Studies on the fungal infestation of five traditionally smoke-dried freshwater fish in Ago-Iwoye,Nigeria

Samples of traditionally smoke-dried Clarias gariepinus (Burchell), Chrysichthys nigrodigitatus (Lacepede), Sarotherodon galilaeus (Trewavas), Heterotis niloticus (Cuvier) and Heterobranchus bidorsalis (Geoffroy) were obtained from Oja Oba Market, Ago-Iwoye, Nigeria and examined for fungal infestation. The fish samples incubated on potato dextrose agar (PDA) for 7 days showed fungal infestation. Fungi isolated and identified included Mucor sp., Aspergillus sp., Rhizopus sp. and Fusarium sp. Six fungal species were isolated from C. nigrodigitatus, five each on C. gariepinus and H. niloticus. This revised version was published online in June 2006 with corrections to the Cover Date.     

Trophic Niche Segregation in the Nilotic Ichthyofauna of Lake Albert (Uganda, Africa)

Synopsis Nile perch, Lates niloticus, and Nile tilapia, Oreochromis niloticus, were originally transplanted from Lake Albert in western Uganda to the African Great Lakes, Lake Victoria and Lake Kyoga, where they are partially implicated in reduction of the fish species diversity. Lake Albert is facing multiple environmental changes, including declining fish species diversity, hyper-eutrophication, hypoxia, and reduced fish catches. To examine the role of Nile perch and Nile tilapia in the food web in their native Lake Albert, we estimated their diets using stable nitrogen and carbon isotopes. In Lake Albert, the tilapiine congeners (closely related species), Tilapia zillii, Oreochromis leucostictus, and Sarethorodon galilaeus, and the centropomid Nile perch congener, Lates macrophthalmus, have narrower diet breath in the presence of the native O. niloticus and L. niloticus. A computerized parameter search of dietary items for five commercially important fish species (Hydrocynus forskahlii, Bagrus bayad, L. niloticus, Alestes baremose and Brycinus nurse) was completed using a static isotopic mixing model. The outcome of the simulation for most fish species compared favorably to previously published stomach contents data for the Lake Albert fishes dating back to 1928, demonstrating agreement between stable isotope values and analyses of stomach contents. While there were some indications of changes in the diets of L. niloticus and A. baremose diets over the past 20 years in parallel with other changes in the lake, for the most part, food web structure in this lake remained stable since 1928. The Lake Albert fish assemblage provides insight into the invasion success of L. niloticus and O. niloticus.     

Fish assemblages in deep Italian subalpine lakes: history and present status with an emphasis on non-native species

We provide a comprehensive overview of the status of fish assemblages in eight Italian subalpine lakes using multiple data sources: historical records, standardised sampling and fishery catch statistics. Thirty-four fish species were recorded, twenty of which are native, seven introduced historically and another seven introduced recently. The number of fish species in individual lakes has increased by between 25 and 65% from 1855 to the present, with the increase being higher in the larger lakes. Non-native species contributed between 4.0 and 71.5% to standardised catches by numbers and between 4.8 and 65.1% by biomass. Roach Rutilus rutilus and pumpkinseed Lepomis gibbosus dominated electrofishing and benthic catches by number, while open-water catches were dominated by the coregonids European whitefish Coregonus lavaretus and gangfish Coregonus macrophthalmus. In terms of biomass, electrofishing catches were dominated by crucian carp Carassius carassius, largemouth bass Micropterus salmoides and wels catfish Silurus glanis, benthic catches were dominated by roach, European whitefish and crucian carp, and open-water catches by coregonids. Commercial fisheries are important ecosystem services provided by subalpine lakes, with their harvests now dominated by non-native species. To deliver effective biodiversity conservation and ecosystem services provision, the prioritisation of targets and interventions of management of non-native species is needed.     

Feeding rhythm in relation to changing patterns of pH in the gut of Sarotherodon galilaeus (Artedi) of Lake Kainji,Nigeria

Different sizes of Sarotherodon galilaeus of Lake Kainji were caught at different hours to determine their feeding time and feeding intensity in relation to pH. It was found that the fish fed with different intensity during the day, and there was no feeding during the night. The pH values were found to vary with the amount of food in the gut.     

Lake Kainji,Nigeria; A summary of the changes within the fish population since the impoundment of the Niger in 1968

The relative composition of the major fish families in Lake Kainji between 1974 and 1975 is analysed and compared with pre- and post-impoundment data collected by previous workers. Trends in the fishery are assessed, and it is concluded that the cichlids, particularly Sarotherodon (= Tilapia) galilaeus Artedi, are becoming the dominant commercially valuable fish. No evidence was found of a significant recovery in the formerly abundant citharinids.The value of the sampling technique is discussed and criticised in relation to under-assessment of certain species, notably S. galilaeus. The Schilbeidae were found to be one of the most numerous families in the lake but are commercially under-exploited.Department of Zoology, University of Reading     

Ichthyofaunal survey of rivers within Ewekoro cement manufacturing operational areas

A total of 298 fish specimens belonging to seven families were caught during ichthyoplanktonic survey of three rivers within the Ewekoro cement facility catchment area located in southwestern Nigeria. The highest numbers of specimens were caught from Alaguntan (37.0%) and Elebute (36.6%) rivers while 28.9% of the fish samples were collected from Itori River. The fish population and species diversity recorded in the catchment rivers were significantly lower (p < 0.05) than comparative catches from Ewekoro River located about 30 km downstream of the factory operational area. The food items ingested by the specimens across the seasons in the catchment rivers revealed obvious differences in diet with some degree of overlap in the fish trophic preferences. However, the omnivorous species dominated the catches in each of the rivers, irrespective of season. Categorization of the fish specimens based on habitat-related adaptive physiology showed that a significant number of the fish from Alaguntan and Itori Rivers have accessory respiratory organs. The four species with accessory respiratory organs were Polypterus senegalus Curv., Clarias gariepinus C. & V., Ctenopoma kingslayae Gun. and Channa obscura Smith. Of the 12 fish species recorded in the Ewekoro cement facility catchment rivers, only P. senegalus, C. gariepinus, C. obscura and Oreochromis niloticus (Trew.) are valuable food fishes in southwestern Nigeria.     

Historical and recent reductions in genetic variation of the <Emphasis Type="Italic">Sarotherodon galilaeus</Emphasis> population in the Sea of Galilee

The Sea of Galilee has great significance as a natural habitat and a freshwater source for Israel. Anthropogenic impacts have been placing significant pressure on the species inhabiting this lake, among which is Sarotherodon galilaeus, an omnivorous fish with a relatively large population and significance for commercial fishing. An alarming decline in annual catch towards 2008 suggested that this unique population might be at risk. With that in mind, we characterized the current genetic variation of this species in Israel with reference to fish from Ghana, based on D-loop and microsatellite markers. Genetic variation and differentiation were found mostly among fish from Ghanaian localities and between fish from Israel and Ghana, whereas fish from all Israeli localities had uniform and limited variation, a signature compatible with historical founder effect followed by local adaptations. Such historical processes could leave a population vulnerable as reflected in the sudden and recent population decline. Comparing genetic variation between archived 30 year-old scales and modern lake fish revealed further reduction in genetic variation coincident with the recent population decline. Thus, a recently occurring genetic bottleneck had placed this unique and isolated population at an even higher risk. We carefully discuss the events leading to the current risk status for S. galilaeus in Israel and highlight the need for vigilant monitoring and active management to support a more sustainable future for this and other fish communities in this important habitat.     

Effects of Nile perch, Lates niloticus, on functional and specific fish diversity in Uganda's Lake Kyoga system

The introduction of Nile perch, Lates niloticus, to Lake Victoria, East Africa, interacted with eutrophication to cause a reorganization of the lake's food web and the extirpation of many endemic fishes. The Lake Kyoga satellite system lies downstream from Lake Victoria. It encompasses species‐rich lakes where Nile perch are absent or very rare, and low diversity lakes where L. niloticus is abundant. In 1999 we surveyed seven lakes in the Kyoga system using experimental monofilament gill nets (1/4–1 inches variable mesh). At Boston University we assessed δ¹⁵N signatures of epaxial muscle from subsamples of the catch (n = 361). These signatures are often highly correlated with the near‐term mean realized trophic position of an individual organism. A neural network analysis of fish length, species name, trophic level, and lake of origin fish explained 94% of the sample variance in δ¹⁵N. We analysed statistical patterns in these signatures at a number of spatial scales. The relationship between trophic level and δ¹⁵N varied greatly among lakes. Higher diversity perch‐free lakes had greater variance in δ¹⁵N values and fish lengths than lower diversity Nile perch lakes, suggesting an important relationship between species diversity and functional diversity. Against expectations, lake size was negatively correlated with δ¹⁵N. Patterns in stable isotope signatures indicated that Nile perch lakes have shorter food chains than perch‐free lakes. The results throw up two management problems for the Kyoga system. Impacted lakes need to be studied to understand and ameliorate the community‐level effects of Nile perch introduction, whereas the species‐rich nonperch lakes, which harbour a large proportion of the remaining diversity of regionally endemic taxa, are in need of conservation planning.     

Use of a minifluviarium to study responses of young Sarotherodon niloticus (L) to hydrogen-ion concentrations and temperature

The reactions of O+ Sarotherodon niloticus (L) to varying pH and temperature were studied in the laboratory using a minifluviarium. S. niloticus was found to tolerate pH — values as low as 5.0 without any marked effect. At values between 3.0 and 5.0 the fish lost orientation and showed signs of hyperactivity. Below 3.0, they died shortly after removal from the test — yard.Thermal behavior was tested for values ranging between 30° and 43 °C. Young S. niloticus were observed to prefer temperatures between 30° and 36 °C and avoid higher temperatures. Temperatures above 41 °C were lethal. Larger fish (6.0 to 8.0 cm.) showed more tolerance to increasing temperatures, however, when pH was considered, there was no significant difference between the sizes studied (P > 0.05).     

Population dynamics of alien gammarid species in the River Odra estuary

During the period of 1988–2000, three alien gammarid species, i.e. Gammarus tigrinus Sexton, 1939, Pontogammarus robustoides G. O. Sars, 1894, and Dikerogammarus haemobaphes (Eichwald, 1841) were recorded in the Odra estuary. This study, the first record of G. tigrinus and P. robustoides in Poland, focuses on the distribution, abundance, and biomass as well as on population structure of the three new species found in the coastal zone of the estuary. G. tigrinus and P. robustoides were first sampled in the Szczecin Lagoon (mid-part of the estuary) in 1988. The densities of both species were high from the time they were first recorded and exceeded 10 000 ind. m^–2, while the biomass was 25 and 140 g m^–2, respectively. G.tigrinus occurred at higher densities in northern and eastern parts of the Lagoon, while P. robustoides was particularly abundant in the south-eastern part, most heavily affected by River Odra discharge. In 1999, the third gammarid, D. haemobaphes, was recorded in the southern part of the estuary. Both in 1999 and 2000, the species was found in qualitative samples (dredge collections of Dreissena polymorpha) taken from the western branch of the river. As estimated from quantitative samples, densities and biomass in the eastern branch were rather low and did not exceed 150 ind. m^–2 and 2.7 g m^–2, respectively. The Szczecin Lagoon population of G. tigrinus produces at least two generations within a year: a summer one and an overwintering one. The latter is dominated by older and larger specimens. The species may reproduce in the Lagoon from April until November.     

Collapse of the native ruffe (<Emphasis Type="Italic">Gymnocephalus cernua</Emphasis>) population in the Biesbosch lakes (the Netherlands) owing to round goby (<Emphasis Type="Italic">Neogobius melanostomus</Emphasis>) invasion

We investigated the change in benthic fish communities in three artificial lakes of the Biesbosch area in the Netherlands between two time periods: before and after the invasion of round goby (Neogobius melanostomus). Native ruffe (Gymnocephalus cernua), the dominant species in benthic gillnet and littoral beach seining catches before the invasion, almost completely disappeared in all lakes only 2 years after the invasion. We found a significant increase in 0 + perch (Perca fluviatilis) and, in some lakes, pikeperch (Sander lucioperca) abundance in gillnet catches after invasion. In the post-invasion period, the 0 + fish community was dominated by perch, and the older fish community was dominated by round goby. The species richness of 0 + fish increased in the post-invasion period owing to the invasion of gobiids. However, it did not change for older fish between periods. Our results clearly show that, owing to a similar benthic lifestyle and high niche overlap, ruffe was the only species negatively influenced by the round goby invasion. The competitive superiority of round goby over ruffe is so strong that the once-dominant species of the overall benthic fish community collapsed after only a few years of coexistence.     

Population parameters and exploitation rate of Sarotherodon galilaeus galilaeus (Cichlidae) in Lakes Doukon and Togbadji,Benin

Growth, mortality, recruitment and relative yield per recruit of Sarotherodon galilaeus galilaeus from Lakes Doukon and Togbadji were studied. Data on total length, total weight and sex were recorded on a monthly basis between January and December 2013 for S. g. galilaeus captured by local fishers. The estimated asymptotic lengths L_∞ were 26.2 and 23.6?cm for Lakes Doukon and Togbadji, respectively, while the growth rate K was 0.73 in Lake Doukon and 0.87 in Lake Togbadji. Estimates of fishing mortality, 0.27 and 0.47 y^?1 for Doukon and Togbadji, respectively, were low relative to natural mortality, 1.51 and 1.74 y^?1, respectively. Sizes at first sexual maturity were 12.8 and 13.2?cm for females and males, respectively, in Lake Doukon, and 11.5 and 12.4?cm for females and males, respectively, in Lake Togbadji. The size at first capture was estimated at 13.3 and 12.7?cm for Lakes Doukon and Togbadji, respectively, which, in the light of the size at maturity estimates, indicates that fish spawn at least once before capture. The current exploitation rates of 0.15 for Lake Doukon and 0.21 for Lake Togbadji suggest that their stocks of S. g. galilaeus are not overexploited in either lake.     

Catch efficiency of a small seine for benthic juveniles of the yellowfin goby <Emphasis Type="Italic">Acanthogobius flavimanus</Emphasis> on a tidal mudflat

Experimental hauls of a small seine for juvenile yellowfin goby, Acanthogobius flavimanus, were carried out on a tidal mudflat in the Shinhama Lagoon, central Japan, between April and June 2001. Immediately before each haul, visual censuses were conducted to evaluate whether juvenile densities estimated from the catches accurately reflected real densities in the area. The densities estimated from the net samples were significantly lower than those determined by visual censuses throughout the study period. The catch efficiency of the small seine for juveniles of ca. 17–40mm in standard length was estimated as 23–71%, a negative relationship between efficiency and fish length being found.     

A laboratory investigation of the filtration and ingestion rates of the tilapia,Oreochromis niloticus,feeding on two species of blue-green algae

Synopsis Quantitative aspects of the filter-feeding of the tilapia,Oreochromis niloticus, on two species of the blue-green algae —Anabaena cylindrica andMicrocystis aeruginosa — were investigated in the laboratory. The ingestion rate of 85 mm SLO. niloticus was best fitted using a linear regression over the range of biovolume concentrations studied (3 × 10⁶ – 3 × 10⁸ m³ ml^–1). The ingestion rate of 40 mm SL fish gave a curvilinear relationship and was best fitted using a logarithmic regression. For each size class of fish, ingestion rates were higher when fed the largerAnabaena thanMicrocystis. The results of ingestion and filtration rates are comparable to work on other aquatic suspension feeders and tend to substantiate a universality in the fundamental regulatory mechanism of filter feeding.     

Freshwater bryozoans (Bryozoa) of Norway II: distribution and ecology of two species of Fredericella

Freshwater bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of the two Fredericella species was evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance and absence. The typical European Fredericella sultana (with glossy statoblasts) occurred at 72 localities, north to 70° 25 N (the northernmost record on a global scale). Its frequency dropped towards the north. Maximum elevation above sea level was 1097 m (maximum recorded for Northern Europe). Another species with pitted statoblasts, tentatively considered to be Fredericella indica, occurred at 50 localities, north to 71° 09 N (the northernmost record reported to date). The geographical distribution reflected a typical northern cold-water species. One third of the 50 records were from lakes situated north of the Arctic Circle, and rich colonies were found on the North Cape plateau, as far north as possible on the European mainland. The few records from southeastern Norway were from high mountain lakes, up to 1397 m above sea level (highest record for Europe). This species was not found in any of the numerous lowland lakes investigated in southeastern Norway where F. sultana was common. Both species tolerated a cold climate, especially Fredericella indica, and they occurred in a wide range of environments. F. sultana preferred lakes with rather low elevation above sea level, rich vegetation with plant species typical for eutrophic environments, gyttja sediments and stony "hard" shores, some wave action, high content of calcium, and slightly coloured water. This species avoided ponds and was absent from ditches and mires, avoided dystrophic lakes surrounded by Sphagnum bog, with dy sediments and strongly coloured water, avoided sites with small wave action, was indifferent to magnesium and low concentrations of calcium, and was absent from lakes with pH below 5.4. F. indica was only recorded from lakes. It preferred rather low temperatures, oligotrophic conditions with poor aquatic vegetation and stony shores, some wave action, pH above 7.0, and low water colour (below 11 mg Pt l^–1). This species avoided lakes with high temperatures and was absent above 20 °C, was absent where aquatic vegetation was rich or consisted of Sphagnum bog, avoided lakes with soft sediments of dygyttja and dy, places with small wave action, acid lakes, was absent at pH below 5.9, tended to avoid water with colour above 10 mg Pt l^–1 and was absent in lakes with colour above 40 mg Pt l^–1. F. sultana and F. indica occurred together in only six lakes, four in the north, and two in the southern mountain areas. The opposite sensitivity and reactions of the two species towards several environmental variables were supported by a logistic regression analysis. The main ecological difference between the two species is that F. indica appears to be more strongly dependent on climatic factors.     

Concurrent evolution of ancient sister lakes and sister species: the freshwater gastropod genus <Emphasis Type="Italic">Radix</Emphasis> in lakes Ohrid and Prespa

Ancient sister lakes are considered to be ancient lakes lying in close geographic proximity, sharing a related origin and significant time of co-existence, usually having hydrological connection as well as a balanced degree of faunal overlap and distinctness. A paradigm for studying sister lake relationships are the ancient lakes Ohrid and Prespa in the Balkans, which are characterized by high degrees of endemicity. Three general patterns of endemic species can be distinguished for these lakes: (1) taxa that are endemic to either lake, with no close relatives in the respective sister lake, (2) closely related but distinct endemic taxa in both lakes (sister species) and (3) shared endemic taxa occurring in both lakes. In the present paper, two endemic freshwater pulmonate gastropod species, Radix relicta (Lake Ohrid) and R. pinteri (Lake Prespa), are used to study the evolution of presumed sister species based on biogeographical and comparative DNA data from world-wide Radix taxa. Phylogenetic, phylogeographical and parametric bootstrap analyses all suggest a sister group relationship of R. relicta and R. pinteri (pattern 2 of endemic diversity). Sister to these two taxa is the widespread R. ampla, which does not occur in the vicinity of lakes Ohrid and Prespa. The southern feeder spring complexes of Lake Ohrid are inhabited by another lineage (Radix sp. 1), which resembles Radix relicta in morphology/anatomy. For Lake Prespa, the widespread R. auricularia was reported in addition to the endemic R. pinteri. Comparative phylogenetic data favour a western Adriatic zoogeographical affinity of lakes Ohrid and Prespa over an Aegean-Anatolian faunal connection. The status of lakes Ohrid and Prespa as sister lakes is evaluated in the light of current knowledge on gastropod speciation and endemism in these hotspots of biodiversity.     

Biotic and abiotic preferences of the cladoceran invader Limnosida frontosa

During the late 1980s and early 1990s, the cladoceran Limnosida frontosa invaded several lakes within its natural range in southeastern Norway. In this project, we wanted to study the types of lakes preferred by Limnosida. We also wanted to evaluate the potential competitive effects on other zooplankton species. In a survey of 65 Norwegian lakes, Limnosida showed preference for lakes of low Ca concentrations and low productivity. This is probably due to decreased competition from species with higher Ca requirements and a lower fish predation on zooplankton in these lakes compared to more productive lakes. Particle size preferences of Limnosida were studied and compared with those of the microfiltrator Daphnia magna, as there was no published information on the food preference of Limnosida.When fed monodisperse fluorescent latex beads (0.5, 1.0, 6.0 m), Limnosida strongly selected the largest beads, while D. magna had a more nonselective feeding behaviour. Mesh sizes of Limnosida's filtering appendages were 0.4–1.2 m depending on the animal size, and the particle selection was correlated with the filter mesh sizes. Limnosida should thus be considered a low efficiency grazer on bacteria and -algae. Hence, this species probably does not interfere significantly with microfiltrators like Diaphanosoma brachyurumand most daphnids. This was supported by community analysis of lakes with and without Limnosida. In general, Limnosida commonly co-occurred with a number of filter-feeding cladocerans, and we found no sign of competitive exclusion in lakes where the species has become established.     

Fishes of floodplain habitats of the Fly River system, Papua New Guinea, and changes associated with El Niño droughts and algal blooms

Biological monitoring of the Fly River system in Papua New Guinea has shown that floodplain habitats (oxbow lakes, blocked valley lakes and seasonally inundated grassed floodplain) support diverse and abundant populations of freshwater fishes. Since monitoring first commenced in the early 1980's, a total of 66 fish species representing 33 families has been sampled, with gillnets and rotenone, from a range of sites located on the floodplains of the Fly and Strickland rivers. The fish fauna was dominated by catfishes in the families Ariidae (11 species) and Plotosidae (7 species), with aquatic invertivores being the dominant feeding group. Herring species (Nematalosa spp.) were often very abundant in the oxbow lakes, forming 66% of the total catch in all the floodplain habitats. The fish communities in the oxbow lakes and blocked valley lakes were distinctly different, with several of the smaller fish species being more abundant in the blocked valley lakes, while the oxbow lakes supported more of the larger predatory species. Catches in the oxbow lakes were also generally higher and more diverse than the blocked valley lakes or grassed floodplain sites. Since the commencement of monitoring, catches from the floodplain sites have varied considerably, both spatially and temporally. Reduced catches seen at some sites are probably associated with natural climatic factors, particularly El Niño-induced droughts and algal blooms. Introduced species and increased commercial and artisanal fishing may also be affecting stocks of native fish. Fish populations were shown to recover only slowly in lakes affected by severe drought conditions, with extensive mats of floating grasses hindering fish recolonisation. Fish stocks in a lake affected by an algal bloom recovered more quickly than stocks in lakes affected by drought.     

Fishes and fisheries of Lake Nubia,Sudan

Developing lake conditions in Lake Nubia were found to offer good commercial fisheries potential. This prospect initiated fishery research since 1967.In this study, 26 fish species belonging to 10 families were recorded. Compared with previous studies the total number has decreased and some of the species that were commercially important during the early years of the lake formation, are now negligible in occurrence (Distichodus, Citharinus, Bagrus). The species widely distributed in the lake are Labeo niloticus, Lates niloticus, Sarotherodon niloticus, Hydrocynus forskallii, Alestes baremose and Eutropius niloticus. Their highest production occurs during two periods: February to May and July to September. The dominant fish species feed on different items in a balanced equilibrium with the ecological and biological conditions.     

African lakes and their fishes: conservation scenarios and suggestions

Synopsis Man has been associated with a variety of lakes throughout his evolutionary history in Africa. Lakeside dwellers have a close association with and understanding of these lakes. In the past four decades, however, overexploitation, introductions of alien fishes and the possibility of oil pollution present frightening prospects of irreversible losses and massive extinction. The development of scientific understanding of the life support processes, the ecosystems and the rich communities of these lakes has been so outpaced by exploitation and manipulations that accurate predictions regarding the future are impossible. Shallow lakes are more sensitive to physico-chemical changes caused by climatic as well as agricultural and industrial development than deep lakes, but their biotae are endowed with a resilience which facilitates recovery from major depletions to population size. In contrast, the speciose endemic cichlid faunae of deep lakes are sensitive to fishing pressure, are awkward to manage and should be regarded as representing a much smaller resource than initially imagined. The clupeids of Lake Tanganyika can sustain intensive fishing, but their introduction into other natural lakes is not recommended. Enormous changes to native faunae followed the introduction of Lates niloticus to lakes Kyoga and Victoria with dramatic consequences for the fisheries, for the socio-economic status of the region and for the maintenance of biotic diversity. Extinction of almost 300 fish species is a possible further consequence of L. niloticus predation. Intensive selective fishing for L. niloticus is being initiated, but is unlikely to resolve the problem. In the time necessary to substantially reduce L. niloticus, numerous endemic fishes may suffer extinction. A viable alternative to extinction of these species is captive propagation. Conservation of fishes by captive propagation is not a common or well documented practice. To encourage the acceptance of this conservation option a theoretical scenario in which the concepts and protocols are applied to the fishes of Lake Victoria is given. The possibility of returning rescued populations to the lake at a later date, assuming L. niloticus populations have been reduced, is also discussed. It is recommended that captive propagation should be practised to conserve species and to retain the option of returning rescued taxa. Scientists are urged to seek the funding to study tropical ecosystems so that conservation and rational development may acquire a sound foundation.