Organochlorine residues in fish from Lake Victoria, Kenya

Eighty-two samples of either nile perch fish fat or muscle were collected from the Kenyan region of Lake Victoria for detection of organochlorine residues. Nine organochlorine residues were detected in the following percentages: α-BHCIHCB-40%; P-BHC/HCB-40%; y-BHC/HCB/lindane-4%; aldrin-9%; dieldrin-1%; p, p'-DDE-73%; p, p'-DDD-9%; o, p'-DDT-170; and p, p'-DDT-11%. All levels of organochlorine residues were below the Extraneous Residue Limit (ERL), apart from just one sample of fish fat which had 4.51 ppm of sum DDT above ERL. There was a higher level of organochlorines from Mbita than from Luanda fishing point.

Résumé

Eighty-two échantillons de graisse ou de muscle de perche du Nil ont été récoltés dans la région kényane du lac Victoria pour rechercher des résidus organochlorés. On a détecté 9 résidus organochlorés, avec les pourcentages suivants: α-BHC/HCB-40%; β-BHC/HCB-40%;γ-BHC/HCB/lindane-4%;aldrine-9%; dieldrine-1%; p, p'-DDE-73%; p, p'-DDD-9%; o, p'-DDT-1%; and p, p'-DDT-11%. Tous les taux de résidus organochlorés ktaient infkrieurs a la 'Extraneous Residue Limit' (ERL) sauf pour un seul échantillon de graisse de poisson qui contenait 4,51 ppm de DDT total au-dessus de 1'ERL. I1 y avait un taux plus élevé d'organochlorés a Mbita qu'au point de pêche de Luanda.     

Population genomic tests of models of adaptive radiation in Lake Victoria region cichlid fish

Adaptive radiation is usually thought to be associated with speciation, but the evolution of intraspecific polymorphisms without speciation is also possible. The radiation of cichlid fish in Lake Victoria (LV) is perhaps the most impressive example of a recent rapid adaptive radiation, with 600+ very young species. Key questions about its origin remain poorly characterized, such as the importance of speciation versus polymorphism, whether species persist on evolutionary time scales, and if speciation happens more commonly in small isolated or in large connected populations. We used 320 individuals from 105 putative species from Lakes Victoria, Edward, Kivu, Albert, Nabugabo and Saka, in a radiation-wide amplified fragment length polymorphism (AFLP) genome scan to address some of these questions. We demonstrate pervasive signatures of speciation supporting the classical model of adaptive radiation associated with speciation. A positive relationship between the age of lakes and the average genomic differentiation of their species, and a significant fraction of molecular variance explained by above-species level taxonomy suggest the persistence of species on evolutionary time scales, with radiation through sequential speciation rather than a single starburst. Finally the large gene diversity retained from colonization to individual species in every radiation suggests large effective population sizes and makes speciation in small geographical isolates unlikely.     

Mechanisms and evolution of hypoxia tolerance in fish

The ability of an organism to acquire O(2) from its environment is key to survival and can play an important role in dictating a species' ecological distribution. This study is the first, to our knowledge, to show a tight, phylogenetically independent correlation between hypoxia tolerance, traits involved in dictating O(2) extraction capacity and the distribution of a group of closely related fish species, sculpins from the family Cottidae, along the nearshore marine environment. Sculpins with higher hypoxia tolerance, measured as low critical O(2) tensions (P(crit)), inhabit the O2 variable intertidal zones, while species with lower hypoxia tolerance inhabit the more O(2) stable subtidal zone or freshwater. Hypoxia tolerance is phylogenetically independently associated with an enhanced O(2) extraction capacity, with three principal components accounting for 75 per cent of the variation in P(crit): routine O(2) consumption rate; mass-specific gill surface area; and whole blood haemoglobin (Hb)- O(2)-binding affinity (P(50)). Variation in whole blood Hb-O(2)P(50) is strongly correlated with the intrinsic O(2)-binding properties of the purified Hb while the differences in the concentration of the allosteric Hb modulators, ATP and GTP, provide a Hb system with substantial plasticity for survival in a highly O(2) variable environment.     

Massive fish kills within the Nyanza Gulf of Lake Victoria,Kenya

The morphometry and hydrology of the Nyanza Gulf of Lake Victoria can be greatly affected by violent storms. This can result in a condition in which nutrient-rich bottom mud is mixed with the sediment-laden runoff water from neighbouring marshes and rivers. This situation can lead to massive fish kills. It is such an event in 1984 which will be described that caused the sudden death of over 400 000 fish weighing over 2400 tonnes.The unusually low precipitation in the catchment area during that year resulted in a drop in the lake level from 12.4 to 11.8 m. This low water level, combined with a severe storm created the conditions which caused this large fish kill. The species affected were Lates niloticus and Oreochromis niloticus. Mortality was attributed to several factors which included high levels of suspended material in the water column (detritus and algae) which clogged the gills of the fish, low dissolved oxygen, low pH, and high concentrations of algae.     

Trade-off between thermal sensitivity,hypoxia tolerance and growth in fish

One outcome of contemporary climate trends is that the involvement of hypoxia and heat tolerance in determining individual fitness will increase in many fish populations. Large fish are believed to be more tolerant to hypoxia than small fish (Nilsson and Östlund-Nilsson, 2008) whereas thermal sensitivity is thought to decrease with body size (Clark et al., 2008). To better understand the bases of inter-individual variation in environmental adaptation performance, the current study examined hypoxia and heat tolerance in a fast growing (FGS; 288.3 ±14.4 g, 26.04±0.49 cm) and a slow growing (SGS; 119.95±6.41 g; 20.98±0.41 cm) strain of 1-year old rainbow trout (Oncorhynchus mykiss). This examination was conducted using two standardized challenge tests aimed at assessing individual incipient lethal oxygen saturation and incipient upper lethal temperature. Results to these tests were then cross-correlated with swim tests during which individual basal and active metabolic rate values were also measured. Measurements of permeabilized ventricular myofibers oxygen consumption were also conducted, as well as various organ-to-body-mass ratios. Experimental data showed that FGS was more hypoxia tolerant than SGS (13.4 to 16.7% air sat versus 14.7 to 18.9% air sat respectively). On the other hand, FGS was found less tolerant to heat than SGS (24.7–27.6 °C versus 28.5 to 29.7 °C respectively). Adding to the body size effect, another source of inter-individual variation in environmental tolerance was found. Residual analysis highlighted that whereas none of the individual morphometric and energetic traits correlated with hypoxia tolerance, permeabilized ventricular myofibers maximal oxygen consumption correlated well with individual tolerance to heat.     

Population-structure and genetic diversity in a haplochromine cichlid fish [corrected] of a satellite lake of Lake Victoria

The approximately 500 species of the cichlid fish species flock of Lake Victoria, East Africa, have evolved in a record-setting 100,000 years and represent one of the largest adaptive radiations. We examined the population structure of the endangered cichlid species Xystichromis phytophagus from Lake Kanyaboli, a satellite lake to Lake Victoria in the Kenyan Yala wetlands. Two sets of molecular markers were analysed--sequences of the mitochondrial control region as well as six microsatellite loci--and revealed surprisingly high levels of genetic variability in this species. Mitochondrial DNA sequences failed to detect population structuring among the three sample populations. A model-based population assignment test based on microsatellite data revealed that the three populations most probably aggregate into a larger panmictic population. However, values of population pairwise FST indicated moderate levels of genetic differentiation for one population. Eleven distinct mitochondrial haplotypes were found among 205 specimens of X. phytophagus, a relatively high number compared to the total number of 54 haplotypes that were recovered from hundreds of specimens of the entire cichlid species flock of Lake Victoria. Most of the X. phytophagus mitochondrial DNA haplotypes were absent from the main Lake Victoria, corroborating the putative importance of satellite lakes as refugia for haplochromine cichlids that went extinct from the main lake in the last decades and possibly during the Late Pleistocene desiccation of Lake Victoria.     

Water circulation and fish larvae recruitment in papyrus wetlands,Rubondo Island,Lake Victoria

A field study was undertaken of the hydrodynamics, water quality and adult and larval fish abundance in papyrus wetlands and surrounding coastal waters at Rubondo Island, Lake Victoria. Because they were exposed to the prevailing wind, the two bays facing east had small (0.01 km²) wetlands and were well flushed, with minimal accumulation of organic detritus and little oxygen depletion. Because it faced west, the third bay, Mlaga Bay, was sheltered and poorly flushed; organic matter accumulated in a large (1.41 km²) papyrus wetland. The rises and falls of the lake level at decadal time scales, may, by drowning or drying out wetlands, contribute significantly to storing organic matter as detritus. Vegetation decay in the wetlands, as well as primary production, resulted in large diurnal fluctuations of pH and dissolved oxygen concentration. Shading in daytime and cooling at night, cooled the wetlands water sufficiently to generate a baroclinic circulation whereby cold, wetland water sank and moved offshore in the lake while warm, lake water intruded in the wetlands near the surface. This flushing prevented the occurrence of anoxic conditions in the wetlands which were used by adult and larval fish, mainly tilapia, and freshwater shrimps (Caridina nilotica). No fish larvae were found at more than 150 m from the shore in the three bays. Both larval fish and Caridina nilotica appeared to move in and out of the wetlands at night, possibly as a result of low dissolved oxygen as well as sheltering from predation. Their abundance varied with the lunar phase, with maximum near new moon and first quarter. Being the only protected wetlands in Lake Victoria, Rubondo Island may increasingly become an important source of replenishment for fisheries in the lake which elsewhere appears overfished.     

Parasite-mediated sexual selection and species divergence in Lake Victoria cichlid fish

We investigate the role of parasite-mediated sexual selection in the divergence of two species of Lake Victoria cichlids. Pundamilia pundamilia and Pundamilia nyererei represent a common pattern of male nuptial colour divergence between haplochromine sister species: metallic grey–blue in P. pundamilia and bright yellow and red in P. nyererei . Female mating preferences for different male colours maintain the genetic and phenotypic differentiation of the two species in clear water. Previous work indicated that the red coloration of P. nyererei males, which is subject to directional sexual selection, may be a carotenoid-dependent signal of parasite infestation rate. In the present study, we find a parallel result for P. pundamilia : bright blue males are infected with fewer species of parasites. We also find that parasite infestation rates differ quantitatively between the two species in a way that is consistent with species differences in diet and microhabitat. We conclude that parasite-mediated sexual selection may have contributed to the divergence of female mating preferences between P. pundamilia and P. nyererei , and may currently strengthen reproductive isolation between these species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94 , 53–60.     

Nitrogenase activity in the papyrus swamps of Lake Naivasha,Kenya

Nitrogenase activity (acetylene reduction activity) was found to occur universally in the Cyperus papyrus swamp in Lake Naivasha. Low rates of acetylene reduction activity (0.9–104.9 nmol C₂H₄ g d.wt. roots^-1 h^-1) were associated with excised roots of C. papyrus but higher rates of activity (89.0–280.4 nmol C₂H₄ g d.wt. roots^-1 h^-1) were associated with intact root systems of the plant. It was estimated that nitrogen fixation associated with young roots alone could supply about 26% of the nitrogen requirements of growing papyrus plants. Acetylene reduction activity in the lake bottom sediments was generally low and associated with adjacent papyrus stands. Plate counts of putative aerobic and facultatively anaerobic N₂-fixing bacteria associated with papyrus roots showed the presence of high numbers of diazotrophs (5.4 × 10⁶ CFU g d.wt. roots^-1). Fewer numbers of N₂-fixing bacteria were detected in the sediments (1.9 × 10³-3.2 × 10⁴ CFU g d.wt. sediment^-1).     

太湖鱼类群落结构及多样性

为了解太湖鱼类群落结构和多样性的分布特征,于2009-2010年利用拖网等网具对该水域的鱼类资源进行了调查.结果表明:本次调查共采获鱼类50种,隶属10目15科40属,其中鲤形目种类最多,占总数的68％;鱼类生态类型以湖泊定居性种类为主,群落优势种为湖鲚(Coilia ectenes taihuensis)、间下鱵(Hyporhamphus intermedius)和陈氏短吻银鱼(Salangichthys jordani)等小型鱼类;与历史资料相比,太湖鱼类的物种数量下降,优势种组成发生较大变化,鱼类群落中体质量＜30 g的小型鱼类占绝对优势,渔业资源小型化趋势明显.由于过度捕捞和湖泊环境恶化,鱼类群落生物多样性指数均表现偏低,物种丰富度指数D为1.54,多样性指数H’N、H’w分别为0.21和0.46,均匀度指数J'N、.J'w分别为0.07和0.14;太湖各湖区间鱼类种群和多样性的差别一定程度上反映出鱼类群落结构与湖泊营养盐、透明度等环境特征相适应的特点.     

Fitness correlates of male coloration in a Lake Victoria cichlid fish

Sexual selection by female choice has contributed to the rapidevolution of phenotypic diversity in the cichlid fish speciesflocks of East Africa. Yet, very little is known about the ecologicalmechanisms that drive the evolution of female mating preferences.We studied fitness correlates of male nuptial coloration ina member of a diverse Lake Victoria cichlid lineage, Pundamilianyererei. In this species, male red coloration is subject tointraspecific sexual selection by female mate choice. Male nuptialcoloration plays a critical role also in reproductive isolationbetween this species and the closely related sympatric speciesP. pundamilia. Here, we show that P. nyererei male colorationis carotenoid based, illustrating the potential for honest signalingof individual quality. In a wild population, we found that variationin male coloration was not associated with variation in a setof strongly intercorrelated indicators of male dominance: malesize, territory size, and territory location. Instead, the 2male characters that predominantly determine female choice,territory size and red coloration, may be independent predictorsof male quality: males with bright red coloration and largeterritories had lower parasite infestation rates. As a result,female preferences tended to select against heavily parasitizedmales. Consistent with parasite-mediated sexual selection, maleshad higher and more variable parasite loads than females.     

PERMANENT GENETIC RESOURCES: Isolation and characterization of microsatellite loci in the cichlid fish in Lake Victoria, Haplochromis chilotes

Twelve short tandem repeat markers were successfully isolated from a cichlid, Haplochromis chilotes, in Lake Victoria, and characterized in Haplochromis pyrrhocephalus. The microsatellite regions of these markers were found to have between two and 48 alleles with heterozygosity ranging from 0.07 to 0.97. No loci showed significant departures from the Hardy–Weinberg or linkage equilibrium after the Bonferroni correction (P > 0.05). Cross‐species amplification in other cichlids of Lake Victoria, Haplochromis laparogramma, Lithochromis rubripinnis, L. rufus and Haplochromis sp. ‘rockkribensis’, was successful.     

Papyrus swamps, hypoxia, and faunal diversification: variation among populations of Barbus neumayeri

To test whether patches of papyrus swamp contribute to diversification of populations of non-air-breathing fishes, the gill morphology of Barbus neumayeri was compared between a papyrus swamp and several tributaries which differed in oxygen regime. Total gill filament length differed among sites and was negatively related to dissolved oxygen availability, supporting strong selection pressure for low-oxygen tolerance in the swamp interior. Among recaptures of marked B. neumayeri over a 4·5-year period among the focal swamp and connected stream and river sites, 93% of fish were recovered at the site of capture. Some of the individuals that moved crossed physicochemical gradients and traversed long distances within the swamp/stream system. This movement rate would theoretically be sufficient to homogenize gene frequencies among populations. However, randomly amplified polymorphic DNA (RAPD) markers indicated significant genetic differentiation among sites and no relationship between genetic differences and geographical distances among sites suggesting habitat-specific selection pressures on dispersers, rather than insufficient dispersal.     

Difference in the hypoxia tolerance of the round crucian carp and largemouth bass: implications for physiological refugia in the macrophyte zone

The hypoxia tolerance of larval and juvenile round crucian carp, Carassius auratus grandoculis, and largemouth bass, Micropterus salmoides, was determined using respirometry to examine the potential of hypoxic areas in the macrophyte zone as physiological refugia for round crucian carp. The tolerance, which was measured as the critical oxygen concentration (Pc), was 1.32 mg O₂/l in the round crucian carp and 1.93 mg O₂/l in the largemouth bass. As the round crucian carp tolerated hypoxia better than the largemouth bass, hypoxic areas in the macrophyte zone might function as physiological refugia for round crucian carp.     

罗霄山脉地区鱼类物种多样性

罗霄山脉是赣江和修水流域与湘江流域的分水岭, 是中国生物多样性保护的关键地区之一。然而, 罗霄山脉地区的鱼类缺乏系统性的研究, 其鱼类物种组成、分布以及受威胁因素尚不清楚。为此, 我们于2014-2018年对罗霄山脉地区11条河流的鱼类进行了系统的调查。结果表明, 该地区共有鱼类5目17科64属113种, 山脉东坡鱼类108种, 高于西坡的72种。从生态类型看, 罗霄山脉鱼类以肉食性、底栖性、定居性类群为主。区系组成上以东亚江河平原类群为主。从物种多样性看, 遂川江、袁水、蜀水和修河的鱼类物种多样性较高, 锦江和富水的鱼类物种多样性较低; β多样性指数揭示遂川江与锦江、禾水、富水间鱼类物种出现一定的分化现象。     

Anthropogenically induced fish diversity reduction in Lake Valencia Basin, Venezuela

Lake Valencia in north central Venezuela, one of the largest natural inland bodies of water north of the equator, is undergoing a very rapid deterioration process as a consequence of anthropogenically induced changes. At the Ichthyology Laboratory of Instituto de Zoología Tropical, we have been studying the fishes of the northern tributaries of Lake Valencia since the early 1990's. As a result of collections made in seven northern tributaries of the basin from 1990 to 1993, we have identified 15 species of fish in 6 families. Comparison of our results with those of several authors who have collected in the area since the 1920's, indicate a 59.5%decrease in fish diversity in a 30 year span. The Lake Valencia region has undergone a rapid, considerable industrial and urban growth in recent years. This rapid increment in population size has produced a vast contamination of the lake and its tributaries by activities associated with a growing population. This study will contribute to the understanding of the biodiversity of the region by recording changes in the characteristics of the ichthyofauna in a highly modified environment.     

Gastropod diversity,distribution and abundance in habitats with and without anthropogenic disturbances in Lake Victoria,Kenya

We investigated freshwater gastropod diversity, abundance and distribution in habitats with and without anthropogenic disturbance in two localities, Ndere in the Winam Gulf and Mbita Point, Lake Victoria, Kenya, from May 2002 to January 2004. A total of 133 984 gastropod specimens belonging to 15 species were recorded, 14 from Mbita and 12 from Ndere. Two species, Ferrissia kavirondica and Cleopatra cridlandi, which were recorded only from undisturbed habitats, could be indicators of least disturbed habitats. Water chemistry did differ between fish landing sites and undisturbed habitats at some sampling times, indicating that differences due to human impact do exist, but these are dependent on periods of calm weather. The study shows that anthropogenic disturbances cause ecological changes that can be exploited by some snail species, especially Biomphalaria choanomphala and Melanoides tuberculata, while other species may not tolerate these changes. In order to protect gastropod diversity and avoid dominance of intermediate hosts, such as B. choanomphala, a management plan for the use of these fish landing sites should be developed. This could include rules on how to dispose of fish remnants and other wastes so as to reduce local eutrophication, thereby reducing risks associated with transmission of potential snail-borne diseases.     

Microhabitat distributions and species interactions of ectoparasites on the gills of cichlid fish in Lake Victoria,Tanzania

Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other’s effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host–parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host–parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.     

Enhancing the fish production potential of Lake Victoria papyrus wetlands,Kenya, using seasonal flood-dependent ponds

We present the findings of a participatory experiment on integrated aquaculture-agriculture systems (Fingerponds) at the Lake Victoria wetlands, Kenya. Fingerponds are flood-based lacustrine or floodplain wetland fishponds. The aim of the study was to explore, within a wetland/floodplain interface environment, the potential of semi-intensive fish production to enhance the wetland fishery and protect the natural ecosystem from wide-scale, destructive encroachment. The ponds were stocked naturally by flood water. After flood recession, livestock manure was added to the ponds and the effects of manuring on water and sediment quality and fish yields were studied. Manuring had positive effects on the nitrogen, phosphorous and chlorophyll a concentrations of the pond water. Regression analysis results indicated that site, manuring and environmental and climatic variables explained 58–70% of the variation in dissolved nitrogen and phosphorous, and 71% of the variation in chorophyll a. Manuring enhanced the total phosphorus concentration in the sediment but it only had marginal effects on total nitrogen. Although the net fish yields were highly variable between sites and seasons, ranging from 402 to 1069 kg ha⁻¹, the data showed that manuring was advantageous. The duration of the culture period, site variability and manuring explained 82% of the variation in fish yields. We conclude that Fingerponds fertilized with livestock manure from abutting riparian subsistence agriculture can improve fish production, enhance food diversity and security and contribute to more efficient use of papyrus wetlands for food production. This in turn may reduce large-scale conversion of wetlands to agriculture.