Preliminary surveys of the fish and fisheries of the Nzoia, Nyando and Sondu Miriu rivers, Kenya

Three Lake Victoria rivers were sampled to assess fish abundance and distribution in preparation for assessment of catches from the river systems. Preliminary fish abundance data indicate that fishing potential upstream is negligible but that important commercial species are present in the downstream floodplain areas. Three catfish species were recorded in the Nzoia river system that have not been found previously in the Kenyan sector of the Lake Victoria system, together with possibly two undescribed Barbus species.

The Co-management survey: results of the fish processing factory survey

This book section analyses the role of fish processing factories in the process of co-management related to the LVFRP.

Current status of the fish stocks of Lake Victoria (Uganda)

A total of 457 hauls were taken during experimental bottom trawl surveys in the Uganda sector of Lake Victoria between November 1997 and June 1999 to estimate composition, distribution and abundance of the major fish species in waters 4-60 m deep. Fifteen fish groups were caught with Nile perch, Lates niloticus (L.), constituting 94% by weight. Haplochromines and L. niloticus occurred in all areas sampled, while Nile tilapia, Oreochromis niloticus (L.) and other tilapiines were restricted to waters 30 m deep or less. The mean trawl catch rate in the zone where artisanal fishermen operate (i.e. in waters less deep than 30 m was 165 kg hr, of which 93.6% comprised L. niloticus. Species diversity and relative abundance decreased with increasing water depth.

Distribution and abundance of fish stocks in Lake Victoria, Tanzania

Trawl surveys to assess the stocks of Lake Victoria for estimates of biomass and yield, together with the establishment of exploitation patterns, are being undertaken under the Lake victoria Fisheries Research Project. Preliminary surveys to establish the sampling stations and strategy were carried out between October 1997 and February 1998. Three cruises to cover the whole of the Tanzanian waters were undertaken with a total of 133 sampling stations. Data on catch rates, species composition and distribution were collected.

Relative abundance and distribution of fish in Kenyan waters of Lake Victoria

Bottom trawl surveys were conducted in Kenyan waters of Lake Victoria during the period September 1997 and March 1999. The means of fish biomass for the two most important species: Lates niloticus (L.) and Oreochromis niloticus (L.) were estimated at 61.5 kg ha and 4.5 kg ha respectively. There were few L. niloticus greater than 80 cm TL and O. niloticus greater than 50 cm TL, though these species attain maximum sizes of 205 cm and 65 cm respectively. Oreochromis niloticus was mostly found shallower than 5 m though some specimens were encountered deeper than 10 m, suggesting that the species has extended its ecological range. Very low catches were obtained from areas under water hyacinth cover. Water in such areas was turbid with oxygen levels below the critical 3.0 mg L.

The relationship between boat size and fish catches in the gillnet fishery of Lake Victoria, Uganda

The number and size composition of gillnets, fishing grounds, and the quantity and composition of fish catches were related to the size of fishing boat. The overall number of gillnets per boat increased from 20.9 + or - 2.3 nets in 5-6 m long boats to 88.6 + or - 11.8 nets in 11-12 m long boats. The proportion of large mesh sizes, + or more than 127 mm, also increased from 40% in 5-6 m long boats to 100% in boats longer than 10 m. Fish catches are related to the size of boat and this should be considered when formulating management guidelines of the lake's fishery. Promotion of large fishing boats 8 m or longer and restriction on the number and/or mesh size of gillnets of smaller boats could increase ecological and socio-economic benefits.

On the toxicity of some pesticides for fish [Translation from: Izv.gos.nauchno-issled.Inst.ozern.rybn.Khoz. 121, 95-96, 1977]

In the piscicide laboratory of GosNIORKh over a series of years was carried out the ichthyological evaluation of different agricultural pesticides, used both in our country and abroad. In all more than 300 different chemical substances were tested. Here, it was established that around 10% of them possessed high ichthyotoxic properties. Experiments were conducted under laboratory conditions on aquarium fish in groups, and also on representatives of different species of lake ichthyofauna. The basic criterion of evaluation of toxicity was the death of experimental fish during 120 hours. This short paper summarises the findings of this reasearch and offers a table presenting acute toxicity of pesticides for fish.

Avoided temperatures by young fish [Translation from: Informatsionnyi Byulleten Biologiya Vnutrennikh Vod No.50, 45-47, 1981]

Directed local changes of water temperature for the purpose of controlling the behaviour of fish are based on the knowledge of the characteristics of seasonal-age dynamics of their thermoadaptation possibilities. These possibilities are still inadequately studied especially in relation to avoided temperatures. By the authors the attempt was made to determine zones of avoided temperatures for the young of five species of fish (bream, roach, blue bream, perch, peled) in the summer period of the year, and also to assess the influence on them of additional factors, in particular mechanical driving. In parallel in two-fold repetition were conducted experiments on the determination of selected, shock and lethal temperatures of these fish. Experiments were conducted with fish, caught in the littoral of the Rybinsk reservoir.

Zooplankton - fish interaction in the littoral zone of Nyanza Gulf, Lake Victoria

The zooplankton community of the littoral zone of Nyanza Gulf, Lake Victoria, was studied between June 1998 and June 1999 to identify and quantify various zooplankton groups, and investigate the interactions that occur between them and the littoral fish through the food chain. Zooplankton samples were collected from five stations using a 83 micro-m mesh size plankton net hauled vertically through the water column. Fish samples were obtained by beach seine, except at Gingra (May 1999), where trawl samples were used. Gut/stomach analysis was carried out on the three major commercial species, Lates niloticus (L.), Oreochromis niloticus (L.) and Rastrineobola argentea (Pellegrin).

Socio-economic implications of the fish export trade on the fishers and fisheries of Lake Victoria in Uganda

The purpose of this study was to investigate the implications of the fish export trade on the fishers and the fisheries resources of Lake Victoria, Uganda with respect to sustainability. Eight fish processing factories and ninety fishers were qualitatively investigated. Socio-economic characteristics of fishers and the economic characteristics of fish factories formed a basis for the analysis. Results of the research indicate that there is a relationship between the growth in fish export trade, particularly the growth in industrial fish processing (for export) and declining fisheries resources of the lake. However, whether or not that impact is positive or negative, and to what extent there is an impact, is highly dependent upon the underlying socio-economic considerations of the fishers to the process. The fish-ban imposed by the European Union countries was particularly decried by fishers and factory owners as the main cause for the present poverty among the fishers. Fundamentally, several conflicting issues: ecological, physical and economic activities are a threat to the sustainability of the Lake Victoria fisheries, and for all that depend on and interact with the lake. There is urgent need to address the immediate issue of the growing riparian population and the global fish trade, to educate and train all the relevant actors in appropriate fisheries management techniques. Attitudes of fishers towards the fish factory developments are positive and this is a way forward for co-management for the sustainability of the fisheries resource.

Progress report on fish counting on the Rivers Itchen and Test

This progress report summarises work on NSHEB Mark 10 fish counters which are installed at Woodmill on the River Itchen and Nurseling Mill and Connegar Bridge on the River Test. Counters are evaluated and salmon behaviour regarding the counters examined. The report includes a a list of equipment needed for the efficient running of the project in the future.

Factors affecting the susceptibility of salmonid fish to disease

A review article discussing the degree of susceptibility of fish to outbreaks of disease and whether, besides from changes in the physical and chemical characteristics of the environment, this susceptibility is instrumental in determining whether or not pathogenic challenge results in disease. The article summarises a decade of work on this subject at the Windermere laboratory of the Freshwater Biological Association and suggests possible directions for future research. The article covers experimental design, effects of environmental stress (including discussion on the hypothalamic-pituitary-interrenal (HPI) axis in salmonid fish), sexual maturation, research areas for future development and evolutionary considerations. There are a number of accompanying figures and images.

Variation in bacterial populations in time and space

Obtaining a reliable estimate of the bacterial population is one of the main problems facing the bacterial ecologist. The author discusses the various methods available and concludes that the observed variability in bacterial populations depends on the sampling interval used.

The impact of Cow Green Reservoir on invertebrate populations in the River Tees

Cow Green is a new reservoir situated in Pennine moorland. It has an area of 312 ha, a capacity of 40 . 9 x 10 SUP-6 m SUP-3 and a maximum depth of 22 . 8 m. The function of the reservoir is to regulate flow in the River Tees to provide industrial Teesside with sufficient water during the dry spells. Invertebrate studies were carried out in the Tees to monitor changes resulting from the construction of the reservoir both in the flooded basin and below the dam. The overall effect of the reservoir on the Tees has been to increase the numbers and biomass of certain taxa, but generally not at the expense of previous fauna. Some of the positive effects, ie. increase in number and biomass, and maintenance of faunal diversity, may in part be attributable to the presence of the rapids and waterfall. Turbulence resulting from this rapid flow over heterogeneous bottom is sufficient to prevent clogging of interstitial spaces by silt and to maintain the variety of ecological niches necessary for a diverse fauna.