Total Number Of Fish Research Articles

Effective size of a wild salmonid population is greatly reduced by hatchery supplementation

Many declining and commercially important populations are supplemented with captive-born individuals that are intentionally released into the wild. These supplementation programs often create large numbers of offspring from relatively few breeding adults, which can have substantial population-level effects. We examined the genetic effects of supplementation on a wild population of steelhead (Oncorhynchus mykiss) from the Hood River, Oregon, by matching 12 run-years of hatchery steelhead back to their broodstock parents. We show that the effective number of breeders producing the hatchery fish (broodstock parents; N(b)) was quite small (harmonic mean N(b)=25 fish per brood-year vs 373 for wild fish), and was exacerbated by a high variance in broodstock reproductive success among individuals within years. The low N(b) caused hatchery fish to have decreased allelic richness, increased average relatedness, more loci in linkage disequilibrium and substantial levels of genetic drift in comparison with their wild-born counterparts. We also documented a substantial Ryman-Laikre effect whereby the additional hatchery fish doubled the total number of adult fish on the spawning grounds each year, but cut the effective population size of the total population (wild and hatchery fish combined) by nearly two-thirds. We further demonstrate that the Ryman-Laikre effect is most severe in this population when (1) >10% of fish allowed onto spawning grounds are from hatcheries and (2) the hatchery fish have high reproductive success in the wild. These results emphasize the trade-offs that arise when supplementation programs attempt to balance disparate goals (increasing production while maintaining genetic diversity and fitness).

Infection situatus of parasites in freshwater fishs collected in Lam river, Do Luong district, Nghe An province

The results obtained from our research about the parasitic worm, which parasitized freshwater fishs of Lam river (Do Luong district, Nghe An province) provide us the basic knowledge about parasites of freshwater fishs in North Central Vietnam. Total 217 individuals of freshwater fish were carried out an autopsy for checking fish parasites. Among them, 118 fishes (occupied 54.4% total number of surgical fish) belonged to 13 species of Cypriniformes (occupied 54.2% total number of fish species). Of the total 832 samples of fish parasites collected, there were 504 samples of Monogenea, 212 Trematodes, 25 Cestodes, 16 Acanthocephala, 44 Nematoda and 31 Copepoda. Infected rate of fish in study site was not too high, the prevalence was 39.2%. and the density of parasites per each infected host was 9,8 individuals/host. Monogenea was the highest infected group (26.3%), while other groups were lower: from 1.4% to 7.4%. The infected rate was highest in cranoglanis 90%, the next was hemicultus 54.5%, tilapia 50%, red - eyed carp and major carp 40%, mudfish 28.0%. In case of 14 fish species, with 10 surgical fish individuals, the infection rate fluctuated between 16.7% and 90%. The infected rate was observed as the highest in Cranoglanis sinensis (90%) and the lowest in Tilapia (16.7%). Parasite infection intensity in not too high, one individual of fish infected with 9.8 worms in average (min - max: 1 - 84). The highest infected intensity was found in common carp 33.0 worms/fish (1 - 64), the next is red - eyed carp 29.0worm/fish and cranoglanis 13.9worms/fish; the lowest infection intensity was found in hemicultur 12.3 worms/fish. The certain host are normally infected with 2 or 3 parasite groups their prevalence and density is not too high.

어류군집 특성과 하안형태복잡도와의 관계

Numerous studies suggested that fish assemblage structure reflects the status of stream ecosystems. The status of streams integrity, including various trophic levels, water quality and habitat degradation, can be assessed by fish assemblages. In this study, we investigated the relationships between fish assemblages and streamline geometry of streams. Previous studies suggested that geomorphologic parameter can be a critical factor of permeability between adjacent two systems. From a landscape ecological perspective, edges may partially control the flow rate of energy between two adjacent systems. Thus, the Streamline geometry can be a geomorphologic parameter that exhibits the integrity of stream. We selected the Nakdong river for study areas, which is one of major rivers and the longest (525 km) River in South Korea. We used the revised IBI representing overall ecological characteristics of Korean fish assemblages and eight sub-assessment criteria of IBI, collected from 82 sampling sites in the Nakdong River. For calculating the Streamline geometry, we measured fractal dimension index that generally used in biology, ecology and landscape ecology. We used the digital land-use/land-cover map and generated a 1-km buffer for each sampling site and refined the shape of the Streamlines. Pearson correlation analyses were performed between Streamline geometry and IBI and sub-assessment criteria of IBI. The results show that IBI and eight sub-assessments of fish are significantly correlated with geometry of Streamline. The fractal dimension of Streamline geometry were related with IBI (r = 0.48) and six sub-assessments of IBI, including total number of native fish and native species, the number of riffle benthic species, sensitive species, tolerant species and native insectivore. Especially, the number of tolerant species(r = -0.52) and native insectivore(r = 0.52) show strong correlation with geometry of Streamline. These results indicate that lower Streamline geometry can result in poor fish assemblages, while higher geometry of Streamline can enhance fish assemblages by potentially supplying insects and better habitat conditions. We expect the results of our study to be useful for stream restoration and management. However, we see the necessity of study investigating the mechanisms how Streamline geometry affect fish assemblages.

A GEOGRAPHIC INFORMATION SYSTEM TOOL FOR AQUATIC RESOURCE CONSERVATION IN THE RED AND SABINE RIVER WATERSHEDS OF THE SOUTHEAST UNITED STATES

ABSTRACTOur goal was to build a geographic information system (GIS) tool to enhance modeling and hypothesis testing relevant to watersheds and fish fauna of the Red and Sabine Rivers in the southeastern United States. Species of concern were identified from wildlife action plans and Web sites. Spatial distributions of fish species and mercury in fillets were delineated using data from states. Public georeferenced data were obtained on land cover, soil type, forest canopy, impervious surfaces, wastewater facilities and 303(d) impaired waters. Overlay maps highlighted patterns across 8‐digit hydrologic unit codes (HUCs). Bossier City, Louisiana and Beaumont, Texas areas displayed impervious surfaces over 10% and 303(d) waters per HUC were 20% and 8%, respectively. Because bowfin (Amia calva) (n = 299) and bass (Micropterus spp.) (n = 1493) occurred in up to 44% of HUCs and fillets contained elemental mercury concentrations across ranges monitored, they were appropriate indicators of bioavailable mercury. Of the total fish number showing >0.5 ppm, 81% of records were derived from bowfin and bass, and stepwise multiple linear regressions indicated fish with mercury at these concentrations correlated with environmental variables. Detrended correspondence analysis showed total species occurrence and environmental relationships significant, where 81.6% of the variability in fish occurrence was explained by impervious surface, land cover other than canopy or impervious surface (such as wetlands and agricultural area) and canopy (forest type). Two‐way indicator species analysis delineated species co‐occurrence in HUCs (14 groups) and similarity of species composition (nine groups). Results identified three HUC groupings as potential targets for managerial interest. Quality control concerns for GIS development included site name data and priority rankings of critical fish species. This tool can be used to support modeling and trend analyses for several purposes, such as those relevant for developing and reporting on water quality standards and critical habitat assessments. Published in 2011 by John Wiley & Sons, Ltd.

Evaluation of the design and efficiency of the Norwegian self-sampling purse-seine reference fleet

Abstract Pennington, M., and Helle, K. 2011. Evaluation of the design and efficiency of the Norwegian self-sampling purse-seine reference fleet. – ICES Journal of Marine Science, 68: 1764–1768. A self-sampling reference fleet is employed by the Institute of Marine Research to estimate the characteristics of the Norwegian commercial catch for a number of species. The reference fleet is composed of commercial fishing vessels that are paid to measure a subsample of fish from selected catches and, less frequently, to take and preserve otolith, stomach, and genetic samples. In this study, the sampling design for monitoring the catches of herring, mackerel, and blue whiting used by the recently established purse-seine segment of the reference fleet is evaluated. The precision of the estimated mean lengths, and hence that of the estimated length distributions of the entire commercial catch, was bounded by the number of boats in the purse-seine reference fleet. Therefore, the only way to improve survey precision significantly is to increase the number of boats in the reference fleet. In addition, the effective sample sizes were much smaller than the total number of fish measured, from which it followed that too many fish were measured in each selected catch. Based on this analysis, the prescribed number of fish sampled from each selected catch has been reduced by more than 50%.

The Effect of Mannan Oligosaccharide Supplementation on Atlantic Salmon Smolts (Salmo salar L.) Fed Diets with High Levels of Plant Proteins

An experiment was conducted to investigate the effect of dietary mannan oligosaccharide (MOS) supplementation on Atlantic salmon ( Salmo salar L.) smolts (~ 47 g) reared in sea cages. The first treatment (control) consisted of fish fed the basal diet and the second treatment (MOS) fish were fed the same basal diet supplemented with 0.4% MOS. In the basal diet, 51.8% of the diet protein was derived from fish meal and 48.2% from vegetable protein (e.g. soy and wheat). After 14 weeks feeding on the experimental diets the results demonstrated that MOS supplementation did not affect growth performance, however, body protein composition was significantly increased. Additionally, liver histochemistry revealed that glycogen deposition in liver tissue increased from 1.80 ± 0.73 AU in the control fed fish to 2.58 ± 0.91 AU in the MOS fed fish. Histology of the anterior intestine demonstrated that MOS supplementation produced a significantly higher absorptive surface of 4.63 ± 0.62 AU compared to the control fed fish of 3.65 ±0.49 AU. The microvilli density was also significantly higher in the anterior intestine in the MOS fed fish,12.02 ± 5.95 AU, when compared to the control fed fish 5.90 ± 1.53 AU. Similar results for the absorptive area and microvilli density were observed in the posterior intestinal region.Microvilli length increased in the posterior intestine from 1.10 ± 0.18 μm in the control group to 1.41 ± 0.19 μm in the MOS fed fish. Furthermore, counts of sea lice attached to fish and total number of fish infected by sea lice were significantly lower in the MOS fed fish. The present study shows that 0.4% MOS supplementation was able to improve intestinal morphology, increase carcass protein content and glycogen deposition in the liver.

Effect of flooding on fish assemblages in small streams in South Korea

The impact of Typhoon-Rusa-generated flood on fish assemblages was investigated in small streams in the northeastern part of South Korea. As a result of high precipitation (870 mm day−1) during the typhoon, stream morphology and substrate composition changed. Stream depth and width decreased and slightly enlarged, respectively. Substantial amounts of mud and silt flowed into the streams and modified substrate composition to a simple state. Although the total number of individual fish significantly decreased after the flood, the dominant species remained the same relative to before the typhoon, and their relative abundance subsequently increased. However, the rank order of fish assemblages before and after the flood changed. Three years after the flood, fish assemblage recovered, but the number of individuals per site was still lower than prior to the flood. Flooding affects fish assemblages both directly and indirectly. Indirect impacts, such as habitat alteration, more critically affected the change in local fish assemblage and delayed recovery time. Nonetheless, fish assemblages persisted at sites where floods occurred.

Differences in root architecture influence attraction of fishes to mangroves: A field experiment mimicking roots of different length, orientation, and complexity

Benthic structure plays an important role as shelter and feeding habitat for demersal fauna. While many studies have investigated the relationship between structural complexity of aquatic vegetation and the number of species or abundance of motile organisms, little is known of the attractiveness of submerged mangrove roots. We tested the importance of various root attributes in attracting fish species in a field experiment using different artificial mangrove units (AMUs) with PVC pipes mimicking roots to exclude interaction with other environmental and biotic factors. We manipulated length, vertical orientation, and three-dimensional structural complexity of root mimics in the AMUs to explore their effects on the fish community variables: fish abundance, number of species and community composition. Pipe length and three-dimensional structure did not have an effect on fish community variables. Vertical pipe orientation had a significant effect and AMUs with standing pipes showed higher total fish abundances and number of species than AMUs with hanging pipes. Also community composition differed greatly between AMUs with standing versus hanging pipes. At species level, demersal fish species mainly occupied AMUs with standing pipes and occurred only at very low abundances when hanging pipes dominated in the AMUs; in contrast, the semi-pelagic swimmer Sphyraena barracuda showed a trend of higher abundance in AMUs with mainly hanging pipes. When analyzed across all AMUs, fish abundances of demersal as well as semi-pelagic species decreased significantly with increasing interspatial pipe distance among AMUs, suggesting that distance to refuge may be the underlying mechanism for the observed patterns. The above findings are important in the context of the worldwide degradation of mangroves, because human alteration to mangrove vegetation affects its structure and thus composition and size of fish communities.

Pisces, Teleostei, Gobiidae, illustrated list of additions to the fauna of the Raja Ampat Islands, Indonesia

Previous surveys of the reef-associated ichthyofauna of the Raja Ampat Islands in West Papua, Indonesia recorded a total of 1,320 species of reef fishes, including 271 species of Gobiidae. A recent survey focused on the cryptic gobies of Raja Ampat resulted in 36 new records (including nine species of both Trimma and Eviota). Sixteen of the new records are currently undescribed species, with seven of these identified as Raja Ampat endemics, while the remaining nine species are also known from localities outside Raja Ampat in the western Pacific. Five species previously recorded from the area have been re-identified, two of them representing undescribed species, and a new record from the literature has been added. This brings the total number of reef fishes known from Raja Ampat waters to 1,357, of which 308 belong to the Gobiidae. The number of species (including the undescribed taxa) apparently endemic to the Bird’s Head Peninsula of West Papua now totals 33.

Spatial pattern of coastal fish assemblages in different habitats in North‐western Mediterranean

AbstractVariability of fish assemblages across habitat structures can depend on spatial scales. A hierarchical sampling design was used to assess the spatial variability of temperate fish assemblages in different habitats and at multiple scales. Underwater visual censuses were carried out along the coasts of Elba Island (NW Mediterranean) on Posidonia oceanica beds, rocky algal reefs and sandy habitat at three spatial scales, namely tens of metres (individual replicates), hundreds of metres (sites) and tens of kilometres (locations). At the assemblage level, there was a clear relationship between fish and habitat type and the observed habitat‐related differences were largely dependent on species identity. Fish assemblages on P. oceanica beds and rocky reefs shared a high number of species, whereas overlap with sandy assemblages was negligible. Multivariate analyses revealed significant differences in fish assemblages among habitats, although there was also a significant habitat × site interaction. These differences relied mainly upon assemblage composition and species richness. Assemblages on rocky reefs and P. oceanica meadows usually harboured a higher number of species and individuals compared with sandy assemblages. Nevertheless, the patterns of habitat‐related differences in species richness and, especially, in the total number of fish, changed significantly from site to site. Eight species showed significant differences over habitats, but they were not consistent due to the interaction of habitat with site. Predictability of fish at both assemblage and population levels decreased with the scale of observation, and the spatial pattern of fish observed at the smallest scale was likely dependent on factors other than habitat type.

Characterization of mesonephric development and regeneration using transgenic zebrafish.

The zebrafish is a valuable vertebrate model for kidney research. The majority of previous studies focused on the zebrafish pronephros, which comprises only two nephrons and is structurally simpler than the mesonephros of adult fish and the metanephros of mammals. To evaluate the zebrafish system for more complex studies of kidney development and regeneration, we investigated the development and postinjury regeneration of the mesonephros in adult zebrafish. Utilizing two transgenic zebrafish lines (wt1b::GFP and pod::NTR-mCherry), we characterized the developmental stages of individual mesonephric nephrons and the temporal-spatial pattern of mesonephrogenesis. We found that mesonephrogenesis continues throughout the life of zebrafish, with a rapid growth phase during the juvenile period and a slower phase in adulthood such that the total nephron number of juvenile and adult fish linearly correlates with body mass. Following gentamicin-induced renal injury, the zebrafish mesonephros can undergo de novo regeneration of mesonephric nephrons, a process known as neonephrogenesis. We found that wt1b expression was induced in individually dispersed cells in the mesonephric interstitium as early as 48 h following injury. These wt1b-expressing cells formed aggregates by 72-96 h following injury which proceeded to form nephrons. This suggests that wt1b may serve as an early marker of fated renal progenitor cells. The synchronous nature of regenerative neonephrogenesis suggests that this process may be useful for studies of nephron development.

A comparison between fish assemblages in mangrove forests and on intertidal flats at Ungwana Bay, Kenya

Fish assemblages of mangrove forest patches and adjacent intertidal flats in Ungwana Bay were compared using stake-net sampling in the mangrove forest and intertidal flat habitats between December 2002 and November 2003. Four forest sites were compared with paired intertidal flat sites with either sand or mud substrata. Distinct ichthyofaunal differences were found between the habitats. Pooled data indicated a significantly higher fish density and biomass in the forests compared to the intertidal flats. Mean fish densities were 0.2–2.7 fish m−2 in the forest and 0.1–2.1 fish m−2 on the flats. Thirty-five species were sampled, eight of which occurred exclusively in the forest and six were limited to the intertidal flats. However, species exclusive to either the forest or intertidal flats contributed <1% towards the total number of fish sampled. Anchoviella commersonii dominated the forest habitat and Pellona ditchela the open intertidal flats. Cluster analysis grouped fish assemblages into two groups, based primarily on whether the substratum was sand or mud, rather than on mangrove forest or open flat habitats. This study represents a component of a larger project on artisanal mangrove fisheries within the area.

A Capture-Recapture Problem When Information is Obtained From Two Qualitatively Different Sources

We first consider a wildlife-related capture recapture problem with a known total number of fish. Our objective is to estimate the number of healthy fish, H. We first use a rod that only attracts healthy fish, which are tagged and returned to the water. Later, we use a net that scoops both sick and healthy fish. Three assumptions regarding the probability of being caught by the net, conditional on health status and being caught by the rod, lead to three different estimates of H. We give approximations to expected values of the three estimates and give a condition under which they bracket H. A potential application of these methods is to the follow-up of World Trade Center responders. Responders are disease-free when they arrive at the clean-up site and are asked to report for a visit after a fixed period of time, but some fail to do so. Some responders, whether they come to the scheduled return visit or not, spontaneously report a disease before the scheduled visit, but absence of disease is never reported in this manner. We use the methods developed to estimate the total number of subjects with disease by the time of the scheduled return visit.

Fish responses to increasing distance from artificial reefs on the Southeastern Brazilian Coast

Artificial reefs have been deployed worldwide in shallow marine environments to enhance attraction and capture of fish, but, despite their potential as a fishery management option, few studies addressed whether fish assemblages will change with distance from a reef. We experimentally assessed the relationship between fish abundance and richness to increased distance (0, 25, 100, and 300 m) to reef balls deployed on a flat and homogeneous bottom, 9-m deep, on the north coast of Rio de Janeiro, Southeastern Brazil. A total of thirty fish species was associated with the reefs and the variation in species composition with sampling period or technique did not account for changes in fish assemblages with reef distance. Fish abundance and richness were significantly greater at the nearest distances (0 m and 50 m) to the reefs than at 300 m, but while the first dependent variable decreased exponentially with reef distance the later diminished linearly. Fish responses to reef distance were clearly species-specific and the tomtate ( Haemulon aurolineatum — the dominant species that probably used the reefs for shelter purposes) strongly influenced the exponential decreasing pattern found for the total number of fishes and abundance of Haemulidae. The abundance of the close congener Haemulon steindachneri, and of Chaetodon striatus, Serranus flaviventris and serranid species as a group also decreased, but linearly, with reef distance, probably related to variation in home-range. Acanthurus chirurgus and Scorpaena isthmensis decreased linearly in number with reef distance, probably due to feeding rather than refuge purposes. The abundance of Isopisthus parvipinnis tended to increase with reef distance, suggesting that artificial reefs might be unprofitable for those species less dependent on clear water or structurally complex habitats to obtain refuge or food. Overall, our study indicates that artificial reefs are a promising management tool to enhance fish capture in the oligotrophic waters and structureless bottoms of the north coast of Rio de Janeiro, but with varied rates of success, depending on the target species and fishing distance from the reefs.

Local v. microhabitat influences on the fish fauna of tidal pools in north‐east Brazil

This study explored the influence of microhabitat characteristics, such as sandy, rocky and algal bottom, holes, area and depth, on tide-pool fish descriptors (evenness, total number of fish, diversity and species richness). Even when the rockpool microhabitats differed amongst beaches, the tidal fish assemblages were closely grouped by site rather than by characteristics of the tide pools. Fish assemblages were mostly represented by juvenile fishes from 29 species, of which 14 were observed in only one of the three sites. This indicates that sites, rather than microhabitat association, might play a major role for the rockpool ichthyofauna in north-east Brazil.

Monthly occurrence and prevalence of viral haemorrhagic septicaemia virus (VHSV) in whiting Merlangius merlangus

A field survey was carried out to determine the occurrence and spread of viral haemorrhagic septicaemia virus (VHSV) in whiting Merlangius merlangus (L.), a key prey species in the southeastern Black Sea region. In March, April, September and December 2007 and monthly in 2008, 70 to 105 M. merlangus captured by gill nets were examined in pools of 7 fish per pool (total number of fish = 1603). After determining the seasonal occurrence of VHSV in whiting, 43, 80 and 88 whiting were sampled individually in January, February and March 2009, respectively, to determine age and size of whiting commonly infected with VHSV. The samples were tested in duplicate using BF-2 and EPC cell lines for virus isolation. Positive cultures (those demonstrating cytopathic effect, [CPE]), were tested further with a commercial ELISA kit to confirm that the observed CPE was caused by VHSV. VHSV was detected in M. merlangus only between February and April following a drop in the surface water temperature to 9 degrees C. All infected fish from the sampled whiting were asymptomatic carriers with low levels of virus. The estimated prevalence from pooled samples ranged between 1.35% (2.5 to 97.5 percentiles; 0.04 to 7.32%) to 3.14% (0.36 to 10.95%), whereas prevalence estimated from individual sampling was 7, 5 and 1% in January, February and March, respectively. Individual sampling also revealed that prevalence was higher among young fish (1 to 1.5 yr old) and decreased with increasing age. This is the first report of VHSV infection in whiting in the Black Sea.

Relative abundance of Ponto-Caspian gobiids in the lower Vistula River (Poland) 3- to 4 years after first appearance

In the years 2000–2001, specimens of two Ponto-Caspian gobiids (racer goby Neogobius gymnotrachelus and monkey goby Apollonia fluviatilis) were recorded for the first time in the lower Vistula River, which is a part of the central inland corridor used by Ponto-Caspian species to migrate in Europe. In 2004, seine net surveys were made in the river course to examine relative abundance of the non-indigenous gobiids in the local small-fish community. Altogether 4420 specimens with total lengths ranging from 10 to 340 mm (mostly <100 mm) belonging to 18 species were recorded in 70 hauls. Monkey goby was one of the subdominant species (18.1% of total number of fish captured; 64.3% frequency of occurrence in hauls) together with bleak Alburnus alburnus (21.0, 54.3), roach Rutilus rutilus (18.2, 67.1) and three-spined stickleback Gasterosteus aculaetus (17.3, 37.1). Racer goby was less abundant but quite common (2.5, 32.9), similar to common bream/white bream Abramis brama/Blicca bjoerkna (6.4, 47.1), Eurasian perch Perca fluviatilis (5.7, 57.1), dace Leuciscus leuciscus (4.2, 40.0) and European bitterling Rhodeus sericeus amarus (3.4, 27.1). The study shows that Ponto-Caspian gobiids dispersed successfully in the lower Vistula, becoming species common to its nearshore zone 3- to 4 years after their first appearance.

The infection of freshwater fishes with three species of Henneguya in Qena, Upper Egypt

It is so for the first time to do general surveyof protozoan parasites that infect freshwater fishes in Qena Province.The total number of fishes examined were 581 belonging to 10 familiesrepresented by 14 Species during the period from January 2006 to May 2008 . Threespecies of Henneguya were recorded from two species of fishes. The firstspecies is suggested to be a new one called Henneguya mandouri sp.nov. Thesecond species is Henneguya assuiti, Mandour etal., 1988 and the third one is Henneguya nilotica, Marwan, 1998.

Ecological aspects of metazoan endoparasites of Metynnis lippincottianus (Cope, 1870) (Characidae) from Upper Paraná River floodplain, Brazil

Abstract We examined 44 specimens of Metynnis lippincottianus (Cope, 1870) (Characidae), collected in the Upper Paraná River floodplain, Brazil, from March 2006 to December 2007. Of the total number of fishes, 32 (72.7 %) were infected by at least one species of helminth (endoparasites). One digenean, Dadayus pacupeva, and four nematode species, Spinoxyuris oxydoras, Contracaecum sp. (larval stage), Procamallanus (Spirocamallanus) inopinatus and Raphidascaris (Sprentascaris) mahnerti were identified. D. pacupeva and S. oxydoras showed the highest values of prevalence, mean intensity and abundance. The typical pattern of overdispersion or aggregation was observed for all endoparasites. Dominance by D. pacupeva and S. oxydoras was observed in the parasite community. Positive association between D. pacupeva and two nematode species (S. oxydoras and P.(S.) inopinatus) was observed, including positive and significant covariation between their abundances. These results suggest that species are coexisting without competition. There was no correlation between parasitism and sex for M. lippincottianus.

Effects of irrigation pumps on riverine fish

Abstract The total number and condition of fish extracted via high and low flow irrigation pumps was assessed over a 2‐year period in the Namoi River, Australia. A combination of boat electric fishing and fyke netting was used for 10 weeks during the peak irrigation period to determine species and size classes susceptible to entrainment during water abstraction. Over 2300 fish passed through the pump outlets over the study period, with many individuals (7.5% of total) both killed and injured. The maximum number of fish entrained in a single day was 232. Mortality was significantly higher from the high volume pump site, but only large (&gt;200 mm long) or small (&lt;50 mm long) fish were killed. Medium‐sized fish (50–200 mm long) largely survived the abstraction process; although 70 were injured (3% of total), only one was killed (0.07%). The Electric fishing surveys showed that only four species were present in storage dams, suggesting that survival through the pump systems may be size and species specific. Fish that survived the water abstraction process had no opportunities to return to the main river system and were effectively classified as lost from the main river population. The development of suitable mitigation measures, including operational changes and screening, are suggested as mechanisms to prevent extraction and minimise any adverse impacts arising from irrigation development.