Seasonal and interannual variation of the ichthyoplankton off the coast of Northern Morocco

Changes in the qualitative and quantitative composition of the ichthyoplankton off the coast of Northern Morocco (36–28° N) are analyzed in different seasons of 1994–2008. Pelagic eggs and larvae of over 80 fish species belonging to 57 families are recorded. In cold periods at the Morocco coast, there is maximum spawning of fish belonging to the subtropical (Mediterranean-Atlantic) fauna, the dominant of which are European pilchard Sardina pilchardus, common scad Trachurus trachurus, and Atlantic mackerel Scomber japonicus. In warm periods, in addition to the aforementioned species, the ichthyopankton often comprises eggs and larvae of fish form the tropical fauna. Among the latter are round sardinella Sardinella aurita and West-African mackerel T. trecae dominate. The spawning biomass of principal commercial fish is also calculated by the quantity of eggs laid by females.     

The reproductive traits of Scomber japonicus (Houttuyn, 1782) in the Eastern Adriatic Sea

The aim of the present study was to investigate the fisheries biology of Scomber japonicus (Houttuyn, 1782) in the Adriatic Sea, to enable implementation of appropriate regulatory measures for fisheries. Reproductive biology and sexual patterns of S. japonicus (chub mackerel) were examined from monthly random samples of commercial catches from purse seine nets (10 mm stretched mesh size) in the eastern Adriatic Sea. The annual mean chub mackerel fork length (FL) was examined from 1998 to 2007. Average fork lengths were approximately 25 cm between 1998 and 2002, decreasing to 22 cm between 2003 and 2007. In addition, sex ratios fluctuated as a function of size and month: females were more abundant in the smaller length classes, as well as before and after spawning; males were more abundant in the larger length classes and during spawning. The overall sex ratio was 0.68; females were significantly predominant. 50% of the chub mackerel population was sexually mature at a FL of 18.3 cm, and both males and females reached sexual maturity at FLs of 20.4 cm and 16.8 cm, respectively. Based on gonad maturity stages, gonad weight and gonadosomatic index, chub mackerel spawned from May to August, with peak spawning in June for both sexes. The mean absolute fecundity was 181 277 ± 62 090 oocytes per ovary. A positive exponential correlation was found between fecundity and fork length, gonad weight, and total chub mackerel weight (r² = 0.640; r² = 0.686 and r² = 0.607, respectively).     

Isolation and characterization of microsatellite loci for the jack mackerel (<Emphasis Type="Italic">Trachurus murphyi</Emphasis> Nichols, 1920)

Eight microsatellite loci were developed for the jack mackerel (Trachurus murphyi), a fish of significant commercial importance in the Southeast Pacific. Genetic variation at these loci was examined in 15 samples from the locality of Talcahuano (Chile). All eight were highly polymorphic, with a number of alleles per locus ranging from 4 to 22 and an observed heterozygosity from 0.429 to 1. These markers will be useful to address issues of population genetics, ecology, conservation and fisheries management related to that species.     

Identification of small juvenile scombrids from northwest tropical Australia using mitochondrial DNA cytochrome <Emphasis Type="Italic">b</Emphasis> sequences

Small juveniles of the nine species of scombrids in Australian waters are morphologically similar to one another and, consequently, difficult to identify to species level. We show that the sequence of the mitochondrial DNA cytochrome b gene region is a powerful tool for identification of these young fish. Using this method, we identified 50 juvenile scombrids collected from Exmouth Bay, Western Australia. Six species of scombrids were apparent in this sample of fish: narrow-barred Spanish mackerel (Scomberomorus commerson), Indian mackerel (Rastrelliger kanagurta), frigate tuna (Auxis thazard), bullet tuna (Auxis rochei), leaping bonito (Cybiosarda elegans), and kawakawa (Euthynnus affinis). The presence of Indian mackerel, frigate tuna, leaping bonito, and kawakawa is the first indication that coastal waters may be an important spawning habitat for these species, although offshore spawning may also occur. The occurrence of small juvenile S. commerson was predicted from the known spawning patterns of that species, but other mackerel species (Scomberomorus munroi, Scomberomorus queenslandicus, Scomberomorus semifasiciatus) likely to be spawning during the sampling period were not detected among the 50 small juveniles analyzed here.     

Discards in bottom‐trawl fishery in the western Black Sea (Turkey)

The aim of this study was to estimate the discards of target and non‐target species from bottom trawlers (rhombic and 40 mm cod end mesh size nets) in the Black Sea. On‐board sampling was conducted on the southwestern coasts of the Black Sea in the fishing ports of Rumelifeneri and Igneada for a total of 66 hauls on two commercial bottom trawlers from October 2012 to April 2013 and from October 2013 to April 2014. A total of 32 species were captured, including 25 species of fish, three crustacea, two echinodermata and two mollusca. Mullus barbatus and Merlangius merlangus euxinus were the target species, whereas 24 species were always discarded. Scophthalmus maximus and Pomatomus saltatrix were always retained. The two regions were similar in terms of catch and discard compositions, CPUE, DPUE and discard ratio. Discarding is important in the Black Sea commercial bottom trawl fishery and accounts for as much as 31.4% of the total bottom trawl catch. The results showed that the discard rates varied among species, depths (p = .04) and seasons (p = .0001). Finally, it was concluded that in the western Black Sea, when the impacts of depth and season are considered, that the discard quantity can be reduced.     

Six polymorphic microsatellite loci in the Japanese Spanish mackerel,Scomberomorus niphonius

Six polymorphic microsatellite loci were isolated for genetic structure studies of the Japanese Spanish mackerel, Scomberomorus niphonius, a severely exploited marine fish species. The number of observed alleles for each locus ranged from seven to 41, and the values of expected and observed heterozygosities were 0.546–0.946 and 0.602–1.000, respectively. These microsatellite markers should prove to be a useful tool for estimating the population genetic structure and genetic variability of Japanese Spanish mackerel.     

Spatial distribution and diversity of commercial demersal fish species in the shelf waters of the Caspian Sea

The Caspian Sea (CS) is a unique ecosystem known for its several fish species, especially sturgeons. To exhaustively manage the fish stocks of this ecosystem, detailed knowledge of species composition, abundance, distribution, and the habitat traits of the living organisms is necessary. This study analyzed the diversity, spatial, and seasonal distribution of commercial demersal fish species, and examined the relationships between community structure and environmental variability in Iranian shelf waters of the CS. For this purpose, seasonally fish sampling took place between 2009 and 2011 with a bottom trawl. Among 11 fish species captured, Chelon spp., Rutilus kutum, and Vimba vimba showed the highest abundances (i.e. 88.49%, 10.67%, and 0.69%, respectively). Univariate and multivariate analyses showed differences in commercial fish assemblages (abundance and species richness) according to seasons and regions. Distance-based Linear Model (DisTLM) showed that eight environmental variables display significant linear relationships with the fauna resemblance matrix (p < .05). Based on AIC criteria, the combination of silt&clay, TOM, longitude, depth, bottom, and surface temperature used to build the parsimonious DisTLM model explain 67.03% of the total variability. The results revealed a biogeographical and temporal gradient from the west to the east and summer to winter, in terms of commercial demersal fish assemblages and species diversity, as a consequence of different geomorphological, bottom substratum conditions and benthic communities.     

New record of a sharpnose sevengill shark Heptranchias perlo (Elasmobranchii,Hexanchidae) from the Balearic Sea,western Mediterranean Sea

In March 2018, an immature female sharpnose sevengill shark Heptranchias perlo was caught by a commercial bottom trawler in the Ibiza Channel. This represents the first substantiated record of the species around the Balearic Islands (GSA05) and the second record from off the Spanish Levantine coasts. This paper includes a review of the records of H. perlo in the Mediterranean as an aid to future conservation assessments.     

Discards in bottom trawl fishery in the Aegean Sea (Izmir Bay,Turkey)

Sampling was carried out on a seasonal basis during 2007–2009, using a conventional bottom trawl net with 44 mm codend mesh size in Izmir Bay, Aegean Sea. A total of 116 valid hauls: 27 in autumn, 28 in winter, 35 in spring and 26 in summer, were conducted at depths ranging from 30 to 70 m. A total of 112 species: 15 Chondrichthyes, 83 Osteichthyes, 11 Cephalopoda and 3 Crustacea were obtained in the trawl codend. All captures were separated into commercial (C) and non‐commercial (NC) species. The C ratio was 69.6%, while NC (i.e. discards) was 30.4%. Diplodus annularis was the most abundant species in all seasons, followed by Mullus barbatus, Merluccius merluccius, Citharus linguatula, Serranus hepatus, Lepidotrigla cavillone, Spicara maena, Myliobatis aquila, Diplodus vulgaris, and Trisopterus minutus in decreasing order of abundance. These top ten species constituted 75% of total catch weight. Biomass ratios of total discards to commercial species were 0.44 : 1.     

Planktivory in benthic nototheniid fish in McMurdo Sound,Antarctica

Synopsis Four species of nototheniid fish were sampled from below the sea ice near Cape Armitage, McMurdo Sound:Pagothenia borchgrevinki from just below the ice 1.5 km offshore,Trematomus bernacchii, Trematomus hansoni andTrematomus centronotus from off the bottom in about 20 m of water near the shore. Scale worms and isopods were conspicuous non-planktonic prey, and present in the three benthic fish species. The planktonic pteropod molluscLimacina helicina was numerically common in all four species of fish. The planktonic hyperiid amphipodHyperiella dilatata was also found in all fish species. WhereasP. borchgrevinki is planktivorous in accord with its pelagic habit, theTrematomus spp. clearly also feed on plankton from the water column.T. hansoni is particularly planktivorous, taking smaller copepods thanP. borchgrevinki.     

Comparison of the early life histories of two <Emphasis Type="Italic">Cynoglossus</Emphasis> species in the inner estuary of Ariake Bay,Japan

The larval distribution and feeding habits of Cynoglossus abbreviatus and Cynoglossus lighti were investigated around the Rokkaku estuary in Ariake Bay during October 2004 and March and April 2005. Cynoglossus abbreviatus started and completed metamorphosis at larger sizes than C. lighti. Developmental phases consisted primarily of individuals at metamorphosis and postmetamorphosis, which were mainly distributed inside and just outside the Rokkaku River in March–April for C. abbreviatus and October for C. lighti. Tidal changes in vertical distribution just outside the river mouth differed between the closely related species; C. abbreviatus was distributed in the surface and middle layers at flood tide, and aggregated near the bottom (where the current speed was lowest) at ebb tide. Cynoglossus lighti stayed mainly near the bottom during all tidal phases. Larvae of both Cynoglossus species selectively fed on copepods (Pseudobradya sp.), which were scarce in the waters. These facts suggest that the nursery grounds of the two Cynoglossus species were different in terms of their tidal vertical distribution patterns.     

Rapid PCR-RFLP method for discrimination of imported and domestic mackerel

With the ever-decreasing domestic fishery catch of Japanese mackerel Scomber japonicus, alternative Atlantic mackerel Scomber scombrus has been increasingly imported and currently accounts for approximately 34% of mackerel consumption in Japan. As there is no morphologic difference between the species after removal of their skin, not only fresh and frozen fillets but also processed seafood of S. scombrus are frequently marketed with mislabeling as S. japonicus. In this study, a rapid and reliable polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) analysis was developed to discriminate imported mackerel S. scombrus and domestic mackerel S. japonicus. PCR amplification for the nuclear 5S ribosomal DNA nontranscribed spacer was performed using Scomber-specific primers. Direct digestions of the PCR products using either PvuII or HaeIII restriction enzymes generated species-specific profiles, indicating that both enzymes enable the accurate identification of S. scombrus and S. japonicus. This robust and reproducible method can serve as molecular-based routine food inspection program to enforce labeling regulations.     

The complete mitochondrial genome of the mackerel icefish,Champsocephalus gunnari (Actinopterygii: Channichthyidae), with reference to the evolution of mitochondrial genomes in Antarctic notothenioids

The mackerel icefish (Champsocephalus gunnari Lönnberg, 1905) is a ray‐finned fish living in the Southern Ocean around Antarctica. We sequenced the complete mitochondrial (mt) genome of the mackerel icefish and a segment from cytochrome b to the control region (CR) in 32 individuals. The mt genome of the mackerel icefish was rearranged, containing two nicotinamide adenine dinucleotide (reduced form) dehydrogenase subunit 6 (ND6), two tRNA^Glu, and two CRs. However, variations in numbers of ND6 and tRNA^Glu were observed amongst individuals. These variations included type 1 (containing two ND6 and two tRNA^Glu), type 2 (containing one ND6, one incomplete ND6, and one tRNA^Glu), and type 3 (containing one ND6 and one tRNA^Glu). The gene orders of types 1 and 2, and variations in numbers of ND6 and tRNA^Glu were not previously found in any Antarctic notothenioids, whereas type 3 is the same as that of Racovitzia glacialis. Phylogenetic analyses of CR DNA sequences showed that duplicated CRs of the same species formed a monophyletic group, suggesting that duplication of CRs occurred in each species. The frequent duplication of mt genomes in Antarctic notothenioids is an unusual feature in vertebrates. We propose that interspecific hybridization and impairment of mismatch repair might account for the high frequency of gene duplications and rearrangement of mt genomes in Antarctic notothenioids.     

Relationship of otolith length to fish total length in six demersal species from the NW Mediterranean Sea

Relationships between otolith major axis length (mm) and fish size (total length, cm) were described by means of linear regression analysis for six demersal fish species from the NW Mediterranean: blue whiting (Micromesistius poutassou), greater forkbeard (Phycis blennoides), red mullet (Mullus barbatus), poor cod (Trisopetus minutus capelanus), horse mackerel (Trachurus trachurus), and Mediterranean mackerel (Trachurus mediterraneus). Results show that reconstruction of body size from otolith measurement is possible by applying this approach based on the relationship of otolith length – fish length.     

Species composition,distribution, and specific features of feeding of Fish Larvae,and fry in the Sea of Okhotsk from October to December 2007

Ichthyoplankton of the Sea of Okhotsk from October to December 2007 comprised larvae and fry of eight fish species belonging to five families. The larvae of lord Hemilepidotus gilberti, white-spotted greenling Hexagrammos stelleri, and Atka mackerel Pleurogrammus monopterygius were the most widespread and numerous in the study period. Fish larvae from October to December 2007 were seined over the vast water area of the Sea of Okhotsk, maximum catches were made in waters of western Kamchatka. The food spectrum of larvae of five fish species (H. gilberti, Hexagrammos octogrammus, H. stelleri, P. monopterygius, and Bathymaster signatus) included approximately 20 plankters. Irrespective of species belonging, copepods Pseudocalanus minutus and Oithona similis, eggs and nauplii of copepods, as well as juveniles of pteropods were common food items for all fish. Larvae of all considered fish species in the Sea of Okhotsk fed mainly during the light hours of the day.     

Diet and trophic position of two mackerel species in the archipelago of Madeira,Portugal

The Atlantic chub mackerel Scomber colias and the blue jack mackerel Trachurus picturatus are two abundant species in the Macaronesia region which includes the archipelago of Madeira, Portugal. Both are key species in the trophic web, being important prey for several local top predators, such as seabirds and marine mammals. Nonetheless, little is known about their feeding ecology in oceanic environments. In this study, the authors describe the seasonal variation in the diet of S. colias and T. picturatus in the oceanic region of Madeira throughout a year. Visual inspection of stomach contents revealed that S. colias fed on a broader range of prey groups than T. picturatus, but for both species, zooplankton (particularly calanoid copepods) and fish were the most important food items. The diet of S. colias included a higher proportion of fish, namely Atlantic saury Scomberesox saurus and S. colias, than that of T. picturatus, that included mostly the longspine snipefish Macroramphosus scolopax. T. picturatus consumed a higher proportion of decapods and other copepods. Seasonal variation was found in the diet of both species, with zooplanktonic species being more important in colder months (February to April) for S. colias and during warm months (May to October) for T. picturatus. Their diet in other seasons was dominated by fish. Although they consume similar prey, carbon and nitrogen stable isotope analysis of muscle of S. colias and T. picturatus showed little overlap in their diets, and T. picturatus showed higher δ¹⁵N and a narrower isotopic niche.     

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.     

Hyperproduction of Orotic Acid and Orotidine by Mutants of Bacillus subtilis

The fatty acid composition of lipids in various organs and in the stomach contents of two species of frigate mackerel, Auxis rocheri and Auxis thazard, related to the tuna species was determined. Docosahexaenoic acid was the dominant unsaturated fatty acid accounting for 20% or more of the total fatty acids in all organs of the two frigate mackerel species (mean ±S.D.: 22.6 ± 6.0% for rocheri, 28.0 ± 4.3% for A. thazard), while the fatty acids in lipids from their stomach contents were comparatively low (1.5–13.0% for A. rocheri, 15.4–16.5% for A. thazard). It is suggested that the high content of DHA in the lipids of tuna species is a general characteristic.     

GROWTH RESPONSES TO SALINITY VARIATION IN FOUR ARCTIC ICE DIATOMS1,2

During spring, extensive blooms of microalgae grow on the underside of arctic sea ice. The brownish, algal layer penetrates ca. 2 cm into the bottom surface of the ice and the algae are potentially exposed to very high salinities. Four diatom species, Melosira juergensii Ag., Porosira glacialis (Grun.) Jørg., Navicula transitans var. derasa (Grun.) Cleve, and Coscinodiscus lacustris Grun., isolated from, sea ice samples taken from the Beaufort and Chukchi seas near Barrow, Alaska, were grown at 11 salinities ranging from 5 to 70‰ at 5 C under constant illumination. All of the species grew at 5‰ except N. transitans whose lower growth limit was 15‰. Growth was high over a broad range of salinities, but none of the species grew at salinities above 60‰. These diatom species appear to be well suited to tolerate the salinities in the brine pockets near the bottom of annual arctic sea ice where they are found. High brine-cell salinity, however, may limit the upward, penetration of ice algae into the bottom of sea ice.     

Age,growth and mortality of scaldfish (Arnoglossus laterna Walbaum, 1792) from the Adriatic Sea

The population dynamics parameters of scaldfish, Arnoglossus laterna, from the Adriatic Sea were studied. Specimens ranging from 4.5 to 17.1 cm in total length were collected from commercial bottom‐trawl catches (2000–2006). Spawning from April through the end of August with a peak in May, A. laterna is one of the non‐target species usually present in mixed bottom trawl catches. The overall male to female ratio was 1.00 : 0.61. The oldest individual was 6 years of age. Length–weight relationships showed positive allometric growth (b = 3.36 for males and b = 3.39 for females). Parameters of the von Bertalanffy growth equation were: L_∞ = 17.3 cm; K = 0.258 per year; t₀ = ?1.0026 year; R² = 0.925. The relatively low value of total mortality (Z = 0.90) and relatively high value of constant rate of natural mortality (M = 0.64) was estimated. Presumed calculated fishing mortality (F = 0.26) and the consequently estimated exploitation ratio (E = 0.29) indicated no danger of an over‐exploitation of this species in the study area at the current level of fishing pressure. The low T max and correspondingly high M suggest that this small benthic predator plays an important role in the Adriatic ecosystem as a prey species for large benthic predators. However, the estimates include uncertainties and require further confirmation, especially with regard to natural mortality.