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.     

Protein quality of larval feed with increased concentration of hydrolysed protein: effects of heat treatment and leaching

Four heat coagulated early weaning diets with increasing concentrations of pepsin hydrolysed protein, were investigated with regard to the change in protein quality during feed production and exposure to leaching. Water-soluble N, trichloroacetic acid-soluble N and amino acid (AA) profiles were determined in finished diets and in diets leached for 6 min. In vitro diet digestibility was measured and related to increasing inclusion of hydrolysed protein and N leakage. Seventeen to 47% of soluble N in the feed ingredients was made insoluble by heat denaturation during feed production, but the concentration of peptides and free amino acids (FAA) were not influenced. All peptides/FAA and 70–80% of water-soluble protein were lost after exposure to leaching. Increased inclusion of hydrolysed protein increased the loss of crude protein (15–30%). All taurine and 30% of histidine was lost during leaching, no other major changes in AA profile were found. There was no difference in digestibility between diets exposed to leaching. However, leached diets showed reduced digestibility as compared to diets that had not been exposed to leaching. In conclusion micro-bound type diets as used in this study have a low efficiency in delivering soluble N to fish larvae and should be carefully considered for this purpose.     

Substrate choice of territorial male Topeka shiners (Notropis topeka) in the absence of sunfish (Lepomis sp.)

Abstract –  Topeka shiners ( Notropis topeka ), an endangered minnow species, typically spawn on or around breeding Lepomis sunfish (Centrarchidae) nests. Why spawning Topeka shiners are attracted to these nests is unclear, but having the nesting sunfish provide shiner eggs with improved aeration, a lessening of siltation, and protection from egg predators are possibilities. We tested the substrate utilisation of Topeka shiners in outdoor tanks in the absence of sunfish to determine the shiner's fundamental choice. Shiners were provided with substrate patches of cleaned sand, small gravel, large gravel, and small cobble, and the bare floor of the tank. The substrate above which a male shiner established his territory was used as evidence of choice. A statistically significant choice for sand substrates was demonstrated. This fundamental choice might influence which sunfish nests Topeka shiners use, given that nest substrate characteristics differ both between sunfish species and within species by spawning site location.     

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.     

细鳞鱼的生物学特性及其在华北分布范围的变化

本文报导了细鳞鱼(Braochymystax lenokP.)的形态构造、食性及其生态环境。调查了华北地区细鳞鱼分布变化情况,并阐明由于生态环境等因素的变化是引起该种在华北地区分布范围缩小的原因,同时提出保护细鳞鱼资资源的措施。     

Habitat relationships with fish assemblages in minimally disturbed Great Plains regions

Abstract – Effects of local environmental influences on the structure of fish assemblages were evaluated from 159 sites in two regions of the Great Plains with limited anthropogenic disturbance. These regions offered an opportunity to evaluate the structure and variation of streams and fish assemblages within the Great Plains. We used canonical correspondence analyses to determine the influence of environmental conditions on species abundances, species occurrences and assemblage characteristics. Analysis of regions separately indicated that similar environmental factors structured streams and fish assemblages, despite differences in environmental conditions and species composition between regions. Variance in fish abundance and assemblage characteristics from both regions was best explained by metrics of stream size and associated metrics (width, depth, conductivity and instream cover). Our results provide a framework and reference for conditions and assemblage structure in North American prairie streams.     

鱼类休闲食品的研制

本文主要介绍了用新鲜或冻藏草鱼制作鱼肉松和五香鱼干的制作工艺，对制品的风味，工艺条件，包装材料，包装方法作了较详细的研究，根据多次实验的结果，找出了最佳工艺条件，制成了味道醇美，咸中带甜，鲜美可口，营养丰富的鱼肉制品。     

淡水鱼肝脏中维生素A1,A2含量的研究

本试验建立了用高效液相色谱法同时测定淡水鱼肝脏中的ＶＡ１和ＶＡ２的方法。以μ－Ｐｏｒａｓｉｌ３．９ｎｍ×１５０ｍｍ（Ｗａｔｅｒｓ Ｃｏ．）为色谱柱，正己烷：乙醚（８７：１３）为流动相，紫外３５０ｎｍ，荧光Ｅｘ３２５ｎｍ，Ｅｍ４８０ｎｍ双道检测，ＶＡ１和ＶＡ２的保留时间分别为２６．２５ｍｉｎ和２８．００ｍｉｎ。采用不同波长条件下的紫外吸收特性，对ＶＡ２予以定性，以ＶＡ１为内标物对ＶＡ２予以定量。实验     

富碘鱼面的生产工艺

介绍了富碘鱼面生产工艺，该工艺是对传统食品进行探讨性改造中较为成功的一例。它不仅提高了当地传统食品——鱼面的品质，促进了传统食品的生产，也说明我国食品行业有相当一部分商业机会是隐藏于传统食品的改造创新中。