Acquired Predator Recognition by Fathead Minnows: Influence of Habitat Characteristics on Survival

In this study we conditioned fathead minnows (Pimephales promelas) to recognize the odor of a perch (Perca flavescens) by exposing them to perch odor coupled with minnow alarm cue. We then staged encounters between the predator and prey in order to assess whether the predator odor training had any effect on survival of the prey. We tested for a survival effect in the presence and absence of shelter. Our results indicate that fish trained with alarm signals to recognize predators gained a survival benefit during staged encounters with a predator and that habitat characteristics influenced the survival of conditioned fish.     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.     

Importance of biotic interactions in large rivers: an experiment with planktivorous fish,dreissenid mussels and zooplankton in the St. Lawrence River

Physical conditions are usually considered pre‐eminent in controlling river plankton, but biotic interactions may be important in slackwater areas. To begin testing this general hypothesis, we conducted a 12‐day, predator–prey experiment in 3500 litre mesh enclosures in a slackwater area of the St. Lawrence River using planktivorous, juvenile yellow perch (Perca flavescens) and Dreissena mussels. Results generally supported our hypotheses that: (1) perch would directly suppress large zooplankton via predation but benefit microzooplankton through indirect interactions; and (2) dreissenids would directly depress rotifer densities via predation and have indirect negative effects on macrozooplankton. Based on gut contents of experimental fish, cladocera were the principal prey of smaller yellow perch (c. 46–50 mm), followed by copepods, ostracods, and rotifers. Larger juvenile perch (c. 67–73 mm) fed almost exclusively on copepods and ostracods. Densities of calanoid copepodids, nauplii, and some cyclopoid copepods (Diacyclops thomasi) were significantly depressed by perch, and adult Eurytemora affinis (99% of adult calanoids) essentially disappeared from fish enclosures. Despite being a favourite prey item of small perch, densities of the small cladoceran Bosmina (Sinobosmina) spp. were significantly higher when fish were present (150% greater than control densities on Day 12). Densities of the very abundant rotifer Polyarthra were >300% greater in fish enclosures than controls by Day 12, and the rotifers Synchaeta and predaceous Ploesoma were significantly more abundant in the presence of perch. Increases in rotifers and cladocera suggest indirect, positive effects of fish related to significantly higher phytoplankton biomass or decreased densities of predaceous copepods. Densities of eight of ten zooplankton groups examined declined significantly when mussels were present, and calanoid copepodids also declined but not significantly. Chlorophyll‐a concentrations were slightly lower in mussel enclosures. This evidence suggests biotic interactions play important roles among potamoplankton in slackwater habitats, but river‐wide implications of these findings require further study. Copyright © 2003 John Wiley & Sons, Ltd.     

Nature‐like fishways as compensatory lotic habitats

Damming of rivers disrupts migration of fish and results in lotic habitats being both scarcer and spaced further apart, ultimately affecting riverine fish communities. Nature‐like fishways are often designed as bypass channels, constructed with natural materials that reroute part of the water around weirs and dams, restoring longitudinal connectivity as well as forming nature‐mimicking habitats. We evaluated the potential of such bypasses to function as compensatory lotic habitats by comparing fish fauna in 23 bypasses to adjacent lotic stream habitats in a same‐river pairwise design. Bypasses were narrower, shallower, and less shaded than adjacent stream habitats, but very few significant differences could be detected in the fish communities, indicating the potential of such nature‐like fishways to constitute compensatory lotic habitats for fish. Analyses also indicated how bypass design may be altered to favour or disfavour certain target species. Generally, narrower and shallower bypasses with high gradient favoured brown trout (Salmo trutta), whereas European eel (Anguilla anguilla) were more abundant at sites with lower gradient. Finally, to increase the impact of these compensatory habitats on running water ecosystems, we suggest that the size of bypasses should be maximized in areas where natural stream habitats have been lost.     

Nutritional quality and safety of European perch (Perca fluviatilis) from three lakes of Central Italy

European perch (Perca fluviatilis) harvested from three lakes of Central Italy were studied in different seasonal periods of a year to evaluate their nutritional quality and some safety aspects related to the pollution of the aquatic environment. The lakes considered, located in the Latium region, differed with respect to their volcanic (Bolsena and Bracciano Lakes) or artificial (Salto Lake) origin. Fillets of fish caught in the three lakes were characterised by good protein (17–19%) and mineral contents and low lipid levels (0.6–1.2%) throughout the year. Total lipids were characterised by low cholesterol levels (41.9–74.7 mg/100 g) and high percentages of total n − 3 polyunsaturated fatty acids (27.7–33.8% of total fatty acids), in particular docosahexaenoic acid (14.2–25.3% of total fatty acids). The qualitative analysis of the stomach content of perch confirmed their predatory feeding behaviour. The chemical and nutritional profiles of perch from the three lakes were comparable except for rubidium and cesium levels, which were higher in the muscle tissues of perch from the volcanic lakes. These minerals may represent elements of traceability of the origin of fish. Low levels of organochlorine pesticides and polychlorinated biphenyls, well below the Italian and European action limits, were detected in the muscle tissue of perch from all three lakes.     

Fatty acid profile of muscles,liver and mesenteric fat in wild and reared perch (Perca fluviatilis L.)

This study addressed determinations of the fatty acid profile of muscle, liver and mesenteric fat in European perch originating from natural aquifers and from intensive rearing in a closed circuit on an artificial feed mixture. The qualitative composition of fatty acids was identical in both groups of perch, except for 16:4 acid identified exclusively in the reared perch. The study demonstrated equal concentrations of saturated (SFA) and unsaturated (UFA) fatty acids in muscles, liver and mesenteric fat of both groups of perch. The wild fish, however, were characterised by lower concentrations of monoenoic (MUFA) and higher concentrations of polyenoic (PUFA) fatty acids. Analyses also demonstrated similar contents of n − 3 PUFA in muscles and their diversified concentrations in liver and mesenteric fat (higher in the wild fish), as well as a higher content of n − 6 PUFA in all samples. The lower content of MUFA in the wild perch was mainly due to lower concentrations of cis18:1 n − 9 and 20:1 n − 9, whereas the higher content of n − 3 PUFA was due to a higher concentration of DHA, and the higher content of n − 6 PUFA was due to a higher concentration of arachidonic acid (AA). The biggest differences between wild and reared perch were detected for AA. The wild and reared perch were also found to differ in the n − 3/n − 6 ratio (higher in the reared fish) and to have similar values for atherogenic index (AI) (except for liver and mesenteric fat) and thrombogenicity index (TI).     

基于GC-IMS和化学计量学分析海鲈鱼肉蒸制过程中风味物质的变化

以海鲈鱼为对象,采用气相色谱-离子迁移谱（gas chromatography-ion mobility spectroscopy,GC-IMS）技术分析鱼肉蒸制过程中挥发性风味物质的变化情况。结果表明,采用GC-IMS法从海鲈鱼肉中共鉴定出43 种挥发性物质,包括醛类、酮类、醇类、酸类和酯类化合物等。不同蒸制时间下海鲈鱼肉的风味物质组成存在明显差异,其中新鲜鱼肉中3-甲基丁醇、二甲基二硫和丙酸等物质的含量较高,经蒸制后鱼肉中的辛醛、壬醛、3-甲基丁醛、(E,E)-2,4-辛二烯醛、苯甲醛、2-庚酮、2-丁酮、1-辛烯-3-醇、1-庚醇和1-丁醇等物质的含量显著增加。采用正交偏最小二乘法判别分析筛选出11 种特征标志物（变量重要性投影值大于1）,通过热图聚类分析可以区分不同蒸制时间下海鲈鱼肉样品的挥发性风味差异,其中3-甲基丁醇、1-庚醇、糠醇和(E)-2-庚烯醛可作为生熟海鲈鱼肉的特征挥发性标志物。本研究结果表明GC-IMS可有效区分鱼肉的熟化过程。     

Sensory Preference and Discrimination of Wild-caught and Cultured Yellow Perch (Perca flavescens)

ABSTRACT: Wild-caught and cultured yellow perch ( Perca flavescens ) were compared for overall difference and preference. Judges ( n = 52) completed 2 replications each of both a paired preference and a triangle test. Results were analyzed using the p-binomial model. Findings indicate that samples were significantly different from each other ( P = 0.0001) but there was no significant preference for either sample ( P = 0.1167). For both tests, overdispersion, or panelist variability was very low, indicating judges were acting similarly and the binomial model better fit the data. Judges' comments were contradictory and inconsistent, making it impossible to determine the exact nature of the difference.     

Consumer Perception of Cultured Yellow Perch (Perca flavescens) and Its Market Competitors

ABSTRACT:  Aquaculturists are concerned with performance of cultured yellow perch against its wild-caught market competitors. In this study, consumer perception of cultured yellow perch was compared to that of wild-caught walleye, ocean perch, and zander. In 2 experiments, species were ranked for preference, rated for liking, and rated for degree of difference from a reference (cultured perch). Results were analyzed using Friedman's analysis of ranks, analysis of variance, and method of maximum likelihood. In Experiment 1 ( n = 50), there was no significant difference in preference or liking, and all wild-caught species were significantly different from the reference. In Experiment 2 ( n = 68), the species were trimmed to the same thickness for a more fair comparison of these species. Cultured yellow perch was equally preferred to all species but was rated significantly higher than walleye in overall liking. In addition, ocean perch and walleye were found to be significantly different from cultured perch, while zander was not.     

Reproductive status in female perch (Perca fluviatilis) outside a sewage treatment plant processing leachate from a refuse dump

Reproductive failure and endocrine disruption in female perch (Perca fluviatilis) and female brook trout (Salvelinus fontinalis), naturally exposed to toxic leachate from a municipal refuse dump, has raised concerns about the reproductive status in female fish outside the sewage treatment plant (STP), which now treats the same leachate. Female perch from the receiving water, Lake Siljan, were therefore sampled in a gradient from the STP in Fornby and Osterviken and compared with reference females from Isunda or Solleron. A high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) technique enabled the analysis of circulating steroids in blood plasma: the sex steroids progesterone (P), 17alpha-hydroxyprogesterone (17alpha-OHP), androstenedione (A), testosterone (T), estrone (E1), and 17beta-oestradiol (E2), the maturation-inducing hormone (MIH) 17alpha,20beta-dihydroxy-4-pregnen-3-one (17alpha,20beta-P), and the glucocorticoids 11-deoxycortisol (11-DC) and cortisol (C). Body and organ measurements, ratio of sexually mature (SM) females, and frequencies of body lesions, were also recorded. The percentages of SM females found in Fornby on Oct 23 (83.8%) and in Osterviken on May 14 (54.0%) were lower compared with Isunda (100%). The lack of differences in gonadosomatic index (GSI) and liver-somatic index (LSI) indicated a normal vitellogenesis in SM females from Fornby and Osterviken. No differences in circulating levels of steroids were observed between the sites, except at the time of spawning, when elevated P and 17alpha-OHP levels in females from Osterviken indicated a steroidogenic shift from the synthesis of sex steroids towards the production of the MIH 17alpha,20beta-P. The significant peak-levels of both 17alpha,20beta-P and 11-DC in female perch from Osterviken at the same time suggest that both are involved in controlling final oocyte maturation in perch. The elevated levels of androgens (A and T) in females caught on the same occasion in Fornby implied that these females were at an earlier stage of oocyte maturation, prior to the steroidogenic shift towards MIH-production. This study confirms the results of an earlier study revealing low numbers of SM female perch outside the STP in Fornby. The lack of associated effects on organ indexes and circulating levels of steroids does not indicate exposure to endocrine disrupting substances (EDSs) from the treated sewage. The consistently high numbers of SM females in the northern part of Siljan suggest, however, that natural factors are not responsible for the reproductive failures in the southern part of the lake.