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Most species of Keratella possess dome-shaped, dorsal plates comprising a network of polyhedral units (facets), delineated by slightly raised ridges. The arrangement of facets define a species' facet pattern (FP), with the resulting structure resembling a geodesic dome. Researchers have sorted species into categories based on their FPs, but those have not been analyzed. Additionally, while a strong lorica has been suggested to protect Keratella from predatory attack or other actions causing blunt force trauma (BFT), we know little of how that occurs. Thus, in our study we tested two hypotheses. (1) There is support for categorizing Keratella species into unique groupings based on their FPs. (2) FPs provide resistance to physical stresses. To test that hypothesis we used the structural analysis software SkyCiv©. Our results indicate support for four FP categories. Additionally, the SkyCiv analysis provided preliminary 'proof-of-concept' that Keratella FPs have a functional significance: i.e., adding or subtracting facets in our model was followed by a change in predicted structural reliability. We posit that FPs are adaptations protecting Keratella from fractures to the lorica that may result from BFT incurred during predatory attack by copepods or while caught within the branchial chambers of daphnids. [ABSTRACT FROM AUTHOR]

The human-mediated transfers of tilapia for aquaculture as a panacea for food insecurity in Africa have led to unprecedented and irreversible impacts on native ichthyofaunal biodiversity. Though aquaculture has been pointed to as the main gateway to species introductions in the Pangani system, formal documentation on how it has contributed to such colonization is anecdotal. The present study aimed to genetically identify, update the list of introduced tilapia taxa, and authenticate if aquaculture is the main gateway to their widespread. We genetically identified non-native tilapias from the Pangani Catchment and aquaculture facilities by genotyping partial Mitochondrial DNA Control region. Molecular analyses depicted the Pangani Catchment to be exclusively inhabited by six non-native tilapiine taxa, particularly Oreochromis niloticus, Oreochromis leucostictus, Coptodon rendalli, Oreochromis esculentus, Oreochromis spilurus, and Oreochromis urolepis hornorum. Oreochromis niloticus, O. leucostictus, and C. rendalli were also predominant in aquaculture and shared haplotypes with their counterparts from the Pangani Catchment. We identified commercial strains of O. niloticus that also shared haplotypes between the two systems. Such haplotype sharing proves aquaculture is the gateway to introducing non-native tilapias into the Pangani Catchment. Thus, fish farming in the region should adhere to regional and international legislation to prevent future spillage. [ABSTRACT FROM AUTHOR]

The tribe Hemichromini is an early diverging, mainly Central and West African lineage within the species-rich African cichlid fishes (Cichliformes, Cichlidae) including two genera, Hemichromis Peters 1858 and the monotypic Anomalochromis Greenwood 1985. Though many of the species are popular aquarium fish, the number of hemichromine species is still a matter of debate with their phylogenetic relationships largely unknown. Based on DNA sequence data of two mitochondrial and two nuclear genes, we present the first comprehensive phylogeny of the Hemichromini. Using an integrative approach based on these DNA sequences data, morphometrics, meristics, and a qualitative assessment of body coloration, we revise the genus Hemichromis and discuss intrageneric relationships. Two major groups within the genus Hemichromis that diverged roughly 6–12 MYA are recognized, of which the first one represents Hemichromis sensu stricto, for the second one a new genus, Rubricatochromis, is described. Diversification with these two main groups started about 3–6 MYA, with different trajectories of colonization in the two groups. Hemichromis populations from the most southern (Cuanza, Zambezi, and Okavango) part of the genus' distribution range constitute a well-supported clade distinct from all other members of Hemichromis, for which the taxon H. angolensis Steindachner, 1865 is confirmed. [ABSTRACT FROM AUTHOR]

Available ecological information, an extensive distributional range, conflicting osteological data, and a proposed early Miocene origin provide the impetus for the present study which investigates genetic structuring, biogeographic, and phylogenetic relationships within the Aplocheilichthys spilauchen lineage. Through the analysis of the mitochondrial gene COI, species delimitation methods (ABGD, GB, GMYC, bPTP) were applied, recognizing 6–7 OTUs with absolute pairwise genetic distances ranging between 8 and 22%. The onset of diversification is estimated to be within the middle Miocene and both dispersal and vicariance-shaped A. spilauchen diversity and distribution, as suggested by time-calibrated and ancestral range reconstruction (S-DIVA) analyses. We report for the first time, a pattern of diversification within a lineage of brackish water fish that is concordant with the historical distribution of coastal mangroves forests, shaped by a series of historical events that likely affected forest cover since the middle Miocene (e.g. major climate shifts and sea-level fluctuations, onset of the modern Congo River outlet, increased volcanism in the Cameroon Volcanic Line). [ABSTRACT FROM AUTHOR]

Beaver impoundments modify the structure of river reaches and lead to changes in ecosystem function and biogeochemical processes. Here, we assessed the changes in dissolved organic matter (DOM) quality and the biodegradation patterns in a set of beaver systems across Sweden. As the effect of beaver impoundments might be transient and local, we compared DOM quality and biodegradability of both pond and upstream sections of differentially aged beaver systems. Newly established dams shifted the sources and DOM biodegradability patterns. In particular, humic-like DOM, most likely leached from surrounding soils, characterized upstream sections of new beaver impoundments. In contrast, autochthonous and processed compounds, with both higher biodegradation rates and a broader spectrum of reactivities, differentiated DOM in ponds. DOM in recently established ponds seemed to be more humic and less processed compared to older ponds, but system idiosyncrasies determined by catchment particularities influenced this ageing effect. [ABSTRACT FROM AUTHOR]

We evaluated the statistical models that best describe the selectivity of common fishing gears used in Lake Koka for four freshwater species widely distributed in Ethiopia and elsewhere: tilapia Oreochromis niloticus (L.), catfish Clarias gariepinus (B.), common carp Cyprinus carpio (L.), and barb Labeobarbus intermedius (R.). Sampling was conducted from October 2012 to March 2013 using gillnets (60, 80, 100, and 120 mm stretched mesh), longlines (4/0, 6/0, and 8/0 hooks size), and a beach seine with covered codend. Size at maturity ( L) was determined for each species. The SELECT method was used to explore unimodal selectivity models for gillnet and longline gears, while the logistic function was used for beach seine. Results show that a log-normal model best described gillnet selectivity for all species, while a normal scale model best described longline selectivity for C. gariepinus. Gillnets with ≥100 mm mesh and longlines with >4/0 hooks could be safely used, as they allow target resources to attain L before becoming vulnerable to fishing. The mesh size of the beach seine needs to be enlarged, as the estimated length of capture was much smaller than all L values. The results have important management implications for protecting juveniles and mega-spawners of the studied species in Lake Koka and beyond. [ABSTRACT FROM AUTHOR]

Aquatic food webs are supported by primary production from within the system (autochthony) as well as organic matter produced outside of and transported into the system (allochthony). Zooplankton use allochthonous resources, especially in systems with high terrestrial loading and moderate to low internal primary production. We hypothesized that due to high terrestrial loads and remnant submerged terrestrial material, allochthonous resource use by zooplankton would be significant in all reservoirs and would decline along an increasing reservoir age gradient. Using hydrogen stable isotopes and a Bayesian mixing model, we estimated the contribution of allochthonous sources to organic matter pools and crustaceous zooplankton biomass for ten reservoirs. Dissolved organic matter (DOM) in all systems was dominated by allochthonous sources (posterior distribution median >92% allochthonous), while particulate organic matter (POM) composition varied (2-68% allochthonous) and had a lower allochthonous fraction in older reservoirs. There was no relationship between zooplankton allochthony and reservoir age. Crustaceous zooplankton allochthony varied among systems from 26 to 94%, and Chaoborus allochthony, measured in four reservoirs, was similarly variable (33-94%). Consumer allochthony was higher than POM allochthony in some reservoirs, potentially due to terrestrial DOM pathways being important and/or algal resources being inedible (e.g., cyanobacteria). As with many lakes, in the reservoirs we studied, allochthonous inputs account for a significant fraction of the organic matter of basal consumers. [ABSTRACT FROM AUTHOR]

Intra-specific morphological variation in the cichlid Tropheus duboisi from 10 localities over its entire known distribution area along the central eastern and northern shore of Lake Tanganyika was investigated. This revealed significant differences between various populations that are geographically isolated. These morphological observations only partially correspond to the results of a haplotype network, based on mtDNA. In addition, a difference in the timing of the onset of the adult colour pattern was discovered for one isolated population. The occurrence of morphological intra-specific differentiation is discussed with respect to the basal position of T. duboisi within Tropheus as well as to the presumed morphological stasis of the genus. [ABSTRACT FROM AUTHOR]

Phytoplankton is widely recognized as being regulated mainly by resources (nutrients and light) and predation by higher trophic levels. In reservoirs, these controls also can be modulated by hydrology, for example through the influence of flow pulses generated by the operation of the dam. In this study, we tested the influence of light, nutrients, and zooplankton grazing pressure, and also hydrology (as water residence time) on the phytoplankton biomass in eight tropical hydroelectric reservoirs, which differ in size, morphometry, location, trophic state, and water residence time. Our hypothesis was that, as these reservoirs are used for hydroelectric purposes, the control that would otherwise be exerted on phytoplankton biomass primarily by resource availability and grazing will also be modulated by hydrology. Low phytoplankton biomass (range of system medians = 12-299 μg C l) occurred in most systems, except for one highly eutrophic reservoir (median = 1331 μg C l). Our data showed that phosphorus was more often likely to be the limiting nutrient in these systems, as assessed through nutrient limitation indexes (nitrogen and phosphorus), based on concentrations and ratios. For most reservoirs, excluding the eutrophic system with high cyanobacteria biomass, seasonal water residence time was the variable that best explained phytoplankton variation among the several environmental variables analyzed in this study ( P < 0.0001; adjusted r = 0.38). Hydrology was an important and additional factor modulating phytoplankton in these tropical reservoirs, directly removing phytoplankton populations and their potential zooplankton grazers by washout, and also affecting nutrient availability. [ABSTRACT FROM AUTHOR]

Haplochromine cichlids form the most species-rich lineage of cichlid fishes that both colonized almost all river systems in Africa and radiated to species flocks in several East African lakes. The enormous diversity of lakes is contrasted by a relatively poor albeit biogeographically clearly structured species diversity in rivers. The present study analyzed the genetic structure and phylogeographic history of species and populations of the genusPseudocrenilabrusin Zambian rivers that span two major African drainage systems, the Congo- and the Zambezi-system. The mtDNA phylogeny identifies four major lineages, three of which occur in the Congo-system and one in the Zambezi system. Two of the Congo-clades (Lake Mweru and Lunzua River) comprise distinct albeit yet undescribed species, while the fish of the third Congo-drainage clade (Chambeshi River and Bangweulu swamps), together with the fish of the Zambezi clade (Zambezi and Kafue River) are assigned toPseudocrenilabrus philander. Concerning the intraspecific genetic diversity observed in the sampled rivers, most populations are highly uniform in comparison to lacustrine haplochromines, suggesting severe founder effects and/or bottlenecking during their history. Two bursts of diversification are reflected in the structure of the linearized tree. The first locates at about 3.9% mean sequence divergence and points to an almost simultaneous colonization of the sampled river systems. Subsequent regional diversification (with about 1% mean sequence divergence) occurred contemporaneously within the Kafue River and the Zambezi River. The clear-cut genetic biogeographic structure points to the dominance of geographic speciation in this lineage of riverine cichlid fishes, contrasting the importance ofin situdiversification observed in lake cichlids. [ABSTRACT FROM AUTHOR]

Phylogenetic relationships among four genera and nine species (Mugil cephalus,Mugil soiuy,Liza ramada,Liza aurata,Liza abu,Liza saliens,Liza carinata,Chelon labrosus,Oedalechilus labeo) of the Mediterranean mullets (Mugilidae) were investigated by means of allozyme electrophoresis using a seven-enzyme system (CK*,GAPDH*,G3PDH*,IDHP*,ME*,MDH*,PGM*) comprising eleven putative loci. The highest genetic divergence was 1.299, detected betweenM. cephalusandL. aurataand the lowest (0.280) was found betweenL. carinataandL. saliens. The amount of genetic divergence between the generaChelonandOedalechilusdid not appear to be high (0.285). In a UPGMA tree, all nine species were grouped in two main branchings. In the first branch,C. labrosusandO. labeoclustered as closest taxa and were sister group toL. ramada. The other fourLizaspecies produced two sub-branching in this group;L. carinatabranched together withL. saliens, andL. auratabranched together withL. abu. In the second branch the two species of the genus Mugil,M. cephalusandM. soiuy, clustered together and were clearly isolated from the other three genera. [ABSTRACT FROM AUTHOR]

The diet of the brackish water tilapia Sarotherodon melanotheron is studied in various riverine and lacustrine systems of the Bia River basin (Côte d'Ivoire). Comparison of the diet between sampling sites (upper course, lower course and man-made Lake Ayame) shows significant differences. In the man-made lake, prey described as preferential include Asterionella (Bacillariophyceae) and Bosmina (Cladocera). In the lower course, the preferential preys are represented by Lyngbya (Cyanophyceae) while in the upper course Lyngbya and chironomid larvae are preferential. These differences are related to the altered environmental conditions generated by the construction of the dam on the Bia river main stream. In the man-made lake, there is no shift in diet either with the seasons (dry and rainy seasons) or with size. [ABSTRACT FROM AUTHOR]

Examines the role of tubifex tubifex in the food chain transfer of hexachlorobenzene from contaminated sediment to fish. Link provided by some tubificid species in the food chain transfer; Details of the laboratory procedure used for the measurement of biomagnification; Risks posed by sediments contaminated with poorly water-soluble organic chemicals to aquatic food chains.

The diet of 223 specimens of Mormyrus rume (Mormyridae) from the BiaRiver on which a hydro-electric dam was built in 1959, was studied in relation to locality, season and fish size. A feeding index was computed by combining the occurrence, numerical and weight percentages of the items identified in the stomach contents. This index showed that M. rume in the river ate principally invertebrates, especially chironomid larvae. In contrast, M. rume from the man-made lake contained mostly phytoplankton. This difference was statistically significant. In the lake, chironomid larvae and Bacillariophyceae constituted the main source of the diet of young fish. In larger specimens, Chaoborussp. formed the main part of the diet. No significant temporal variation occurred in the dietary composition. The overall food compositionwas similar in each locality of the Bia River from one period to another. [ABSTRACT FROM AUTHOR]