Age and growth of Heterotis niloticus around Pategi in the middle River Niger, Kwara State

Biological studies of Heterotis niloticus were conducted for three years in the middle River Niger. Scales were found to be the most suitable structure in ageing Heterotis which was validated by length/histogram curve. Annual rings were found to be formed between March to June. Growth was rapid in the first two years and they reached sexual maturity at 2 years. The male grow longer while the female are bulkier. The length-weight relationship of male and female Heterotis did not differ significantly and the resulting equation for male was W = 1.25L super(2.5) and W = 1.6L super(2.7) for females respectively where W = weight (g) and L = total length. The total length to body scale relationship was found to be L = 14.3R super(2.6) where (R = oral radius of scale Heterotis growth was found to be allometric

A chemical survey of standing waters in south-east England, with reference to acidification and eutrophication

This study looks at the distribution and magnitude of acidification and eutrophication in south-east England where there are no natural lakes but a large number of shallow artificial ponds. The study area is defined as the region lying within a 100 km radius of central London but excluding the area within the M25 motorway. Water samples were taken from 120 sites between mid-January and the end of February 1990, with a subsequent monthly survey of a subset of 31 of these waters. Twelve chemical variables were measured in the laboratory using standard techniques. PH values for the full dataset ranged from 3.2 to 8.4, although the majority of sites had pH values in the range 7.0 to 8.5; only five sites had a pH of less than 6.0. The five low pH sites expectedly had low alkalinities and are the only sites with values below 0.1 meq per litre. Concentrations of calcium, sodium, potassium, magnesium, chloride, sulphate and nitrate had normal distributions. The majority of sites had total phosphorus concentrations in the range 25 to 200 mu g per litre, although 10 sites had concentrations above 400 mu g per litre. The low number of acid sites suggests that surface water acidity is not a widespread regional problem in south-east England. However the survey shows that a large number of standing waters in the region have high total phosphorus and nitrate concentrations, and 89% may be considered moderately to considerably eutrophic.

An analysis of records of gillnet fishing in Pilkington Bay, Lake Victoria

Among the commercially valuable species occurring in Lake Victoria the two endemic species of Tilapia, T. esculenta (Graham) and T. variabilis (Boulenger) still provide the basis for the fishery in many areas, though in some places the non-cichlid species are more important, for example in the Kagera river area where large numbers of Labeo victorianus and Schilbe mystus migrate seasonally into the river. Although certain species show these habitat preferences. Most of the coastline of Lake Victoria supports a wide variety of species, all of which contribute to the commercial fishery. Over the past ten years the East African Fisheries Research Organisation has fished experimentally a number of stations within a radius of fifty miles from Jinja. These stations have been selected so as to cover a variety of habitats which range from sheltered bays to exposed coastlines. The records discussed in this paper are the result of fishing operations carried out in Pilkington Bay over the period December 1954 to November 1956. This series of fishing operations was carried out in an attempt to assess the composition of the fish populations contained in this area. To this end a variety of nets of differing mesh sizes were used. Pilkington Bay is about ten square miles in extent and is an irregular and deep indentation on the north coast of Buvuma Island. It lies within the sleeping siclmess area where fishing by Africans is prohibited. When selecting an experimental fishing ground, it is important to have some idea of the amount of commercial fishing being carried out in the area. Throughout the period of this experiment a few African fishermen were seen operating illegally in the area, but it is unlikely that their efforts greatly affected the results obtained. Pilkington Bay was fished by E.A.F.R.O. in 1949 and 1950 (Lowe McConnell 1956) but since then till the present experiment, fishing in the area has been infrequent.

National report of the frame survey 2010 on the Uganda side of Lake Victoria

This is a report on the results of the Frame Survey conducted in the Uganda side of Lake Victoria during August 2010 by the LVFO Institutions, namely: the Department of Fisheries Resources (DFR) Uganda and the National Fisheries Resources Research Institute (NaFIRRI) in close collaboration with the District Fisheries offices of Busia, Bugiri, Mayuge, Jinja, Mukono, Kampala, Wakiso, Mpigi, Masaka, Kalangala and Rakai. The authors are grateful to the LVEMP II, for providing funds for the survey and the LVFO secretariat coordination. Fisheries Frame surveys have been carried out on Lake Victoria biannually since 2000 to determine the number of fishers, fish landing sites, and facilities at the landing sites, as well as the composition of fishing crafts, their mode of propulsion, fishing gears and the fish species they target. This information is used to guide development and management of the lake’s fisheries. Following the reorganisation of landing sites into Beach Management Units (BMUs), the number of landing sites decreased from 597 in 2000 to 435 in 2008. The survey in 2010 showed an increase to 503 landing sites, an indication that new landing sites are coming up. The fish landing sites continue to have inadequate facilities such as fish shades, cold rooms to service the fisheries industry and very few (5%) have access to electricity and 32% had access to all weather roads. There has been some progressive improvement in the landing site coverage of basic hygiene and sanitation facilities, especially public toilet facilities from 17% in 2000 to 39% in 2010; and portable water from 4% to 17% respectively. However more effort is required to cover all landing sites. Most landing sites (83%) have access to mobile phone networks which eases communication. 46% of landing sites had access to a Health clinic and 64% had a Primary school within a radius of 2 km.

Incidence of epizootic ulcerative syndrome (EUS) in freshwater fishes in the endemic area of Punjab, Pakistan

Incidence of Epizootic Ulcerative Syndrome (EUS) has been recorded for the first time in freshwater fishes in the endemic area of Punjab, Pakistan. Survey of private fish farms, hatchery and natural water bodies was conducted in a radius of 14 Km from around river Ravi near Lahore (Punjab Province) Pakistan. Out Of 1628 fishes belonging to 18 genera, 517 fishes of 10 genera were found affected with EUS. The incidence of EUS in culturable fishes was higher in Cirrhina mrigala (15.4%) moderate in Catla cat/a (13.3%) and lower in Labeo rohita (5.0%). Exotic fish, Chinese carp Ctenoparyngodon idella and Hypophthalmicthys molitrix were not affected with EUS. In non-culturable fishes the incidence of EUS was highest in Channa punctatus (72.8%) moderate in by C. straitus (65.45%) and comparatively lower Puntius ticto (43.7%). A slow growing temperature sensitive Saprolegnia spp. was isolated from all of EUS infected fish species. Aeromonas spp. and Pseudomonas spp. were isolated from the diseased fishes. Ectoparasites viz. Lernaea, Argulus and Triclwdina spp. were also isolated from the skin and gills of infected fish species. The disease was more severe in water having low alkalinity (70 mg/1), hardness (75 mg/1) and low temperature of 10-12 °C.

A stationary visual census technique for quantitatively assessing community structure of coral reef fishes

A new method is described and evaluated for visually sampling reef fish community structure in environments with highly diverse and abundant reef fish populations. The method is based on censuses of reef fishes taken within a cylinder of 7.5 m radius by a diver at randomly selected, stationary points. The method provides quantitative data on frequency of occnrrence, fish length, abundance, and community composition, and is simple, fast, objective, and repeatable. Species are accumulated rapidly for listing purposes, and large numbers of samples are easily obtained for statistical treatment. The method provides an alternative to traditional visual sampling methods. Observations showed that there were no significant differences in total numbers of species or individuals censused when visibility ranged between 8 and 30 m. The reefs and habitats sampled were significant sources of variation in number of species and individuals censused, but the diver was not a significant influence. Community similarity indices were influenced significantly by the specific sampling site and the reef sampled, but were not significantly affected by the habitat or diver (PDF file contains 21 pages.)

Scale-Dependent Habitat Selection of Nesting Great Egrets and Snowy Egrets

Foraging habitat selection of nesting Great Egrets ( Ardea alba ) and Snowy Egrets ( Egretta thula ) was investigated within an estuary with extensive impounded salt marsh habitat. Using a geographic information system, available habitat was partitioned into concentric bands at five, ten, and 15 km radius from nesting colonies to assess the relative effects of habitat composition and distance on habitat selection. Snowy Egrets were more likely than Great Egrets to depart colonies and travel to foraging sites in groups, but both species usually arrived at sites that were occupied by other wading birds. Mean flight distances were 6.2 km (SE = 0.4, N = 28, range 1.8-10.7 km) for Great Egrets and 4.7 km (SE = 0.48, N = 31, range 0.7-12.5 km) for Snowy Egrets. At the broadest spatial scale both species used impounded (mostly salt marsh) and estuarine edge habitat more than expected based on availability while avoiding unimpounded (mostly fresh water wetland) habitat. At more local scales habitat use matched availability. Interpretation of habitat preference differed with the types of habitat that were included and the maximum distance that habitat was considered available. These results illustrate that caution is needed when interpreting the results of habitat preference studies when individuals are constrained in their choice of habitats, such as for central place foragers.