Biodiversity of estuarine fish faunas in West Africa

In West Africa (between Ivory Coast and Sénégal), estuarine environments vary from lagoons to high discharge rivers to inverse hypersaline estuaries. This results in a high diversity of estuarine fish species, with an important turnover and a core of ubiquitous species. The species richness of a given estuary depends on the combination of hydrological factors (marine or freshwater dominance) and biogeography (continental biogeographic regions). The catch rate is higher in lagoons and inverse estuaries than in normal estuaries, which can be explained by the predominance of small juveniles in the latter. Clupeids are the most abundant fishes all over the region, but different systems have different dominant species. Assessing the functioning of West-African estuaries provides useful comparisons to Asian estuarine systems.

The durability of different fish cage materials and the pros and cons of cage rotation

The procedures described are standard methods used in the European Union to quantify wood quality. Samples used here were smaller than the standards laid down in the DIN system (12 x 12 x 16 cm) as Litsea is a small tree and planks of the required size are unobtainable. The use of quality sized samples means that the results presented here can be compared with each other but unfortunately not with data in the literature. Wood is dried first at ambient temperature in the shade to reduce moisture content to an even 11-12%. Part of the sample was then oven-dried to 0% moisture content and its specific density determined by weighing a subsample of 128 cm super(3) (4 x 4 x 8 cm). Strength of expansion of the wood is determined as the percentage by which the wood sample can be pulled apart parallel and vertical to the grain before it breaks. Compression and bending strengths and elasticity are measured by compressing, bending and pulling wood sample in a machine specially designedto determine the forces required.

Problems for the conservation of freshwater fish genetic resources in India and some possible solutions

Many interconnected problems involved for the conservation of freshwater fish genetic resources of India are enumerated. Some possible solutions to the problems are also discussed.

A list of commercial fish species from Santarem, state of Para, Brazil

A list, comprising 129 species in 23 families, is presented of the fish commonly caught in 1992/93 in the commercial fisheries around Santarem, Para State, Brazil. The most important families were the Pimelodidae (22 spp.), Cichildae (20) and Serrasalmidae (15), and six species contribute over 50% of the catch in weight.

Markets, marketing and production issues for aquaculture in East Africa: the case of Uganda

Aquaculture is currently responsible for an insignificant proportion of total fish production in Uganda. However, given the increasing demand for fresh fish in urban and peri-urban araes, and threats to the supply of fish from natural catch fisheries, the potential exists for a strong market in aquaculture. Small-scale fish farmers located relatively close to markets or all-season roads, and who can supply consistent and high quality produce, will have the widest range of marketing opportunities, and will likely be within the area of operation of potential traders and intermediaries that deliver fish to markets. Fish farmers that are not close to roads, or produce unreliable quantities and variable quality products may face high transaction costs of marketing their product, and decreasing net returns to production. The authors found that significant on-farm labor, and access to input markets are important factors leading to positive net returns to fish production. Areas with high population density and relatively low wages will be well suited to labor intensive aquaculture. The authors concluded that aquaculture development has good potential in certain areas of Uganda and should therefore be pursued as a potential development pathway. However, policy makers should consider the importance of the price of fresh fish relative to the cost of labor, as well as other factors including the importance of smallholder credit and access to extension services, when directing investments in aquaculture technology.

Length-fecundity relationships of Nigerian fish populations

Parameters of the exponential body length (L)-fecundity (F) relationship of the form F=a.L super(b) are presented for 47 populations and 26 species of Nigerian fishes. Estimates of b varied between 1.563 (Ilisha africana) and 5.771 (Barbus callipterus) with a mean of 3.054 (s.d. = 1.024). The maximum sizes of fish populations examined did not significantly influence the relative magnitudes of b. The parameters Alpha and Beta of the linear length-fecundity relationships of the form F = Alpha + BetaL are also presented for five fish populations. Estimates of Beta ranged from 243.5 (Chrysichthys walkeri) to 1,334,895 (Tilapia mariae).

Growth performance of Nigerian fish stocks

Parameters of the von Bertalanffy growth function are presented for 42 fish stocks belonging to 16 families, 22 genera and 27 species. The growth performance index, Phi '(= log K + 2logL sub( infinity )), was computed for each stock and was found to be highest in male Gymnarchus niloticus (Gymnarchidae) from Lake Chad and lowest in Chrysichthys auratus (Bagridae) from the Cross River. Mean Phi ' for major fish genera and families are also presented and was highest in brackishwater fishes, closely followed by freshwater and inshore marine water fishes.

Weight-fecundity relationships of Nigerian fish populations

Parameters a and b of the power body weight (W) - fecundity (F=a W super(b)) are presented for 25 populations comprising 15 species of Nigerian fishes. Estimates of b varied between 0.511 (Parauchenoglanis akin) and 1.654 (Periophthalmus barbarus) with a mean of 1.087 (s.d.=0.520). The maximum weight of populations examined did not significantly influence the relative magnitude of b. The parameters proportional to and beta of the linear weight-fecundity relationship (F= proportional to + beta W) are also presented for 27 fish populations from 22 species. Estimates of beta ranged from 4.22 (Chromidotilapia guntheri) to 2,062.94 (Pellunula min), with a mean of 243.80 (s.d.=477.89). The magnitude of beta declined with increasing maximum weights of fishes examined.

Length-weight relationship of marine fish species off Sao Sebastiao system, Sao Paulo, Southeastern Brazil

The parameters a and b of the length-weight relationship of the form W = a . L super(b) were estimated for 57 fish species sampled in Sao Sebastiao Channel and shelf system in 1997, Sao Paulo, Brazil. The b values ranged from 2.746 to 3.617. The Student's t-test revealed that mot (44) species had b values significantly different from 3. A normal distribution of the calculated LWR exponents (b) was obtained.

Updating names, distribution and ecology of riverine fish of Kenya in the Athi-Galana-Sabaki river drainage system

Few studies of the riverine fish of the Athi-Galana-Sabaki river drainage area in Kenya have been carried out since the last comprehensive surveys of the 1950s and early 1960s. This paper presents updated information on scientific and recommended common names, distribution and ecology of selected fish species of this catchment. At least 28 riverine fish families consisting of 46 genera and 62 species occur in the drainage system, of which, 39 species are strictly freshwater (4 introduced) while 23 species are of marine origin. Five unique behavioural categories of the riverine fish of the drainage system are discussed. The four most speciated riverine fish in the system belong to the families Cyprinidae (14 species), Cichlidae (6 species), and Mormyridae and Gobiidae (4 species each). Thirty fish species occur in areas below the River Tsavo-Athi confluence, 18 fish species above the confluence, while 12 fish species occupy the entire drainage system. One cichlid fish, Oreochromis spilurus spilurus (Gunther, 1894), only occurs in the Tsavo river, while the occurrence in the entire system of one snoutfish species, Mormyprops anguilloides (Linnaeus, 1758) is uncertain. The use of information from this study is recommended when carrying out further studies of fish from the Athi-Galana-Sabaki river drainage.