African Fish Research Articles

Diversity Matters

Basic research in neuroscience and clinical research on neurological disorders synergistically increase our understanding of the human brain. Traditionally, functional and clinical studies of the human brain were limited to postmortem histology, "natural experiments" (eg, lesions to brain areas caused by trauma or disease), and crude measures of electrical activity such as electroencephalography. More recently, the development of transcranial magnetic stimulation and rapid advances in imaging technology have greatly facilitated human brain research. In rare cases in which treating a neurological disorder involves implanting electrodes, researchers can even record the electrical activity of individual neurons. Although these approaches have led to important insights, they do not allow for a precise dissection of the underlying mechanisms by which the brain mediates perception, cognition, and behavior. Thus, neuroscientists and neurologists remain severely limited in the types of experiments they can perform on human subjects and much of our understanding of brain structure and function is based on research in animal models. In this article, I highlight the enormous potential for synergy between neuroscience and evolutionary biology. Nervous systems have been shaped by evolution, and comparative approaches take advantage of the resulting diversity to gain insight into the neural mechanisms of behavior. On the other hand, nervous systems and the behaviors and perceptions they mediate can play a fundamental role in the evolutionary processes that generate this diversity. To emphasize these points, I describe recent findings from research on African fishes that use electricity to communicate and navigate in their dark underwater world.

32 Mechanisms of Ageing and Longevity

Aging, long thought to be solely the byproduct of wear and tear, is actually a highly controlled process, regulated by a combination of genetic and environmental factors. Our overarching goals are: (1) to understand the molecular mechanisms by which known ‘longevity genes’ regulate aging in mammals; and (2) to discover novel genes and processes that control lifespan using two genetic models for aging: the nematode C. elegans and the extremely short-lived African fish N. furzeri. We are particularly interested in the aging of the nervous system. My presentation will be focused on the importance of stem cells in the brain during aging in mammals. In the nervous system, neural stem cells (NSCs) are thought to be important for learning, memory, and mood regulation. During aging, both the pool of NSCs and their ability to give rise to new neurons decline, raising the possibility that NSC depletion may underlie part of the cognitive dysfunctions during aging. However, the molecular mechanisms that regulate the maintenance of the NSC pool throughout lifespan are largely unknown. We have found that FoxO3, a member of a transcription factor family known to extend lifespan in invertebrates, maintains the NSC pool in adult mice. Analysis of the program of genes regulated by FoxO3 in NSCs suggests that FoxO3 maintains the adult NSC pool by inducing a program of genes that preserves cellular quiescence and regulates oxygen metabolism. Because NSCs are thought to be important for cognitive function and mood regulation, the ability of FoxO3 to maintain the NSC pool in adult organisms might have important implications for counteracting brain aging in long-lived species, including humans.

Relationships and biogeography of the fossil and living African snakehead fishes (Percomorpha, Channidae, Parachanna)

ABSTRACT The ability to determine relationships of Cenozoic fossil fishes relies heavily on having osteological information from their extant relatives with which to compare the fossil remains. For many higher teleost fishes, these osteological data do not exist. For example, †Parachanna fayumensis, from Eocene and Oligocene deposits of Egypt, was placed in the Recent snakehead genus Parachanna, but in the absence of data from extant members of the genus, this hypothesis could not be tested. Three other fossil channids were each given their own new genera, without an analysis of their relationships to one another or to the living genera. In order to properly test the relationships of these fossil species, the osteological information for living species is needed. This paper documents the osteology of the African snakehead, Parachanna obscura, for the first time. The documentation of the osteology forms the basis of a phylogenetic study of the relationships of the African fossil, †Parachanna fayumensis, with living African snakeheads. This study supports the generic placement of †P. fayumensis as being correct, as well as reciprocal monophyly of the two living snakehead genera and monophyly of the family. Monophyly of the Asian genus Channa and the relationships of the other fossil species need to be further assessed using a broader range of species, but this preliminary study is an essential first step. Apomorphic osteological characters are given for the family and genera, as well as a discussion of the biogeographical relationships of species of Parachanna.

Demand Elasticities for East African Fish Exports to the European Union

In this study, the authors estimate demand elasticities for East African fish exports to the European Union. Today, fish is one of the most important renewable resources in East Africa, and ranks as the region's highest nontraditional agricultural export earner. Furthermore, fish represents a vital contribution to the food and nutritional security of millions of people in the region and the sizeable export revenue it generates plays an important role in advancing the region's development strategy of increasing overall foreign exchange earning capability. In this respect, elasticity is one of the basic indicators when discussing policy impacts, but currently there are no elasticity estimates for East Africa's fish export demand to guide trade policy formulation. The results for the estimated export demand equation showed evidence of lower price and higher income elasticities, implying that, on one hand, the European Union's demand for East Africa fish is more sensitive to income changes than price changes and, on the other hand, the East African fishery industry can simultaneously reduce the rate of resource use while boosting fishery income through higher prices.

Analysis of omega-3 fatty acid content of South African fish oil supplements.

Substantial evidence describes the protective effects of marine-derived omega-3 (n-3) polyunsaturated fatty acids (PUFA) on cardiovascular diseases as well as many other conditions. Numerous fatty acid preparations are marketed for supplementing the Western diet, which is low in n-3 fats. Since these preparations may vary in their n-3 PUFA content, we tested 45 commercially available products on the South African market for their fatty acid composition. Forty-five commercially available n-3 fatty acid supplements were analysed using gas-liquid chromatography to determine their fatty acid content. More than half of the n-3 supplements available on the South African market contained ≤ 89% of the claimed content of EPA and/or DHA as stated on the product labels. To meet ISSFAL's recommendation of 500 mg EPA + DHA/day can cost consumers between R2 and R5 per person per day (R60 to R150 p/p/month). Regarding rancidity, the majority of capsules contained conjugated diene (CD) levels higher than that of vegetable oil obtained from opened containers (three months) used for domestic cooking purposes, despite the addition of vitamin E as antioxidant. Since no formal regulatory structure for dietary supplements currently exists in South Africa, consumers depend on self-regulation within the nutraceutical industry for assurance of product quality, consistency, potency and purity. Our results indicate that more than half of the n-3 fatty acid supplements on the South African market do not contain the claimed EPA and/or DHA contents as stated on product labels, and they contained CD levels higher than that in unused vegetable oils obtained from opened containers used for domestic cooking purposes.

Fishes of the Kwilu River (Kasai basin, central Africa): A list of species collected in the vicinity of Kikwit, Bandundu Province, Democratic Republic of Congo

A list of fishes collected in the vicinity of Kikwit on the Kwilu River, a large left bank tributary of the Kasai River in the Democratic Republic of Congo is provided. One hundred and thirteen species distributed in 21 families are reported, and of these 29 species are recognized as representing new records for the region. Lack of up-to-date taxonomic and distributional knowledge of African fishes, a problem particularly acute in the central Congo basin, is clearly reflected in this high number of range extensions. While preliminary, this contribution serves as a useful starting point for efforts to understand the ichthyofaunal composition and biogeographic history of the Kasai system; one of the most poorly documented river systems in central Africa.

Fatty acids of polar lipids in heart tissue are good taxonomic markers for tropical African freshwater fish

The fatty acid profiles in total, neutral and polar lipids in the heart tissues of five freshwater fish species (Nile perch Lates niloticus, Nile tilapia Oreochromis niloticus, marbled lungfish Protopterus aethiopicus, Bagrus docmak and African catfish Clarias gariepinus) from Lakes Victoria and Kyoga were determined chemometrically by methanolysis of the lipid extracts and gas chromatography of the resulting methyl esters. The analytical data were treated using multivariate principal component analysis. In neutral and polar lipids palmitic acid (16:0) and stearic acid (18:0) were the dominant saturated fatty acids. The polyunsaturated fatty acids in the polar lipid fraction ranged from 33% to 56% and in the neutral lipid fraction from 23% to 30%, dominated by arachidonic acid (20:4n6) and docosahexaenoic acid (22:6n3). The amount of cholesterol in the neutral fraction was 57–89 mg g−1 lipid. The amount of plasmalogen was 12–27 mg g−1 and 14–37 mg g−1 lipid in the polar fraction and total lipid, respectively. In the principal component plots, the fish species from the two lakes were distinguished by fatty acid profiles in neutral, polar and total lipid from the heart tissue. However, polar lipid fractions were better markers of fish species and populations than the neutral fraction and total lipids. Heart tissues have low lipid levels dominated by polar lipids (phospholipids), with polyunsaturated fatty acids as the principal components. The dominance of genetically controlled phospholipids in the heart tissue makes heart tissue most suitable for differentiating between species and populations.

Environmental Influences on South African Fish Catch: South Coast Transition

This study considers environmental factors influencing aggregate fish catch in the South Coast transition of South Africa. The environmental forcing is studied via (i) seasonal analysis of SeaWifs chlorophyll and related variables, (ii) composite analysis of atmospheric and oceanographic reanalysis data, (iii) statistical analysis of annual FAO fish catch with climatic indices, and (iv) analysis of depth-latitude hydrographic sections over the shelf (33–36S, 22–26E). In years of higher fish catch there is a northward shift of the subtropical anticyclones and upwelling that is partially related to Pacific El Nino. Westerly troughs skirt the Agulhas Bank creating onshore Ekman transport. Higher sea surface height inshore, and cooler sea temperatures and lower salinity offshore induce a gradient that weakens the Agulhas Current. These environmental conditions favour the southeastward migration of juvenile fish from west to south coast. A multivariate model of aggregate fish stocks, using four environmental variables: salinity and zonal currents in the Agulhas Current, sea temperature in the Agulhas source region, and geopotential height over the Cape, accounts for 53% of variance at 0-1 year lead. Freshening of the boundary current is a factor influencing aggregate fish catch in the South Coast transition.

Cytogenetic analysis in Polypterus ornatipinnis (Actinopterygii, Cladistia, Polypteridae) and 5S rDNA

Polypteridae is a family of archaic freshwater African fish that constitute an interesting subject for the study of the karyological evolution in vertebrates, on account of their primitive morphological characters and peculiar relationships with lower Osteichthyans. In this paper, a cytogenetic analysis on twenty specimens of both sexes of Polypterus ornatipinnis the ornate “bichir”, coming from the Congo River basin, was performed by using both classical and molecular techniques. The karyotypic formula (2n = 36; FN = 72) was composed of 26 M + 10 SM. The Alu I banding, performed to characterize heterochromatin in this species, was mainly centromeric. Both the chromosome location of the ribosomal 5S and 18S rRNA genes were examined by using Ag-NOR, classical C-banding, CMA 3 staining and FISH. CMA 3 marked all centromerical regions and showed the presence of two GC rich regions on the p arm of the chromosome pair n°1 and on the q arm of the pair n°14. Staining with Ag-NOR marked the only telomeric region of the chromosome n°1 p arm. After PCR, the 5S rDNA in this species was cloned, sequenced and analyzed . In the 665 bp 5S rDNA sequence of P.ornatipinnis, a conserved 120 bp gene region for the 5S rDNA was identified, followed by a non-transcribed variable spacer (NTS) which included simple repeats, microsatellites and a fragment of a non-LTR retrotransposon R-TEX. FISH with 5S rDNA marked the subtelomeric region of the q arm of the chromosome pair n°14, previously marked by CMA 3. FISH with 18S rDNA marked the telomeric region of the p arm of the pair n°1, previously marked both by Ag-NOR and CMA 3. The (GATA) 7 repeats marked the telomeric regions of all chromosome pairs, with the exclusion of the n°1, n°3 and n°14; hybridization with telomeric probes (TTAGGG) n showed signals at the end of all chromosomes. Karyotype evolution in Polypterus genus was finally discussed, including the new data obtained.

Growing, losing or introducing? Cage aquaculture as a vector for the introduction of non-native fish in Furnas Reservoir, Minas Gerais, Brazil

Cage aquaculture has been developed in many countries, including Brazil. This form of production, although economically productive, may cause several impacts to the environment. Considering the historical relationship between aquaculture and species introduction, our study investigated the potential of cage aquaculture in spreading non-native species into hydroelectric reservoirs. We interviewed 19 fish farmers in Furnas Reservoir, Grande River basin. All producers have grown exclusively Nile tilapia (Oreochromis niloticus), an African fish, and all producers reported the occurrence of fish escapes. Releases were mainly accidental, but highly frequent during some management procedures, such as length classification, fish capture and juvenile stocking. Escapes were also reported due to cage damage and deliberate releases. These results indicate that, in cage aquaculture facilities, fish are frequently released to the external environment. When raising non-native species (e.g. Furnas Reservoir), these facilities constitute an important vector for fish introductions.

Oxygen limitation and tissue metabolic potential of the African fish Barbus neumayeri: roles of native habitat and acclimatization

BackgroundOxygen availability in aquatic habitats is a major environmental factor influencing the ecology, behaviour, and physiology of fishes. This study evaluates the contribution of source population and hypoxic acclimatization of the African fish, Barbus neumayeri, in determining growth and tissue metabolic enzyme activities. Individuals were collected from two sites differing dramatically in concentration of dissolved oxygen (DO), Rwembaita Swamp (annual average DO 1.35 mgO2 L-1) and Inlet Stream West (annual average DO 5.58 mgO2 L-1) in Kibale National Park, Uganda, and reciprocally transplanted using a cage experiment in the field, allowing us to maintain individuals under natural conditions of oxygen, food availability, and flow. Fish were maintained under these conditions for four weeks and sampled for growth rate and the activities of phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS), and cytochrome c oxidase (CCO) in four tissues, liver, heart, brain, and skeletal muscle.ResultsAcclimatization to the low DO site resulted in lower growth rates, lower activities of the aerobic enzyme CCO in heart, and higher activities of the glycolytic enzyme PFK in heart and skeletal muscle. The activity of LDH in liver tissue was correlated with site of origin, being higher in fish collected from a hypoxic habitat, regardless of acclimatization treatment.ConclusionsOur results suggest that the influence of site of origin and hypoxic acclimatization in determining enzyme activity differs among enzymes and tissues, but both factors contribute to higher glycolytic capacity and lower aerobic capacity in B. neumayeri under naturally-occurring conditions of oxygen limitation.

‘Carry on sampling!’- assessing marine fish biodiversity and discovery rates in southern Africa

Aim Biodiversity inventories are not yet complete, with potentially thousands of species unknown to science. This paper aims to (1) elucidate the historical discovery rate of endemic southern African marine fishes and (2) to estimate the number of potentially undescribed endemic marine fishes in the region using a statistical model and which factors (e.g. size/depth) contribute to unknown diversity. Thirdly, all species described globally for eight families (Blennidae, Clinidae, Gobiidae, Lutjanidae, Rajidae, Sciaenidae, Scyliorhinidae, Sparidae) were analysed to elucidate unknown diversity in these groups. Location The oceans of southern Africa, including Namibia, South Africa and Mozambique, encompassing sections of the south-eastern Atlantic Ocean and the western Indian Ocean. Methods Literature surveys from a number of sources were carried out to compile lists of species descriptions from 1758 onwards. Species-accumulation curves were plotted for all endemic species, as well as for different components of size and depth. A maximum likelihood model was used to estimate the number of undescribed endemic marine fishes in southern Africa, as well as for all other categories, including global families. Results Fish discovery rates in southern Africa have varied with time. Estimates suggest that at least 25% of the total endemic fish fauna remain unknown and that size is the greatest predictor of whether a fish has been described. Smaller-sized fishes and those inhabiting shallow areas are most likely to be undersampled. It is likely that most undescribed fishes inhabit the subtropical/tropical waters of the east coast. Main conclusions At the current rate of fish description, it will take at least 50 years to describe the total endemic fish fauna. However, estimates of unknown species are probably higher because of cryptic species within currently recognized taxa. Climate change may also contribute to range expansions of marine species, further complicating the status of endemicity in southern African marine fishes.

Burial Cloth Removed

Burial Cloth Removed Jill Noel Kandel (bio) Ten years of my life lie hidden. I missed the 1980s altogether. When people talk about '80s TV shows, politics, or movies I hardly have a clue. Reagan went missing somewhere and I never really found him. A part of me went missing, too. I turned up later with a sort of confused amnesia. While I cannot say who won Oscars, Super Bowls, or pennants, I can tell you other useless trivia. I can tell you about being mugged in Zimbabwe, being held at spear point in Lusaka, having army ants eat all my chickens and ducks—alive—down to the bone. I can tell you how the mist feels falling upward off of the magnificent Mosi-oa-Tunya Waterfalls, how an African fish eagle holds its heavy morning prey, about the pungent wild smell emitted by a herd a hundred strong of wildebeest. I can tell you about being alone. When Lazarus was sick unto death, Jesus knew and waited. He let Lazarus lie dead and cold for three days before He came. Before He wept. Does it matter what Lazarus missed those three days in the tomb? And when they pulled the cloth away—Mary and Martha longing to see that beloved irreplaceable face again—was it the same as they remembered? I love a God who is difficult to explain and hard to understand. He crushes what He loves. Take Joseph of the Old Testament. Joseph the [End Page 131] good boy. Joseph the good man. There's not one sentence, not one word in the Bible that shows he ever did anything wrong, yet—beware of being too good—his brothers threw him in a pit, sold him as a slave, and told his father he was dead. God hides His face from those He favors. Hide Abby—Minnesota 2009 My youngest daughter, Abigail, has never lived outside of North Dakota and Minnesota. These are her boundaries. At the age of three, she liked to tell stories about Africa. "Mom, the babies in Africa were all born with their eyes shut," she said to me. "Abigail, you've never been to Africa." "Yes, I have. The babies' eyes are shut. For five days. I've seen it. Just like my puppies." She persisted not only in her made-up memories but also in her play. Her favorite game became Hide and Seek the Bear. It started while visiting friends in California. Their three big boys—all close to six feet tall and football built—hid her tiny brown bear in various rooms while she toddled around looking for it. The boys soon tired of the bear. Abby, little bigger than the bear herself, proved more appealing. "Let's play Hide Abby," one of the boys called out. And so they did. She was just a handful in those big palms. "I'll hide her first," the oldest one said. The others hid their eyes and he plunked Abby down inside an oval basket. They hid her again and again, throughout the house for hours. Hold Her—Zambia 1985 I am six months pregnant, and big. We are on our way home—back to Kalabo Village—from Lusaka, the capital city of Zambia. My husband sits in the right-hand seat, driving. One-and-a-half-yearold Melinda plays between us. We are driving through Kafue Game Park, on narrow, tall-grass roads. A bus, in front on the right, has stopped in the middle of the road. My husband slows down—ever the cautious driver. We're barely going twenty. [End Page 132] He honks repeatedly and moves left to pass. We're exactly even with the bus, not able to see around it. There is less than a blur of movement. A thud sends a shudder through the truck. I see his knuckles; they are white. A motionless girl, with one arm thrown across a pothole, lies on the cracked tarmac, sweet potatoes scattered all around. Her black hair hides her face and blends into the pavement. It is no different than the hair of all the young girls who stand looking down at her still form, clothed...

Evolution: Dreampond revisited

A once-threatened population of African fish is now providing a view of evolution in action. Laura Spinney asks what Lake Victoria cichlids have revealed about speciation.

An Historical Review of African Freshwater Ichthyology

The history of ichthyology in Africa is reviewed. From the time of the Ancient Egyptians to the present, more than 3200 species have been discovered, drawn and described. Michel Adanson initiated the first material collections during the 18th century. During the 19th century, the work of travelling scientists (Étienne Geoffroy Saint-Hilaire, Andrew Smith) and explorers (including Mungo Park, Pierre Savorgnan de Brazza and Henry Morton Stanley) added substantially to developing zoological collections from their field trips. At that time, many species descriptions were based on fish preserved in these collections. Towards the end of the 19th and into the early part of the 20th century, knowledge of African fishes was greatly enhanced, especially through the work of Georges A. Boulenger, Albert C.L.G. Günther and Franz Steindachner, who, respectively, described 640, 119 and 53 species. The majority of the naturalists working in Africa during the middle and later parts of the 20th century tended to specialise in particular groups. In addition to conventional systematic studies, there was a steady rise in the numbers of contributions invoking genetics, specific parasites, and electrophysiology, amplifying fish identification using criteria other than morphology. These methods have proved helpful in finding explanations for the radiation of cichlids in the Rift Valley Lakes of East Africa, one of the most rapid and extensive involving vertebrates. Blending all these methods, descriptions of hitherto unknown species continue to be published. Whereas, until the mid-20th century, descriptions of new species and inventories of existing ones were the principal objectives of ichthyology, interests during the last 50 years have moved much more to the ecology of fish and to its application in aquaculture and aquariology: it is only during this period that most of the publications dealing with the biology and ecology of freshwater fishes and the science of fish culture have appeared. Brief biographies of the modern ichthyologists are presented, together with outlines of their main contributions.

West Indian Ocean variability and East African fish catch

We describe marine climate variability off the east coast of Africa in the context of fish catch statistics for Tanzania and Kenya. The time series exhibits quasi-decadal cycles over the period 1964–2007. Fish catch is up when sea surface temperature (SST) and atmospheric humidity are below normal in the tropical West Indian Ocean. This pattern relates to an ocean Rossby wave in one phase of its east–west oscillation. Coastal-scale analyses indicate that northward currents and uplift on the shelf edge enhance productivity of East African shelf waters. Some of the changes are regulated by the south equatorial current that swings northward from Madagascar. The weather is drier and a salty layer develops in high catch years. While the large-scale West Indian Ocean has some impact on East African fish catch, coastal dynamics play a more significant role. Climatic changes are reviewed using 200 years of past and projected data. The observed warming trend continues to increase such that predicted SST may reach 30 °C by 2100 while SW monsoon winds gradually increase, according to a coupled general circulation model simulation with a gradual doubling of CO 2.

Tissue responses of Clarias gariepinus (Catfish) to experimental Eimeria subepithelialis infection

Coccidial infection is a common feature in most African fishes. As a result of the chronic nature of the disease in fish, mortality is gradual (Kim and Paperna, 1993a) and is often overlooked in most farms, with losses becoming evident only at the end of the production cycle. This study evaluates the tissue responses of Clarias gariepinus (Catfish) in an experimental infection with Eimeria subepithelialis using 200 laboratory-bred Juveniles. Four groups (A, B, C and D) of 50 Juveniles each were preconditioned for 2 weeks. Groups A and B were infected per os with 200 E. subepithelialis sporocysts per juvenile, while groups C and D served as uninfected controls. At the onset of demonstrable oocysts in liver and spleen tissues, groups B and C were treated for a week in Amprolium(R) dip (0.6 mg/L) at the rate of 1 h a day. Five fish from each group were culled at intervals of 3 days to study the tissue responses to infection. At gross pathological level, intestinal and testicular congestion, splenomegaly and hepatomegaly were the common features of the infection. Histological lesions in the infected and treated group (group B) were confined to the small intestine while extra-intestinal lesions were seen in the infected and untreated fish (group A). The presence of pathological lesions in tissues, following experimental infection of C. gariepinus with E. subepithelialis sporocysts, indicated that the parasite is pathogenic to the catfish. Contrary to coccidiosis of terrestrial animals, sporulation of oocysts in piscine coccidiosis appeared to occur endogenously within the host. The use of Amprolium in the control of piscine coccidiosis is effective only when used early in the course of the infection, prior to onset of clinical signs. Proper certification of brooder and replacement stock, improved plane of nutrition and adequate stocking density are recommended aquacultural practices that may minimize the incidence of visceral coccidiosis in cultured fish.

Potential negative impacts and low effectiveness in the use of African annual killifish in the biocontrol of aquatic mosquito larvae in temporary water bodies

Commentary and discussion on a recent paper promoting the use of Nothobranchius guentheri, a small African annual fish from the Island of Zanzibar as a tool to control mosquito larvae in temporary bodies of freshwater throughout Africa is presented.Arguments on major points; (1) expected low success of annual fish introductions, (2) low success of mosquito control in the field, (3) ecological threats, and (4) ethical issues are detailed.Despite serious problems with mosquito-borne diseases in tropical Africa and elsewhere, we encourage responsible means of biological control of parasite vectors. We show that effectiveness of Nothobranchius translocations is low (the previous attempts failed), likelihood of effective mosquito larvae control under field condition is negligible and ecological threats from Nothobranchius translocations from within and outside the naturally occurring range are serious. We advocate against the proposed next step of the project, i.e. field trials in Tanzania.

Mapping Loci Associated With Tail Color and Sex Determination in the Short-Lived Fish Nothobranchius furzeri

The African fish Nothobranchius furzeri is the shortest-lived vertebrate species that can reproduce in captivity, with a median life span of 9-11 weeks for the shortest-lived strain. Natural populations of N. furzeri display differences in life span, aging biomarkers, behavior, and color, which make N. furzeri a unique vertebrate system for studying the genetic basis of these traits. We mapped regions of the genome involved in sex determination and tail color by genotyping microsatellite markers in the F(2) progeny of a cross between a short-lived, yellow-tailed strain and a long-lived, red-tailed strain of N. furzeri. We identified one region linked with the yellow/red tail color that maps close to melanocortin 1 receptor (mc1r), a gene involved in pigmentation in several vertebrate species. Analysis of the segregation of sex-linked markers revealed that N. furzeri has a genetic sex determination system with males as the heterogametic sex and markedly reduced recombination in the male sex-determining region. Our results demonstrate that both naturally-evolved pigmentation differences and sex determination in N. furzeri are controlled by simple genetic mechanisms and set the stage for the molecular genetic dissection of factors underlying such traits. The microsatellite-based linkage map we developed for N. furzeri will also facilitate analysis of the genetic architecture of traits that characterize this group of vertebrates, including short life span and adaptation to extreme environmental conditions.

Comparison of the ovaries and oogenesis of some Australian and South African viviparid clinid fishes (Clinidae, Blennioidei, Perciformes)

The ovaries of the studied 16 viviparous blenny species of the fish family Clinidae (Teleostei, Perciformes) from Australia and South Africa, are of the cystovarian type and bilobed, ending in a common short oviduct at the gonopore; they are elongated in juvenile fish, becoming bottle-shaped or oval with maturation and onset of embryogenesis, when they comprise 18–20% of the total body weight. The ovarian lumen is covered by the germinal epithelium, resting on a basal membrane. The primordial germ cells are situated along the inner side of each lobe, juxtaposed internally to the lumenal epithelium. Single primary oocytes or nests of such, each in a follicular envelope and covered externally by the lumenal epithelium forming clusters protruding into the lumen, along which the inoculated sperm settle. Two different types of reproductive strategies are demonstrated by the Australian species of Heteroclinus and Cristiceps and the South African species of Clinus and related forms. The Australian species produce high numbers of small (350 ± 50 µm in diameter) eggs that develop synchronously, while the South African species produce much fewer and larger (1.0 ± 0.1 mm) eggs, asynchronous in development. An exception in the latter group is Blennophis striatus, with eggs of ca.1.4 mm that develop synchronously. The Australian species are thus mass releasers that bear and release up to 1000 small (11 ± 1.5 mm in length) embryos/spawn, while the South African Clinus species are discrete releasers that bear eggs of various sizes and small numbers of mature for release embryos that reach up to 22 mm in length, and are released throughout the year. The cytogenesis of the oocytes and surrounding envelopes is discussed.