Lantern fish (Benthosema pterotum) resources as a target for commercial exploitation in the Oman Sea

The skinnycheek lantern fish Benthosema pterotum (Myctophidae) represents a virgin resource in the Oman Sea. Because of its potential importance for fishmeal production there has been great interest during the last decade in starting commercial exploitation. Acoustic surveys to estimate stock biomass and trial fishing using pelagic trawls were carried out in Iranian waters of the Oman Sea from 1992 to 1998. Lantern fish schools are found in offshore waters, on the edge of the continental shelf wherever sea depth is more than 100 m. During the day the fish occur in two vertical layers, with the densest schools in the shallower layer (80–130 m), whereas at night B. pterotum occur in a single dispersed layer closer to the surface (mainly at 30–70 m). Biomass estimates range from 1 to 4 million tonnes (t), with an average of 2.3 million t. Densities vary seasonally, with the highest densities recorded in spring (May–June) and lowest in autumn (October–November). The highest densities were seen in the western Oman Sea. Although recommendations can be made with regard to the best fishing seasons, areas and depths, trial catch rates were too low (<30 t daily per boat) to support a commercially viable fishery. Further trials are needed to identify the best gear and vessel size.     

Lights out: the evolution of bacterial bioluminescence in Loliginidae

Representatives of several metazoan clades engage in symbiotic interactions with bioluminescent bacteria, but the evolution and maintenance of these interactions remain poorly understood. Uroteuthis is a genus of loliginid squid (Cephalopoda: Loliginidae) characterized by paired ventral photophores (light organs) housing bioluminescent bacteria. While previous phylogenetic studies have suggested that Uroteuthis is closely related to Loliolus, a genus of non-bioluminescent species, this relationship remains unresolved. To illuminate Uroteuthis and Loliolus phylogeny and its implications for the evolution of bioluminescence in Loliginidae, we generated sequences from two mitochondrial genes from Uroteuthis specimens sampled from several sites in the Indian and western Pacific Oceans. We combined these data with data from GenBank, analyzed the concatenated data set using maximum likelihood and Bayesian methods, and reconstructed the evolution of bacterial bioluminescence on the resulting phylogenies. Our analyses support the hypothesis that Uroteuthis is paraphyletic with respect to Loliolus. Furthermore, our reconstructions suggest that the symbiosis between loliginid squid and bioluminescent bacteria evolved once in the ancestor of Loliolini (the clade comprising Uroteuthis and Loliolus), but was subsequently lost in the ancestor of Loliolus. These findings could have profound implications for our understanding of the evolution of symbiotic bioluminescence in squid.     

Molecular identification and phylogenetic relationships of Coleoidea (Mollusca: Cephalopoda) from the Persian Gulf and Oman Sea reveals a case of cryptic diversity

The Persian Gulf and Oman Sea constitute one of the most important marine ecosystems and have many economically important aquatic species, including several coleoid cephalopods. Some coleoids are difficult to identify using traditional morphological characteristics. In this study, two mitochondrial fragments, cytochrome oxidase I (COI) and the large ribosomal subunit (16S rRNA), were used for identification of coleoid species in four regions in the northern Persian Gulf and Oman Sea. The study led to the identification of potential cryptic species of Sepia, Amphioctopus and Uroteuthis. Furthermore, Euprymna hyllebergi was reported for the first time from the Persian Gulf. A high diversity of Coeloidea was found in the study area. Mean intraspecific and interspecific nucleotide distances for COI were 0%–2% and 2%–7%, respectively, while these values for 16S rRNA sequences were 0%–1% and 1%–4%. Given the uncertainty about species identity and the high levels of intraspecific genetic diversity reported for some species in GenBank, a comprehensive global study will be needed to resolve the taxonomic status of several coleoid species.     

Phylogeography of the pharaoh cuttle Sepia pharaonis based on partial mitochondrial 16S sequence data

The pharaoh cuttle Sepia pharaonis Ehrenberg, 1831 (Mollusca: Cephalopoda: Sepiida) is a broadly distributed species of substantial fisheries importance found from east Africa to southern Japan. Little is known about S. pharaonis phylogeography, but evidence from morphology and reproductive biology suggests that Sepia pharaonis is actually a complex of at least three species. To evaluate this possibility, we collected tissue samples from Sepia pharaonis from throughout its range. Phylogenetic analyses of partial mitochondrial 16S sequences from these samples reveal five distinct clades: a Gulf of Aden/Red Sea clade, a northern Australia clade, a Persian Gulf/Arabian Sea clade, a western Pacific clade (Gulf of Thailand and Taiwan) and an India/Andaman Sea clade. Phylogenetic analyses including several Sepia species show that S. pharaonis sensu lato may not be monophyletic. We suggest that “S. pharaonis” may consist of up to five species, but additional data will be required to fully clarify relationships within the S. pharaonis complex.     

Taxonomic Status and Molecular Systematics of an Endemic Fish,Herklotsichthys lossei (Clupeidae) from the Persian Gulf: Insights into Non-monophyly of the Genus

Journal of Ichthyology - The endemic Persian Gulf herring, Herklotsichthys lossei, has similar characteristics with other congeners, especially H. punctatus, which makes it difficult to recognize....     

Age and growth of Benthosema pterotum (Alcock, 1890) (Myctophidae) in the Oman Sea

Juvenile and adult specimens of Benthosema pterotum (skinnycheek lanternfish) were collected during several surveys conducted on the Iranian continental shelf of the Oman Sea. Age was estimated by enumeration of growth increments in sagittae otolith sections on the assumption of their daily deposition. Three distinct growth zones in otolith microstructure (central, middle, and external) were defined. These three zones presumably represent increments deposited during successive life history stages, characterized by a different migratory behavior and depth occurrence. The number of increments in the central zone of the B. pterotum otolith (26.8 on average) was thus far one of the lowest in myctophid species studied. A negative correlation between the number of increments in the central and middle zones was observed. This might suggest a functional relation between these two periods of early life history, when fewer larvae in the epipelagic layers may be compensated by a longer non‐migratory behavior of metamorphosis larvae and early juveniles. The maximum number of growth increments in B. pterotum otoliths, i.e. 315, indicated a short lifespan of probably <1 year. The relationship between otolith length and standard length was described by linear regression model (r² = 0.902), and between the body length and weight as an isometric growth in 274 juvenile and adult specimens (r² = 0.922). The growth model estimated only for juveniles and adults was curvilinear (SL = 1.150 × Age^0.616; r² = 0.868). Back‐calculated hatch dates might suggest a spawning season of B. pterotum from May to September, but due to the limited number of investigated specimens a prolonged spawning cannot be excluded. Further trials are needed to measure the population parameter dynamics.     

Length–weight relationships for 10 elasmobranch species from the Oman Sea

Length–weight relationships (LWRs) were estimated for ten elasmobranch species from Iranian waters of the Oman Sea. All specimens were collected by bottom trawl (mesh size 80 mm in the cod end) between May and December 2014. A total of 509 individuals (107 Torpedo sinuspersici, 68 Rhinobatos punctifer, 63 Chaenogaleus macrostoma, 72 Himantura walga, 80 Himantura gerrardi, 58 Gymnura poecilura, 4 Himantura uarnak, 4 Rhinoptera javanica, 14 Aetobatus flagellum, and 39 Pastinachus sephen) were sampled and studied. Results showed that most species had positive allometric or isometric growth but that more studies were needed for final decisions on growth patterns. Both the disk length‐body weight (DL/BW) and disk width‐body weight (DW/BW) relationships also showed a good fit, reinforcing the credibility of the data in relation to the LWRs. This study is the first report of LWRs for these elasmobranchs in the northern Oman Sea.