Population differentiation of the African cyprinid Barbus neumayeri across dissolved oxygen regimes

Population level response to hypoxia has become an issue of global significance because of increased frequency and intensity of hypoxic events worldwide, and the potential for global warming to exacerbate hypoxic stress. In this study, we sequenced two nuclear intronic regions and a single mitochondrial region across seven populations of the African cyprinid, Barbus neumayeri from two river drainages in Uganda: the Rwembaita Swamp‐Njuguta River System and the Dura River. We then examined two indices of population structure, G_ST and Jost's D, to detect links between oxygen availability and genetic variation and to determine if population genetic structure was associated with (i) dissolved oxygen regime (hypoxia or normoxia), (ii) geographical distance, or (iii) a combination of dissolved oxygen regime and geographical distance. Our results indicate that over a large scale (between drainages), geographical distance significantly affects the genetic structure of populations. However, within a single drainage, dissolved oxygen regime plays a key role in determining the genetic structure of populations. Within the Rwembaita‐Njuguta system, gene flow was high between locations of similar oxygen regimes, but low between areas characterized by divergent oxygen regimes. Interestingly, G_ST analyses appear to yield less realistic measures of population structure than Jost's D, suggesting that caution must be taken when interpreting and comparing the results from different studies. These results support the idea that aquatic dissolved oxygen can act as a selective force limiting gene flow among populations of aquatic species and therefore should be considered when implementing conservation plans and assessing environmental impact of human activities.     

Interdemic variation in the foraging ecology of the African cyprinid, Barbus neumayeri

In the African cyprinid, Barbus neumayeri, populations from hypoxic waters have larger gills than populations from well-oxygenated streams. Differences in trophic morphology and feeding performance between these populations suggest a reduction in feeding efficiency in large-gilled fish that may reflect spatial constraints of the gills. However, this variation may also reflect interdemic variation in diets. In this study, we describe patterns of variation in diet, gut morphology, and prey availability for populations of B. neumayeri from swamp (low-oxygen) and stream (high-oxygen) sites in Kibale National Park, Uganda. Our results indicate that B. neumayeri are omnivorous, feeding primarily on benthic prey items; however, diets differed among swamp and stream sites for certain prey types. The observed dietary differences do not provide direct support for predictions based on variation in trophic musculature; hard-bodied prey were more common in low-oxygen sites. Prey availability also differed among sites; in particular, insect abundance and richness was generally lower in the swamp sites. Gut length was longer in one of the four populations, but did not conform to expectations based on diet differences. Condition and growth rates did not differ between populations from hypoxic and well-oxygenated sites, despite observed differences in prey availability and diet, suggesting that B. neumayeri may be distributed in a way that equalizes fitness among populations in different habitats.     

Interdemic variation in haematocrit and lactate dehydrogenase in the African cyprinid Barbus neumayeri

This study evaluated whether the African cyprinid Barbus neumayeri from Rwembaita Swamp (low‐oxygen) and Njuguta River (high‐oxygen) in the Kibale National Park, Uganda differed in traits related to aerobic and anaerobic metabolic potential. Haematocrit was measured as an index of blood oxygen‐carrying capacity, and tissue activities and isozyme composition of lactate dehydrogenase (LDH) were measured as indices of tissue anaerobic capacity. To address whether site‐dependent differences were acute responses v . longer‐term adjustments to environmental conditions, these variables were measured in fish sampled shortly after collection and after laboratory maintenance under well‐aerated conditions. In fish sampled in the field, those from the low‐oxygen site had significantly higher haematocrit, but this difference disappeared after long‐term laboratory maintenance. In contrast, fish from the low‐oxygen site had higher liver LDH activities than fish from the high‐oxygen site, and this difference persisted during laboratory maintenance. Polymorphism was detected at both the LDH‐A and LDH‐B loci, and genotype frequencies for LDH‐B differed significantly between collection sites. These results demonstrate physiological, biochemical and genetic differences in B. neumayeri from habitats differing in dissolved oxygen availability and suggest both acute and long‐term responses to local environmental conditions.     

Geographic variation of Barbus radiatus Peters,a widely distributed African cyprinid fish

Synopsis Barbus radiatus is a widely distributed, polytypic species with three recognized subspecies: radiatus Peters (1853), aurantiacus Boulenger (1910), and profundus Greenwood (1970). A phenetic analysis of relative similarity was conducted for specimens of B. radiatus from throughout its known range. The study focuses on several large population samples taken recently along the presumed central Zambian interface between the subspecies aurantiacus and radiatus. New data on meristic and morphometric variation in B. radiatus and recent rediscovery of typical radiatus in Lake Victoria demonstrate that profundus is a species distinct from radiatus. With respect to the remaining two subspecies, results indicate a populational mosaic of highly variable morphs rather than two discrete, allopatric morphs. Thus, aurantiacus is placed in synonymy of radiatus. It is hypothesized that the populational mosaic of morphology in radiatus reflects adaptive ecotypic responses to water temperature and current velocity. The characters which accounted for most of the geographic variation of radiatus were body depth, caudal peduncle length, longitudinal meristic counts, dorsal fin height, and orbit diameter.     

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.     

The distribution of Posthodiplostomum cuticola metacercariae in young-of-the-year cyprinid fishes

The lowest frequency of metacercariae of Posthodiplostomum cuticola on the bodies of six young-of-the-year cyprinid species was found on the head and ventral body. Metacercariae distribution differed among host species which may have been related to the behaviour of the fish host.     

Structure of the gills of Barbus sophor (Ham), a cyprinid with tertiary lamellae

A study of the structure of the gills using light and transmission electron microscopy showed that though the basic organisation of the filaments and secondary lamellae is very similar to that of other bony fishes, there was also a number of unusual features. Most of the blood channels of the secondary lamellae remain embedded in the tissue of the primary lamellae. The secondary lamellar surface is increased by the presence of irregular expansions which may be referred to as tertiary lamellae. The presence of an unusual structure on one side of many secondary lamellae was observed; this structure might possibly be due to the presence of a parasite. The possible functional significance of these observations is discussed and indicates the need for morphometric and experimental investigation of the respiration of this species.     

Papyrus swamps and the respiratory ecology of Barbus neumayeri

Synopsis In seasonally flooding fresh waters, dissolved oxygen and fluctating water levels combine to create strong seasonal changes in habitat availability and dispersal pathways for fishes. In this study we demonstrate how respiratory mode can affect the use of and dispersal through hypoxic papyrus swamps for a small cyprinid fish, Barbus neumayeri, a species which uses aquatic surface respiration (ASR) in response to severe hypoxia. Monthly records of the distribution and relative abundance of B. neumayeri across 28 stations in a papyrus swamp in Uganda were used to examine seasonal patterns of habitat use and movement. The distribution of B. neumayeri was very restricted during the drier months. Most fish were captured in open pools and channels with large areas of open water surface and higher oxygen. Movement of B. neumayeri was limited to short periods during the wet season when peak water levels produced high levels of oxygen and pathways for movement. Three lines of evidence suggest that these patterns relate to its respiratory mode. These include: the positive :relationship between dissolved oxygen and the number of stations used per month, the positive relationship between fish density at dry season stations and dissolved oxygen, and the absence of fish from stations with. little open water surface area during the dry season. Significant differences in the gill morphology between B. neumayeri from the papyrus swamp and those from the main river suggest that papyrus swamps may contribute to the diversification of B. neumayeri by limiting movement and demanding specialization for extremely hypoxic waters.     

Four rows of pharyngeal teeth in an aberrant specimen of the small African barb Barbus paludinosus(Cyprinidae): novelty or atavistic alteration?

An extra fourth row of pharyngeal teeth was found on both pharyngeal arches in a specmen of the small African barb, Barbus paludinosus , a species normally exhibiting three rows of pharyngeal teeth. Possible phylogenetic significance of this alteration is discussed in connection with occurrence of extra fourth rows of pharyngeal teeth in other cyprinid lineages.     

New evidence of hexaploidy in' large' African Barbus with some considerations on the origin of hexaploidy

Three species of' large' African Barbus from the Republic of Guinea (West Africa), were characterized by the chromosome numbers (2N) of 148 (B. bynni occidentalis and B. wurtzi ) and 150 (B. petitjeani Daget, 1962). All these species have a karyotype which corresponds to the evolutionary hexaploid level. The karyotype of B. petitjeani is composed of chromosomes clearly grouped into morphologically homomorphic sextets which may document the origin of hexaploidy via an autopolyploidic event. Present findings extend the known distribution of evolutionary hexaploidy in' large' African Barbus to West Africa and show evidence of the pan-African distribution of this phenomenon.     

Garra tibanica ghorensis subsp.nov. (Pisces: Cyprinidae), an African element in the cyprinid fauna of the Levant

Garra tibanica ghorensis subsp. nov. is described from the southern Dead Sea Valley. In the Levant it represents the only cyprinid fish with African affinities known to date. It is suggested that G. t. ghorensis reached the area of its present distribution from the south and is not to be regarded as a relict of an earlier migration of the species to Africa via the Levant.Results of the travels of R. Kinzelbach to the countries of the Middle East, No. 18.Results of the travels of R. Kinzelbach to the countries of the Middle East, No. 18.     

Effects of a flow-gauging weir on the migratory behaviour of adult barbel, a riverine cyprinid

Barbel Barbus barbus exhibited substantial movements in the River Nidd between March and July 1994, with some individuals moving nearly 20 km upstream, although there was considerable individual variation. Most upstream movement occurred during May. Fifteen of the 23 fish tracked attempted to pass the weir, and of these six were successful. Barbel tended to approach the weir around dusk and dawn, reflecting observed patterns of localized activity, or at night, but crossed the weir only at night. Those fish which crossed the weir moved substantial distances upstream to spawn, while those that were unsuccessful moved down-stream. The weir delayed the net upstream progress of all adult barbel. Successful traversal was not closely related to flow or water temperature conditions. The study emphasizes the impact of relatively minor obstructions on the natural migrations of barbel.     

The effect of temperature and mass on routine oxygen consumption in the South African cyprinid fish Barbus aeneus Burchell

Routine metabolism was measured for Barbus aeneus ranging in mass from 4.1 g to 520 g over the temperature range 9.5–26°C. The mean slope of the double logarithmic relationship between total oxygen consumption and mass was 0.69. The slope of the response of specific oxygen consumption to temperature increased with increasing mass. It is suggested that the lesser effect of temperature on specific oxygen consumption in smaller fish is because osmosis is a passive physical process, with a Q ₁₀ in the range 1.1–1.4, while the Q ₁₀ for biochemical processes is typically in the range 2–4. At lower temperatures a greater proportion of the total metabolism would therefore be devoted to osmoregulation. This would have implications for the energy balance of small fishes, since in these the ratio surface area: mass is greater and accordingly the proportion of total metabolism devoted to osmoregulation would be higher than in larger individuals.     

Pattern of movements of adult Barbus haasi in a small Mediterranean stream

Most adult Barbus haasi , at a 1950 m-long site in Vallvidrera creek, were highly sedentary and resided within a home range <20 m (32 m²), while a small group were more mobile. On successive sampling occasions, between 52·3 and 64·9% of fish were recaptured in the same 10-m-long section in which they had previously been captured. Movements over long distances were infrequent, and only 5·6% of the fish moved >100 m. The movement pattern of the population was seasonally stable, although the mean distances were slightly greater in summer because of the medium-range movements of a few individuals. Overall, upstream and downstream movements were equally common but a significant downstream movement occurred in spring. The size of the fish did not influence the movement rate. Fish inhabiting those sections of the stream with greater depth, slower current and more cover had a lower movement rate than fish occupying shallower, exposed sections. The restricted movement of B. haasi could increase the survival of fish by increasing the probability of staying in the remaining pools during summer dry-out, and may therefore be of adaptive significance.     

The attachment of the monogenean parasite Callorhynchicola multitesticulatus to the gills of its holocephalan host Callorhynchus milii

Llewellyn J. and Simmons J. E. 1984. The attachment of the monogenean parasite Callorhynchicola multitesticulatus to the gills of its holocephalan host Callorhynchus milii. International Journal for Parasitology14: 191–196. C. multitesticulatus when juvenile (up to about 10 mm long) attaches itself by four pairs of clamps to the secondary gill lamellae of its host the elephant fish Callorhynchus milii. However, in adult parasites the haptor invades the host tissue and the stalk connecting the haptor with the body-proper becomes surrounded by a sleeve of fibrous host inflammatory reaction tissue. The stalk is provided with annuli with anteriorly-directed flanges which are pressed into the walls of the sleeve of host tissue when the diameter of the stalk increases as a result of the contraction of well-developed sub-tegumentary longitudinal muscles.     

Adaptive and evolutionary significance of a reproductive thermal threshold in Barbus barbus

From 1989 to 1996, barbel in the River Ourthe started spawning under variable environmental conditions, except for water temperature. Each year, spawning was initiated when water daily minimum temperature reached or exceeded 13·5° C. Any decrease of temperature below this value later in the spawning period caused spawning to be suspended. Analyses of offspring growth provided evidence that 13·5° C was the value below which 0+ barbel stop growing. It was hypothesized that barbel trade off the lower initial probability of survival against a larger size at the onset of winter. To test empirically for this hypothesis, the adequacy of alternative—theoretical—strategies associated with other thermal thresholds (12, 15·0, 17·1 and 20·2° C) was modelled with respect to: (1) the feasibility of spawning (inhibition of sexual maturation by a decreasing photoperiod); (2) the impact of the temperature on embryonic development; (3) the effect of water level variations on the integrity of spawning grounds until the emergence of larvae; (4) the size of the offspring at the onset of winter. On an 8-year (1989–1996) average, the present spawning strategy would have produced a higher recruitment than alternative strategies (relative adequacy of 33·23, 85·64, 93·17 and 17·62%, respectively). However, alternative strategies would have produced better annual scores on five of eight occasions in the River Ourthe environment, and a better overall score in environments 1·5 or 3·5° C warmer than now. The consistency of the thermal threshold over years, despite a low selection pressure by the environment, was interpreted as the expression of a phenotypic mechanism (thermal homing) promoting the selection of the lowest efficient thermal threshold, and enabling breeders to relay to the next generation some form of thermal stability in a variable environment.     

Early development of the cephalic skeleton of Barbus barbus (Teleostei, Cyprinidae)

The inception, and development of the cephalic skeleton of Barbus barbus from hatching to 24 days passes through periods of fast and slow growth; these rates are not the same in different parts of the skull. Trabeculae, parachordal plates, Meckelian cartilages and hyposymplectics are present at hatching. Then the cartilaginous floor of the neurocranium develops, the pars quadrata, the hyoid bars and branchial arches elements appear shortly before the first movable dermal bones, the dentaries, maxillae and opercles. The first bone of the braincase to appear is the parasphenoid; other bones develop subsequently and at the same time: the angular, quadrate, interopercle and fifth ceratobranchial. Later the splanchnocranium continues to develop at a relatively fast rate while the neurocranium shows little growth. The braincase does not begin to close before the 24th day, nor do the first bones of the skull roof appear, while the bucco-pharyngeal apparatus is complete, having the adult shape. The early constitution of the latter structures seems to be linked with the mechanical demands of biological functions such as breathing and feeding.     

Effects of habitat availability on dispersion of a stream cyprinid

Synopsis We analyzed temporal changes in the dispersion of the rosyside dace,Clinostomus funduloides, (family Cyprinidae) in a headwater stream, to assess the role of habitat availability in promoting fish aggregation. The dace foraged alone and in groups of up to about 25 individuals, and dispersion varied significantly among monthly censuses conducted from May through December. In two of three study pools, dace aggregated during July, October and/or December, but spread out during other months, especially during September when dispersion did not differ significantly from random. Dispersion was not significantly correlated with the total amount of suitable habitat available to foraging dace, but during summer, corresponded to the availability of depositional areas adjacent to rapid currents. Foragers aggregated in eddies or depositional areas during high stream discharge in July, and shifted out of depositional areas when current velocities declined from July to September. During late autumn, however, aggregations formed independently of changes in habitat conditions, and dace dispersion did not vary significantly among months in a third pool. The study suggests that dace dispersion cannot be predicted from the overall availability of suitable habitat as estimated from point measurements of depth and velocity; both the occurrence of a specific habitat feature (i.e., eddies adjacent to high velocity currents) and seasonal differences in behavior more strongly influenced the spatial distribution of foragers.