Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology

This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems. Handling editor: J. Trexler     

Biology of the cardinalfishGlossamia gjellerupi (Perciformes: Apogonidae) from the Sepik-Ramu River basin,Papua New Guinea

Synopsis Glossamia gjellerupi forms a considerable part of the fish biomass (25%) and density (12%) in floodplain margin streams and lower foothill streams throughout the Sepik-Ramu basin where it occurs up to an altitude of 320 meters above sea level. It prefers habitats with slow flow rates: pools, alongside banks, under cover of vegetation, etc. Biomass and density decreased with increasing current speeds. Condition factor and fat deposits were negatively correlated to current speeds, with populations from floodplain margin streams having the highest averages for both these indices. Fluctuations in population size appeared to be related to the irregular occurrence of spates. No seasonality in reproduction, condition and fat deposits were noted although peaks occurred according to specific local conditions. Fecundity was found to be low, increasing with fish size. Eggs in a ripe ovary were all in the same stage of development, with sizes of around 3.3 mm.G. gjellerupi is a male mouth brooder. Mouth-breeding may restrict the species to well oxygenated waters. Reproductive activity takes place throughout the year but is not random since clear peaks in gonad development occurred within different populations. Reproductive activity and/or survival rate of juveniles are possibly directly related to floods. Prolonged periods of environmental stability, such as those occurring in periods of less rainfall, seem to be conditional for the survival of juveniles. Fish up to 30 mm length fed predominantly on small benthic insect larvae. Fish larger than 60 mm are carnivorous top-predators feeding predominantly on crabs, bottom dwelling fish and large terrestrial insects. Fish of all sizes, except the largest, fed on caridinid prawns. Feeding habits varied between different habitats depending on local environmental conditions.     

Diversity and ecology of algae from the Nahal Qishon river,northern Israel

In 59 samples of periphyton and phytoplankton collected in 2002 - 2003 from the Nahal Qishon (Qishon River), northern Israel, we found 178 species from seven divisions of algae and cyanoprocaryotes. Diatoms, clorophytes, and cyanoprocaryotes prevail. Nitzschia and Navicula (Bacillariophyta) are the most abundant. Most of the species are cosmopolitan or widespread, except Lagynion janei (Chrysophyta), which is endemic for the Mediterranean Realm. About 17% of species (26) are new for Israel and five of them represent the first recorded genera: Crinalium endophyticum Crow, Actinocyclus normanii (Gregory) Hustedt, Rhizoclonium hieroglyphicum (Agardh) Kütz (Chlorophyta), Lagynion janei Bourelly, and Stylococcus aureus Chodat. Most of them come from a rare riverine assemblage with red alga Audouinella pygmea, as well as from the estuarine assemblage. Alkaliphiles predominate among the indicators of acidity, with few acidophiles confined to the communities under the impact of industrial wastes. Among the indicators of salinity, most numerous are the oligohalobien-indifferents and species adapted to a moderate salinity level. The relative species richness of ecological groups and the indices of saprobity are correlated with changes in conductivity, pH, and N-nitrate concentration. Indicators of organic pollution fall in the range of betameso- to alfamesosaprobic self-purification grades. Our studies show ecological significance of the Nahal Qishon as a model for a strongly disturbed aquatic ecosystem in the coastal zone of eastern Mediterranean.     

Prioritization of fish assemblages with a view to conservation and restoration on a large scale European basin,the Loire (France)

The hierarchical organization of important sites for the conservation or the restoration of fish communities is a great challenge for managers, especially because of financial or time constraints. In this perspective, we developed a methodology, which is easy to implement in different locations. Based on the fish assemblage characteristics of the Loire basin (France), we created a synthetic conservation value index including the rarity, the conservation status and the species origin. The relationship between this new synthetic index and the Fish-Based Index allowed us to establish a classification protocol of the sites along the Loire including fish assemblages to be restored or conserved. Sites presenting disturbed fish assemblages, a low rarity index, few threatened species, and a high proportion of non-native species were considered as important for the restoration of fish biodiversity. These sites were found mainly in areas where the assemblages are typical of the bream zone, e.g. with a higher number of eurytopic and limnophilic species. On the contrary, important sites for conservation were defined as having an important conservation potential (high RI, a lot of threatened species, and few non-natives fish species) and an undisturbed fish assemblage similar to the expected community if habitats are undisturbed. Important sites for conservation were found in the Loire basin’s medium reaches which host assemblages typical for the grayling and the barbell zones, e.g. with a higher number of rheophilic species. The synthetic conservation value index could be adapted and completed with other criteria according to management priorities and capacities.     

Fish yield estimates for the Sepik River, Papua New Guinea, a large floodplain system east of 'Wallace's Line'

The fisheries of floodplain river systems in Africa, South America and Asia are similar and their yields can be estimated from various morphological, edaphic and other parameters. There is a close similarity in the ichthyofauna of these regions enabling comparisons between systems to be made. The native fauna of New Guinea (Australasia) is devoid of the primary freshwater fishes that compose the majority of the catch from other regions. Various estimates suggest that the present yield of the Sepik River fishery is about 3000–5000 t year⁻¹ This is approximately 10% of the yield of 30 000–45 000 t year⁻¹ predicted by comparison with African rivers. Much of the present catch is introduced tilapia. Considering the native fish species alone, the present yield is only about 5–7% of that predicted. Fishing effort in the Sepik may be low by comparison with African rivers but the faunal difference is probably the main factor involved. This low yield still represents one of the largest and most important fisheries in the country. Such yeild estimates, even if only rough approximations, are vital for planning and management decisions.     

Disappearance of koaro,Galaxias brevipinnis,from Lake Rotopounamu,New Zealand,following the introduction of smelt,Retropinna retropinna

Synopsis Koaro, Galaxias brevipinnis, were once the only fish present in Lake Rotopounamu but, after a comprehensive survey in 1990, none were found in the lake or its tributary streams. Introduced native fish, specifically smelt, Retropinna retropinna, and the common bully, Gobiomorphus cotidianus, now occur in this lake. As koaro co-exist with bullies in other lakes, but have declined in landlocked lakes containing smelt, the disappearance of koaro in Lake Rotopounamu is attributed to the introduction of smelt alone. Interspecific competition for food between 0 + year old koaro and smelt, combined with predation by 2 + year old smelt on koaro larvae, are thought to be responsible. Such a mechanism would be consistent with theoretical predictions of predator-prey regulation systems within same chain food webs. Rainbow trout, Oncorhynchus mykiss, which were introduced into a number of local lakes before smelt, and which preyed on the koaro, have been blamed for the decline of the koaro populations. However, the disappearance of koaro in Lake Rotopounamu shows that smelt can reduce koaro populations independently of trout predation.     

Aspects of ecology and conservation of sympatric,prosobranch snails in a large river

We examined factors influencing distribution of prosobranch snails with field surveys, lab substrate-choice and movement experiments, and outdoor artificial stream experiments manipulating current, substrate and temperature. Restriction of Lithasia obovata to shallow, isolated rock patches and the more continuous distribution of Pleurocera canaliculatum on diverse substrates (shallow to deep water) seem related to food availability, predator vulnerability, wave resistance and dispersal abilities. Shallow, rocky habitats favored by the relatively fragile-shelled Lithasia maximize the more nutritious, epilithic microalgal food while minimizing wave displacement (firmer substrate) and exposure to molluscivorous fish inhabiting deeper waters. The broader distribution of the heavily-armored Pleurocera is attributed mostly to greater dispersal abilities (e.g. via deep water, gravel pathways), prevalence in more substrate types, and resistance to fish predators, but their relatively small foot may account for low densities in very shallow, wave-swept habitats. Lithasia is vulnerable because of its restriction to isolated, shallow rocky habitats, inability to reach deeper gravel dispersal pathways, and greater susceptibility to cold temperatures (slowing colonization of other habitats). Impoundments increase this threat by blocking inter-reach dispersal and hindering intra-reach dispersal through siltation. Pleurocera's survival is threatened by biofouling from zebra mussels which are more prevalent in depths inhabited by this species.     

由气单胞菌的一个新种引起的一次爆发性鱼病的病原学研究

本文报告1988年夏季对北京地区一次爆发性鱼病病原学研究的结果。从病鱼脏器和池塘疫水中分离到革兰氏阴性杆菌,其中氧化酶阳性菌株占75.6%,大多数为溶血性菌株,而不发病鱼池的健康鱼中氧化酶阳性菌株为0.1～1%,详细的生化检定证明这些细菌为气单胞菌,且为同一血清型,但不同于现已报告的亲水气单胞菌,豚鼠气单胞菌,温和气单胞菌,凡隆气单胞菌和舒伯特气单胞菌,而为气单胞菌的一个新种。流行病学资料与实验感染健康鱼发病成功,证明该菌是这次鱼病的病原菌。     

Origins and ecology of the tropicalpine flora of Mt Wilhelm, New Guinea

Floristic elements within the tropicalpine flora of Mt Wilhelm are defined on taxonomic and distributional criteria, and are compared ecologically. The hypothesis that elements of apparently most recent immigration would retain to the largest degree characteristics appropriate to colonists of insular locations and to plants of temperate zone environments is confirmed. Good colonizing ability, rapid growth rate, continuous flowering and growth in the field, successful flowering in cultivation, vulnerability to frost, lack of preference for slopes of particular aspect, and wide and generally low altitudinal range were all present to a greater extent in more recently immigrant floristic elements. Dispersal ability was not significantly correlated with floristic elements. It is concluded that the tropicalpine flora is a youthful one consisting largely of the descendants of immigrant herbs which arrived by dispersal over long distances in Plio-Pleistocene times. A few forest plants of ancient status in New Guinea have become adapated to the tropicalpine environment, and several established aliens provide indications of migration ability lost to varying extents by elements within the native flora.     

Diadromy,history and ecology: a question of scale

The existence of diadromous migrations has significant implications for understanding a broad series of biogeographical and ecological questions and for doing so across a broad range of spatial and temporal scales. Understanding these implications is important for interpretation of patterns in historical and ecological biogeography as well as in community ecology and conservation. This article explores these implications. Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot Fish and diadromy in Europe (ecology, management, conservation)     

Impact of terrestrial protected areas on the fish diversity and habitat quality: Evidence from tropical river Pranhita,India

The conservation and management of inland fish and freshwater ecosystems immensely contribute to global sustainable development. The existing ‘Protected Area’ (PA) network does not represent freshwater resources well and seldom considers its fish communities, while designating PAs. A study was undertaken to quantitatively assess the role played by the three terrestrial PAs (IUCN category IV) in conserving fish diversity and preserving habitat quality in the river reaches bordering the three PAs of the river Pranhita. It is a unique river system in the Indian Deccan Plateau in terms of fish diversity and community structure. Field surveys were conducted during the non-monsoon and monsoon seasons in 2020–21, that recorded 53 species including endemic and threatened fishes from river Pranhita, which represent more than one-third the number of fish species of Telangana state. The higher diversity and lower dominance index value (p < 0.01) reported in PAs compared to Eco Sensitive Zones and unprotected areas during the non-monsoon season indicate the role of intact physical habitat in providing refuges to the fish species in monsoon dependent tropical rivers. The optimal water quality revealed no significant difference (p > 0.0001) between protected and unprotected river reaches, and healthy biotic integrity assessed on the basis of fish community structure was attributed to the contiguous flow and less anthropogenic disturbance. This study supports that it can be considered as a representative zone for the conservation and protection of indigenous and endemic fish species of the Godavari Basin. The results concluded that the scope of the terrestrial PA network in India could be potentially extended to their bordering aquatic ecosystems, especially rivers to maintain pristine habitat conditions and conserve the fish genetic resources to ensure the flow of ecosystem services.     

Variability in body physique, ecology, and subsistence in the Fly River region of Papua New Guinea

There are some 40,000 indigenous peoples of the Fly River drainage in Papua New Guinea. The 4,000-mm rainfall contour ecologically demarcates hunter-horticulturalist peoples living in the rainforests of the Upper Fly from hunter-gatherer peoples living in the savanna-swamplands of the Middle and Lower Fly. A complex of factors operate to create significant physical differences between Upper Fly peoples and those of the Middle and Lower Fly. The ecological division between rainforests and savanna-swamplands demarcates a clear clinal separation by stature of Upper Fly peoples from those of the Middle and Lower Fly.     

Morphological correlates of necromass accumulation in the traps of an Eastern tropical pitcher plant, Nepenthes ampullaria Jack, and observations on the pitcher infauna and its reconstitution following experimental removal

I studied the trap morphology, necromass accumulation rates and pitcher infauna of an eastern tropical pitcher plant, Nepenthes ampullaria, that grew in `kerangas' heath forest in the Sungei Ingei Conservation Area, Brunei. I surveyed 164 pitchers distributed among 35 plants and extracted the necromass and larval infauna from the pitchers and then resampled the pitcher contents after 14 days. Plants varied significantly in the morphology of their pitchers, in their rate of necromass accumulation per pitcher and in the abundance and composition of the pitcher infaunas. On average, pitchers accumulated 11.5 mg dry weight over 14 days, but larger pitchers accumulated more necromass than smaller ones. Pitcher morphology explained 45% of the variation in necromass accumulation among plants. On average, pitchers initially contained 26.3 individual larval inquilines. Collectively, the larval infauna was composed of nine taxa of dipteran larvae and infrequent anuran tadpoles. These ten taxa were never found together in a single pitcher and the mean species richness per pitcher was 4.0. Of the six taxa that could be assessed, all except Toxorhynchites spp. had a contagious distribution among the pitchers. Pitcher morphology and necromass accumulation explained only 15% of the variation in inquiline abundance among plants. I found little evidence for the existence of density-dependent interactions between inquiline species: a partial correlation analysis detected only one statistically significant pairwise relationship between the abundances of inquiline taxa, which was a positive association. Fourteen days after being emptied, pitchers contained an average of 9.6 inquilines. There was no evidence that the species composition of the infauna recolonising each pitcher was related to that of its pre-removal infauna. Received: 2 June 1997 / Accepted: 9 September 1997     

Effects of flow regulation, basin characteristics and land-use on macroinvertebrate communities in a large arid Patagonian river

Longitudinal distribution and abundance of macroinvertebrate communities were examined in relation to hydrochemical variables along the Chubut River in the Patagonian Precordillera and Plateau, Argentina. The Chubut River (>1000 km) is the largest river in the area and its basin is subject to multiple uses: agriculture, cattle raising, urbanization and the hydrological regime of the lower section is modified by a reservoir. Quantitative benthic samples were collected at 13 sites in the higher, middle and lower sections of the river basin. Sites were visited four times during 2004 and physicochemical parameters, chlorophyll a and particulate organic matter (POM) were assessed. Ninety-five taxa were collected in the study, with total species richness per site ranging from 5 to 51, and benthos density averaging 299–5024 ind m⁻². Altitude and turbidity were implicated as important factors determining macroinvertebrate assemblages along the river system, and an eutrophication gradient was documented in the regulated/urbanized section of the main river. High turbidity (TSS) and sedimentation limited algal productivity in the middle basin. Below the dam, TSS, total phosphorus (TP) and POM decreased, whereas soluble reactive phosphorus (SRP) and chlorophyll a increased. Macroinvertebrate density increased three fold in this area possibly due to habitat improvement and enhanced trophic resources. Mean species richness did not change below the impoundment; however the community was dominated by gastropods, chironomids and flatworms. The Chubut River is complex and its biotic community reflects the landscape attributes. While benthic composition and density was governed by turbidity and flood disturbance in some river segments, a greater environmental heterogeneity resulted in an unexpected high number of species at the main channel upper basin.     

Recovery and succession in a multi-species tropical seagrass meadow following experimental disturbance: the role of sexual and asexual reproduction

Recolonisation and succession in a multi-species tropical seagrass meadow was examined by creating gaps (50×50 cm) in the meadow and manipulating the supply of sexual and asexual propagules. Measurements of leaf shoot density and estimates of above-ground biomass were conducted monthly to measure recovery of gaps between September 1995 and November 1997. Measurements of the seeds stored in the sediment (seed bank) and horizontal rhizome growth of colonising species were also conducted to determine their role in the recovery process.Asexual colonisation through horizontal rhizome growth from the surrounding meadow was the main mechanism for colonisation of gaps created in the meadow. The seed bank played no role in recolonisation of cleared plots. Total shoot density and above-ground biomass (all species pooled) of cleared plots recovered asexually to the level of the undisturbed controls in 10 and 7 months, respectively. There was some sexual recruitment into cleared plots where asexual colonisation was prevented but seagrass abundance (shoot density and biomass) did not reach the level of unmanipulated controls. Seagrass species did not appear to form seed banks despite some species being capable of producing long-lived seeds.The species composition of cleared plots remained different to the undisturbed controls throughout the 26-month experiment. Syringodium isoetifolium was a rapid asexual coloniser of disturbed plots and remained at higher abundances than in the control treatments for the duration of the study. S. isoetifolium had the fastest horizontal rhizome growth of species asexually colonising cleared plots (6.9 mm day⁻¹). Halophila ovalis was the most successful sexual coloniser but was displaced by asexually colonising species. H. ovalis was the only species observed to produce fruits during the study.Small disturbances in the meadow led to long-term (>2 years) changes in community composition. This study demonstrated that succession in tropical seagrass communities was not a deterministic process. Variations in recovery observed for different tropical seagrass communities highlighted the importance of understanding life history characteristics of species within individual communities to effectively predict their response to disturbance. A reproductive strategy involving clonal growth and production of long-lived, locally dispersed seeds is suggested which may provide an evolutionary advantage to plants growing in tropical environments subject to temporally unpredictable major disturbances such as cyclones.     

Regulation of the abundance and turnover of copepod species by temperature,turbidity and habitat type in a large river basin

Freshwater copepods were sampled in the La Plata River basin to identify the processes that affect beta diversity and to determine the main factors influencing their geographical distribution and patterns of endemism. Beta diversity patterns exhibited strong dissimilarity between locations; the turnover process was predominant and indicated a replacement of species along the basin. Redundancy analysis indicated the presence of two large sets of species separated geographically by a boundary zone, with several associated variables. Northern species were associated with water transparency and temperature, mean air temperature, mean air temperature during winter and minimum air temperature of coldest month, indicating that these species are not tolerant to low temperatures and are abundant in reservoirs that are common in the upper stretch of the Paraná River basin. Southern species were related with amplitude of air temperature, turbidity, total phosphorus and total suspended matter, indicating that these species are polythermic and have adapted to live in river stretches. From 20 environmental variables analyzed in our study, partial least squares analysis indicated four variables with increased retention of effects on copepod abundance: air temperature, minimum temperature of coldest month, turbidity and transparency. Because almost all of the species found in this study occurred across a wide range of habitat types, the cause of the separation between river and reservoir species could be considered to be more anthropogenic than natural, and it primarily affected species abundance. For certain members of the northern group of copepod species, distribution was dependent on high temperatures, whereas the distribution of the southern group indicated that the species were polythermic.     

Matching research and policy tools to scales of climate-change adaptation in the Murray-Darling, a large Australian river basin: a review

Climate change is likely to cause deleterious hydrological and ecological impacts in many of the world’s major river basins. Using the Murray-Darling Basin, Australia, as a case study, we present an adaptation framework which addresses the hydrological impacts of climate change at three spatial scales: the high-conservation value asset, the water management unit and the entire basin. At each scale, the appropriate scientific, policy and operational tools differ, though should be applied in concert. At the scale of the asset, hydrodynamic modelling has improved the capacity of site managers to anticipate the effects of management interventions. These models have also contributed to improve hydrological modelling of the water management unit. When combined with ecosystem response models, hydrological models can compare ecological outcomes over a range of timescales, leading to improvements in the representation of environmental requirements in water sharing plans. At the scale of the basin, the Australian government has used a legislative mechanism to set overarching ecological and diversion objectives. In addition, the purchase of water-use entitlements has created a flexible mechanism to use the water market as a climate-change adaptation mechanism, responding to the changing water availability and conservation priorities that emerge over the coming decades.     

Effects of exposure to multiple trace metals on biochemical, histological and ultrastructural features of gills of a freshwater fish, Channa punctata Bloch

The trace metals are frequently encountered as mixtures of essential and non-essential elements. Therefore, evaluation of their toxic effects individually does not offer a realistic estimate of their impact on biological processes. We studied effects of a mixture of four essential and toxic metals (Cu, Cd, Fe and Ni) on biochemical and morphological characteristics of the gills of a biomarker freshwater fish Channa punctata (Bloch) using environmentally relevant concentrations. Fish were exposed to metal mixture through tank water for 7, 15 and 30 days. Biochemical studies as well as light microscopy (LM) and scanning electron microscopy (SEM) revealed significant metal exposure-induced alterations in gills. Besides ultastructural changes, activities of antioxidant enzymes such catalase (CAT), glutathione S-transferase (GST) and superoxide dismutase (SOD) were significantly altered in the gills of exposed fish. The reduced glutathione (GSH) was significantly (p<0.001) decreased, while lipid peroxidation (LPO) was significantly (p<0.001) increased. The main alterations in general morphology of fish gills included spiking and fusion of secondary lamellae, formation of club-shaped filaments, and vacuolization and necrosis of filament epithelium in the interlamellar regions. SEM studies showed gradual increase of the density and apical surface area of the chloride cells and transformation of the surface structure of the pavement cells. The results of this study indicate adaptive as well a toxic responses in fish gills exposed to mixture of trace metals. Low concentrations of trace metal appear to compromise the antioxidant defense of gills. Lesions in the gill morphology caused by the effect of low concentrations of trace metals could lead to functional alterations and interference with fundamental processes such as maintenance of osmoregulation, gas exchange and xenobiotic metabolism in the exposed fish populations.     

Emerging directions in the study of the ecology and evolution of plant-animal mutualistic networks: a review

The study of mutualistic plant and animal networks is an emerging field of ecological research. We reviewed progress in this field over the past 30 years. While earlier studies mostly focused on network structure, stability, and biodiversity maintenance, recent studies have investigated the conservation implications of mutualistic networks, specifically the influence of invasive species and how networks respond to habitat loss. Current research has also focused on evolutionary questions including phylogenetic signal in networks, impact of networks on the coevolution of interacting partners, and network influences on the evolution of interacting species. We outline some directions for future research, particularly the evolution of specialization in mutualistic networks, and provide concrete recommendations for environmental managers.