Metal enrichment in water and fish in a semi-urban Nigerian lake,and their associated risks

Trace metal (Zn, Pb, Cu, Cr and Cd) concentrations in the water column and in the liver, muscle and gill tissues of Parachanna obscura and Clarias gariepinus in Agulu Lake, Nigeria, were investigated in June 2014 and compared with WHO and FAO safe limits for water and fish. Hazard index (HI) values were estimated to assess the potential public health risk of consuming contaminated fish. Lead and cadmium exceeded WHO guideline values for drinking water. In most cases, variations in concentration of the metals in organs were liver > muscle > gill. Differences in tissue-specific concentrations between species were not significant, except for zinc in muscles and gills. Cadmium and chromium were not detected in the fish, but lead was above the FAO maximum value for consumption. Hazard index values were below 1, indicating a low risk to public health. However, trace metal contamination in Agulu Lake is increasing.     

Fish communities in the eastern,seasonal-floodplain of the Sudd,Southern Sudan

Annual flooding of the permanent Sudd swamps innundates large areas of Oryza longistaminata grasslands. Fish migration into a southeast section of the seasonal floodplain was led by Clarias gariepinus, Polypterus senegalus and several small species which were intent on spawning. Channa obscura and juveniles of Oreochromis niloticus were prominent among later entrants. From a total of 23 species caught in seasonal habitats, 7 contributed over 97% of total estimated numerical and biomass densities. The latter ranged from 435–580 kg ha^–1. In the 1982–83 flood-season entry to the floodplain was essentially restricted to species tolerant of oxygen-deficient waters and thereby able to penetrate the papyrus and Typha swamps of the permanent wetland. Migrants became stranded in temporary pools and subject to heavy cropping by birds.     

Unexpected deep-sea fish species on the Porcupine Bank (NE Atlantic): Biogeographical implications

Four specimens corresponding to three rare deep-water fish species were caught on the Porcupine Bank (Northeast Atlantic) in September 2019. These catches include the new northernmost records of Azores rockling Gaidropsarus granti and deep-water dab Poecilopsetta beanii in the Atlantic Ocean and the second record of the latter species in its eastern zone. Three of the specimens were retained and their molecular identification also allowed the Cataetyx alleni DNA barcode to be obtained for the first time. The appearance of P. beanii, a West Atlantic species, in its eastern zone is discussed in relation to a possible phenomenon of transoceanic drift in the larval stage.     

Predation on invasive redclaw crayfish Cherax quadricarinatus by native fishes in the Kafue River,Zambia

The stomach contents of eight species of predatory or omnivorous fish caught in gillnets in the Kafue River in May and June 2010 were examined to determine the relative importance, expressed as ‘prominence value’ (PV), of crayfish Cherax quadricarinatus in their diet. Four species, Clarias gariepinus, Schilbe intermedius, Serranochromis robustus and Serranochromis angusticeps, had fed on C. quadricarinatus. The PV of C. quadricarinatus was highest in C. gariepinus, in which the quantity and size of crayfish eaten was significantly correlated with standard length (SL) of fish >200 mm SL. Predated C. quadricarinatus were significantly smaller (mean carapace length [CL] 30 mm; SE 1.2) than those caught in gillnets (mean CL 76 mm; SE 0.9). No C. quadricarinatus remains were found in the stomachs of Oreochromis andersonii, Synodontis macrostigma, Serranochromis macrocephalus or Mormyrus lacerda.     

A review of biology, ecology and prospect for aquaculture of Parachanna obscura

Parachanna obscura is the most common African Channidae. Various studies are being conducted on its biology and ecology. It lives in fresh water in quiet and muddy areas. It has accessory respiratory organs allowing it to live in hypoxic environment. It has a varied diet and feeds on fish, remains of fish, insects, other invertebrates and plant detritus. It is a species with iteroparous asynchronous oogenesis which breeds throughout the year but much more during and just after the flood. It size at first maturity is 24.5 cm. Eggs and larvae of P. obscura are yellow and guarded by one or both parents. Hardiness, rapid growth, high tasty flesh and commercial value of this species represent significant aquaculture potentiality. Natural stocks of P. obscura are overexploited and are not sufficient to met local demands. Its extensive farming system has already started in some African countries. Successful farming of this species in intensive systems and semi—intensive can help not only to preserve and enhance natural stocks of P. obscura but also to continuously produce fingerlings remediation technologies for direct human consumption.     

The Response of Blood Biomarkers of the Round Goby <Emphasis Type="Italic">Neogobius melanostomus</Emphasis> (Pallas, 1814) (Perciformes: Gobiidae) to Chronic Coastal Pollution in the Sea of Azov

The long-term variations in blood biomarkers and weight–size characteristics of the round goby, Neogobius melanostomus (Pallas, 1814), have been studied in specimens collected from two sites of the southwestern Sea of Azov. The fish from catches of 2011–2012 showed a decrease in the size and weight parameters and an increase in the antioxidant enzyme activities and the level of oxidized serum proteins compared to the values in the fish caught in 2003. The ecological causes of the observed differences and the possibility of using the studied fish blood biomarkers in programs of monitoring the marine coastal waters are discussed.     

Significance of a floodplain in the formation of fish communities in small rivers of Ryazan oblast

In total, 37 fish species from 30 genera and 10 families are registered in small rivers of the Ryazan oblast. In addition to other significant factors, the floodplain width is important for the formation of species structure of fish communities. In the rivers with small floodplains (less than 0.2 km in width), mainly small and short-lived fishes are represented in the catches. In the rivers or in their parts with wide floodplains (0.2–0.5 km), the dominant complex (in addition to short-lived fish species) includes roach Rutilus rutilus and/or perch Perca fluviatilis. In the rivers with wider floodplains (more than 0.5 km), long-lived phytophils represented by mainly the limnophilous group prevail.     

Studies on the fungal infestation of five traditionally smoke-dried freshwater fish in Ago-Iwoye,Nigeria

Samples of traditionally smoke-dried Clarias gariepinus (Burchell), Chrysichthys nigrodigitatus (Lacepede), Sarotherodon galilaeus (Trewavas), Heterotis niloticus (Cuvier) and Heterobranchus bidorsalis (Geoffroy) were obtained from Oja Oba Market, Ago-Iwoye, Nigeria and examined for fungal infestation. The fish samples incubated on potato dextrose agar (PDA) for 7 days showed fungal infestation. Fungi isolated and identified included Mucor sp., Aspergillus sp., Rhizopus sp. and Fusarium sp. Six fungal species were isolated from C. nigrodigitatus, five each on C. gariepinus and H. niloticus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biological features of the common fish species in Olyutorsky-Navarin region and the adjacent waters of the Bering Sea: 1. Gadidae (cods) family

Biological features of the three common fish species, pollock Theragra chalcogramma, Pacific cod Gadus macrocephalus, and saffron cod Eleginus gracilis (Gadidae), have been studied using a 20-year dataset (1995?2015). These species inhabit the northwestern Bering Sea in the summer–autumn period and form the schoolings in Olyutorsky-Navarin region. The size–age parameters, as well as the peculiarities of the body length and body weight dynamics, spawning periods, spawning range, and conditions, of the fish caught by different sampling gear have been analyzed. Due to the construction peculiarities and catch efficiency of the different catching gear, the largest specimens are found in the setlines and snurrevads; the fish caught by the trawls are characterized by the smallest size. The body length and body weight of pollock is greater in the pelagic trawl catches compared to the bottom trawl catches. The abundant brood of Gadidae may well be tracked on the multiyear dynamics graphs reflecting the size distribution, as well as by the decrease of biological parameters of the fish. The studied species inhabit the vast growth areas, so smaller body size of them in the coastal waters may be a result of a high ratio of the young specimens there.     

Homogeneity of parasite assemblages of Dules auriga (Serranidae) in hydrographically heterogeneous sites

Parasite assemblages of Dules auriga are described for the first time from samples caught during research cruises in two localities of the Argentine–Uruguayan Common Fishing Zone (AUCFZ) and are compared with four additional samples collected by commercial catches from the same region. A total of 178 fish were examined and 13 parasite species were found. This showed low species richness, a condition observed in some other small benthic species at a low trophic level. The composition of the parasite fauna was similar to those found on other host species in the region, sharing the same set of dominant species with other sympatric fishes, which have been identified as both typical and as indicators of this ecoregion: Grillotia carvajalregorum, Corynosoma australe and Hysterothylacium sp. Multivariate similarity analyses at the infracommunity and the component community levels indicated that the two samples caught at different latitudes in the AUCFZ display almost identical parasite assemblages. This repeatability in assemblage structure was also observed across samples from commercial catches. The homogeneity of the parasite assemblages is considered to be an intrinsic property of fish inhabiting the AUCFZ, independent of their ecology and trophic level.     

Temporal distribution of perch (Perca fluviatilis L.) in a lake-reservoir (Moselle,France): analysis of catches with vertical gill nets

Four fishing periods within a yearly cycle between 1990 and 1991 were carried out in the lake-reservoir of Mirgenbach, lake of the nuclear power station in Cattenom (Moselle, France). The catches of perch (Perca fluviatilis L.) were analyzed.In all, about 630 perch were caught in 8 sampling stations. The analysis of seasonal catches of this carnivorous fish was made according to size and mesh; a simple correspondence factor analysis enabled us to establish that this species lived in different areas depending on the season.     

The response of tsetse flies to artificial baits in relation to age, nutritional and reproductive state

In various vegetation types in Zimbabwe, the catches of Glossina pallidipes Austen and G. morsitans morsitans Westw. (Diptera: Glossinidae) at a target baited with odour (acetone, 1-octen-3-ol and two phenols) were positively correlated with catches of the same species at an unbaited net. No correlation existed between target catches and hand net catches of tsetse flies sitting on the vegetation. G. pallidipes females caught at a target and at an unbaited net were older than those caught from vegetation. Of the female G. pallidipes caught at the target, 46% were in the first 3 days of pregnancy. Of those caught at the unbaited net, significantly fewer, 21%, were in this stage. G. pallidipes males caught from vegetation contained more fat (3.07±0.333 mg) than those caught at the unbaited net (2.06±0.339 mg) or at the target (2.19±0.218 mg). It is inferred that target catches consisted predominantly of tsetse which were already in flight when they sensed the stimuli from the target, and that target catches were biased towards female G. pallidipes in the first 3 days of pregnancy.     

Isolation and pathogenicity of a Bacillus sp. associated with a septicaemic condition in some tropical freshwater fish species

Observations made over a three-year period at the Fish Diseases Laboratory of the African Regional Aquaculture Centre (ARAC), Nigeria, revealed the gradual emergence of a new, highly infectious septicaemic condition in some widely cultivated freshwater fish species. The broad host range included: Heterobanchus bidorsalis, Clarias gariepinus, “Heteroclarias” (a hybrid of these two species, male and female respectively), Chrysichthys nigrodigitatus, and Cyprinus carpio. Clinical signs and pathological lesions associated with the condition were tyical, irrespective of the fish species affected; natural outbreaks apeared to be associated with stress due to environmental factors. The bacterium isolated from moribund and freshly-dead fishes was identified as a Bacillus sp., based on the observed cultural, morphological and biochemical characteristics. Fish reinfection trials confirmed that the isolate was the causative agent of the condition. Antibiotic sensitivity tests showed that the organism was sensitive to tetracycline hydrochloride.     

Histopathology and helminth parasites of African catfish Clarias gariepinus (Burchell, 1822) in relation to heavy metal pollution in a subtropical river system

In a study aimed to determine the histopathology, component parasite communities and level of selected heavy metals, African catfish Clarias gariepinus from three rivers in Zimbabwe (Gwebi, Manyame and Mukuvisi) were analysed for heavy metals (Cd, Cr, Cu, Fe, Ni, Pb, Zn) in the gills, liver, kidney and muscles. The histopathology of these tissues was assessed by microscopic examination of stained thin sections. Metazoan parasite diversity and species composition in fish along different sites of the rivers were determined and compared. Levels of Cd, Fe, Pb and Zn were lowest in the Gwebi, Cr and Cu in the Manyame, and Ni in the Mukuvisi River. There were significant differences (P < 0.5) in concentration of iron and nickel in the gill and liver tissues of fish among the three rivers while significant differences in concentration of iron and lead were observed in muscle tissue. Gill chronic inflammation and ossification were significantly different (P < 0.5) in fish from among the three rivers. Chronic inflammation, hemosiderin deposits and bile accumulation in the liver were also significantly different (P < 0.5) among the three rivers and so was the extent of chronic inflammation in the kidney tissue. Lamellar fusion was slightly more present in gills of catfish from the Mukuvisi than the Gwebi River. The parasite community of C. gariepinus comprised three monogenean, two cestode and three nematode species. The least polluted Gwebi River had the highest parasite community diversity while the most polluted Mukuvisi River had the lowest diversity. Fish parasite community structure is thus a potential indicator of river pollution, while heavy metal pollution is a potential threat to fish and human health in the system.     

Redescription of a brooding nemertine,Cyanophthalma obscura (Schultze) gen. et comb.n., with observations on its biology and discussion of the species of Prostomatella and related taxa*†

A new genus, Cyanophthalma, is erected with the type species Tetrastemma obscura Schultze, 1851. Cyanophthalma obscura is transferred from Prostomatella and is redescribed from observations of more than 300 living specimens and serial sections of 59 specimens from the northeast coast of North America. Comparison is made with serial sections of C. obscura from the Baltic and with serially sectioned specimens of three other described species of Prostomatella. Two of these, P. enteroplecta and P. merula, do not fit either genus and are provisionally placed in the aggregate genus Tetrastemma, whose present diagnosis they do fit. Prostomatella remains with only its type species, P. arenicola. Amphiporus cordiceps is also transferred to Cyanophthalma. Some of the characters that form the basis for classifying Monostilifera are assessed for phylogenetic significance. Cyanophthalma obscura in Nova Scotia lives in salt marshes. Young are brooded through the winter while ice covers most of the marsh.     

Effect of large weirs on abundance and diversity of migratory Labeobarbus species in tributaries of Lake Tana,Ethiopia

Lake Tana has a remarkable fish diversity, including 17 endemic Labeobarbus species, of which nine spawn in the inflowing rivers. Three of the migratory species are threatened, namely the endangered Labeobarbus macrophtalmus and the vulnerable L. acutirostris and L. platydorsus. In July–November 2016 during the wet season netting upstream and downstream of large weirs in two rivers and in two undammed rivers showed that weirs had a severe negative effect on migratory Labeobarbus, including the three threatened species. Of eight Labeobarbus species caught below the Gelda River weir, only L. intermedius was recorded above the weir, and in the Shini River, five Labeobarbus species were caught below the weir, but none above it. Labeobarbus diversity below the Gelda River weir (H’?=?1.4) was significantly different to that above the weir (H’?=?0), whereas in the two rivers without any weirs, Labeobarbus diversity downstream (H’?=?1.39 and 1.55) was not significantly different from that upstream (H’?=?1.52 and 1.40). Therefore, specific mitigation measures, such as fishways, need to be designed from the outset of proposed weir and instream dam construction.     

Fish use of an inundated saltmarsh flat in a temperate Australian estuary

Abstract Fish associated with Australian saltmarshes have previously been sampled from within creeks or semi-permanent pools on the marsh; this is the first record of fish use of marsh flats inundated on high tides but emergent on low tides. Buoyant pop nets (9 m², 1 mm mesh) were used to collect fish from two areas of the marsh flat on Torrens Island in the Barker Inlet-Port River estuary. South Australia. Fyke nets of the same mesh size were used to collect fish from small creeks draining the marsh flat. Fish were caught in only four of 48 pop net releases, for a total of 19 fish of two species (families Gobiidae and Atherinidae). A total of 1109 fish from six species were caught in creeks draining the same areas, and the two species caught on the flats were the most common species in the creeks. Economically important species were poorly represented, with just four specimens of the mugilid Aldrichetta forsteri (Valenciennes).     

Hook selectivity as a mitigating measure in the catches of the stingray Pteroplatytrygon violacea (Bonaparte, 1832) (Elasmobranchii,Dasyatidae)

Hook selectivity, sex ratio of catches and relative abundance (Catch Per Unit Effort – CPUE) were assessed for the pelagic stingray Pteroplatytrygon violacea (Bonaparte, 1872), caught by longline gear in the southwestern Atlantic Ocean over the continental slope and adjacent oceanic area. The catches were carried out at depths of 200–4000 m by research cruises in 2002 and 2003, from Cabo Frio (22°52′S) to Laguna (28°28′S); and by hook selectivity experiments from 2004 to 2008, from Itajaí (26°54′S) to Tramandaí (29°59′S). Hook selectivity experiments indicated higher catches of stingrays with ‘J’ hooks (9/0, 10° offset) commonly used by the pelagic longline fleet than with ‘circle’ hooks (18/0, 10° offset). ‘circle’ hooks reduce the longline by‐catches of this species. Most of the stingrays caught were males (6 : 1). One female aborted mid‐term embryos at the time of capture. CPUE was highest between spring and autumn and lowest during winter.     

Catchment-Scale Conservation Units Identified for the Threatened Yarra Pygmy Perch (Nannoperca obscura) in Highly Modified River Systems

Habitat fragmentation caused by human activities alters metapopulation dynamics and decreases biological connectivity through reduced migration and gene flow, leading to lowered levels of population genetic diversity and to local extinctions. The threatened Yarra pygmy perch, Nannoperca obscura, is a poor disperser found in small, isolated populations in wetlands and streams of southeastern Australia. Modifications to natural flow regimes in anthropogenically-impacted river systems have recently reduced the amount of habitat for this species and likely further limited its opportunity to disperse. We employed highly resolving microsatellite DNA markers to assess genetic variation, population structure and the spatial scale that dispersal takes place across the distribution of this freshwater fish and used this information to identify conservation units for management. The levels of genetic variation found for N. obscura are amongst the lowest reported for a fish species (mean heterozygosity of 0.318 and mean allelic richness of 1.92). We identified very strong population genetic structure, nil to little evidence of recent migration among demes and a minimum of 11 units for conservation management, hierarchically nested within four major genetic lineages. A combination of spatial analytical methods revealed hierarchical genetic structure corresponding with catchment boundaries and also demonstrated significant isolation by riverine distance. Our findings have implications for the national recovery plan of this species by demonstrating that N. obscura populations should be managed at a catchment level and highlighting the need to restore habitat and avoid further alteration of the natural hydrology.