Diel drift behaviour of fish eggs and larvae, in particular barbel, Barbus barbus (L.), in an English chalk stream

To estimate the potential loss of fish larvae to downstream stretches, the downstream drift behaviour of fish eggs and larvae, in particular barbel, Barbus barbus (L.), was examined in the River Lee, a small, nutrient-rich chalk stream in England, using drift nets over nine consecutive 24-h periods in June 1993 at one location and over ten 24-h periods, once a week for 10 weeks from May to July 1995 at a location slightly more upstream. The density of drifting fish larvae was not correlated with river discharge in 1993 or 1995. A clear diel pattern was found in the drift of fish eggs and larvae, with barbel being a predominant species. Almost all fish larvae drifted at night both in 1993 and 1995, but the drift of eggs in 1995 occurred regardless of luminosity, although most eggs drifted during the day and at dawn. The highest densities of drifting fish larvae (in particular barbel) were found in the nets set in the highest water velocities, with the opposite pattern observed for fish eggs, suggesting either active response to the water current or shape-related differences in the drift behaviour of passive particles.     

Reciprocal hybrids of tench Tinca tinca (L.) × bream Abramis brama (L.), and tench × carp Cyprinus carpio L., and some characteristics of their early development

Reciprocal hybrids between tench Tinca tinca (L.) and carp Cyprinus carpio L., and tench and bream Abramis brama (L.) were produced artificially. The survival of all these hybrids during embryogenesis was quite high. The highest survival rate (over 60%) at the eyed stage was observed for tench and bream hybrids (both sex combinations). The hatching rates of these hybrids were also over 60%. The number of larvae with some abnormalities (i.e. deformed body) was low. In contrast, the hatching rates of tench and carp hybrids were very low (0.2%). From over 1000 fertilized eggs, only three specimens started swimming, and only one specimen survived to juvenile stage. Embryos of hybrids and their parental species differ in morphological features. These differences were also visible in the juveniles. Body parameters of juvenile hybrids produced from three species had intermediate values in comparison to parental fish.     

Further Aids to the Reconstruction of Digested Prey Lengths

Studies of the feeding of the zander (Stizostedion lucioperca L.) required a method of reconstructing digested prey lengths. A linear relationship between pharyngeal bone dimensions and prey fork lengths of roach (Rutilis rutilis L.) and common bream (Abramis brama L.) were determined. For unidentified prey and fish species lacking pharyngeal bones, a scale based on the percentage change in length with stage of digestion was employed.     

Patterns of drift and power station entrainment of 0+ fish in the River Trent, England

Entrainment of 0+ riverine fish (mostly pelagic cyprinids) by a power station intake, and down-river drift over a nearby weir, followed the same pattern, occurring throughout the year and being greatest during the night in the first weeks of life (i.e. in summer), reaching a peak shortly after dusk. Entrainment and drift of benthic species, and of fish older than 0+, were negligible. Mortality following entrainment was 100%. Impingement of fish on the intake screens was negligible, probably because individuals larger than the screen mesh were able to escape the intake current. The species composition and length-frequencies of the drifting fish, but not their overall abundance, showed some variation with distance from the river margin. It is argued that the fish vulnerable to entrainment are those 0+ individuals which are dispersing in the river by drifting.     

The effects of an underwater fish observation technique on stream macroinvertebrates at two spatial scales

Abstract – We examined the effects of snorkeling, a commonly used fish observation technique, on the distribution and abundance of benthic macroinvertebrates at both the reach (i.e., 10 m) and patch scale (i.e.,< 1 m) within a southern Appalachian stream (North Carolina, USA). At the reach scale, we quantified increases in macroinvertebrate drift rates associated with snorkeling and used these values to calculate the percentage of the macrobenthos that drifted out of snorkeled reaches. We also used a simple decay model of macroinvertebrate drift to quantify patch scale effects of snorkeling. The model incorporated size specific macroinvertebrate settling rates to estimate the total number of benthic macroinvertebrates that entered the drift in response to snorkeling disturbance. We found that snorkeling consistently produced significant increases in the number of drifting macroinvertebrates. Nevertheless, these increases comprised a very small percentage (<1%) of the total number of organisms in the benthos, suggesting that snorkeling probably did not strongly affect macroinvertebrate assemblages at either the reach or patch scale. However, our analyses also indicated that snorkeling had a disproportionate effect on the drift of small ephemeropterans (4–5% entered the drift in response to snorkeling) relative to other macroinvertebrate taxa. Consequently, the microdistribution of early instar mayflies may have been altered within snorkeled reaches. We conclude that snorkeling related disturbance to the benthos should have a minimal effect on the behavior and distribution of most stream fishes at either the reach or patch scale. However, because snorkeling had a substantial effect on the drift of small mayflies, snorkeling may influence the behavior of fishes that depend on early instar mayflies as a primary food resource. ^Note     

Spawning grounds and reproductive traits of anadromous and resident pond smelt, Hypomesus nipponensis, in Lake Ogawara, Japan

SUMMARY: The objective of this study was to reveal the spawning grounds and reproductive characteristics of anadromous and resident pond smelt, Hypomesus nipponensis , coexisting in Lake Ogawara. Life history styles of females shedding in spawning grounds in the lake and its inflowing rivers were differentiated by otolith increment analysis. Size, dry weight, and water content of mature oocytes and fecundity of fish were compared between resident and anadromous fish. Both anadromous and resident fish spawned in the lake. In contrast, no resident fish were found in any of the inflowing rivers, where only anadromous fish spawned. Regression of fecundity against standard length was discontinuous with an inflection point at 63.8 mm, which is the body size that differentiates large anadromous spawning groups from small resident spawning groups. Mean oocyte diameters were not significantly different between resident and anadromous fish. The eggs of resident fish had significantly more water content and a significantly lower dry weight than those of anadromous fish. These differences might influence the growth and developmental processes of progeny.     

Feeding behaviour of wild Atlantic salmon, Salmo salar L., parr in mid- to late summer in a Scottish river

Abstract. From 25 July to 11 September 1984 Atlantic salmon, Satmo salar L., parr were observed underwater between 0800 and 1600 h, feeding actively from defended territories at two sites in the River Tilt, Perthshire, Scotland. Territories comprised one or more preferred stations on or just above the substrate, from which the fish intercepted drifting particles (75% of feeding), or foraged on the substrate (25%). Drift feeding occurred 36% at the surface, 35% in mid-water and the remainder at the feeding station. 35% of prey particles were attacked directly from the feeding station, and 65% indirectly after preliminary inspection, sometimes involving a drift downstream by the fish. 20% of captures were made upstream of the station and 80% downstream. 12–15-cm fish fed more frequently at the surface, while 10-cm fish fed in mid-water or at their stations. Surface feeding decreased proportionately during rainfall. Frequency of feeding increased with temperature. Feeding was depressed in the presence of large salmonids.     

Artificial daily fluctuations of river discharge affect the larval drift and survival of a tropical amphidromous goby

Amphidromous fish species reproduce in rivers, and their larvae immediately drift to the sea after hatching. Most of these larvae survive in freshwater for a few days only, rapidly reaching sea water is thus essential. Being of small size, especially among species of the Sicydiinae subfamily, the larvae possess poor swimming abilities; their drift dynamics is considered to be mainly passive and influenced by flow conditions. The influence of daily fluctuations in flow regime on Sicyopterus lagocephalus (Sicydiinae) larval drift patterns was studied using drift nets at three sites along the dammed Langevin River in Reunion Island. The river flow was stable at the upstream site when frequent anthropogenic river flow fluctuations were observed at the two sites downstream to the dam. Weak diel larval drift dynamics were detected at the upstream site and the first site under anthropogenic river flow conditions. In contrast, larval drift dynamics at the most downstream site was strongly influenced by anthropogenic daily fluctuations of discharge: the abundance of drifting larvae increased with peaks of discharge, regardless of the time. As higher mortality rates of drifting larvae were observed during discharge peaks, the benefit of a more rapid travel to the ocean associated with these peaks should be lower than expected. It is concluded that peaks of discharge increase the number of larvae drifting to the sea probably due to higher physical constraints on the egg clutches, but also decrease the chance of survival for larvae that may be nonfully developed.     

Long-term development of fish populations in the Římov Reservoir

Abstract  The inshore fish community of the Římov Reservoir in the Czech Republic was evaluated over 21 years using shore seining at night. The development of the fish community was divided into two separate phases: a highly dynamic and unstable phase dominated by perch, Perca fluviatilis L., was replaced by an extremely stable cyprinid phase dominated by roach, Rutilus rutilus (L.), and bream, Abramis brama (L.). The abundance of both these species oscillated during the cyprinid phase, but with decreasing amplitude. The proportion of piscivorous fish species such as asp, Aspius aspius (L.), pike, Esox lucius L., and pikeperch, Sander lucioperca (L.), increased slightly with time but remained low. The biomass of large Cladocera was negatively correlated with fish biomass only during the perch phase. The Shannon–Weaver index of diversity increased during the fish community succession, mainly because of greater evenness amongst the species.     

Functional response and size‐dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)

Gustafsson P, Bergman E, Greenberg LA. Functional response and size‐dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.).Ecology of Freshwater Fish 2010: 19: 170–177. © 2010 John Wiley & Sons A/S Abstract – Terrestrial invertebrate subsidies are believed to be important energy sources for drift‐feeding salmonids. Despite this, size‐specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and ≥2+) when fed either benthic‐ (Gammarus sp.) or surface‐drifting prey (Musca domestica) in laboratory experiments. To test for size‐specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two‐prey experiments also showed that 1+ trout ate significantly more surface‐drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ≥2+ trout. Analyses of the vertical position of the fish in the water column corroborated size‐specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size‐specific differences in foraging and vertical position suggest that larger trout may be able to use surface‐drifting prey to a greater extent than smaller conspecifics.     

Quantifying fish avoidance of small acoustic survey vessels in boreal lakes and reservoirs

Mobile hydroacoustic surveys are increasingly used to assess the distribution and abundance of freshwater fish; yet, fish may avoid moving vessels, potentially introducing bias in these assessments. In this study, avoidance in boreal lakes and reservoirs was quantified by developing a simple method based on paired drift:drift (D:D) and drift:motor (D:M) transects. Two systems in eastern Manitoba, Canada were studied: Lac du Bonnet reservoir and Nopiming. Acoustic data were collected using a digital DTX echosounder (BioSonics, Seattle, WA, USA), with a downward facing 200‐kHz split‐beam transducer, deployed from 5.5‐m vessels (Boston Whalers) modified for acoustic research. An avoidance coefficient (Ac) was developed based on comparisons of acoustic fish densities while the vessel moved over the same transects by drifting, and by motoring at survey speeds. Ac did not differ significantly from 1 (no avoidance) at Nopiming (median of 0.81, n = 13), but did at Lac du Bonnet (median of 0.51, n = 31, P < 0.05). Variability in Ac was as high in transect pairs and was unrelated to fish depth (mean 6.9 m at Lac du Bonnet; 13.1 m at Nopiming) or survey speed (up to 3.70 m·s^?1, 7 knots). Results indicated that fishes did not dive in the presence of the motoring vessel, nor was avoidance size‐based. We did not detect any evidence of fish attraction to our drifting vessel. Our results suggest that boat avoidance during acoustic surveys of shallow boreal lakes may vary in relatively similar water bodies but can be quantified experimentally.     

Host-parasite interface of Caryophyllaeus laticeps (Eucestoda: Caryophyllidae) in three species of fish

Abstract. The host-parasite interface of Caryophyllaeus laticeps has been investigated in naturally infected bream, Abramis brama (L.), chub, Leuciscus cephalus (L.), and roach, Rutilus rutilus (L.), by light and electron microscopy. The fish were caught in the Ruhr-lake near Bochum. Bream showed the highest rate of infection and also harboured the largest worms compared to the two other host species. In all three cyprinids, the worms' scolices caused local compression of the host's intestinal epithelium. At the attachment site of scolices of medium- to large-sized worms, the intestinal epithelial cells were vacuolized and their brush border ruptured. These pathological effects were most pronounced in bream, which also showed conspicuous granulomas in the tunica propria adjacent to the scolices. A heavy infiltration of eosinophilic granulocytes was noted in chub and roach at the worms' attachment site. In bream, only the smallest worms provoked a slight eosinophilic reaction. It is concluded that the worms within the three host species were of different ages and that the chronic stage of infection, associated with the formation of granulomas, was only reached in bream, the major host.     

Upstream migration activity of cyprinids and percids in a channel,monitored by a horizontal split-beam echosounder

A 200 kHz digital echosounder (HTI) with two split-beam transducers was aimed horizontally to monitor the upstream migration activity of fish, from 24 April to 28 June, in Äijälänsalmi channel (mean width 35 m, length 700 m, and maximum depth 5 m) from large mesotrophic Lake Päijänne to small eutrophic Lake Jyväsjärvi. This study was part of a larger project which aims to analyse the movement of commercially unimportant fish species and reduce the abundance of these fish in L. Jyväsjärvi. Catch samples were collected with a trap net located immediately upstream from the acoustic beams. The most common species in the catch were roach (Rutilus rutilus), perch (Perca fluviatilis), bream (Abramis brama), ruffe (Gymnocephalus cernuus), and white bream (Abramis bjoerkna). The upstream migration of fish was correlated with water temperature (r = 0.40) with time lag of 1 d. In spring, L. Jyväsjärvi warmed faster than L. Päijänne, causing spawning migration from L. Päijänne to L. Jyväsjärvi. Clear diurnal rhythm in activity was observed. The migration rate through the channel peaked around dawn and dusk. Catch per unit effort of the trap net suggested that the peak of the spawning migration of different species was separate. Upstream migration was induced by the temperature difference between two lakes, and the activity of the migration was regulated by temperature changes and light rhythm.     

The role of the environment in partial migration: food availability affects the adoption of a migratory tactic in brown trout Salmo trutta

Abstract –  Alternative reproductive tactics are commonly reported for salmonids (Pisces) and typically involve large migratory and small resident individuals. Variation in migratory tendency should reflect the different benefits and costs that the two different phenotypes face with regard to fitness. Therefore, the effect of food availability on the adoption of a migratory tactic in brown trout was investigated. Fifty trout were placed in each of 12 tanks and fed at three different levels. Growth-related variables were measured regularly, and at the end of the experiment, the proportion of migrants and residents was recorded. Low food availability led to increased numbers of migratory fish. The expected sex-bias was also present, with a lower percentage of resident females than resident males. As all fish originated from the same gene pool, the changing proportions of the migratory tactics can be classified as phenotypic plasticity. The study provides evidence that the different phenotypes reflect alternative tactics within a conditional strategy. Some differences in growth-related variables were present between the sexes, and a very pronounced difference in condition factor was found between resident and migratory males, but not in females. Thus, the results provide evidence that different selective forces may be acting on the sexes.     

Effects of habitat and internal prey subsidies on juvenile coho salmon growth: implications for stream productive capacity

Abstract –  To evaluate the effects of habitat, foraging strategy (drift vs. limnetic feeding) and internal prey subsidies (downstream transport of invertebrate drift between habitats) on fish production, we measured the growth of juvenile coho salmon confined to enclosures in flowing (pond inlets and outlets) or standing water (centre of pond) habitats in a constructed river side-channel. The effects of habitat and foraging strategy on fish growth were mediated primarily through habitat effects on prey abundance. Invertebrate drift biomass was nearly an order of magnitude higher at pond inlets relative to outlets. Drift-feeding coho in inlet enclosures grew 50% faster than drift-feeding coho at pond outlets or limnetic feeding coho in the centre of ponds, suggesting that elevated drift at inlets was sufficient to account for higher inlet growth rates. Forty per cent of prey biomass in stomachs was terrestrial in origin. These results indicate that, in addition to dependence on external terrestrial subsidies, streams with alternating slow and fast water (i.e., pool-riffle) sequences are also characterised by internal prey subsidies based on transport of drifting invertebrates from refuge habitats (high velocity riffles) to habitats more suitable for drift-feeding predators (e.g., pools), which may result in higher maximum fish growth in systems where internal subsidises are large. Restoration of small streams to maximise productive capacity for pool-rearing salmonids will require a better understanding of the length and interspersion of habitats that maximises both internal prey subsidies and available rearing habitat for juvenile salmon.     

Smolt characteristics of small first-time migrant, and resident Arctic charr, Salvelinus alpinus (L.), from a river system in northern Norway

Smolt characteristics were investigated in sympatric anadromous and resident Arctic charr. Salvelinus alpinus (L.), of a similar size (11-20 cm), A group of first-time migrant anadromous charr was caught while descending the Hals River and two groups of resident conspecifics were caught in Lake Storvatn. one before, and one after, the sea-run of anadromous fish had terminated. When sampled immediately after capture in fresh water the anadromous group had a higher proportion of fish visually classified as smolts. and these charr had higher gill Na⁺-K⁺ ATPase activity, higher densities of developed chloride cells in the gills, a lower condition factor, and lower plasma osmolality, than resident fish. When exposed to sea water (33%o S), only minor differences in mortality and plasma electrolyte levels were observed between anadromous and resident fish, average values of plasma osmolality and chloride concentrations being 377 mOsm and 169 mM and 387 mOsm and 174 mM, respectively. The results suggest that the first-time migrant Arctic charr had undergone some of the physiological changes that are considered typical for a parr-smolt transformation before they left fresh water. Such changes did not appear to have occurred in sympatric, resident, fish of a similar size. The parr-smolt transformation in the first-time migrants may, however, have been incomplete, because the fish did not appear to have the ability to rapidly re-establish osmo- and ionoregutatory homeostasis after direct transfer to sea water.     

长江上游江津江段鱼类早期资源时空分布特征研究

于2009年5—7月对长江上游江津江段卵苗的时空分布进行了调查。结果显示:在5月14日、6月3日及6月9日前后该江段有卵苗汛发生,卵苗的平均密度为9.36 ind/100 m3,最大密度为37.73 ind/100 m3;经威氏符号秩次检验,卵苗密度的昼夜分布没有显著性差异(P>0.05);卵苗密度垂直分布没有显著性差异(P>0.05);在水平分布上,南岸和北岸之间的卵苗密度没有显著性差异(P>0.05),两岸和江中间的卵苗密度均存在极显著性差异(P<0.01)。     

Larval fish movement in the River Lohajang,Tangail, Bangladesh

Larval fish drift and distribution patterns were studied in the River Lohajang, a tributary of the River Jamuna, Bangladesh, during the monsoon seasons (June - October) of 1992, 1993 and 1994. Larval fish drift peaks with the water levels of the River Jamuna. In all three years, the Indian carp, Catla catla, Labeo rohita L. and Cirrhinus mrigala, were associated with the first pulses, but were absent from drift samples after September. Hilsa species and other non-identified fish species were found throughout the monsoon season. The highest larval fish densities were found in the upper strata of the river, near the shore. The drift densities of these fish became evenly distributed through time. Water turbidity probably influenced the vertical and horizontal distribution, and the absence of diel patterns. The most important species in the larval drift were Hilsa spp., followed by Labeo rohita L., Glossogobius giuris L. and Rasbora daniconius. Among the major carp, Labeo rohita was the dominant species, contributing 80-90%. The impact of flood control programmes on the reproduction of riverine and larval fish drift is discussed.     

Larval lake sturgeon production and drift behaviour in the Menominee and Oconto Rivers,Wisconsin

Lake sturgeon (Acipenser fulvescens) have been negatively impacted by barriers to migration, pollution and overharvest. Biological data such as the timing of spawning activity and larval drift have provided a better understanding of larval production success or failure on a site-specific basis. However, many river systems that serve as reproductive locations for remnant lake sturgeon populations remain understudied. The objective of this study was to compare and contrast aspects of larval lake sturgeon drift within and between the Oconto and Menominee Rivers over multiple reproductive seasons. Differences in larval drift chronology, the size of drifting larvae during the season and the cross-sectional profile of drifting individuals as a function of river velocity were evaluated. D-frame drift nets were deployed at a single transect below spawning sites in the Menominee (2012, 2013 and 2014) and Oconto Rivers (2013, 2014 and 2015). A total of 4,442 larvae were captured across all seasons. Larvae exhibited nonrandom drift profiles related to water velocity, and larvae size was related to horizontal drift location. The seasonal increase in body size of drifting larvae also differed among drift events within and between years and across rivers. This information will provide a better understanding of lake sturgeon early life history and has practical management connections including spawning site protection/enhancement and river flow mitigation.