Movements of adult Atlantic salmon in relation to a hydroelectric dam and fish ladder

The movements of adult Atlantic salmon were recorded as they approached, entered and ascended the pool-and-orifice fish ladder at Pitlochry Dam, Scotland. Thirty-nine returning salmon were captured in the River Tummel by rod-and-line angling, radio-tagged and released near where they were caught. The subsequent movements of each fish were then monitored. An electronic fish counter collected additional data on movements of untagged fish past a fixed point in the ladder. Of the 39 fish that were radio-tagged, 29 individuals were recorded approaching and ascended the ladder. The remaining fish either did not approach the dam (three fish), approached the dam after detailed tracking had ended (two fish), were recaptured by anglers (three fish), or the radio tags failed (two fish). Salmon released earlier in the year delayed longer before first approaching the dam. Delays between first approaching the dam and ascent of the ladder were greater for fish that approached the dam earlier. The majority of salmon visited the ladder entrance more than once (maximum 10 visits) before ascending. Having entered, all but four salmon ascended the fish ladder successfully on their first attempt. The four individuals that failed to do so succeeded on their second attempt. The rate at which salmon ascended the ladder was related directly to temperature. The shortest ascent time of a radio-tagged salmon was 5·25 h. Movements of eight of 11 tagged fish through the ladder ceased with the onset of darkness but continued on the following morning. No radio-tagged fish entered the ladder at temperatures below 9) C. Similarly, few untagged fish were recorded ascending the ladder by the electronic fish counter at water temperatures below 8·5) C. Records from the fish counter indicated that 92% of upstream movements were made during daylight.     

Movement and site fidelity in young brown trout Salmo trutta populations in a southern Irish stream

Populations of brown trout Salmo trutta were monitored at a number of sites within a single stream, using an individual marking technique and recapturing uniquely marked fish repeatedly over a period of 12 months. Individual 1 + and 2 + resident brown trout in the Glenfinish River were found to consist of stationary and mobile component populations. The latter population consisted of a number of individuals observed moving mostly in an upstream direction, within a range of 0.03–2.24 km. On a large spatial scale, individuals in the stationary component population exhibited some degree of home site fidelity within the stream, over a period of 3–4 months, after which the fish tended to move from the site. Within sites, fidelity to either riffle or pool habitats, mostly the latter, was apparent in a proportion of the population. On a smaller scale, fidelity to the exact position with respect to boulders in the stream was also evident in a number of individuals. Home range size was calculated amongst these individuals, with ranges of up to 20 m recorded.     

Molecular analysis of a NOR site polymorphism in brown trout (Salmo trutta): organization of rDNA intergenic spacers.

Using restriction endonuclease mapping, we have analyzed the organization of rDNA (DNA coding for ribosomal RNA (rRNA)) units in the salmonid fish Salmo trutta, as an initial step toward understand the molecular basis of a nucleolar organizer region (NOR) site polymorphism detected in this species. The size of the rDNA units ranged between 15 and 23 kb, with remarkable variation both within individuals and between populations. Three regions of internal tandem repetitiveness responsible for this length polymorphism were located to the intergenic spacers. NOR site polymorphic individuals showed a higher number of length classes, in some cases forming a complete 1 kb fragment ladder. The amount of rRNA genes was as much as 8-fold higher in polymorphic individuals compared with standard individuals. All individuals from the most polymorphic population showed a 14-kb insertion of unknown nature in a small proportion (below 25%) of the 28S rRNA genes.     

Morphological and physiological changes of female tropical eels, Anguilla celebesensis and Anguilla marmorata, in relation to downstream migration

Acoustic telemetry and microchemical analysis of otolith strontium-calcium ratios were used to evaluate how exotic brown trout Salmo trutta have responded to Japanese riverine environments of south-western Hokkaido by observing their migratory patterns. The existence of anadromous S. trutta was also verified. Most S. trutta caught in rivers for otolith analysis were freshwater residents (95·6%), whereas those caught in the sea were mainly smolts (91·3%), which had just migrated from rivers during spring. Anadromous S. trutta (n = 6) were captured in rivers and in the sea, confirming the existence of mature pre- and post-spawning fish. According to telemetry results, both mature and immature S. trutta used the river in winter, and their estimated sea-run timings showed individual differences. Through the combination of these two methods, migratory patterns on various spatio-temporal scales were observed. This first documentation of the presence of both male and female anadromous S. trutta in the same region within Japan indicated the risk of further colonization of exotic S. trutta via oceanic migration.     

Marine feeding of anadromous Salmo trutta during winter

Juvenile and adult anadromous trout Salmo trutta utilize the sea for feeding during the winter in the Skagerrak. This finding conflicts with the traditional view that anadromous trout overwinter in fresh water. Adults, just prior to spawning, were captured at sea in October to December, and spent fish were caught at sea from October to April, showing that the fish may leave the stream and move to sea just after spawning and spend the winter there. During mid‐winter (January to February), the feeding probability (chance of finding a fish with food in its stomach) increased markedly with increasing body length, with no similar effect during early and late winter (October to December and March to April). Among individuals with food in their stomach (72·5%), there was no evidence for variation in feeding intensity [stomach fullness = (mass of stomach content)(fish body mass)⁻¹] among early, mid‐, and late winter.     

Pre‐migratory differentiation of wild brown trout into migrant and resident individuals

In February to March, wild brown trout Salmo trutta were captured by electrofishing in a natural watercourse (tributaries of the River Lille Aa, Denmark), individually tagged (Passive Integrated Transponders), and released. Representatives of the tagged brown trout were recaptured on the release sites in April by electrofishing and eventually caught in downstream smolt traps ('migrants') placed in the main river or by electrofishing ('residents') on the initial sites in June. Upon each capture, smolt appearance and body size were evaluated, and a non‐lethal gill biopsy was taken and used for Na⁺,K⁺‐ATPase analysis. Based on repetitive gill enzyme analysis in individual fish, a retrospective analysis of the rate of development in individual brown trout ultimately classified as migrants or residents was performed. Two months prior to migration, a bimodal morphological and physiological (gill Na⁺,K⁺‐ATPase) development concurred and was related to the subsequent differentiation into resident and migratory fractions of each population. This differentiation was unrelated to growth rate and body size of individual fish but skewed in favour of migratory females. Individuals destined to become migrants developed a smolt‐like appearance before the onset of migration and had higher rate of change of gill Na⁺,K⁺‐ATPase activity than fish remaining residents. The rate of change of gill Na⁺,K⁺‐ATPase activity was independent of the distance migrated to the trap (3–28 km). Thus in bimodal wild brown trout populations a major increase in enzyme activity takes place before migration is initiated and is a characteristic of migratory individuals only.     

Visual isolation furthers access to drift‐feeding positions for subordinate juvenile brown trout (Salmo trutta) in dominance hierarchies

Juvenile salmonids are visual predators that primarily feed on drifting invertebrates and compete for suitable feeding positions in swift water. We used an outdoor experimental stream to test the effect of visual isolation on agonistic interactions and habitat use by age‐1 brown trout ( Salmo trutta ) in riffle‐pool sections. We hypothesized that dominant fish defend suitable feeding positions in riffle and that visual obstruction between individuals enhance access to riffle for subordinates. Groups of juveniles, caught in the wild, were stocked in high and low visibility treatments. Visual isolation was manipulated by placing dark plastic ribbons or opaque Plexiglas boards onto the substrate of riffles. As expected, dominant fish held profitable positions in riffle and the proportion of fish in riffle significantly increased in presence of artificial structures. In high visibility treatment, the dominant fish despotically excluded subordinates from the riffle. In low visibility treatment, the proportion of fish that foraged on benthic prey in the pool and the number of major aggressive acts (chase, nip) decreased. Our results support the hypothesis that screening effect of physical structures in the water column loosen resource monopolization in dominance hierarchies of juvenile salmonids.     

An investigation of the advantages of autumn and spring stocking with brown trout Salmo trutta L. in a Yorkshire reservoir

Batches of trout have been introduced into Chelker Reservoir in Yorkshire in the autumn and spring since the 1870's for angling purposes. Six batches of tagged, hatchery-reared brown trout Salmo trutta L. were introduced from autumn 1966 to spring 1969. During the angling season fish introduced in the spring give better catches than those stocked in the autumn. At the beginning of the season the larger fish in the spring batch are caught more often than the smaller fish from the same batch. The larger fish in the autumn batch are caught more often than the smaller fish from that batch throughout the season. The population, available to the angler from the shore was estimated to be 1491 in 1968, with 722 fish/km of shoreline. More fish survive to a second year in the reservoir than is apparent from the number of tags returned. Fish introduced in the spring usually begin growing before those introduced in the autumn, thereafter growth rates varied. The growth rate was independent of the number offish stocked up to the numbers put in.
Batches of tagged trout were retained at the hatchery up to nine months to gain relevant experience of post-tagging mortalities, tag loss rate and effect of tags on growth.     

Factors affecting migrations of burbot

In autumn, burbot Lota lota migrations through a fish ladder in the regulated Ohře River, Czech Republic, were stimulated by an increase in discharge and a decrease in water temperature but the number of burbot in the ladder was significantly lower when compared with other seasons. The maximum number of burbot in the ladder was recorded in spring when discharge decreased. A sudden decrease in water level caused burbot to leave the refuges in the riverbanks that they had occupied during high winter discharges. The results indicate that the relatively low short-term variability of physical conditions represented by the modified discharge regime can induce a stronger response in fish migrations even in comparison with typical reproductive migrations of these species.     

Study on Centrocestus armatus in Korea. I. Infection status of Zacco platypus and Z. temminckii with the metacercariae of C. armatus

This study was performed to observe the infection rate and infection intensity of fresh water fish such as pale chub (Z. platypus) and dark chub (Z. temminckii) with the metacercariae of C. armatus. The fish were caught in several rivers and streams from June to September, 1988 and examined by artificial digestion technique. Total 370 fish were caught at 19 rivers. The metacercarial (C. armatus) infection rate and average burden in Z. platypus were 86.8% and 224, and those in Z. temminckii were 78.5% and 131. The infection rate and burden per fish were 73.4% and 32 in the fish caught from the Han river, and 88.0% and 44 from the Youngsan river. All fish caught from the Keum and the Tamjin river were infected and their mean metacercarial density was 45 and 59 respectively. The infection rate and density in fish caught from the Seomjin and Nagdong rivers were 100% and 119, and 81.0% and 348 respectively. From this study, it is confirmed that C. armatus is widely distributed along 5 major rivers in Korea.     

Evaluating catches of salmonids taken by gillnets

Data from 10 185 gillnetted brown trout ( Salmo trutta L.) and 5777 Arctic charr [ Salvelinus alpinus (L.)] were analysed. Relative to mesh size, the most efficiently caught fish length (the modal length) was somewhat larger with floated nets than with smaller nets placed on the bottom. There were no such consistent differences between the two species. Fish that exceeded the modal lengths were caught more efficiently than smaller fish. The relationship of most efficient mesh size to fish length and condition factor fitted excellently to a linear equation. Based on this equation, the selectivity curve for Arctic charr gillnetted in the Nesjø reservoir, the different efficiency of nets of 0.1 and 0.17mm twine and an equation expressing the increasing height of the selectivity curve with increasing mesh size, a model is presented to compare length frequencies and total numbers of gillnet catches taken with any combination of mesh sizes.     

Ecology of inshore notothenioid fish from the Danco Coast,Antarctic Peninsula

A total of 1,103 inshore notothenioid fish were caught by means of trammel-nets in 4 sites surrounding Cierva Point (Moss Island 1; Moss Island 2; Sterneck Island; Leopardo Island), Danco Coast, West Antarctic Peninsula, during February and March 2000. The families Nototheniidae, Channichthyidae and Bathydraconidae were represented in the samples, Notothenia coriiceps being the dominant fish of the area. Gobionotothen gibberifrons and Trematomus newnesi followed in importance. In general, the fish sampled agreed in terms of number and mass with those of the South Shetland Islands area, except for a marked higher occurrence of G. gibberifrons in the Danco Coast. This supports the hypothesis that the commercial fishery around the South Shetland Islands at the end of the 1970s was responsible for the decrease in the inshore population of G. gibberifrons in that area during the last 17 years. Information on morphometry, reproduction and diet of the fish species caught is provided.     

Effect of Pomphorhynchus laevis (Acanthocephala) on putative neuromodulators in the intestine of naturally infected Salmo trutta

Immunohistochemical and pathological studies were carried out on the digestive tract of parasitized and uninfected specimens of Salmo trutta (L.). A total of 124 brown trout were collected on several occasions from 3 tributaries of the Brenta River, northern Italy. Twenty-eight individuals of S. trutta (22.6%) were parasitized with Pomphorhynchus laevis (Miller, 1776). The occurrence of P. laevis in the trout gut significantly increased the number of endocrine cells immunoreactive to calcitonin gene-related peptide (CGRP), beta-endorphin, met-enkephalin, neuropeptide Y (NPY) and Substance P (SP) antisera. Moreover, bombesin-, cholecistokinin-8- (CCK-8), leu-enkephalin- and serotonin- (5-HT)-like immunoreactive cells were less numerous in the intestine of the parasitized brown trout. A strong positive immunoreactivity was observed in nerve fibres and neurones of the myenteric plexus of the parasitized fish; the antisera involved in this positive reactivity were bombesin, met-enkephalin, SP and vasoactive intestinal peptide (VIP). More neurones immunoreactive to anti-CGRP and anti-5-HT sera were noted in the myenteric plexus and in the inner layer of the tunica muscularis of the infected fish. Most of the above-mentioned neuromodulators are known to control gut motility, digestive/absorptive processes, as well as the immune response. The changes induced by parasites in the neuroendocrine system of the brown trout are discussed.     

An examination of the fish population in the River Trent, Nottinghamshire using angler catches

During this study, anglers caught over 580 kg of fish, comprising over 29 500 individuals of 14 species. Nine times as many gudgeon, Gobio gobio , as roach, Rutilus rutilus , were caught. Gudgeon represented 35.94% of the total catch weight compared with 44.64% for roach. The mean total catch per man-hour was 8.9 fish and the mean catch rate was 176 g per man-hour. Population estimates for fish longer than 12 cm for all species other than gudgeon and bleak, Alburnus alburnus , gave fish densities of 0.21 fish m⁻², the roach population was 0.15 m⁻², and that for dace Leuciscus leuciscus , 0.02 m⁻². The population density for all sizes of all species caught was estimated to be 2.25 fish m⁻².
The fish biomass available to the angler was 447 kg ha⁻². The rate of exploitation of the fishery over the period of sampling was high at 17%, representing an annual exploitation rate of 94%.     

Movements of brown trout, Salmo trutta L., in the River Gwyddon, South Wales

Movements of native brown trout, Salmo trutta , 1 + and older, were limited with up to 93% of recaptured marked fish occupying sites where previously caught. Movements > 50 m were rare with the majority < 15 m. Between sampling occasions, the population could be separated into a static component and a smaller mobile component but there was no evidence of a permanently mobile group. The proportion of mobile native fish increased after stocking with hatchery-reared trout. Displaced native trout (1 + and older) showed the ability to home from 75 m upstream to 111 m downstream of a release site.     

Effects of angling on feeding by largemouth bass

Angling practice significantly effected the time required for largemouth bass Micropterus salmoides to begin feeding. Mean ± s.e. time until feeding resumed was longest for fish that experienced a simulated tournament (15·6 ± 2·2 h) followed by fish that were caught and released (8·4 ± 2·2 h) and controls (0·3 ± 1·6 h). Effects on feeding related to angling practices were maintained throughout the 48 h observation period. Using multiple logistic regression and bioenergetics simulations, decreased growth in fish subjected to competitive or catch-and-release angling events was predicted. Fish subjected to multiple captures in a pond experiment had greater mass loss than those not captured, supporting model predictions.     

Histochemistry of glycoconjugates in mucous cells of Salmo trutta uninfected and naturally parasitized with intestinal helminths

Mucus secreted onto the surface of the intestine forms a physical barrier to invading parasites so that a possible attachment of helminths to the surface is prevented and their expulsion by peristalsis facilitated. In mammals, intestinal parasites induce hyperplasia and hypertrophy of intestine goblet cells and provoke changes in the mucus composition. In fish, this topic has received less attention. In the present investigation, histochemical methods were employed to compose intestinal mucous cell numbers and their glycoconjugate composition were compared by uninfected brown trout Salmo trutta and in S. trutta parasitized with Cyathocephalus truncatus or Pomphorhynchus laevis. When P. laevis was present in the intestine of the brown trout, the total mucous cell number, and the number of mucous cells containing acid or mixed glycoconjugates were significantly enhanced. No significant change in the total mucous cell number was detected in the intestine of fish parasitized with C. truncatus in comparison with uninfected brown trout. A significant increase was observed in the number of both acid (especially sulphated) and mixed glycoconjugates containing mucous cells as well as a significant decrease in the number of neutral glycoconjugates containing mucous cells. When intestinal helminths were present, the thickness of the adherent mucous gel increased. In a limited number of other fish species, the occurrence of gill and intestinal parasites has been reported to increase the mucosal glycoconjugate secretions. Our study is the first quantitative report on the effects of intestinal helminths on the density of mucous cells and mucus composition in a fish species.     

Isolation and characterization of microsatellite DNA in the piracema fish Prochilodus lineatus (Characiformes)

We described five novel microsatellite loci for the piracema fish species Prochilodus lineatus (Characiformes), endemic to South America and of extreme importance to both commercial and artisanal fisheries across its occurrence area. A primary, unenriched genomic library was constructed and radioactively screened for repetitive motifs. Positive clones were automatically sequenced and based on the design of new primers, polymerase chain reaction assays were carried out to determine optimum reaction and electrophoretic conditions for each characterized locus. We evaluated its usefulness in population genetic studies by determining Hardy-Weinberg equilibrium, FIS and a jackknife estimate of the number of alleles for a sample of fish caught below the Funil Hydroelectric Power Plant dam (N = 95), Grande River, Brazil. The number of alleles varied from 3 to 21 and expected heterozygosities ranged from 0.58 to 0.91. Two of five loci were in Hardy-Weinberg equilibrium. Jackknife estimates of the number of alleles were higher than the observed number of alleles for three loci and could provide a measure of sampling bias. These markers should provide important tools for the determination of genetic structure, stock delimitation and reservoir fish management in the Grande River as well as to improve hatchery practices for environmental mitigation measures and to help sustain fisheries in the river.     

Seasonal occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal habitats of south-east Tasmania

Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the broadnose sevengill shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (L(T) ) classes (<80 cm) from the catches suggests that N. cepedianus are not using these coastal habitats as nursery areas. Of the 457 individuals tagged, 68 (15%) were recaptured. Time at liberty ranged from 6 days to almost 4 years and all but one of the recaptures were caught in its original tagging location, suggesting site fidelity. The large number of N. cepedianus in these coastal systems over summer indicates that these areas are important habitats for this species and that N. cepedianus may have a significant influence on community dynamics through both direct and indirect predator-prey interactions.     

插网网目尺寸及采样时间对潮沟游泳动物采样的影响

在长江河口九段沙盐沼湿地的一条潮沟中,我们比较了两种不同网目尺寸（4mm和8mm）的插网（fyke net）及日夜潮对游泳动物群落采样效率的影响。共捕获鱼类16种5476尾、虾2种4982只。采用方差分析、柯尔莫诺夫-斯米尔诺夫非参数检验法和无度量多维标定分析对两种网目插网的捕获效率,样品的体长分布,群落结构及日夜潮间的差异进行了分析。结果表明,网目尺寸对样品中游泳动物的物种数和鱼类的多度没有影响,但是小网目的插网对虾类有较高的捕获率。两种网目尺寸的插网均在夜潮中捕获较多的鱼类个体,但虾类在日潮捕获较多。在日潮中,网目尺寸对捕获物中五种优势游泳动物的体长分布无显著影响。在夜间,小网目的插网对斑尾复缎虎和脊尾白虾的较大个体具有较高的捕获率,但对较大个体鲅的捕获率不如大网目的插网。样品中游泳动物的群落组成在日夜潮间存在明显差异,大网目捕获物的样本间差异比小网目小。