Age estimation,growth rate and size at sexual maturity of tigerfish Hydrocynus vittatus from the Okavango Delta,Botswana

The aims of this study were to determine relative age, growth rate and size at maturity of tigerfish in the Okavango Delta as a basis for the development of a fisheries management plan. A total of 206 tigerfish Hydrocynus vittatus, collected by angling in August 2005,2006 and 2007, was assessed for sexual maturity and relative ages were estimated from 135 of these, using scales and whole and sectioned otoliths. Sectioned otoliths were the most appropriate method for ageing H. vittatus of up to 20 years old. Males were present in all relative age classes, proving that they do not disappear from the population at a young age, as previously thought. Males matured at 451 mm TL and females at 522 mm TL, corresponding to an approximate relative age of four years for both sexes. Males lived for up to 20 years, females for up to 16 years.     

Notes on the induced reproduction and development of the tigerfish,Hydrocynus vittatus (Characidae), embryos and larvae

Synopsis In South Africa, the distributional range of tigerfish,Hydrocynus vittatus, has diminished over the past fifty years mainly as a result of migration barriers and reduced river flow. A project to restock traditional tigerfish waters has been envisaged for many years but did not materialise due to an inability to spawn this species artificially. Several hormones were therefore tested for their potency to induce ovulation in this species. Gonadotropin releasing hormones (GnRh) were used in combination with dopamine receptor antagonists. Human chorionic gonadotropin (HCG) was administered in conjunction with catfish pituitary gonadotropin. Both sexes were successfully stripped and the eggs were inseminated artificially. Tigerfish eggs are small (0.65 mm diameter), demersal and slightly adhesive. Hatching occurs 22 h 30 min after insemination and free embryos are pelagic and display continuous vertical movement for a period of three days. Embryonic development was photographed until first feeding, 5 days after hatching. From these results as well as field observations, it is concluded that tigerfish spawns on a sandy substrate in the vicinity of aquatic vegetation.     

A Comparison of Floy and Soft VIalpha tags on Hatchery Arctic Charr, with Emphasis on Tag Retention, Growth and Survival

The Floy FTF-69 'fingerling' tag and the soft VIalpha tag are designed to be used on small salmonid fishes (> 100 and > 150mm, respectively). The two tags were compared for 160 days on hatchery-reared Arctic charr, Salvelinus alpinus, (170–209mm). Tag retention and effects on growth rate and survival were analysed. VIalpha-tagged and untagged control fish had similar growth rates and grew significantly faster than Floy-tagged fish during the experiment. Tag retention was significantly higher for Floy tags (94%) than for VIalpha tags (78%). Most VIalpha tag loss (11%) took place within the first 10 days of tagging while there were no Floy tags lost during this period. Survival rates were about equal for all three groups (96–98%), and thus the tags did not seem to affect the survival of charr under hatchery conditions.     

Cryptic diversity of African tigerfish (genus Hydrocynus) reveals palaeogeographic signatures of linked neogene geotectonic events

The geobiotic history of landscapes can exhibit controls by tectonics over biotic evolution. This causal relationship positions ecologically specialized species as biotic indicators to decipher details of landscape evolution. Phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, including fishes, can reveal key events of drainage evolution, notably where geochronological resolution is insufficient. Where geochronological resolution is insufficient, phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, notably fishes, can reveal key events of drainage evolution. This study evaluates paleo-environmental causes of mitochondrial DNA (mtDNA) based phylogeographic records of tigerfishes, genus Hydrocynus, in order to reconstruct their evolutionary history in relation to landscape evolution across Africa. Strong geographical structuring in a cytochrome b (cyt-b) gene phylogeny confirms the established morphological diversity of Hydrocynus and reveals the existence of five previously unknown lineages, with Hydrocynus tanzaniae sister to a clade comprising three previously unknown lineages (Groups B, C and D) and H. vittatus. The dated phylogeny constrains the principal cladogenic events that have structured Hydrocynus diversity from the late Miocene to the Plio-Pleistocene (ca. 0-16 Ma). Phylogeographic tests reveal that the diversity and distribution of Hydrocynus reflects a complex history of vicariance and dispersals, whereby range expansions in particular species testify to changes to drainage basins. Principal divergence events in Hydrocynus have interfaced closely with evolving drainage systems across tropical Africa. Tigerfish evolution is attributed to dominant control by pulses of geotectonism across the African plate. Phylogenetic relationships and divergence estimates among the ten mtDNA lineages illustrates where and when local tectonic events modified Africa's Neogene drainage. Haplotypes shared amongst extant Hydrocynus populations across northern Africa testify to recent dispersals that were facilitated by late Neogene connections across the Nilo-Sahelian drainage. These events in tigerfish evolution concur broadly with available geological evidence and reveal prominent control by the African Rift System, evident in the formative events archived in phylogeographic records of tigerfish.     

Histological assessment of selected tissues in tigerfish (Hydrocynus vittatus Castelnau, 1861) from the Sanyati Basin,Lake Kariba,Zimbabwe: a DDT-sprayed area

A pilot investigation was conducted in 2014 in the Sanyati Basin of Lake Kariba to ascertain whether long-term DDT spraying in the Kariba catchment had a negative effect on fish health. The aim was to assess the health of tigerfish, Hydrocynus vittatus, by means of histological analysis and to analyse water, sediment and tissue samples for bioaccumulated levels of chlorinated pesticides, including DDT. Eighteen tigerfish were collected by seine netting along the north-eastern shoreline of the Sanyati Basin in April 2014 and samples of their gill, liver, kidney, muscle and brain tissue were processed for histology and assessed using light microscopy. No detectable levels of DDT and/or its metabolites were found in the water or sediment samples and only a low concentration of p,p′-DDE in fish tissues. No major histological alterations were observed in the fish tissues. Consequently, there seems to be no risk of DDT exposure following the consumption of tigerfish from the Sanyati Basin of Lake Kariba. These results were unexpected, given the historical use of DDT within the current study area. It is recommended that these findings be compared with those from other regions of Lake Kariba.     

Comparative ecology of the African pike, Hepsetus odoe, and tigerfish, Hydrocynus forskahlii, in the Zambezi River floodplain

The ecology of sympatric African pike, Hepsetus odoe (Hepsetidae), and tiger fish, Hydrocynus forskahlii (Characidae), were compared during high (May-August) and falling water (September-December) conditions in the Upper Zambezi R. drainage of Zambia. Both species were common in the central and southern regions of the river and associated floodplain, and Hydrocynus was common in the northern region in swift flowing tributaries where Hepsetus was rare. Hepsetus inhabited vegetated environments of river backwaters, lagoons, and sluggish tributaries, whereas Hydrocynus occupied the open water of the main river channel almost exclusively. During the period of annual flooding, juveniles of both species coexist in flooded savanna regions. Size distributions of adult Hydrocynus and Hepsetus changed relatively little between high and low water conditions. Stomach contents analysis indicated that adult size classes of both species are almost entirely piscivorous, and both show diet shifts with changes in size. Only very small seasonal diet shifts were noted. Approximately 50% of the diet of Hepsetus consisted of haplochromine cichlid fishes, but also included large numbers of tilapine cichlids and mormyrids, Hydrocynus consumed primarily cichlid fishes, but also consumed large percentages of Hepsetus and small characid fishes. Small size classes of Hepsetus fed heavily on small machokid catfishes (Synadontis spp.) and later shifted to a diet of cichlids and mormyrids, and small Hydrocynus preyed heavily on Barbus spp. (Cyprinidae), small characids, and mormyrids. Ratios of prey length-predator length averaged approximately 0·26 for Hydrocynus and nearly 0·40 for Hepsetus. The large potential for food resource competition appears not to be realized due to a very high degree of habitat partitioning between larger size classes of the two species. At the interface between river backwaters and channel habitats, Hydrocynus is a significant predator of Hepsetus, a factor that should further restrict the occurrence of the latter in open areas of the main channel.     

Mercury in tigerfish (Hydrocynus vittatus, Castelnau), green happy (Sargochromis codringtonii, Boulenger) and kapenta (Limnothrissa miodon, Boulenger) from Lake Kariba, Zimbabwe

Concentrations of total mercury were determined in Hydrocynus vittatus (Castelnau), Sargochromis codringtonii (Boulenger), and Limnothrissa miodon (Boulenger) from two localities in Lake Kariba, Zimbabwe.
The mean concentrations of total mercury in H. vittatus from Basin 5 and Basin 2 were 0.08 mg kg⁻¹ and 0.094 mg kg⁻¹, respectively. In S. codringtonii, mean concentrations were 0.004 mg kg⁻¹ and 0.026 mg kg⁻¹ for Basins 5 and 2, respectively. No mercury was detected in L. miodon from Basin 2 while samples from Basin 5 had a mean concentration of 0.069 mg kg⁻¹ (wet weight). Total mercury concentrations were also determined on a dry weight basis.
Within each sampling area, total mercury concentrations were significantly different among species ( P  < 0.05). For H. vittatus and S. codringtonii, total mercury concentrations (in the same species) were not significantly different between the two localities ( P  < 0.05).
The factors causing the observed differences in total mercury between similar species from different localities and among different species in the same locality (sampling area) are discussed. From the observed low levels of mercury in all three species, it was concluded that the mercury constituted 'background levels'. These levels are below the maximum concentrations permissible in human fish foods.     

Some notes on the population dynamics of Hydrocynus vittatus (Castelnau) in Lake Kariba

Summary The data obtained from a routine gillnetting research programme carried out on Lake Kariba from October 1963 to September 1965 have been presented.Length-frequency ofH. vittatus was correlated with gonad activity.It was found that the gillnetting technique used provided sufficiently adequate data to trace the monthly growth of four separate year-classes from 14 cm up to 34 cm in length. This growth rate was found to be less when compared to data collected in 1959, just after the lake had filled. H. vittatus of 31 cm possessed the most active gonads during January 1965 and comprised 93% males, which were two years old. The catchability ofH. vittatus in the research gillnets decreased considerably for fish over 34 cm in length, which might account for the fact that females in breeding condition were scarce in the catches.The results obtained have been discussed with reference to previous literature.It was concluded that mostH. vittatus in Lake Kariba started to breed at the end of their second year during the rainy season.

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Zusammenfassung Die vorliegende Mitteilung stützt auf Daten, die während eines Forschungsprogramms mittels Kiemennetzen in der Kariba-Talsperre, in der Zeit vom Oktober 1963 bis September 1965, gesammelt wurden.Die Längengruppen beim Tigerfish,Hydrocynus vittatus (Castelnau), werden mit den Gonadenentwicklungsstadien korreliert.Die Kiemennetzmethode hat sich zum Verfolgen des monatlichen Wachstums von vier unterschiedlichen Jahresklassen, zwischen 14 cm und 34 cm als zulänglich erwiesen.Das Wachstum war langsamer in den Jahren 1964–65 als in den Jahren 1959–60, den ersten zwei Jahren nach dem Vollaufen der Talsperre.Die Gonaden vonH. vittatus, von einer durchschnittlichen Länge von 31 cm, waren im Januar 1965 am stärksten entwickelt. Diese Gruppe enthielt 93% Männchen, deren Alter sich als zweijährig feststellen liess.Die Fangbarkeit vonH. vittatus mit den benutzten Kiemennetzen war bedeutend geringer für Fische mit einer Körperlänge von mehr als 34 cm. Vielleicht wurden aus diesem Grund so wenig reife Weibchen gefangen, da deren Durchschnittskörperlänge 35 cm beträgt.Die erhaltenen Resultate werden mit Angaben aus dem einschlägigen Schrifttum verglichen.Es wird gefolgert, dass die meisten in der Kariba-Talsperre gefangenenH. vittarus and Ende ihres zweiten Lebensjahres, während der Regenzeit, anfangen sich fortzupflanzen.

     

Odonata,Amphibia and Environmental Characteristics in Motorway Stormwater Retention Ponds (Southern France)

Water and its protection against pollution is an urgent priority for all countries around the world. In that context, France, through its Water Law in 1992 obliged the motorway companies to build stormwater retention ponds along roads in order to protect the water resource from transport pollution and to control water flow during rainstorms. We propose to evaluate how much these ponds can be attractive for aquatic species and then evaluate their role in regional biodiversity. Six retention ponds, localized in the Mediterranean region, were investigated during one year (March 2002–March 2003) for their chemical and biological characteristics such as bottom type, trace metal composition, water quality and phytocenose composition. These variables were recorded and correlated with species richness of amphibian and dragonfly communities. Stormwater retention ponds showed a high concentration of copper and zinc in top sediment layer and herbicides in water column. Dragonfly richness was higher in ponds with a natural bottom than ones with an artificial bottom (PEHD membrane) while amphibian richness was more sensitive to the structure of the surrounding landscape. These habitats appeared to be very attractive for Odonata species and tend to favorize uncommon species present in the survey region such as Ischnura pumilio and Erythromma viridulum. Amphibian were found to be representative of anthropophilous guild.     

Long-term retention of internal elastomer tags in a wild population of painted crayfish (Panulirus versicolor [Latreille]) on the Great Barrier Reef

Many crustaceans are highly exploited fisheries species, but determining the population parameters of these animals via mark-recapture techniques is problematic, primarily due to tag-loss during moulting of the exoskeleton. Recently developed internal elastomer tags may overcome this challenging problem, since they are completely encased in the tissues beneath the exoskeleton. In this study, we evaluated the effectiveness of internal elastomer tags in a wild population of painted crayfish (Panulirus versicolor) over an 18-month period. Seventy animals were double-tagged in the abdominal musculature, with individuality obtained using different combinations of tag colour and tag location. Forty individuals were recaptured after 6, 12 and (or) 18 months, giving an overall recapture rate of 57%. Annual tag retention was estimated to be 98%, since only one instance of tag-loss was observed, despite numerous episodes of moulting among tagged individuals. The majority of tags (95%) were easily visible, even after 18 months at liberty. Nonetheless, small reductions in tag condition were observed after the first six months (mostly due to fading and [or] fragmentation), but this did not interfere with overall tag readability. Tag condition did not decline in the following 12 months, nor did it vary with gender or tag location. It is concluded that internal elastomer tags are an effective method for marking wild crayfish over long-term periods. Given the durability of elastomer, and the capacity for individual identification of large numbers of animals, such tags may be suitable for commercial-scale fishery applications.     

Use of epitope tags for routine analysis of transgene expression

Peptide and RNA epitope tags as tools for routine analysis of transgene expression and protein accumulation in transformed plant cell cultures was evaluated using three genes that encode very structurally and functionally different proteins. A T7 peptide was introduced at the amino- and carboxyl-termini of phosphinothricin-N-acetyl transferase and avidin and at the carboxyl-terminus of galactose oxidase. An RNA sequence that forms a higher order structure that is recognized by antibodies raised against the FLAG peptide was separately introduced into the 3 nontranslated region of these genes. Constructs were introduced into maize cell cultures using particle bombardment and transgene expression, protein accumulation, protein function and presence of the tags in RNA and/or protein as appropriate were evaluated in up to approximately 25 culture lines per construct. Results indicate that, while there will likely always be a need for some empirical evaluation of any tag-protein combination, introduction of the peptide tag at the amino-terminus was generally more successful than was incorporation at the carboxyl-terminus. RNA tags show promise for this purpose, but routine application will require development of a very sensitive immunoassay.Both of these authors contributed equally to this work and should be recognized as first authors.     

Behaviour of tigerfish Hydrocynus brevis in the River Niger,Mali, as revealed by simultaneous telemetry of activity and swimming depth

The ecology and behaviour of tigerfishes (Hydrocynus spp., Alestiidae) remains largely unknown despite these piscivores play a crucial role in tropical ecosystems. A 44-cm tigerfish H. brevis was equipped with two transmitters using accelerometer and depth sensors, the signals of which were simultaneously recorded while tracking the fish over four 24-h cycles during February and March 2001 in the River Niger near Bamako, Mali. This methodology permitted discriminating between different behaviours, including hunting sequences. Over 1 month, the tigerfish occupied an area of no more than 3 ha over one third of the river width, and showed consistent fidelity to the same activity core (circa 0.1 ha), which consisted in a calm (<10 cm s^–1) glide with depth ranging from 60 to 100 cm, and comprising many large immersed rocks. Activity was essentially diurnal, with no hunting sequence observed at light intensities <0.01 Lux. It decreased under gusting winds or when boat traffic was intense and forced the fish to deeper (c. 1.5 m) waters. These preliminary results support the idea that H. brevis is essentially a diurnal, visually orientated predator with strong sedentary habits during the mid-dry season, and that its predatory activity might be compromised by the intensification of boat traffic.     

Identifying spawning behavior in Pacific halibut, <Emphasis Type="BoldItalic">Hippoglossus stenolepis</Emphasis>, using electronic tags

Synopsis Identifying spawning behavior in Pacific halibut, Hippoglossus stenolepis, is particularly challenging because they occupy a deep, remote environment during the spawning season. To identify spawning events, a method is needed in which direct observation by humans is not employed. Spawning behavior of seven other flatfish, species has been directly observed in their natural environment by investigators using SCUBA. All of these flatfish species display almost identical spawning behavior that follows a routine. Therefore, it is reasonable to believe that this spawning behavior occurs in other flatfish species, including Pacific halibut. As part of a larger study, we recaptured two Pacific halibut on which Pop-up Archival Transmitting (PAT) tags had been attached during the winter spawning season. Because the tags were physically retrieved, we were able to collect minute-by-minute depth records for 135 and 155 days. We used these depth data to tentatively identify spawning events. On seven separate occasions between 20 January 2001 and 9 February 2001, one fish displayed a conspicuous routine only seen during the spawning season of Pacific halibut and the routine parallels the actions of other spawning flatfish directly observed by humans using SCUBA. Therefore, we propose this routine represents spawning behavior in Pacific halibut. The second tagged fish did not display the conspicuous routine, thus challenging the assumption that Pacific halibut are annual spawners. PAT tags may prove to be a useful tool for identifying spawning events of Pacific halibut, and that knowledge may be used for improved management in the future.     

Mapping of expressed sequence tags from a porcine early embryonic cDNA library

The goal of this study was to identify and map genes expressed during the elongation phase of embryogenesis in swine. Expressed sequence tags were analysed from a previously described porcine cDNA library prepared from elongating swine embryos. Average insert length of randomly selected clones was approximately 600 bp, with a range from < 100 to > 2500 bp. Single-pass, coding strand sequences from 1132 independent clones were compared with the GenBank non-redundant (nr) database via BLASTN analysis to identify potential porcine homologous of known genes. Among these sequences, 781 (69%) showed significant (score > 300) homology to non- mitochondrial sequences previously deposited in GenBank. Sequences matching interleucin 1 beta and thymosin beta 10 were most frequently observed (24 and 18 clones, respectively), in addition to matches with 310 other distinct genes. No significant match in the GenBank nr database was obtained for 303 sequences. Analysis demonstrated that 151 (50%) had open reading frames (ORF) extending at least 50 codons from the first base of the clone insert. Genetic markers were developed and used to map a subset of 17 genes, selected on the basis of function or of the ability to design primers that successfully amplified porcine genomic DNA, to 10 different porcine chromosomes, providing a set of mapped markers corresponding to genes expressed during conceptus elongation.     

Retention and Degradation of N-Glycoproteins in the Rough Endoplasmic Reticulum

Recent studies have shown that newly synthesized proteins and glycoproteins are submitted to a quality control mechanism in the rough endoplasmic reticulum (ER). In this report we present two models: One model will illustrate a transient retention in rough ER leading to a further degradation of glycoproteins in the cytosol, (soluble alkaline phosphatase expressed in Man-P-Dol deficient CHO cells lines). The second model will illustrate a strict retention of glycoproteins in rough ER without degradation nor recycling through the Golgi (E1, E2 glycoproteins of Hepatitis C virus in stably transfected UHCV-11.4 cells and in infected Hep G2 cells).In both cases, oligomannoside structures are markers of these phenomena, either as free soluble released oligomannosides in the case of degradation, or as N-linked oligomannosides for strict retention in rough ER.     

Identification of expressed sequence tags (ESTs) of the highly transcribed genes in Aspergillus niger

Determined sequences of 285 randomly selected clones in a 3-directed cDNA library of Aspergillus niger could identify expressed seqeunce tags (ESTs) of genes highly expressed. One EST appeared seven times, one six times, one five times, four three times and 12 twice. Out of these 19 ESTs, ten were identified in GenBank, but none was of A. niger, suggesting that there are a lot of unidentified genes highly expressed in A. niger.