Seasonal and interannual variation of ichthyoplankton off the coast of the Moroccan Sahara

Changes in the qualitative and quantitative composition of ichthyoplankton off the coast of the Moroccan Sahara (21–28° N) in different seasons of 1994–2007 are analyzed. In this region, the pelagic eggs and larvae of over 100 fish species belonging to 62 families have been recorded. In cold periods, off the coast of the Moroccan Sahara there is peak in the spawning of fish of the subtropical fauna. The majority of them are European pilchard Sardina pilchardus, common scad Trachurus trachurus, and Atlantic mackerel Scomber japonicus. In warm periods there is intensive spawning of fish of the tropical fauna. Among them, dominants are round sardinella Sardinella aurita, West-African scad Trachurus trecae, and Atlantic bonito Sarda sarda. The spawning biomass of principal commercial fish is calculated by the quantity of eggs laid by females. The environmental factors are indicated that influence the fluctuation of abundance and distribution of ichthyoplankton in the region under consideration.     

Feeding of pelagic fish in waters of Mauritania: 3.—Atlantic Chub mackerel <Emphasis Type="Italic">Scomber colias</Emphasis>, Atlantic horse mackerel <Emphasis Type="Italic">Trachurus trachurus</Emphasis>, Cunene horse mackerel <Emphasis Type="Italic">Trachurus trecae</Emphasis>

Feeding peculiarities of mass pelagic everyphagous fish Atlantic Chub mackerel Scomber colias, Atlantic horse mackerel Trachurus trachurus, Cunene horse mackerel Trachurus trecae from the Canary upwelling and the frontal zones of Mauritania were investigated. Atlantic Chub mackerel feeds mainly on fish inhabiting the zone of epipelagial, crustaceans and other organisms distributing in the sound scattering layers and also detritus and detritus–algal mixture. Cunene horse mackerel and Atlantic horse mackerel feed on mesopelagic fish and the organisms from the sound scattering layers. Feeding competition between these species does not occur due to non-concurrence of the places for concentration and nourishment. Correlation of food components, their occurrence and nourishment change for all species in conformity with fish sizes, physiological conditions and the season.     

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.     

Ichthyoplankton of the Azores seamounts

Species composition and quantitative distribution of ichthyoplankton in the region of the oceanic seamounts of the Azores complex from 2000 to 2004 are considered. The spawning biomass of the main fishery item of this region—Atlantic jack Trachurus picturatus—is calculated. The ichthyoplankton of the Azores seamounts in the period under consideration included eggs and larvae of 60 fish species from 26 families. In the summer, 20 species of eggs and larvae from 11 families and, in winter, 57 species from 24 families were recorded. Larval Myctophidae and Gonastomatidae have the most mass in the plankton in both seasons. The eggs and larvae of commercial fish species (T. picturatus and Pacific mackerel Scomber japonicus) were recorded mainly in the cold period. The species and quantitative composition of ichthyoplankton of the South Azores seamounts is far more numerous than in the North Azores seamounts. The region of the seamounts of the South Azores complex, judging from the estimation of biomass of commercial fish with different methods, can be regarded as a reserve for the fishery of Russian vessels in the central eastern Atlantic.     

The ichthyofauna of coastal waters southwest of Crimea in 2003–2004

The ichthyofauna of the narrow coastal zone of southwest Crimea in 2003–2004 was represented by 79 fish species belonging to 36 families. The structure of the species composition of eggs, larvae, and adult fish in these years indicated to its restoration in comparison with the late 1980s to early 1990s. The abundance of commercial fish increased: Engraulis encrasicolus ponticus, Trachurus mediterraneus ponticus, and Mullus barbatus ponticus. The quantity of migratory fish increased: Pomatomus saltatrix and Sarda sarda. The presence in winter catches of Trachurus mediterraneus ponticus and Pomatomus saltatrix indicated favorable conditions for their wintering off South Crimea. Appearance in catches of the fish of elder age groups is evidence of the restoration of their age structure. The competitor for food Mnemiopsis leydyi still influences the food resources of the fish and, thus, their survival. If they appear in plankton simultaneously, the abundance of larvae drastically decreases. The obtained data indicate to the vulnerability of coastal biocenoses to anthropogenous impact and to the necessity of monitoring of fish resources and of their protection.     

The Taxonomic Status and Intraspecific Differentiation of the Black Sea Horse Mackerel, <Emphasis Type="Italic">Trachurus mediterraneus ponticus</Emphasis> (Aleev, 1956) (Carangidae)

The taxonomic status of the horse mackerel, Trachurus mediterraneus ponticus (Aleev, 1956), which inhabits the Black Sea, has been clarified based on the analysis of variation in the nucleotide sequence of the mtDNA cytochrome b (Cyt-b) locus. A comparison of this species with the horse mackerel from the Mediterranean basin and the World Ocean has shown that the Black Sea horse mackerel is neither an independent species nor a subspecies and can only be qualified as the species Trachurus mediterraneus (Steindachner, 1868) distributed throughout the Mediterranean Sea basin. A hypothesis has been made about the possible cause of the origin and existence of two forms, “large” and “small”, of the horse mackerel. By using the technique of calculating ontogenetic trajectories, it has been found that these are two morpho-ecological forms, whose differentiation is most likely determined by the type of feeding.     

Feeding of pelagic fish in waters of Mauritania: 2. Representatives of Families Carangidae,Scombridae, Pomatomidae,and Trichiuridae

Feeding peculiarities of mass pelagic ichtyophagous fish from the Canary upwelling waters and frontal zones of Mauritania have been investigated: vadigo Campogramma glaycos, false scad Caranx rhonchus, bluefish Pomatomus saltatrix, Atlantic bonito Sarda sarda, West African Spanish mackerel Scomberomorus tritor, large-eyed hairtail Trichiurus lepturus and pompano Trachinotus ovatus. These species feed on epipelagic fish living or forming temporary agglomerations at the depths up to 200–250 m from the surface.     

Summer-autumn ichthyoplankton of the Sea of Okhotsk and the Sea of Japan and special traits of feeding of fish larvae and fry in 2003–2004

In summer-autumn of 2003–2004, the ichthyoplankton of the Sea of Okhotsk comprised 35 species. In this period the most widely distributed and numerous were larvae of the lord Hemilepidotus gilberti, the Pacific stout sand lance Ammodytes hexapterus, and the Sakhalin dab Limanda sakhalinensis. The maximum catches of fish larvae were attributed to coastal waters off eastern Sakhalin and to the shelf of the northern part of the Sea of Okhotsk. In November of 2003, the ichthyoplankton of the Sea of Japan was represented by fish larvae belonging mainly to the boreal ichthyocomplex. The catches consisted predominantly of larvae of the arabesque greenling Pleurogrammus azonus, the ronquil Bathymaster derjugini, and the rockfish Sebastes owstoni. Fish larvae and fry in the northwestern part of the Sea of Japan were caught principally within 43°–45° N and 137°–139° E above the depth 1500–2000 m. The food spectrum of fish larvae in the Sea of Okhotsk and the Sea of Japan comprised over 20 plankters of various size belonging to seven taxa. Irrespective of fish species, the food items common of all fish were copepods Pseudocalanus minutus and Oithona similis. The daily rations were calculated for mass species (Hemilepidotus gilberti, Ammodytes hexapterus, Hexagrammos stelleri, Pleurogrammus azonus, Bathymaster derjugini, and Sebastes owstoni). The larvae of all considered species in the Sea of Japan and in the Sea of Okhotsk fed predominantly in the light period of the day.     

Ichthyoplankton of Rockall-Hutton seamounts

Species composition and quantitative distribution of ichthyoplankton in areas of the Rockall-Hutton seamounts are considered in a comparative aspect, and the spawning biomass of the blue whiting Micromesistius poutassou, the main commercial item of this region, is calculated. Maximal catches of eggs and larvae were recorded in spring 2006 and minimal catches were recorded in spring 2003. The highest number of species was recorded in March–April 2006 and the lowest number was recorded in March–April 2003. In the seasons under consideration, M. poutassou had the most mass of the commercial fish in the plankton; haddock Melanogrammus aeglefinus and gurnard Eutrigla gurnardus were less numerous. Of the noncommercial species, the larvae of myctophids (fam. Myctophidae) and of other mesopelagic fish occurred more frequently in the ichthyoplankton. The species and quantitative composition of ichthyoplankton was considerably more numerous at the Rockall Seamount than at the Hutton Seamount, which is explained by specific oceanographic features of the region and the more southern location of this seamount. According to the data of the ichthyoplanktonic method, the spawning biomass of M. poutassou exhibited a tendency for an increase in the period of 2002 to 2006.     

Study on properties and regulation peculiarities of glycogenolysis enzymes in fish skeletal muscles depending on peculiarities of the species motor activity

The activity values, properties and peculiarities of activation of glycogen phosphorylase (GP, EC 2.4.1.1) and glycogen phosphorylase kinase (GPK, EC 2.7.138) were studied in the white skeletal muscle of fishes differing in motor behavior. No differences in the GP and GPK activity levels were revealed in porgy Diplodus annularis (L.), horse mackerel Trachurus mediterraneus ponticus, trout Salmo trutta morphario, scorpionfish Scorpaena porcus, flounder Scophtalnus maeoticus maeoticus, and carp Cyprinus carpio; however, properties of the isolated enzymes and peculiarities of formation of their activated forms during swimming in a hydrodynamic tube are determined by functional peculiarities of the muscle tissue and are associated with the motor activity character of the species. The more rapid ion regulation prevails in fishes capable for the burst swimming type (scorpionfish, trout). The glycogenolysis hormonal regulation leading to a change of the GPK activity index has been found in other species.     

Species composition and distributional pattern of ichthyoplankton of the Southern Pacific Ocean

Distributional pattern and qualitative composition of ichthyoplankton in waters of the Southern Pacific in September 2002?CJanuary 2003 and in August?CNovember 2009 are analyzed. We noted approximately 70 species of fish pelagic eggs and larvae of fishes belonging to 34 families in this region. Change in distribution of the basic object of commercial fishery of this region, i.e., Peruvian-Chilean jack mackerel Trachurus murphyi, in early ontogenesis are considered in detail. The obtained data on the species composition, distribution, and abundance of ichthyoplankton in this region are compared with the results of investigations in the past years. The spawning biomass of jack mackerel is also estimated in the work by the amount of the eggs spawned by females in the places of their greatest concentrations.     

Distribution of ichthyoplankton in the eastern Peter the Great Bay,Sea of Japan,in June and July of 2007

Comparison of the results of ichthyoplankton surveys conducted at 97 stations in the eastern part of the Peter the Great Bay of the Sea of Japan, in June–July 2007 with the similar research data of the 1950s shows that at present, as was the case 50 years ago, flatfish eggs belonging mainly to the yellowfin sole Limanda aspera and brown sole Pleuronectes herzensteini prevail in the local ichthyoplankton (up to 86%). The highest concentrations of these species’ eggs were recorded in the Vostok Bay and Strelok Bay. The spawning activity of flatfish in 2007 is found to be lower than in the mid 1900s, but the significance of the eastern part of the Peter the Great Bay for flatfish reproduction remains large. The importance of long-term monitoring in this area, which is being subjected to steadily growing anthropogenic impacts, is also proven.     

Summer Ichthyoplankon in Onega Bay of the White Sea: Species Composition and Spatial Distribution

Data on the species composition and distribution of ichthyoplankton in Onega Bay of the White Sea are presented for June–July 2007, 2010–2012, and 2015–2016. In the ichthyoplankton, the specimens of the early developmental stages of 21 fish species were registered; the larvae of the White Sea herring Clupea pallasi marisalbi, capelin Mallotus villosus, and Pacific sand lance Ammodytes hexapterus were the most abundant. It is shown that the northwestern and southeastern zones, distinguished in Onega Bay by hydrophysical parameters, also differ in species composition and in ichthyoplankton abundance.     

Fish assemblage structure in an estuary of the Atlantic Forest biodiversity hotspot (southern Brazil)

We described the fish assemblage in the estuary of the Guaraguaçu River (one of the largest tributaries of the Paranaguá Bay Estuary, located within Brazil’s Atlantic Forest Biosphere Reserve) from June 2005 to May 2006, and assessed the seasonal and spatial effects of abiotic environmental attributes on the fish assemblage structure. Despite some oscillations in salinity, the upper and lower estuaries had year-round persistent oligohaline and polyhaline conditions, respectively. Despite high species richness (55 species), the Guaraguaçu River Estuary fish community contains a few dominant taxa; 11% of the richness accounts for >60% of its density and biomass. The most abundant species (in terms of both biomass and density) was Atherinella brasiliensis. Species whose densities were most strongly associated with the upper estuary were Centropomus parallelus, Ctenogobius schufeldti, Eucinostomus melanopterus, Platanichthys platana, Trinectes paulistanus, and Eugerres brasilianus. Those whose densities were most strongly associated with the lower estuary were A. brasiliensis, Sphoeroides greeleyi, Eucinostomus argenteus, Sphoeroides testudineus, Diapterus rhombeus, and Harengula clupeola. Throughout the year, canonical correspondence analysis identified: (1) the pattern of horizontal stratification of salinity along the river as being the most important variable for explaining most of the fish fauna structure; and (2) a strong relationship between the fish fauna and the salinity gradient along the estuary. Analysis of similarity further confirmed that each estuarine zone supports a year-round persistent and relatively homogeneous fish species assemblage. Total mean density and biomass remained constant over time in each estuarine habitat, but density shifted in the most abundant species, which appears related to recruitment patterns. Such species and abundance persistence likely occurs because seasonal rainfall-induced changes in river discharge are not sufficient to significantly shift runoff and salinity and thus fish assemblage structure (species composition, density and biomass) along the estuary. Such a lack of seasonal fish fauna movement as a response to changes in river flow contrasts with other estuarine systems around the world.     

Reproduction and development of <Emphasis Type="Italic">Pholis picta</Emphasis> (Perciformes: Pholidae) and <Emphasis Type="Italic">Opisthocentrus zonope</Emphasis> (Stichaeidae)

In the Peter the Great Bay (the Sea of Japan), reproduction and embryonic larval development of Pholis picta and Opisthocentrus zonope are investigated. Both species spawn in November–December at the water temperature decreasing from 7.0 to 0.2°C. Fecundity of Pholis picta is 494–1228 eggs, and of Opisthocentrus zonope—368–1360 eggs. Both species lay eggs in empty shells of Gray mussel. Parent fish permanently stay in the shell but do not actively care for the eggs. Morphological changes in the process of embryogenesis are compared between the related species. Prolarvae and larvae are described for identification, with special attention to pigmentation. The spawning behavior of adult fish and behavior of prolarvae are described.     

Diversity of fish species in suichuan river and shushui river and conservation value,China

Based on the data collected from the Suichuan and Shushui Rivers, both tributaries of the Ganjiang River between April and July of 2015, the fish species identified were classified into 68 and 46 species, 14 and 12 families in the Suichuan River and Shushui River respectively. Cyprinidae is the most common family that accounts for 52.9% and 58.7% in the total number of fish species in the Suichuan River and Shushui River, respectively. The dominant species were Pseudohemiculter dispar, Squalidus argentatus, Silurus asotus and Leptobotia elongate for the Suichuan River and Squalidus argentatus, Acrossocheilus parallens, Pseudohemiculter dispar, Silurus asotus, Pelteobagrus fulvidraco, Acrossocheilus fasciatus and Zacco platypus for the Shushui River. The diversity of fish species showed more abundant and diverse for the Suichuan River. The composition of ecotype of fish indicated the rich diversities of ecotype in both the Suichuan and Shushui Rivers. The tributary (Suichuan River) and main stream of the Ganjiang River demonstrated a highly fauna similarity and the fish resources indicated its significance to maintain the fish diversity in the middle of the Ganjiang River and its benefits to the existence of the fish species in mountain streams. Dam construction, sand excavation and heavy metal pollution are the most significant threat to fish diversity and ecosystem functioning in Ganjiang River basin. In order to protect fish diversity and fisheries more effectively, relevant laws should be strengthened and conservation areas should be established for the survival of freshwater fish species.     

Size matters: predation of fish eggs and larvae by native and invasive amphipods

Invasive predators can have dramatic impacts on invaded communities. Extreme declines in macroinvertebrate populations often follow killer shrimp (Dikerogammarus villosus) invasions. There are concerns over similar impacts on fish through predation of eggs and larvae, but these remain poorly quantified. We compare the predatory impact of invasive and native amphipods (D. villosus and Gammarus pulex) on fish eggs and larvae (ghost carp Cyprinus carpio and brown trout Salmo trutta) in the laboratory. We use size-matched amphipods, as well as larger D. villosus reflecting natural sizes. We quantify functional responses, and electivity amongst eggs or larvae and alternative food items (invertebrate, plant and decaying leaf). D. villosus, especially large individuals, were more likely than G. pulex to kill trout larvae. However, the magnitude of predation was low (seldom more than one larva killed over 48 h). Trout eggs were very rarely killed. In contrast, carp eggs and larvae were readily killed and consumed by all amphipod groups. Large D. villosus had maximum feeding rates 1.6–2.0 times higher than the smaller amphipods, whose functional responses did not differ. In electivity experiments with carp eggs, large D. villosus consumed the most eggs and the most food in total. However, in experiments with larvae, consumption did not differ between amphipod groups. Overall, our data suggest D. villosus will have a greater predatory impact on fish populations than G. pulex, primarily due to its larger size. Higher invader abundance could amplify this difference. The additional predatory pressure could reduce recruitment into fish populations.     

Life history and morphology of Eel Larvae in the Gulf of Guinea of western Africa: revisiting Jacques Blache’s research (1960–1977) 40 years later

Eel larvae (leptocephali) are rarely studied extensively both spatially and temporally, and detailed illustrations of most species are limited. This study uses the unique research reported in the monograph of Blache (Leptocéphales des poissons anguilliformes dans la zone sud du golfe de Guinée. ORSTOM Faune Tropicale 10:1–381, 1977, in French) to describe and evaluate the species composition, abundance, life history characteristics and morphology of 10,284 anguilliform leptocephali collected throughout the year during 15 ichthyoplankton surveys (1960–1971) in relation to regional oceanography. Leptocephali of 70 species of 7 families were described, with Ophichthidae (26 species), Muraenidae (13), and Congridae (13) being the most diverse, and local spawning indicated by ≥ 34 species. Larvae of biogeographically restricted Heterencheylidae eels (mud eels) were abundant along the continental shelf and 5 species comprised 35% of total catches. Their larval distributions may reflect adult depth-segregation from nearshore/estuaries to the outer shelf and slope and larval retention. Nettastomatid leptocephali of Hoplunnis punctata were the most abundant species, and Rhynchoconger sp., Uroconger syringinus, Chlopsis olokun, and Dalophis boulengeri were also abundant. Small leptocephali distributions indicated spawning occurred over or near the continental shelf, and length-frequency data indicated most spawning was during the November–May warm-water season. Detailed morphology illustrations showed the characteristics of all stages of larvae. The Gulf of Guinea eel fauna is not diverse compared to the Indo-Pacific possibly due to phylogeography and a lack of coral reef habitats and the unusual low-latitude seasonal influx of cold surface waters, but is unique in being the worldwide center of distribution of the burrowing eels of the Heterencheylidae.     

Reproduction and development in some species of the weakly electric genus <Emphasis Type="Italic">Campylomormyrus</Emphasis> (Mormyridae,Teleostei)

Reproduction in captivity of four species of the mormyrid genus Campylomormyrus was investigated. Cyclical reproduction was provoked by changing water conductivity (C) alone: decreasing C led to gonadal recrudescence, an increase induced gonad regression. Data on the reproduction and development of three species are presented. All three species are indeterminate fractional spawners. Spawning intervals ranged from 6 to 66 days in C. rhynchophorus, 10–75 days in C. tshokwe, and 18 days in C. compressirostris (calculated values). Fecundities (eggs per fractional spawning) ranged from 70 to 1570 eggs in C. rhynchophorus, 100–1192 in C. tshokwe, and 38–246 in C. compressirostris. Spawnings/ovipositions occurred during the second half of the night; no parental care was observed; no special spawning substrates were necessary. C. compressirostris successfully spawned in breeding groups, C. rhynchophorus as pair. Agonistic behavior in the C. tshokwe pair forced us to divide the breeding tank; therefore, only ovipositions occurred. However, injection of an artificial GnRH hormone allowed us to obtain ripe eggs and sperm and to perform successful artificial reproduction. All three species produce yolky, slightly sticky eggs. Egg diameter ranges from 2.3–3.0 mm. Hatching occurred on day 3, feeding started on day 11. Transition from larval to juvenile stage occurred at around 20 mm total length (TL). At this size C. rhynchophorus developed a higher body than the two other species and differences between the species in the melanin pigmentation of the unpaired fins occurred. Between 32 and 35 mm TL the upper and lower jaws started to elongate.     

Species composition and distribution of ichthyoplankton in the waters of northeast Sakhalin

Data on the species composition and abundance of the ichthyoplankton obtained in 2012, 2014, and 2015 in the waters of northeast Sakhalin are presented; these data were collected during the standard accounting surveys to estimate the egg concentration and breeders of Alaska pollock Theragra chalcogramma. The areas of the main concentrations of eggs and larvae of a number of commercial fish species have been determined, interannual variations in their abundance have been analyzed, and the distribution of ichthyoplankton with some parameters of the environment, such as depth, temperature, and main currents, has been linked. During the study period, 30 species representing 11 families were recorded in the ichthyoplankton. The average concentration of ichthyoplankton varies within the range of 113–201 ind./m². The pollock eggs absolutely dominated by 78–89%; followed by the eggs of the Bering flounder Hippoglossoides robustus (5–8%). It was found that the number of eggs and larvae of flounders and of a number of the other fish species in the northern part of the study area increases during the years characterized by a large volume of runoff of Amur River.