The consumption of eggs of the perch, Perca fluviatilis L., by macroinvertebrates in the field

SUMMARY. 1. Perch egg masses, in a late stage of development, were collected from a small stillwater and the composition of the egg masses and the number of invertebrates which colonized them was recorded.
2. All of the invertebrates that colonized the egg masses were tested serologically for the presence of perch eggs and the ability of some invertebrates to eat live and dead perch eggs in the laboratory was determined.
3. Of the nineteen taxa that colonized the egg masses, only two species of flatworm and three species of caddisfly larva ate perch eggs in the field and, of these, only one genus of caddisfly larva ate live eggs in the laboratory.
4. It is concluded that the invertebrates present were not important predators of perch eggs.     

A simple egg box planting technique for estimating the survival of eggs deposited in stream gravel

A simple technique for estimating the survival of eggs during their incubation in stream gravels by planting eggs in specially designed egg boxes is described. This technique ensures that all the live eggs and alevins present in the gravel at the time of sampling can be recovered. Survival can be calculated accurately from the ratio of the number of live recovered to the number of eggs originally planted and the errors caused by the loss of dead eggs and escape of live alevins from the sample area are avoided.     

Environmentally induced spatio-temporal variations in the fecundity of brown trout Salmo trutta L.: trade-offs between egg size and number

1. Resident brown trout Salmo trutta in the Esva River basin (north Spain) live in a patchy environment with tracts of riparian forest or meadow along stream banks. This study assessed whether the reproductive traits of brown trout from four contrasting sites reflected site-specific factors.
2. Length at maturity (10.5–11 cm of 1 + individuals) was the same in the four sites examined but slowest growers in slow-growing sub-populations delayed maturity for 1 year relative to fast-growing fish. The analysis of monthly variations in egg size and number suggest that two 'decisions' in two consecutive years are required to complete spawning. The first concerns the number of eggs, determined when trout are still 0 +, and the second concerns egg size.
3. At three sites, egg size and number did not differ significantly between years but highly significant interannual variations were apparent at another site. Fish length was the major determinant of egg size and number at all sites but for any given length, brown trout at sites where the fish exhibited higher growth rates spawned more, but smaller, eggs than those at slow-growing sites. This spatial pattern was identical to the temporal pattern exhibited by trout at another site. The combination of temporal (year-to-year) and spatial (between rivers) variations in egg size and number showed a significant negative correlation, supporting the operation of a trade-off between these two traits.
4. The trade-off between egg size and number seems to be determined by site-specific factors, with slow-growing trout at sites which are fully covered by canopy spawning fewer, but larger, eggs than fast-growers in unshaded sites.     

Aquarium studies on the consumption of small animals by O–group grass carp, Ctenopharyngodon idella (Val.)

In aquarium experiments common invertebrates from streams and ponds were offered to O-group grass carp, Ctenopharyngodon idella (Val.) in the presence of palatable plants. When there was no cover for the prey to hide under, the carp ate many of the invertebrates, but when stones were provided, considerably more invertebrates escaped. Rainbow trout eggs were not eaten, but trout fry were taken as soon as they had emerged from artificial spawning redds. While searching for food, grass carp never disturbed the stones covering possible food organisms.     

Genetic differences among brown trout, Salmo trutta, stocks and their importance for the conservation and management of the species

SUMMARY. 1. Review of published studies on genetic variation, as shown by electrophoretic studies of protein variation, in natural brown trout ( Salmo trutta L.) populations from Britain and Ireland, Finland, France, Greece, Iceland, Norway, Sweden, U.S.A. and U.S.S.R., revealed abundant geographical variation in gene frequency with individual populations containing only a limited part of the gene diversity of the species.
2. Thirty-eight (54%) of the seventy gene loci examined have been found to be polymorphic in the species with an average population showing polymorphism at 16% of its loci (range 0-34.8%).
3. The brown trout is naturally subdivided into a large number of reproductively isolated and genetically distinct populations within, as well as among, drainages.
4. Two independent post-glacial colonizations, by genetically distinct races, followed by independent evolution in separate drainages over the past 13,000 years is seen as responsible for the genetic diversity of brown trout in north-western Europe.
5. Many genetically unique populations have been lost in the past 100 years and there is an urgent need to identify and conserve the remaining genetic diversity. Genetically unique populations are an irreplaceable resource for rational management in relation to angling and future aquaculture potential.     

Impact of live food on survival and growth of hatchery‐reared sea trout (Salmo trutta trutta L.) parr in the wild

Survival rates and growth parameters of hatchery‐reared sea trout (Salmo trutta trutta L.) fry were determined after stocking in the wild. The larvae were hatchery‐reared for 12 weeks in two groups: fry were fed either on live zooplankton and live chironomidae larvae (LFG), or fed a pellet diet (PFG). The survival rate and specific growth rates were higher in the LFG than in the PFG group. Most effective for hatchery‐reared fish intended for stocking was the natural, live feed. The mean number of chironomid larvae found in the stomachs of fish that were initially captured in the wild was significantly higher in the LFG than in the PFG group. The live diet supplied in the rearing period had a positive impact on the foraging skills of the sea trout fry and their survival in the wild after their release on 24 April 2010.     

The ecology of brown trout Salmo trutta in English chalk streams

SUMMARY. .1. Chalkstream trout are fast-growing, short-lived with a stable age structure that is a consequence of the lack of extremes in the abiotic environment, especially of water temperature and flow.
2. Levels of secondary (invertebrate) production arc high and there is no evidence that interspecific or intraspecific competition for food resources limits growth.
3. Dietary studies show a broad similarity between trout and other species, but indicate differences that reflect variations in the micro-habitat distributions between fish species.
4. Trout numbers appear to be limited initially by the availability of gravel spawning areas, and then by areas suitable for newly-emerged fry. Reduction in stream discharge in the spring, either naturally or by man, can lower the number of 0+ trout that survive.
5. Eels are not important predators on trout eggs or fry. but a reduction in pike numbers can lead to a decrease in the mean weight of pike. Small pike do not pose a serious threat to stocked yearling trout.     

Effects of prey dispersal on predator–prey interactions in streams

1. We studied the effect of mesh size (6 and 3 mm) on interactions between brown trout ( Salmo trutta ) and benthic invertebrates in enclosures placed in a stream in southern Sweden. We also compared how different prey exchange rates affected interactions between trout and invertebrates.
2. Trout had strong impacts on some benthic taxa, and different mesh sizes produced different patterns. Trout affected the abundance of 10 of the 21 taxa examined, six in enclosures with 3 mm mesh and six in enclosures with 6 mm mesh. The abundance of nine of the prey taxa was lower in the presence of trout, only leptocerids were more numerous in the presence of trout.
3. Our measurements of prey immigration/emigration, together with trout diet data, suggest that direct consumption by trout, rather than avoidance behaviour by prey, explains most decreases in prey abundance. There was avoidance behaviour by only two of the twenty-one prey taxa, with trout inducing emigration of the mayflies Baetis rhodani and Paraleptophlebia sp.
4. Trout indirectly increased periphyton biomass in both 3 and 6 mm enclosures. The effect of trout on periphyton was probably due to strong effects of trout on the grazer, Baetis rhodani , Heptagenia sp. and Paralepthoplebia sp.
5. Our results suggest that mesh size, through its effects on exchange rates of prey, may affect interactions between predators and prey in running waters, but that the effects of dispersal and predation on invertebrates are taxon specific.     

Effects of sedimentation on the gravels of an industrial river system

The natural recovery of trout ( Salmo trutta L.) populations in an industrial river, the Ebbw Fawr, South Wales, has been depressed by problems of natural recruitment. Rainbow trout ( Salmo gairdneri Richardson) eggs were planted in river gravels to assess the effects of siltation on salmonid spawning success. In reaches where siltation due to the coal industry has occurred, 98–100% of eggs died during incubation in the gravels. Experiments using standpipe techniques measured gravel permeabilities and rates of dissolved oxygen (DO) supply to artificially planted eggs, the results showed a strong dependence of hatching success and alevin size on these two parameters. The median lethal DO supply rate was about 50 μg cm^-2 h^-1.     

Assessing the status of British wild brown trout, Salmo trutta, stocks: a pilot study utilizing data from game fisheries

SUMMARY. 1. This paper describes an analysis of results from a questionnaire (Giles, 1987) which requested information on the status of game fish stocks (especially wild brown trout Salmo trutta L.) from those Game Conservancy members who own or manage fisheries. Also included are data arising from fishery log book records which are used to indicate trends in brown trout catch per unit effort (CPUE) over past decades.
2. The key finding from questionnaire returns was the widespread reporting of apparent declines of wild brown trout stocks in a total of twenty-seven sites throughout Britain. The affected waters are geographically widespread from the south-west of England through southern and south-east England, south Wales, northern England and Scotland including the Western Isles. Suspected stock declines of migratory (sea) trout, salmon Salmo salar L. and grayling Thymallus thymallus L. were also reported. Where brown trout occur alone, a significantly higher proportion of questionnaire returns recorded a stock decline compared with fisheries containing both brown and rainbow trout Salmo gairdneri Richardson.
3. Trout catch records from a small selection of differing fishery types are presented and the value of such data in fish stock assessment is discussed.     

The influence of introduced trout on the benthic communities of paired headwater streams in the Sierra Nevada of California

1. Non‐native trout have been stocked in streams and lakes worldwide largely without knowledge of the consequences for native ecosystems. Although trout have been introduced widely throughout the Sierra Nevada of California, U.S.A., fishless streams and their communities of native invertebrates persist in some high elevation areas, providing an opportunity to study the effects of trout introductions on natural fishless stream communities. 2. We compared algal biomass and cover, organic matter levels and invertebrate assemblages in 21 natural fishless headwater streams with 21 paired nearby streams containing stocked trout in Yosemite National Park. 3. Although environmental conditions and particulate organic matter levels did not differ between the fishless and trout streams, algal biomass (as chlorophyll a concentration) and macroalgal cover were, on average, approximately two times and five times higher, respectively, in streams containing trout. 4. There were no differences in the overall densities of invertebrates in fishless versus paired trout streams; however, invertebrate richness (after rarefaction), evenness, and Simpson and Shannon diversities were 10–20% higher in fishless than in trout streams. 5. The densities of invertebrates belonging to the scraper‐algivore and predator functional feeding guilds were higher, and those for the collector‐gatherer guild lower, in fishless than trout streams, but there was considerable variation in the effects of trout on specific taxa within functional feeding groups. 6. We found that the densities of 10 of 50 common native invertebrate taxa (found in more than half of the stream pairs) were reduced in trout compared to fishless streams. A similar number of rarer taxa also were absent or less abundant in the presence of trout. Many of the taxa that declined with trout were conspicuous forms (by size and behaviour) whose native habitats are primarily high elevation montane streams above the original range of trout. 7. Only a few taxa increased in the presence of trout, possibly benefiting from reductions in their competitors and predators by trout predation. 8. These field studies provide catchment‐scale evidence showing the selective influence of introduced trout on stream invertebrate and algal communities. Removal of trout from targeted headwater streams may promote the recovery of native taxa, community structure and trophic organisation.     

Caddis larvae cases (Trichoptera,Limnephilidae) as anti-predatory devices against brown trout and sculpin

Brown trout (Salmo trutta L.) and sculpin (Cottus gobio L.) predation on the cased limnephilid larvae Glyphotaelius pellucidus (Retz.) (weak, broad leaf case), Limnephilus pantodapus McLachl. (weak, long cylindrical leaf case), L. rhombicus (L.) (rigid, hedgehog case) and Potamophylax cingulatus (Steph.) (rigid, cylindrical mineral case) was studied in the laboratory. The proportion of larvae ingested was significantly higher in brown trout than in sculpin for all four prey species. Brown trout captured larvae of all four species with equal success, but the higher number of unsuccessful captures resulted in a higher survival rate for P. cingulatus. It was significantly more difficult for sculpin than for brown trout to capture L. pantodapus larvae and to ingest all species except L. rhombicus. P. cingulatus larvae were never ingested by sculpins, and had the highest survival rate after capture by both fish species. In brown trout, the handling time of L. pantodapus was significantly longer than that of P. cingulatus. Sculpin had a significantly longer handling time of G. pellucidus than brown trout. L. pantodapus and L. rhombicus larvae feigned dead significantly longer than did those of G. pellucidus and P. cingulatus upon attacks from sculpins. L. rhombicus larvae also feigned dead for a long time upon attacks from brown trout. The survival rate of a larva attacked by sculpin or brown trout depends on both case rigidity as well as its behaviour. Brown trout was a more successful predator of cased caddis larvae than sculpin.     

Strategies in energy consumption and partitioning in Collembola

Abstract. 1. Consumption (in Joules), partitioning of assimilated energy between maintenance (standard metabolism and locomotory activity) and prcduction (growth and reproduction) and assimilation efficiency were studied in the laboratory using adults of the coexisting species Orchesella cincta (L.) and Tomocents minor Lubbock (Collembola, Entomobryidae).
2. A higher energy demand for maintenance was established in O.cincta , compared with T.minor , caused by a higher mobility and a higher live weight-specific oxygen consumption (metabolic rate).
3. The energy required for higher maintenance in O.cincta , compared with T.minor , was derived from production, both from growth and reproduction.
4. The increase in live weight (in mg) during a moulting interval (feeding instar plus reproductive instar) was less in O.cincta than in T.minor , and was less in males than in females.
5. Reproduction (in Joules) was less in O.cincta than in T.ninor . The numbers of eggs produced were equal, but their energetic content was less in O.cincta . Survival of the eggs was similar.
6. Consumption (in Joules) and assimilation efficiency (on an energetic basis) during a moulting interval (feeding instar plus reproductive instar) were similar in both species.     

Changes in egg colour, egg weight and oviposition rate with the number of eggs laid by wild females of the small heath butterfly, Coenonympha pamphilus

ABSTRACT. 1. The colour of eggs laid by individual Coenonympha pamphilus (L.) (Lep., Satyridae) females changed over their lifespan. The first laid eggs were green, but after having laid about 100 eggs, females laid only yellow eggs.
2. By following females in the field, or by capturing wild females, and noting the colour of their eggs, it was established that younger females showed higher oviposition rates and laid heavier eggs than older females.
3. Hence, wild C.pamphilus females are unable to sustain a constant egg production by extracting amino acids or any other nutrients from nectar. We hypothesize that this is a general phenomenon in nectar feeding butterflies.
4. The egg colour did not seem to match the colour of the substrate on which the female chose to deposit the egg.     

Short term biotic response before and during the treatment of an acid mine drainage with sodium carbonate

The lower portion of Upper Three Runs, a woodland stream in central Pennsylvania, receives acid drainage from a strip mine. In 1974, the effect of this input on pH and benthic invertebrates was studied by Tomkiewicz & Dunson (1977). We sampled the same stations in 1986 and then treated the mine drainage with sodium carbonate for seven days in an effort to evaluate the short term colonization response of brook trout (Salvelinus fontinalis) and invertebrates. No differences in the pattern of pH and invertebrate distribution was found between the 1974 and 1986 results, although pH values and invertebrate densities were higher in 1986. Total number of invertebrates and number of taxa colonizing bricks during three pre-treatment time periods (8, 10, 18 days) did not differ from the single treatment period (7 days). However, two species of Baetis (Ephemeroptera: Baetidae) did increase in the treatment section during sodium carbonate application. The number of brook trout also increased in the treatment section, as compared to one pre-treatment estimate. These results indicate that motile species are able to respond within seven days, whereas, longer treatment may be required to produce community wide responses.Author to whom correspondence should be addressed     

Fish early life stage tests as a tool to assess embryotoxic potentials in small streams

Early life stage (ELS) studies with brown trout(Salmo trutta f. fario L.) andstone loach (Barbatula barbatula L.)were performed between 1995 and 2000 toevaluate embryotoxic potentials in twodifferently polluted streams in southwestGermany. With both species, semistatic exposureexperiments with water samples and sedimenteluates were conducted in the laboratory.Additionally, brown trout ELS tests wereperformed in flow-through systems in thesemi-field and in the field. Thus, differentlevels of complexity of environmentalconditions were addressed which allowed thestudy of effects of xenobiotic contamination,temperature, and sediments on the success ofembryonic development. Additionally, effects ofwater from the polluted stream on fertilizationof brown trout eggs were determined. In themore polluted stream, xenobiotics caused anembryotoxic potential for both brown trout andstone loach, and viability of exposed browntrout eggs was drastically reduced by suspendedsolids in the water which covered the eggs.Additionally, fertilization rates of browntrout eggs were significantly decreased inwater of the more polluted stream. In the lesspolluted stream, low water temperature andinfestations by protozoic ectoparasites causedmortality of embryos. In this stream, pollutionand sediment effects were not observed. Resultsmade evident that in the more polluted streamrecruitment of brown trout was drasticallyimpaired.     

An experimental study of the effects of predatory fish on macroinvertebrates in a Hong Kong stream

SUMMARY. 1. Predation upon macroinvertebrates by the loach Oreonectes platycephalus Günther (Cobitidae) was studied using predator inclusion/exclusion cages in a series of pools along a Hong Kong stream. Treatments employed were predator exclusion, medium (approximately natural) predator densities (1 fish cage⁻¹) and high predator densities (2 fish cage⁻¹). Macroinvertebrate abundance in cages was monitored after 2 and 4-weeks exposure to predators.
2. The presence of fish was associated with significant declines in the total numbers of macroinvertebrates colonizing cages. However, taxa were influenced differently, with mayflies decreasing by a factor of two while the more mobile shrimps (Atyidae) were unaffected. Chironomid abundance (largely Chironominae) was unaffected by predator density and increased in week 4. Detritus acted as a confounding variable at this time because chironomid abundance was significantly correlated with the weight of accumulated detritus in cages.
3. While invertebrates were more abundant in cages lacking fish, there were no fewer invertebrates in cages with 2 fish than with 1 fish. This may indicate the presence of secure refuges among substrates in the cages, preventing the additional fish from depleting prey further, or a lack of precision of methods due to natural variations in prey densities and spatial patchiness.
4. No significant effects of predators on relative prey abundance or species richness were detected.
5. The impact of predation on prey abundance weakened on week 4, perhaps due to extra refuges among the accumulated detritus. However, drying of the stream increased fish densities in pools so that cages may have become zones of relative safety that were colonized readily by macroinvertebrates. This result highlights the need for year-round investigations to quantify predation effects in Hong Kong's seasonal tropical climate.     

Egg population dynamics of naturally spawning dace,Leuciscus leuciscus (L.)

Synopsis Survival of dace eggs in a chalkstream was 8.6 to 21.8% from spawning to hatching. The proportion of dead eggs in samples rose from 4.9% at the end of spawning to 59% after 13 days. The combined number of dead eggs, live eggs and the empty shells of eggs after hatching also began a steady decline soon after the end of spawning. Egg drift was estimated to be 2.0% of the initial egg population. Laboratory studies and field population estimates indicated that macroinvertebrates were capable of eating large numbers of dead eggs but much smaller numbers of live ones. A large part of the fall in egg numbers was accounted for by egg decomposition. There was a close relationship between the percentage of surviving eggs and substrate composition with poor survival in areas of high silt and low gravel content.     

Reproductive variation and adult size in two co-occurring grasshopper species

ABSTRACT. 1. Egg sizes and clutch sizes of the grasshoppers Chorthippus brunneus (Thunb.) and Myrmeleotettix maculatus (Thunb.) were compared among three years and among three sites less than 1.3 km apart. Relationships between these reproductive traits and date of egg laying, body size and body condition were sought.
2. M.maculatus , the smaller species, laid fewer but larger eggs; and only the eggs of this species showed significant differences between sites and years.
3. A negative correlation between egg size and number per clutch was evident between species and years, but generally not among sites and among individuals of a population.
4. However, a hidden negative correlation between egg size and number was uncovered within populations when the relationship was examined for females of a given mature weight.
5. Variation in the number of eggs per clutch was explained statistically by a positive relationship between female body weight and egg number. Also, both interpopulation and intrapopulation comparisons revealed that for M.maculatus , but not for C.brunneus , females with long hind femurs laid large eggs.     

Preliminary empirical models of the historical and future impact of acidification on the ecology of Welsh streams

SUMMARY 1. We describe a preliminary approacb to modelling the impact of acidification on the ecology of two Welsb streams. Output from the hydrochemical Model of Acidification of Groundwaters in Catchments (MAGIC) was used to drive empirical models which predicted brown trout Salmo trulta (L.) survival, trout density and invertebrate assemblage type. The models were used for hindcasts between 1844 and 1984 under conifer forest and moorland conditions. Forecasts involved each of these land uses with sulphate deposition either continued at 1984 levels or reduced by 50%.
2. Trout survival times and trout densities in the models declined markedly between 1844 and 1984. The most severe decline occurred under simulated forest, where high aluminium concentration led to the virtual elimination of trout in both streams.
3. In forecasts, only in simulated moorland with sulphate deposition reduced by 50% of 1984 levels, was further decline in trout population retarded. There was no marked recovery in trout density under any of the conditions examined.
4. Invertebrate assemblages in streams during the nineteenth century may have differed from those now existing in nearby moorland streams which are presently circumneutral. Past chemical conditions were unusual (<3mg 1⁻¹ total hardness, but pH >5.7 and low aluminium) by present-day standards, and were outside the range of the invertebrate model until -1940.
5. Between the 1940s and 1984 there was no change in invertebrate fauna under the moorland scenario despite some acidification. However, simulated forest advanced the appearance of the most impoverished assemblage type, which did not recover in spite of reduced deposition.
6. We discuss several uncertainties with the models in their present form, but suggest some methods for their testing and validation.