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In this study, we explored variation in sperm morphometry of the African cyprinid Barbus neumayeri Fischer, 1884 (Neumayer’s barb) across seven sites with a wide range in dissolved oxygen, from hypoxic swamps to intermittent normoxic streams to well-oxygenated rivers. We explore whether fish physiological condition (K) or hypoxia can affect the reproductive traits, and whether condition–hypoxia dependence of sperm traits including head length (LH), head width (WH), flagellum length (LF), and hydrodynamic ratio (HR) vary across sampling sites. Significant differences were found in fish total length (P = 0.0212), as well as in K, left and right testis masses, total gonad mass, and gonadosomatic index (P < 0.0001 for all traits). Total gonad mass was lower in hypoxic sites than in well-oxygenated sites. Interestingly, the left and right testes from normoxic environments were double the size of testes from hypoxic environments. Despite little variation in sperm flagellum length, sperm heads were longer in swamps than in streams or rivers, giving the sperm head a more hydrodynamic shape. This variation in HR may be beneficial in the more stagnant waters of the swamp compared with the other environments. Future studies are necessary to understand whether variation in sperm morphology correlates with sperm swimming performance and male reproductive capacity.

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.

The taxonomy of the two established barbus species: Barbus neumayeri and Barbus pellegrini has presented problems due to their close relationship and pronounced character variation within and between their populations. In this study, morphomeristic methods were used to investigate Barbus specimens from several populations in the Lake Kivu – Lake Edward area. Meristic and morphometric data on specimens in the RMAC collection from lakes Kivu and Edward, and the Nyabarongo and Mpanga river systems were analysed using principal component analysis in the PAST software programme. The results revealed additional morphomeristic characters useful in distinguishing the two closely related barbus species; hence, both B. pellegrini and B. neumayeri are redescribed incorporating additional characters to their respective original descriptions. Specimens from Nyabarongo river system were significantly different to warrant recognition as new species; thus, a new species B. new species is proposed and described. Meristically, the B. new species and the two established species are distinguished by lateral line scale counts; while predorsal length, head length and body depth at operculum, expressed as percentage of standard length, are the most diagnostic morphometric characters. Resume La taxonomie de deux especes reconnues de Barbus, Barbus neumayeri et Barbus pellegrini, pose un probleme en raison de leur proche parente et de variations tres marquees de caracteres au sein d'une meme population et entre populations. Dans cette etude, nous avons utilise des methodes morphomeristiques pour etudier des specimens de Barbus issus de differentes populations de la region des lacs Kivu et Edouard. Des donnees meristiques et morphometriques obtenues sur des specimens de la collection du MRAC venant des lacs Kivu et Edouard et des systemes hydrographiques des rivieres Nyabarongo et Mpanga ont ete etudiees au moyen de l'analyse en composante principale du programme PAST. Les resultats ont revele des caracteres morphomeristiques supplementaires utiles pour distinguer les deux especes de Barbus tres proches l'une de l'autre, et B. pellegrini et B. neumayeri sont donc decrits de nouveau en integrant les nouveaux caracteres a leur description originale respective. Les specimens du systeme hydrographique de la riviere Nyabarongo etaient significativement differents au point d'inciter a les reconnaitre en tant que nouvelle espece; c'est pourquoi une nouvelle espece de Barbus nouv. esp. est ici proposee et decrite. Au point de vue meristique, la nouvelle espece de Barbus nouv. esp. et les deux especes reconnues se differencient par le nombre d'ecailles de la ligne laterale, alors que la longueur predorsale, la longueur de la tete et l'epaisseur du corps au niveau des branchies, exprimees en pourcentage de longueur standard, sont les principaux caracteres morphometriques du diagnostic.

Environmental factors influence phenotypes directly, as well as indirectly via trait correlations and interactions with other environmental variables. Using nine populations of the African cyprinid Barbus neumayeri, we employed path analysis to examine direct, indirect and total effects of two environmental variables, water flow (WF) and dissolved oxygen (DO), on several morphological traits. WF and DO directly influenced relative gill size, body shape and caudal fin shape in manners consistent with a priori predictions. Indirect effects also played an important role in the system: (1) strong, oppositely signed direct and indirect effects of WF on body shape resulted in a nonsignificant total effect; (2) DO had no direct effect on body shape, but a strong total effect via indirect effects on gill size; (3) WF indirectly influenced gill size via effects on DO. Only through examination of multiple environmental parameters and multiple traits can we hope to understand complex relationships between environment and phenotype.

This study described the behavior of the swamp-dwelling African cyprinid Barbus neumayeri in response to laboratory acclimation to normoxic and hypoxic conditions to detect costs associated with hypoxia exposure. Behavioral observations were conducted every two weeks over a four-week acclimation period in both normoxic and hypoxic conditions, and feeding trials were conducted after six weeks of acclimation. Gill ventilations were shallower in normoxia-acclimated fish than in hypoxia-acclimated individuals, and gill ventilation rate declined over the hypoxia acclimation. There was no effect of hypoxia acclimation on routine activity; however, individuals acclimated to hypoxia showed a depression in feeding rate relative to normoxia acclimation. This decline in feeding activity under hypoxia acclimation may account, at least in part, for the lower condition of the hypoxia-acclimated fish. These findings suggest that hypoxia exposure does not significantly impact routine activity levels of these swamp-adapted fishes, but seems to depress higher energy activities such as feeding rate.

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.

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.

Adaptive change in one character may affect associated, but functionally unrelated, characters in adaptive or nonadaptive ways. For example, adaptive change in gill size (i.e., larger gills in hypoxic habitats) may alter adjacent feeding structures and therefore have indirect effects on feeding behavior. This study examines whether differences in total gill filament length among populations of the African cyprinid Barbus neumayeri correlate with variation in trophic structures and feeding performance. Morphological measurements revealed larger total gill filament length in populations from low-oxygen habitats. Differences in external and internal morphology of the trophic apparatus correlated with those found in gills and suggest a reduction in food capture and processing ability in fish with larger respiratory apparatus. In paired feeding trials on a novel prey type, large-gilled fish spent more time feeding than small-gilled fish of the same body size without ingesting more food. This suggests less efficient food uptake in large-gilled fish from hypoxic habitats. We suggest that variation in gill size facilitates the broad habitat distribution of B. neumayeri but may limit the success of phenotypes crossing physicochemical gradients.

In oxygen-deficient waters, the difficulties of oxygen uptake in gill parasites and their fish hosts may influence host and parasite densities, site selection by the parasite, and effects of the parasite on host condition. This study quantified the prevalence and intensity of the gill monogenean Neodiplozoon polycotyleus in the African cyprinid fish Barbus neumayeri from an intermittent forest stream in western Uganda. Oxygen levels were low in the stream over the 12-month study, averaging only 2.5 mg litre−1 (monthly range = 1.2–4.3 mg litre−1). However, parasite prevalence was high (47.2%), suggesting high tolerance to low oxygen in N. polycotyleus. The prevalence of parasites varied with host body size, with the highest frequency of occurrence in the middle size classes. Prevalence also varied over the year; seasonal peaks of rainfall coincided with a lower frequency of N. polycotyleus. The significantly nonrandom frequency distribution of parasites among hosts suggests regulation of parasite numbers. Of the hosts infected, 37.1% harboured one N. polycotyleus parasite, and 62.9% harboured two parasites. No fish were infected with more than two diplozoons. There was evidence for strong site specificity by N. polycotyleus within hosts; 77.7% of the parasites were located on the filaments of the second gill arch, which may relate to increased oxygen availability. In addition, only one of the 178 infected fish had more than one parasite on one side of the branchial basket. Although N. polycotyleus is undoubtedly parasitic, we found no evidence of a negative parasitic effect on the condition or reproductive status of B. neumayeri. Resume Dans les eaux deficientes en oxygene, la difficulte que rencontrent les parasites des branchies et leurs poissons hotes peut influencer la densite des hotes et des parasites, la selection du site par le parasite et l'effet du parasite sur la condition de son hote. Cette etude quantifie la prevalence et l'intensitede Neodiplozoon polycotyleus chez le cyprinide africain Barbus neumayeri dans un cours d'eau forestier intermittent a l'ouest de l'Ouganda. Le taux d'oxygene du cours d'eau est reste bas pendant les douze mois qu'a dure l'etude, egal en moyenne a 2,5 mg/litre (ecart mensuel = 1,2–4,3 mg/litre). Cependant, la presence parasitaire etait elevee (47,2%), ce qui suggere chez N. polycotyleus une tres bonne tolerance a de faibles taux d'oxygene. La presence de parasites variait avec la taille, elle etait la plus elevee dans les classes de taille moyenne. Cette presence variait aussi au cours de l'annee, et les pics saisonniers des pluies corespondaient a une abondance moindre de N. polycotyleus. La distribution de frequence des parasites qui n'est significativemement pas laissee au hasard chez les hotes suggere une regulation du nombre de parasites. Chez les hotes infestes, 37,1% abritaient un parasite et 62,9% en abritaient deux. Aucun hote n'en avait plus de deux. On a constate l'evidence d'une forte specificite de site de N. polycotyleus chez les hotes: 77,7% des parasites se trouvaient sur les filaments de la deuxieme branchie, ce qui peut avoir un rapport avec une meilleure disponibilite en oxygene. De plus, seul un des 178 poissons infestes avait plus d'un parasite d'un meme cote. Bien que N. polycotyleus soit indubitablement un parasite, nous n'avons trouve aucune preuve d'un effet negatif sur la condition ou sur le statut reproducteur de B. 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 diVered in oxygen regime. Total gill filament length diVered 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 suYcient to homogenize gene frequencies among populations. However, randomly amplified polymorphic DNA (RAPD) markers indicated significant genetic diVerentiation among sites and no relationship between genetic diVerences and geographical distances among sites suggesting habitat-specific selection pressures on dispersers, rather than insuYcient dispersal. ? 1999 The Fisheries Society of the British Isles

ummary Wetlands, dominated by papyrus (Cyperus papyrus), are extensively distributed in east and central Africa. However, the use of papyrus swamps by fishes is limited to species that can tolerate the low oxygen conditions that can prevail in the dense swamp interior. In this study, we ask whether the patchy distribution of papyrus swamps may contribute to variation among fish populations in traits related to oxygen uptake. A series of paired experiments was used to compare the respiratory behaviour of a small water breathing cyprinid Barbus neumayeri from the dense interior of a papyrus swamp in western Uganda, to populations from nearby well-oxygenated rivers and streams. The respiratory behaviour of the swamp population differed from the other populations. Several lines of evidence suggest that B. neumayeri from papyrus swamps are more tolerant of low oxygen conditions than populations from nearby river and stream sites, including lower thresholds for aquatic surface respiration in the swamp population, lower gill ventilation rates in the swamp population and higher loss of equilibrium in fish from the river/stream sites. This small scale geographical variation in behaviour among B. neumayeri populations supports an earlier study that documented variation in gill morphology among sites that differed in oxygen availability, and supports the significance of papyrus swamps in promoting diversification among populations. Resume Les zones humides, dominees par les papyrus (Cyperus papyrus), sont tres largement reparties en Afrique orientale et centrale. Cependant, l'utilisation des marais a papyrus par des poissons se limite aux especes qui peuvent supporter les conditions pauvres en oxygene qui prevalent dans les zones plus denses des marais. Dans cette etude, nous demandons si la distribution eparpillee des marais a papyrus peut contribuer a une variation, entre les populations de poissons, des caracteristiques liees a l'absorption d'oxygene. Une serie d'experiences couplees a servi a comparer le comportement respiratoire d'un petit cyprinide, Barbus neumayeri, venant de l'interieur dense d'un marais a papyrus dans l'ouest de l'Ouganda, a celui de populations provenant des cours d'eau voisins bien oxygenes. Le comportement respiratoire de la population du marais etait different de celui des autres populations. Plusieurs preuves suggerent que les B. neumayeri provenant des marais a papyrus supportent mieux des conditions pauvres en oxygene que ceux des rivieres et cours d'eau voisins, comme par exemple des seuils plus bas pour venir respirer a la surface chez la population des marais, des taux plus bas de ventilation branchiale chez cette merae population, et une perte d'equilibre plus grande chez les poissons des cours d'eau. Cette variation geographique sur une petite echelle du comportement entre les populations de B. neumayeri vient appuyer une etude anterieure qui documentait la variation de morphologie des branchies entre des endroits qui differaient quant a la quantite d'oxygene, et renforce la signification des marais a papyrus pour la promotion de la diversification entre les populations.

I examined the effects of extreme hypoxia and water level fluctuations on the distribution and movement of an air-breathing clariid catfish, Clarias liocephalus, in a papyrus swamp in western Uganda. Monthly records of the distribution and relative abundance of C. liocephalus across 28 swamp stations were used to examine seasonal trends in habitat use and movement. My results suggest that dissolved oxygen did not directly limit use of, or dispersal through, the papyrus swamp. C. liocephalus were found at most stations in the dry season, and there was no significant relationship between the number of stations used per month and mean monthly dissolved oxygen levels. In addition, there was no evidence for a significant effect of oxygen on the relative abundance of fish among stations during the driest months, or during peak flood conditions. However, relative abundance was positively correlated with water depth during the dry season. Fish from deeper habitats exhibited fewer injuries and lower rates of disappearance than fish from shallower waters. This may reflect the risk of aerial predation for surfacing fish. A comparison of habitat use and movements of C. liocephalus with the only other fish species found in the papyrus swamp, Barbus neumayeri, supports the idea that respiratory mode can affect the use of hypoxic papyrus swamps. B. neumayeri, is a small water-breathing cyprinid that uses aquatic surface respiration in response to severe hypoxia. The air-breathing capabilities of C. liocephalus permitted more widespread use of swamp waters than B. neumayeri. This study demonstrates that an understanding of the respiratory mode of fish species may be useful in predicting patterns of habitat use.

Cyprinid fishes apparently constituted the major part of the original fish fauna in Lake Luhondo, Rwanda, at least until 1934. At that time only three species, all cyprinids, were known from the lake:Barbus neumayeri, a small barbel, very common in the lake (described from the lake asBarbus luhondo) and two larger cyprinid species:Barbus microbarbis andVaricorhinus ruandae. These two large species were probably not very common in the lake. Between 1935 and 1938 some youngTilapia were introduced into Lake Luhondo. Since then and certainly since 1952 the large cyprinids seem to have disappeared completely from the lake. The smallBarbus neumayeri has become extremely rare; at present it survives only in some small tributaries of the lake. In the lake itselfTilapia andHaplochromis species are now the dominant fauna. A survey of the available information is given.

Studies on species of Monogenea have shown that these parasites often infect only a specific host species, genus, or family, and that they attach only to specific sites within hosts. Few studies, however, examine habitat specificity across host and habitat scales. In this study, we focused on host, macrohabitat, and microhabitat specificity in the monogenean diplozoon Afrodiplozoon polycotyleus, a gill parasite of African cyprinid fishes, Barbus spp. We first compared the occurrence of A. polycotyleus among 4 species of Barbus from a single location in the Mpanga River of western Uganda; Barbus neumayeri was the only species infected with the parasite. We then quantified parasite prevalence and mean abundance in B. neumayeri from a series of river and swamp sites in the same drainage, looking for environmental predictors of diplozoon prevalence and abundance over a broad habitat scale. The prevalence and mean abundance of A. polycotyleus on gills of B. neumayeri was highest in the hypoxic swamp habitat, followed by the intermittent stream sites, and faster flowing river sites. Parasite prevalence and mean abundance across habitats were negatively related to both water current and dissolved oxygen concentration. Within hosts, A. polycotyleus was strongly specific among hemibranchs in poorly oxygenated water and was found on arch 2, hemibranch 4 most frequently.

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.

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