Electrofishing and salmonid movement: reciprocal effects in two small montane streams

The effects of electrofishing on salmonid movement and of salmonid movement on electrofishing‐derived abundance estimates were studied in two streams in western Montana, U.S.A. Electrofishing increased emigration of salmonids from study reaches for 1 day, but not for succeeding days, whereas immigration to study reaches was unaffected. Movement of most emigrating fishes was downstream. On these small streams, electrofishing did not appear to cause fishes to flee during sampling. Numbers of salmonids migrating between mark and recapture runs were small relative to the fish abundance estimates in study reaches, usually much less than the 95% CL for those estimates, thus disregarding movements of marked fishes from the study reaches would have produced small positive biases in abundance estimates. Overall, for this suite of salmonid species in mid‐summer in these streams, the effects of electrofishing on fish movement and of fish movement on abundance estimates were minor.     

Comparison of fish communities between above‐ and below‐dam sections of small streams; barrier effect to diadromous fishes

To analyse the effects of small‐scale dams on fish communities, species diversity, population density, biomass, migration over dams and trophic relationships were investigated in the above‐ and below‐dam sections of three Japanese streams. The dams were 1·5–3·9 m high, constructed within 400 m of the sea, and had no impoundment or fishway. Fish communities were mainly composed of diadromous fishes. Of the 17 species sampled, only a few species of gobies, Rhinogobius spp. and Gymnogobius spp. were able to climb and migrate upstream over the dams. Consequently the number of species, and total density and biomass of fishes below the dams was high, but low above the dams. One of the most dominant fish below dams, Plecoglossus altivelis altivelis , predominantly fed on benthic algae, whereas other fishes preyed on benthic invertebrates. Trophic relationships above dams were very simple, the few species of gobies preying on chironomid larvae and other aquatic invertebrates.     

Habitat use by a Midwestern U.S.A. riverine fish assemblage: effects of season, water temperature and river discharge

The hypothesis that temperate stream fishes alter habitat use in response to changing water temperature and stream discharge was evaluated over a 1 year period in the Neosho River, Kansas, U.S.A. at two spatial scales. Winter patterns differed from those of all other seasons, with shallower water used less frequently, and low‐flow habitat more frequently, than at other times. Non‐random habitat use was more frequent at the point scale (4·5 m²) than at the larger reach scale (20–40 m), although patterns at both scales were similar. Relative to available habitats, assemblages used shallower, swifter‐flowing water as temperature increased, and shallower, slower‐flowing water as river discharge increased. River discharge had a stronger effect on assemblage habitat use than water temperature. Proportion of juveniles in the assemblage did not have a significant effect. This study suggests that many riverine fishes shift habitats in response to changing environmental conditions, and supports, at the assemblage level, the paradigm of lotic fishes switching from shallower, high‐velocity habitats in summer to deeper, low‐velocity habitats in winter, and of using shallower, low‐velocity habitats during periods of high discharge. Results also indicate that different species within temperate river fish assemblages show similar habitat use patterns at multiple scales in response to environmental gradients, but that non‐random use of available habitats is more frequent at small scales.     

Fish behavioural responses to river discharge trends and the importance of habitat connectivity

Population behaviours associated with the migrations of coarse (non‐salmonid) fishes within river basins are amongst the most poorly understood dispersion mechanisms of temperate freshwater organisms, which in rivers are expected to be influenced by river discharge. We examined the timing and intensity of fish movements (via trapping) between the River Avon (Hampshire, England) and a small floodplain tributary, Ibsley Brook, and tested for correlations with trends in river discharge (i.e. mean cm of change in stage during trapping), water temperature and brook water velocity over twelve months in 1999–2000. 0‐group fishes dominated the catches. Intensities of movement between the brook and the river were similar in most months, but seasonal patterns were observed overall and for individual species. Few significant differences in overall numbers of fish were observed between the discharge trends, but many individual species demonstrated differences, mostly as more intense movement under fast rising discharge. Fish numbers in five species were correlated with river discharge trend, and movements in some species were correlated with the rate of temperature change (Δ° C 10 h sampling), and with changes in brook water velocity. Our results suggest daily movements between the river and small tributary brooks are triggered by changes in light intensity and water velocity, whereas seasonal movements of species between the river and brook are driven by changes in river discharge and water temperature, in particular associated with flood events. This study emphasizes the importance of connectivity in river systems, as fish movement between the Avon and its annexes occur under all flow regimes, but especially with rapidly rising discharge.     

Anti‐predator response of naïve and experienced common bully to chemical alarm cues

Histological analysis of the skin of common bully Gobiomorphus cotidianus , a New Zealand native eleotrid fish, revealed the presence of club cells in the epidermis. Epidermal club cells are frequently associated with the production of alarm substance (Schreckstoff). The behavioural responses of perch‐naïve and perch‐experienced common bullies to either conspecific skin extract or chemical cues from an introduced predator, perch Perca fluviatilis , were then examined. Both perch‐naïve and perch‐experienced common bullies exhibited a behavioural response when exposed to conspecific skin extract, indicating the probable presence of an alarm substance. In contrast, only perch‐experienced common bullies recognized and exhibited a subsequent behavioural response to the odour of perch. This study is the first to document the presence of epidermal club cells and a behavioural response to a conspecific chemical alarm signal for fishes in the Eleotridae. The results indicate that common bully can learn to recognize perch odour as a threat, and that this ability may be a result of previous predator labelling involving a conspecific alarm substance.     

Can Paradise Fish (Macropodus opercularis,Anabantidae) Recognize a Natural Predator? An Ethological Analysis

Predator recognition and avoidance by paradise fish have been studied with allopatric species and model experiments. The effect of sympatric predators has not been investigated. Here I report that reactions of paradise fish towards a sympatric predator (Channa micropeltes) are quantitatively different from those shown towards an allopatric predator or different harmless species of fishes. I investigate the possible cues eliciting this differential response and show that visual as well as olfactory stimuli play roles. Olfactory stimuli from the sympatric predator alone elicit an elevated level of activity from paradise fish; the appearance of the sympatric predator (with or without olfactory stimuli) results in an exploratory and display reaction. I speculate what visual stimuli may play roles in predator recognition in paradise fish and I suggest that previously asserted key stimuli such as the eyes of the encountered heterospecific fish may not differentiate the harmful species from innocuous. I conclude that the antipredatory behavior of paradise fish may be affected by both genetic factors and learning and that the relative importance of the former or latter factor may vary depending on the situation.     

洞庭湖渔业资源现状及其变化

1990－1999年资源监测表明,洞庭湖鱼的种类与70年代基本相同,但其组成结构发生较大变化,明显以鲤,鲫,鲶,黄颡鱼等湖泊定居性鱼类为主,最高达86．1％,“四大家鱼”在渔获物中所占比较不足10％,刀鲚等洄游性鱼类已极为罕见;90年代渔获量平均为3．97万t,渔业产量增加,但多以1－2龄鱼为主,补充群体严重不足,水利工程的兴建,泥沙淤积,围垦,污染加剧以及过度捕捞是造成洞庭湖渔业资源衰退的主要原因。     

Effects of central administration of arginine vasotocin on monoaminergic neurotransmitters and energy metabolism of rainbow trout brain

In a first set of experiments, intracerebroventricular (ICV) treatment of 1 μl 100 g⁻¹ body mass of Cortland saline containing different doses (1–20 nmol μl⁻¹) of arginine vasotocin (AVT) produced after 180 min dose‐dependent changes in levels of brain neurotransmitters in several brain regions and pituitary of rainbow trout Oncorhynchus mykiss . Thus, an enhancement of serotonergic and dopaminergic activity, together with a decreased noradrenergic activity, were observed both in the hypothalamus and pituitary of AVT‐treated fish. In the other brain regions assessed, only increased serotonergic activity in the optic lobes, and decreased dopaminergic activity in the telencephalon of AVT‐treated fish were noticed. Changes observed in monoamine levels resemble those observed during osmotic adaptation of euryhaline fishes. In a second set of experiments, fish were ICV injected with AVT as described above to assess changes in several variables of brain energy metabolism. The results obtained show a dose‐dependent enhancement of brain glycogenolytic potential in the brain of AVT‐treated fish, that again resemble the changes observed in euryhaline fishes during osmotic acclimation.     

Fishes as models in studies of sexual selection and parental care

Fishes are by far the most diverse group of vertebrates. This fact is in no way, however, reflected in their use as model organisms for understanding sexual selection or parental care. Why is this so? Is it because fishes are actually poor models? The usefulness of fishes as models for sexual selection and parental care is discussed by emphasizing some problems inherent in fish studies, along with a number of reasons why fishes are indeed excellently suited. The pros and cons of fishes as models are discussed mainly by comparison with birds, the most popular model organisms in animal behaviour. Difficulties include a lack of background knowledge for many species, and the problems of marking and observing fishes in their natural environment. Positive attributes include the diversity of lifestyles among fishes, and the ease with which they can be studied experimentally in the laboratory. How useful fish models can be is briefly illustrated by the impressive and broadly relevant advances derived from studies of guppies Poecilia reticulata and three‐spined sticklebacks Gasterosteus aculeatus . A selection of topics is highlighted where fish studies have either advanced or could greatly enhance, the understanding of processes fundamental to animal reproductive dynamics. Such topics include sex role dynamics, the evolution of female ornamentation and mate choice copying. Finally, a number of potential pitfalls in the future use of fish as models for sexual selection and parental care are discussed. Researchers interested in these issues are recommended to make much more extensive use of fish models, but also to adopt a wider range of models among fishes.     

Acoustic deterrents to manage fish populations

Finding effective ways to direct native fish away from anthropogenic hazards and limit the spread of invasive species, without physical intervention, harming non-target fishes or interrupting aquatic commerce is a major challenge for fisheries management. One option is to target fish sensory systems to manipulate behavior using attractive or repulsive cues. Many, if not all species of fish, use sound as part of their behavioral repertoire and display varying degrees of phonotaxis. Sound has inherent advantages over other sensory stimuli such as light or odor as underwater sound attenuates slowly, is highly directional and is unimpeded by low light or water turbidity. This review details the use of acoustics to deter and guide fish movements for a wide variety of fishes, before critically assessing the benefits and limitations of the technology. No single method of fish deterrence is a “one size fits all”, and therefore this review will assist both managers and researchers attempting to use acoustic deterrents for different fish orders.

     

气候变化对中国近海8种中上层鱼类潜在生境分布的影响

随着底层和近底层渔业资源的衰退,海洋中上层鱼类在我国海洋捕捞业中逐渐占据重要的地位。预测气候变化情景下中上层经济鱼类的潜在生境分布及其变化规律,可为应对气候变化的鱼类栖息地保护和渔业生态系统管理提供重要科学依据。采用物种分布模型模拟并预测现状及2050年两种气候变化情景下8种中上层经济鱼类在中国近海的潜在分布,通过分布区的收缩-扩张情形和质心迁移距离定量分析气候变化对鱼类空间分布格局的影响。结果表明：(1)模型预测结果良好,各组模型的AUC值均高于0.85,影响目标鱼类潜在分布的主要驱动因子为海水表层温度和溶解氧;(2)8种中上层经济鱼类中,羽鳃鲐(Rastrelliger kanagurta)、鳓鱼(Ilisha elongata)等种类生境分布偏南,气候变化情景下分布北界可扩展至长江口,而鳀鱼(Engraulis japonicus)、青鳞小沙丁鱼(Sardinella zunasi)等种类主要分布在我国北方海域,气候变化情景下生境南缘边界退缩明显;(3)整体来看RCP8.5情景下的空间分布变化率大于RCP2.6情景,其中蓝圆鲹(Decapterus maruadsi)、青鳞小沙丁...     

Differential lifetime success and performance of native and non‐native Atlantic salmon examined under communal natural conditions

The lifetime success and performance characteristics of communally reared offspring of wild native Burrishoole (native), ranched native (ranched) and non‐native (non‐native) Atlantic salmon Salmo salar from the adjacent Owenmore River were compared. Non‐native 0+ year parr showed a substantial downstream migration, which was not shown by native and ranched parr. This appears to have been an active migration rather than competitive displacement and may reflect an adaptation to environmental or physiographic conditions within the Owenmore River catchment where the main nursery habitat is downstream of the spawning area. There were no differences between native and ranched in smolt output or adult return. Both of these measures, however, were significantly lower for the non‐native group. A greater proportion of the non‐native Atlantic salmon was taken in the coastal drift nets compared to the return to the Burrishoole system, probably as a result of the greater size of the non‐native fish. The overall lifetime success of the non‐native group, from fertilized egg to returning adult, was some 35% of native and ranched. The ranched group showed a significantly greater male parr maturity, a greater proportion of 1+ year smolts, and differences in sex ratio and timing of freshwater entry of returning adults compared to native, which may have fitness implications under specific conditions.     

Sex‐biased dispersal in a salmonid fish: implications for growth rate and survival

Migration is widespread among marine fishes, yet little is known about variation in the migration of individuals within localities. We tested the hypothesis that variation in the migratory behaviour among plaice ( Pleuronectes platessa ) in the North Sea could be explained by large‐scale differences in the speed and directions of the tidal streams, which the fish use as a transport mechanism. Towards this end, 752 mature female plaice tagged with electronic data storage tags were released at eight locations with contrasting tidal flow properties, between December 1993 and September 1999. The experiment yielded 20 403 days of data from 145 plaice. The position of each fish was determined at intervals throughout the liberty period using the tidal location method. The results show 3 geographically discrete feeding aggregations during the summer, which dispersed over the southern North Sea and Eastern English Channel to spawn during winter. Our results re‐affirmed the major role of the tidal streams in the southern North Sea in structuring plaice dispersion, both by providing transport and guidance, and by delimiting the extent of distribution due to thermal stratification during the summer. These results confirm the prediction that large‐scale variation in migration behaviour can be explained in part by the tidal guidance and transport mechanisms available. They have revealed features of spatial dynamics not previously observed from a century of conventional tagging experiments and illustrate how the study of individual fish can successfully define the migratory characteristics of populations.     

Partial migration in fishes: definitions, methodologies and taxonomic distribution

Partial migration, where populations are composed of both migratory and resident individuals, is extremely widespread across the animal kingdom. Researchers studying fish movements have long recognized that many fishes are partial migrants, however, no detailed taxonomic review has ever been published. In addition, previous work and synthesis has been hampered by a varied lexicon associated with this phenomenon in fishes. In this review, definitions and important concepts in partial migration research are discussed, and a classification system of the different forms of partial migration in fishes introduced. Next, a detailed taxonomic overview of partial migration in this group is considered. Finally, methodological approaches that ichthyologists can use to study this fascinating phenomenon are reviewed. Partial migration is more widespread amongst fishes than previously thought, and given the array of techniques available to fish biologists to study migratory variation the future of the field looks promising.     

Latitudinal gradients in Atlantic reef fish communities: trophic structure and spatial use patterns

Trophic strategies and spatial use habits were investigated in reef fish communities. The results supported the hypothesis of differential use of food resources among tropical and higher latitude reef fishes, i.e . the number of species and relative abundance of fishes relying on relatively low‐quality food significantly decreased from tropical to temperate latitudes. The species : genus ratio of low‐quality food consumers increased toward the tropics, and was higher than the overall ratio considering all fishes in the assemblages. This supports the view that higher speciation rates occurred among this guild of fishes in warm waters. It was also demonstrated that density of herbivorous fishes (the dominant group relying on low‐quality food resources) in the western Atlantic decreased from tropical to temperate latitudes. Spatial use and mobility varied with latitude and consequently reef type and complexity. Fishes with small‐size home ranges predominated on tropical coral reefs.     

Density‐dependent growth in hatchery‐reared brown trout released into a natural stream

Hatchery‐reared brown trout Salmo trutta stocked in a natural stream in addition to resident wild brown trout grew more slowly than those stocked with an experimentally reduced density of brown wild trout. In both cases, hatchery‐reared brown trout grew more slowly than resident wild fish in control sections. Mortality and movements did not differ among the three categories of fish. The results showed that growth of stocked hatchery‐reared brown trout parr was density‐dependent, most likely as a consequence of increased competition. Thus, supplementary release of hatchery‐reared fish did not necessarily increase biomass.     

Mismatch between fishway operation and timing of fish movements: a risk for cascading effects in partial migration systems

Habitat fragmentation is a growing problem worldwide. Particularly in river systems, numerous dams and weirs hamper the movement of a wide variety of species. With the aim to preserve connectivity for fish, many barriers in river systems are equipped with fishways (also called fish passages or fish ladders). However, few fishways provide full connectivity. Here we hypothesized that restricted seasonal opening times of fishways can importantly reduce their effectiveness by interfering with the timing of fish migration, for both spring‐ and autumn‐spawning species. We empirically tested our hypothesis, and discuss the possible eco‐evolutionary consequences of affected migration timing. We analyzed movements of two salmonid fishes, spring‐spawning European grayling (Thymallus thymallus) and autumn‐spawning brown trout (Salmo trutta), in Norway's two largest river systems. We compared their timing of upstream passage through four fishways collected over 28 years with the timing of fish movements in unfragmented river sections as monitored by radiotelemetry. Confirming our hypothesis, late opening of fishways delayed the migration of European grayling in spring, and early closure of fishways blocked migration for brown trout on their way to spawning locations during late autumn. We show in a theoretical framework how restricted opening times of fishways can induce shifts from migratory to resident behavior in potamodromous partial migration systems, and propose that this can induce density‐dependent effects among fish accumulating in lower regions of rivers. Hence, fragmentation may not only directly affect the migratory individuals in the population, but may also have effects that cascade downstream and alter circumstances for resident fish. Fishway functionality is inadequate if there is a mismatch between natural fish movements and fishway opening times in the same river system, with ecological and possibly evolutionary consequences for fish populations.     

The feeding behaviour of juvenile Atlantic salmon in relation to turbulent flow

The feeding behaviour of juvenile Atlantic salmon Salmo salar in the Sainte‐Marguerite River, Quebec, Canada, varied with the characteristics of turbulent flow. Simulations indicated that juveniles would decrease their swimming costs during attacks by 19·8% in low and by 31·1% in high turbulent conditions by initiating movements in low‐speed flow events. The real swimming costs did not differ from the swimming costs estimated for a situation where fish initiate their movements at randomly selected flow velocities. The juvenile Atlantic salmon did not seem to prefer low‐speed flow events when initiating their movements. The proportion of time used for movements by fish decreased with an increase in the mean and the s . d . of the flow velocity.     

Recording long‐term heart rate in Paranotothenia angustata using an electronic datalogger

A unique heart beat datalogging device was either surgically implanted into the peritoneal cavity (internal‐fish) or attached by nylon anchor tags to the dorsal fin rays (external‐fish) of the black cod Paranotothenia angustata . Both groups had a mean ±  s . e . heart rate of c . 46 beats min⁻¹ after 24 h, and by 20 days external‐fish showed a significant reduction (34 ± 3 beats min⁻¹) whereas internal‐fish did not (44 ± 2 beats min⁻¹). In demersal fishes external attachment of an electronic recording device may be preferable to surgical implantation.     

Consistent trophic patterns among fishes in lagoon and channel habitats of a tropical floodplain river: Evidence from stable isotopes

The relationship between food web dynamics and hydrological connectivity in rivers should be strongly influenced by annual flood pulses that affect primary production dynamics and movement of organic matter and consumer taxa. We sampled basal production sources and fishes from connected lagoons and the main channel of a low-gradient, floodplain river within the Orinoco River Basin in Venezuela. Stable isotope analysis was used to model the contribution of four basal production sources to fishes, and to examine patterns of mean trophic position during the falling-water period of the annual flood cycle. IsoSource, a multi-source mixing model, indicated that proportional contributions from production sources to fish assemblages were similar in lagoons and the main channel. Although distributions differed, the means for trophic positions of fish assemblages as well as individual species were similar between the two habitats. These findings contradict recent food web studies conducted in temperate floodplain rivers that described significant differences in trophic positions of fishes from slackwater and floodplain versus main channel habitats. Low between-habitat trophic variation in this tropical river probably results from an extended annual flood pulse (ca. 5 mo.) that allows mixing of sestonic and allochthonous basal production sources and extensive lateral movements of fishes throughout the riverscape.