yet no studies have sampled these fishes at a density appropriate for addressing any questions requiring a phylogenetic hypothesis as input. This study therefore presents a seven-locus molecular phylogeny of the order, sampling over 50% of all nominal myctophid species. This taxon sampling triples the representation of the next most comprehensive analysis, and reveals several new and well-supported hypotheses of relationships, in addition to supporting traditional hypotheses based on combined morphological data. This analysis shows that the slendertailed myctophids Gonichthys, Centrobranchus, Loweina, and Tarletonbeania are rendered non-monophyletic by a polyphyletic Myctophum; the enigmatic, monotypic genus Notolychnus valdiviae is nested within tribe Lampanyctini; the genus Diaphus is divided into at least two clades, with the suborbital (So) group recovered as monophyletic with strong support; and the genera Lampanyctus and Nannobrachium are recovered as non-monophyletic. These molecular results highlight the potential of myctophids as a premier model system for the application of modern comparative methods to studies of deep-sea evolution.

Representative fossils of three extant lanternfish (Myctophidae) genera (Bolinichthys, Lampanyctus, and Myctophum) from the collections of Natural History Museum of Los Angeles County were identified, based on a combination of osteological and photophore characters. These specimens come from the upper Miocene Modelo Formation (Mohnian-Delmontian) of California, and represent the first skeletal records of Bolinichthys (otherwise identified as otoliths from the Late Miocene of Italy) and Myctophum body fossils in North America, and confirm that both modern myctophid subfamilies exhibited a cosmopolitan distribution by the late Miocene.

A unique specimen of Myctophum phengodes (family Myctophidae) from the South Atlantic is reported with three extraneous primary photophores along one side of the dorsal profile; all usual photophore series for this species are present. The supracaudal gland is encircled by a silvery band instead of a simple black band, a condition not observed in other species of Myctophum examined. Photophore patterns of myctophids are the primary method of determining species identification. Other myctophids have been found with small positional variations for a single photophore (usually only one side of the body), but are readily identifiable to species. While one specimen with extraneous photophores widely separated from and not part of typical series is not considered taxonomically significant, it is important to determine if this is a single abnormal individual or a unique population identifier.

We describe the day–night vertical distribution patterns of 18 species or types of myctophid fish larvae at the transforming stage based on discrete depth sampling from the surface down to 1000-m depth in the subtropical–tropical western North Pacific. A total of 551 transforming stage larvae were collected at the 19 sampling stations. Except for the Diaphus species and Notolychnus valdiviae, all of the transforming stage larvae (including genera Benthosema, Bolinichthys, Centrobranchus, Ceratoscopelus, Diogenichthys, Hygophum, Lampanyctus, Lobianchia, Myctophum, Symbolophorus, and Triphoturus) were collected in the lower mesopelagic zone from 600- to 900-m depth during both day and night, showing no diel vertical migration (DVM). On the contrary, the Diaphus species and N. valdiviae larvae undergo DVM during the transforming stage, occurring below 200-m layer during the daytime and migrating up to the upper 150-m layer at night, i.e., they show earlier adaptation to juvenile–adult behaviors. Most myctophid fish larvae are known to undertake substantial ontogenetic vertical migration (OVM) from the epipelagic to mesopelagic zones during their early life stage. Although considerable sampling effort was carried out in this study, transforming larvae, except for the above two migratory ones, were not collected in the epipelagic and upper mesopelagic zones, strongly suggesting that their sinking speed would be high. It would be advantageous for survival to spend their highly vulnerable transforming stage in the lower mesopelagic zone, where predation pressures are lower and physical conditions are more stable than in the upper layers.

The occurrence of fossil fishes in the Messinian diatomites of Gavdos Island (Greece) was recently observed. This fish fauna is dominated by the Myctophids, which constitute more than two thirds of the collected material. Among them, Myctophum (s. l.) licatae (Sauvage) is by far the most abundant, with more than 50% of the specimens. Although the mesopelagic components are overwhelmingly dominant, epipelagic fishes, like Syngnathus cf. albyi Sauvage, are also present. The composition of this fish fauna is indicative of a sedimentation influenced by the action of upwelling currents, an interpretation that is also suggested by the composition of the diatom flora. Pour citer cet article : J. Gaudant et al., C. R. Palevol 5 (2006) .

The stomach contents of 235 specimens of the squid Sthenoteuthis oualaniensis (4·3–36·5 cm mantle length, ML) were examined. A detailed list of 60 species of prey, comprising young and adult squid, is given together with their frequency of occurrence and proportional contribution. The size and number of each food item was investigated. Three ontogenetic size-groups of S. oualaniensis were distinguished: I, fry and young (4–10 cm ML), micronektonic epipelagic plankton-eaters; II, transient critical size group (10–15 cm ML), converting from feeding on planktonic crustaceans and fish larvae to myctophid fishes; III, medium-sized (adult) nyctoepipelagic nektonic predators (15–36·5 cm ML), feeding primarily on myctophids and secondarily on squid. Myctophids (genera Symbolophorus, Myctophum and Hygophum) were the most abundant prey in the diet of adult S. oualaniensis from different parts of its distribution.