Genetic structure of the migratory catfish Pseudoplatystoma corruscans (Siluriformes: Pimelodidae) suggests homing behaviour

Abstract –  Pseudoplatystoma corruscans is distributed widely in the La Plata Basin in Brazil, where it is a very important species because of its high commercial value and ecological role as a voracious predator. This species undertakes long migrations during the dry and rainy seasons to feed and reproduce, respectively. In this study, we analysed seven microsatellite loci to test the hypotheses of the existence of a single panmictic population of P. corruscans in the La Plata Basin. All microsatellites analysed were highly polymorphic with the number of alleles per locus ranging from seven (Pcor28) to 30 (Pcor10). Across all samples, 107 alleles were detected. Thirty alleles were private, i.e., found in only one sample. Highly significant genetic differentiation was observed among samples in three of the four analyses performed: F _ST (from 0.03435 to 0.16349, P  < 0.05), Analysis of molecular variance (amova) F _ST = 8.25% ( P  < 0.0001) and amova R _ST = 9.72% ( P  < 0.0001). A microsatellite multilocus Bayesian assignment test with the programme structure confirmed the division of the fishes into six groups largely concurrent with main branches on a population neighbour-joining tree. The obtained results rejected the panmixia hypothesis. On the other hand, the documented long-distance movements of P. corruscans and the geographical scale of genetic differentiation found in this study indicate a strong tendency for fish of this species to utilise their natal nursery regions for reproduction, which represents the first demonstrated example of homing in a freshwater catfish in South America.     

Influences of human activity and climate on the stock-recruitment dynamics of whitefish, Coregonus lavaretus, in Lake Geneva

Abstract  Analysis of long-term catches from the deep peri-alpine Lake Geneva, showed a shift in the stock-recruitment relationship of Coregonus lavaretus (L.), a target species of commercial fishing. This change was mainly related to large-scale meteorological factors. Higher spring water temperatures may have improved larval survival and hence recruitment of whitefish via: (1) a better match between the hatching date of whitefish larvae and development of their zooplankton prey; and (2) the positive temperature effect on larval growth. In Lake Geneva, changes in regulatory mechanisms coupled with stocking and improved water-quality have led to an explosion in the C. lavaretus population in recent years. These results highlight the relevance of long-term changes in the stock-recruitment relationship for management of aquatic ecosystems that are sensitive to climate forcing.     

Dissolved oxygen controls summer habitat of Clear Lake Hitch (Lavinia exilicauda chi), an imperilled potamodromous cyprinid

Clear Lake Hitch is an imperilled minnow endemic to Clear Lake, Lake County, California, United States listed as threatened under the California Endangered Species Act (ESA) and a candidate for listing under the United States ESA. It exhibits a potamodromous life cycle whereby adults, which reach up to 6 + years in age and over 350 mm in length, migrate into Clear Lake's ephemeral tributaries briefly during spring to spawn. Conservation and management of Clear Lake Hitch is inhibited, in part, by a lack of information on the lacustrine habitat of nonbreeding individuals within Clear Lake. To address this problem, we sampled Clear Lake Hitch with gill nets in a stratified random sampling design to determine the distribution and habitat associations in early summer 2017 and 2018. We identified abundance-habitat relationships for juveniles and adults using Bayesian zero-inflated negative binomial generalised linear mixed modelling. Results indicated that dissolved oxygen concentration was the most important habitat feature measured; juveniles and adults were substantially more abundant in normoxic (≥2 mg/l) than in hypoxic (<2 mg/l) habitat. Both also exhibited weak positive relationships with chlorophyll fluorescence, suggesting relatively productive habitats may support higher numbers of Clear Lake Hitch. Spatially, juveniles were most abundant in nearshore habitats while adults were ubiquitous, indicating an ontogenetic habitat expansion that may be associated with a resource availability-predation risk trade-off. Management actions undertaken to improve hypoxia problems in Clear Lake would also improve Clear Lake Hitch habitat.     

Apparent digestibility coefficient of protein and amino acids of acid, biological and enzymatic silage for Nile tilapia (Oreochromis niloticus)

Using the fish silage to partially replace proteic feedstuff in aquafeeds is an alternative to mitigate sanitary and environmental problems caused by the lack of adequate destination for fisheries residues. It would also lower feed costs, consequently improving fish culture profitability. However, using fish silages in aquafeeds depends on determination of its apparent digestibility coefficients (ADC). This work aimed to determining the ADC of crude protein and amino acids of acid silage (AS), biological silage (BS) and enzymatic silage (ES) for juvenile Nile tilapia (94.5 ± 12.7 g). The ADC_CP was: 92.0%, 89.1% and 93.7% for AS, BS and SE respectively. The average ADC of amino acids was: 91.8%, 90.8% and 94.6% for AS, BS and ES respectively. Results encourage the use of AS, BS and ES to partially replace protein sources in balanced diets for neotropical fish.     

灌区整体利益下水价模型研究

水资源的合理配置利用,就是在对水资源系统的运行和演化机理进行科学分析的基础上,促进用户进行节水.目前,水资源管理的主要措施大都集中在加强行政管理和水资源配置机制方面.开源节流、加强管理只能是解决问题的外因,水资源的合理配置问题,最好由用水者自己来解决,由用水者的利益激励机制来解决,这样才能从根本上解决水资源的短缺和低效率应用问题.利益激励的关键在于水价的制定,拟从数学和管理2个角度,从供水方和用水方的利益激励出发,提出了同时考虑供水方、用水方统一的数学模型,并对模型进行了求解,为灌区水资源定价提供了依据.最后,对该模型的进一步完善指出了研究方向.     

A spatial linkage between dams and non-native fish species in Hokkaido, Japan

Abstract –  The native and non-native freshwater fish species richness as well as the proportion of native fish species to overall fish species were examined to test a hypothesis of a spatial linkage between the distributions of dams and non-native fishes based on survey data collected in rivers and streams in Hokkaido, Japan. Non-native fish species have steadily increased in Hokkaido since the mid 1970s, as indicated by the decreasing proportion of native fish species per fish survey. Non-native species richness was significantly higher in areas above dams (i.e., reservoirs and their inlet streams) compared to areas without dams. As a result, the proportion of native fish species was lower above dams. This proportion was lower in developed and agricultural areas compared with forest areas, although both native and non-native species richness were higher in areas with development and agriculture. Non-native cyprinids, catfish and snakehead occurred primarily in a particular river basin with the largest drainage area, the longest history of reclamation and highest human population in the island. Non-native salmonids on the other hand, occurred in forest areas at higher elevations and their occurrence was associated with the existence of dams. There was a spatial linkage between the distribution of dams and non-native species, although it was applicable only to salmonids. The management of dams and reservoirs needs a strategy to prevent further expansion of exotic salmonids such as rainbow and brown trout. These species can be a significant threat to native Japanese salmonids as a result of various biological mechanisms.     

Movement patterns of armado, Pterodoras granulosus, in the Paraná River Basin

Abstract –  We studied the migratory behaviour of armado, Pterodoras granulosus , in the Paraná River Basin of Brazil, Paraguay and Argentina, during 1997–2005. This species invaded the Upper Paraná River after upstream dispersal was facilitated when Itaipu Reservoir inundated a natural barrier. Fish were tagged ( N  = 8051) in the mainstems of the Yacyreta and Itaipu reservoirs, bays of major tributaries, the Paraná River floodplain above Itaipu Reservoir, and below dams. In all, 420 fish were recaptured of which 61% moved away from the release area. Fish moved a maximum of 215 km (mean 42), and at a maximum rate of 9.4 km·day⁻¹ (mean 0.6). Of the 256 armados that moved away from the release site, 145 moved upstream towards unimpounded stretches of the Paraná River and 111 moved downstream into the reservoir and bays of its tributaries (maximum 150 km). Based on the observed migratory movements, we suspect that most of the reproductive output originates in tributaries to the reservoirs. The ability of this species to expand its range presents a conundrum by pitting fishery management interests against conservation needs. Maintenance of the important armado fisheries depends on the ability of the species to migrate freely to use spawning and nursery areas in reservoir tributaries and floodplains. However, its ability to migrate long distances can allow this non-native species the opportunity to invade most of the Upper Paraná River.     

Variability in feeding ecology of a South American cichlid: a reason for successful invasion in mediterranean‐type rivers?

Abstract –  Ecological attributes behind the success of the South American cichlid Australoheros facetus in mediterranean-type rivers remain unclear. This study addresses this issue, by analysing its abundance and feeding patterns in the lower Guadiana drainage (Portugal), during the dry season of 2003. Despite slight spatial variations in abundance and individual size, A. facetus seemed well established in the Guadiana, Vascão and Ardila rivers. No seasonal or size-related changes in feeding intensity were found, but the diet changed across rivers, over time and throughout ontogeny. Feeding seemed highly generalist, with fish apparently reacting to both spatial and temporal changes in food supply and tending to use the most abundant and easily accessible food items. Overall prey breadth was broad relative to that of other native and non-native species. It is suggested that a generalist feeding strategy may play a significant role in the establishment of non-native fish in mediterranean-type rivers.     

Seasonal dynamics and age structure of drifting cyprinid fishes: an interspecific comparison

Abstract –  We investigated interspecific differences in the downstream drift of seven species of young-of-the-year cyprinids over a 2-year period in two central European rivers, using a comparison of drifting fish with fish collected from nurseries at the same time and the same site as the drift samples. Species varied in the utilisation of the drift; Rutilus rutilus , Gobio spp., Abramis brama and Carassius auratus gibelio drifted abundantly, while Leuciscus cephalus and Alburnus alburnus were abundant in nurseries, but drifted at low densities. Abramis bjoerkna was equally represented among drifting and resident fish. Generally, fish drifted at two major developmental intervals; L3 stage and the stage at transition between larval and juvenile periods (L6/Juv), with interspecific differences in the ontogenetic timing of drifting. The propensity to drifting of certain developmental stages was also reflected in body size comparisons between drifting and resident fish. The stage-dependent drifting may be attributed to major changes in fish morphology, behaviour and swimming ability.