Freshwater fish ecology

Ecology of larval blue sucker, Cycleptus elongatus, a North American catostomid that has declined throughout its range, is poorly known because larvae have rarely been sampled. A total of 316 young blue suckers (16.0-39.0 mm total length) was captured over 3 years at 14 offchannel sites in Pool 25, Mississippi River. Blue suckers demonstrated distinct temporal and spatial abundance patterns. Blue suckers were only captured in late May/early June, and were more abundant during a year of little flooding. Abundance was correlated with the distance a site was from the main channel, being highest in island borders and island sloughs in proximity to the channel. Fish guts contained a relatively high biomass of chironomids and zooplankton, suggesting islands were providing suitable feeding opportunities. Because of their proximity to flows, slack waters provided by islands were accessible to blue sucker larvae dispersing from channel spawning areas and facilitated their development into rheophilic juveniles.

Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life-history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life-history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3-5 sea-winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life-history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life-history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world-wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in Dempson and O'Connell reviewed the Atlantic salmon, Jonsson and Jonsson the brown trout and Amundsen and Klemetsen the Arctic charr. Mortensen initiated the review and gave constructive criticism to the manuscript.

Aim We investigated genetic variation of Irish pike populations and their relationship with European outgroups, in order to elucidate the origin of this species to the island, which is largely assumed to have occurred as a humanmediated introduction over the past few hundred years. We aimed thereby to provide new insights into population structure to improve fisheries and biodiversity management in Irish freshwaters.

The cichlid species Oreochromis niloticus, Sarotherondon galilaeus, and Coptodon zillii, which are among the most exploited resources in the small-scale fisheries of the Tono, Bontanga, and Golinga reservoirs in northern Ghana, were assessed based on length frequency samples. Growth, mortality, exploitation status, stock size, and relative yield per recruit reference points were determined using bootstrapping fish stock assessment (BFSA), a novel framework that allows for the estimation of uncertainties around the life-history parameters and reference levels (e.g., L∞, K, and F0.1). The results suggest that the 3 species studied are heavily exploited in all 3 reservoirs, but with no alarming signs of overexploitation. The fishing effort at Golinga is comparatively low as a result of insignificant fishing during the agriculture season, which relates to low exploitation rates. Sarotherondon galilaeus and C. zillii have the highest and lowest biomass (t/km2) respectively in all the 3 reservoirs. The small shallow reservoir (Golinga) has the highest biomass of the target resources per unit area. According to a second assessment approach, based on length-based indicators, all species at Bontanga and O. niloticus and S. galilaeus populations at Golinga have spawning stock biomasses below 40% of the unfished biomass. This points to a situation of a possible ongoing recruitment overfishing of those species in the 2 reservoirs and suggests that a further increase in fishing effort should be prevented. Further monitoring of these fisheries will be needed for the improvement of assessments and thus management advice.

Life-history studies comparing landlocked versus diadromous populations reveal factors associated with life-history evolution under different scenarios. We describe several aspects of spawning and development of landlocked Aplochiton zebra in Patagonia (Argentina) based on the presence of eggs, the gonadal development, the analysis of otolith daily growth increments validated by tetracycline marking experiments, and the analysis of standard length frequencies. Among Patagonian galaxiids, A. zebra showed intermediate size and age at first maturity and high fecundity, with vitellogenic oocytes covered with short chorionic filaments. Free embryos of A. zebra were larger than those of Galaxias maculatus and Galaxias platei. This information is particularly significant for conservational purposes when we consider the reduced distribution of landlocked populations of the species and the risks imposed by salmonid introduction.

We conducted underwater surveys using SCUBA gear to examine habitat and microhabitat competition between the Ponto-Caspian racer goby Babka gymnotrachelus and native European bullhead Cottus gobio to assess the potential for competitive displacement of the native species by the invading species. In summer, 88 surveys were made in a tributary of the River Vistula within defined benthic areas across the entire width of the river bed. The occurrence of fish by total length class (small: <6 cm; large: >6 cm) and environmental conditions (depth, water velocity, substratum type, plant cover, shelter type) was recorded. We found a substantial separation between the species and size classes in relation to substratum, shelter type and water velocity. European bullheads were limited to lotic areas with stony bottoms, whereas racer gobies also occupied lentic areas over sand or mud. European bullheads usually took refuge under stones in contrast to a wider range of shelters used by racer goby, including tree roots and rubbish. In general, the breadth of habitat used by the racer goby was wider than that of the European bullhead, although habitat overlap between the species was not statistically significant except for the type of shelter occupied by small fish, selecting smaller stones. An inverse relationship was observed between small European bullheads and all racer gobies in areas where they co-occurred, suggesting that invader may be having an adverse effect on the distribution and habitat use of small native bullheads, particularly in areas of moderate water velocities over small stones and gravel.

Rural communities in South Africa are becoming increasingly reliant on freshwater fish to
supplement their dietary protein requirement. Rising costs of other protein sources, increasing rural poverty
and escalating rural populations are resulting in increasing consumption of fish from contaminated river
systems. The Olifants River, Limpopo Basin, Eastern South Africa, has been systemically impaired and is now
one of the most polluted rivers in South Africa. We measured the concentrations of metals in fish muscle
tissue from two impoundments in the Olifants River (Flag Boshielo Dam and the Phalaborwa Barrage) and
conducted a human health risk assessment following Heath et al., (2004) to investigate whether consumption
of Oreochromis mossambicus from these impoundments posed a risk to the health of rural communities. Our
results show that metals are accumulating in the muscle tissue of O. mossambicus even though the populations
appear to be healthy. No patterns were observed in the ratios of the metals accumulated in the muscle tissue
of O. mossambicus at each impoundment. The human health risk assessment identified that lead, antimony
and chromium at Flag Boshielo Dam and lead at the Phalaborwa Barrage were above acceptable levels for
the safe consumption based on a weekly 150 g fish meal. We conclude that consuming O. mossambicus from
these impoundments could pose an unacceptable risk to the health of rural communities.

A study on the variation amongst the different populations of Labeo rohita on the basis of morphometric parameters was conducted. Samples were collected from fish farm having different weight groups of same age. Data regarding the morphogenetic parameters viz., body weight, fork length, total length and lengths of dorsal, caudal, anal, pectoral and pelvic fins of each individual were measured. Analysis of variance (ANOVA) for the different morphometric parameters of study was done using Minitab 16.0. The Pearson correlation analysis of the morphometric parameters was done by XLSTAT 2012 version 1.02. The results showed that positive correlation between the body weight, total length and average length of paired pectoral fins of L. rohita were non-significantly different (P> 0.05), anal fin length was significantly different (P<0.05), and all the remaining parameters were highly significantly different (P<0.01) among the population groups. The correlation of fish body weight and fork length was highly significant (p<0.001) and positive with all the parameters except with the caudal fin which was positively but non-significant in correlation with fork length (p = 161).

Assessing the impacts of invasive organisms is a major challenge in ecology. Some widespread invasive species such as crayfish are potential competitors and reciprocal predators of ecologically and recreationally important native fish species. Here, we examine the effects of signal crayfish (Pacifastacus leniusculus) on the growth, diet, and trophic position of the chub (Squalius cephalus) in four rivers in Britain. Growth rates of 0+ chub were typically lower in sympatric populations with signal crayfish compared with allopatric populations, and this effect could be traced through to 2+ chub in one river. However, growth rates of older chub (5+ to 6+) were typically higher in the presence of crayfish. Sympatry with crayfish resulted in lower chub length-at-age and mass-at-age in half of the rivers sampled, with no change detected in the other rivers. Stable isotope analyses (δ13C and δ15N) revealed that both chub and crayfish were omnivorous, feeding at multiple trophic levels and occupying similar trophic positions. We found some evidence that chub trophic position was greater at invaded sites on one river, with no difference detected on a second river. Mixing models suggested crayfish were important food items for both small and large chub at invaded sites. This study provides evidence that invasive species can have both positive and negative effects on different life stages of a native species, with the net impact likely to depend on responses at the population level.

The Lernaea parasite was reported in Alburnus hohenackeri Kessler, 1870, collected from the Char-Nimeh (or Chahnimeh) lake, Eastern Iran. Three fishes were infected with L. intestinalis having 3 to 22 parasites increasing with fish
size. The maximum and minimum of parasite lengths were 138.02 mm and 24.54 mm respectively. The prevalence, mean intensity and abundance of infection by plerocercoid of L. intestinalis were 33.33%, 13.33, and 4.44 respectively.

Endemic fish species of Armenian ichthyofauna—Sevan trout (Salmo ischchan Kessler, 1877)—is registered in the Red Book of
Animals of the Republic of Armenia as “Critically Endangered” (corresponds to IUCN category: CR A2cd). Its natural reproduction
hardly occurs as a result of numerous problems related to the use and management of water and bio-resources in the Lake
Sevan drainage basin.Masrik River is formerly known as a spawning river for two ecological races of the Sevan trout, but there is
no up-to-date and in-depth studies of its potential to support natural reproduction. Thus, a set of spawning criteria was arranged as
matrix and state of Masrik River as spawning area for the Sevan trout was assessed. The results showed that the potential of
different parts of Masrik River to support natural reproduction of Sevan trout varied from quite appropriate to inappropriate. The
main limiting factors revealed were water temperature, velocity and substrate conditions.