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1.
Rotenone sampling is the most efficient method for assessing the fish assemblage structure and species abundance of low conductivity Amazonian streams. It does, however, cause fish mortality and disturb aquatic ecosystem. The aim of this study was to search for a non‐destructive alternative. The efficiency of electrofishing was compared against complete removal using rotenone. This procedure was repeated in 12 streams dispersed throughout French Guiana to test for environmental and biological effects such as water conductivity, stream depth, fish family membership and body size. This study revealed that the efficiency of electrofishing was influenced by stream conductivity and stream depth, but not by fish family or body size. The electrofishing method might constitute an efficient alternative to using rotenone in smaller streams (below 25‐cm depth and above 43 μS cm?1), whereas in deeper and/or slightly conductive streams, rotenone still remains the only method able to provide a quick and comprehensive picture of the fish assemblage.  相似文献   

2.
Abstract –  The selection of spawning depth by Eurasian perch Perca fluviatilis was investigated in an experiment using artificial substrata in Lake Constance during the spawning season of 2007. The experiment compared spawning behaviour at substrata between 0.5 and 15 m depth at two sites exposed to different regimes of ship-generated wave action. The total abundance of egg ribbons did not differ significantly between the two sites, but the preferred spawning depth was deeper at the wave exposed site (5 m) compared to the sheltered site (2 m). While water temperatures could not account for the observations, differences in wave exposure may explain the different spawning depth preferences. At both sites, large egg ribbons were generally found in deeper water, and large egg ribbons occurred more frequently at the sheltered site. Because the egg ribbons of perch are likely to have a size-dependent susceptibility to hydrodynamic stress, large females may be expected to select deeper spawning locations where the effects of surface waves are considerably attenuated.  相似文献   

3.
This study investigated the progressive effects of HgCl2 in the testis and sperm of the tropical fish tuvira Gymnotus carapo L. exposed to increasing Hg concentrations (5–30 μm ) and increasing exposure times (24–96 h). Histopathology and metal concentrations in the testis were observed. Hg concentrations in the testis reached 5.1 and 5.2 μg g?1 in fish exposed to 20 and 30 μm of Hg, respectively. Hg effects on testicular tissue were observed even at low Hg concentrations, with no alterations in gonadosomatic index. However, the quantitative analysis of the induced alterations (lesion index) demonstrated that the Hg effects in testis became more severe after exposure to higher concentrations (20 and 30 μm ) and during longer exposure (72 and 96 h), probably leading to partial or total loss of the organ function. Hg exposure (20 μm ) also affected sperm count and altered sperm morphology. This study showed that HgCl2 caused progressive damage to testicular tissue, reduced sperm count and altered sperm morphology. These results are important in establishing a direct correlation between Hg accumulation and severity of lesions.  相似文献   

4.
Abstract As undersized fish have to be released after capture in most recreational fisheries, the potential mortality associated with this practice is of interest to managers and anglers. The objective of this study was to assess the effects of air exposure on mortality and growth in pikeperch, Sander lucioperca (L.), <500 mm (total length) at low water temperatures (around 10 °C). Fish were exhaustively exercised by manual chasing for 120 s, exposed to air for 0, 60, 120 or 240 s, and afterwards stocked into two ponds to measure mortality and growth rates. Neither mortality nor growth was statistically significantly different among different durations of air exposure. However, mortality was the lowest in both ponds for fish with no air exposure, which suggested that air exposure adversely affected survival. Mortality was inversely related to length and body mass of pikeperch in one of the two ponds. From a management perspective, it is suggested to avoid air exposure in angled pikeperch that are to be released.  相似文献   

5.
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.  相似文献   

6.
Abstract –  We used three-dimensional video analysis of feeding experiments to determine the effects of water depth on prey detection and capture by drift-feeding juvenile coho salmon ( Oncorhynchus kisutch ) and steelhead ( O. mykiss irideus ). Depth treatments were 0.15, 0.30, 0.45 and 0.60 m. Mean prey capture probabilities for both species were constant across all treatments (coho = 0.51, steelhead = 0.39), and did not differ significantly between species. In deeper treatments, capture probabilities were lower nearer the surface than they were nearer the substrate, particularly at the lateral edges of the foraging area. In deeper treatments coho had greater capture probabilities nearer the surface than did steelhead. It is unclear if this was a species difference, or one based on the relative amount of foraging experience the fish had in the wild prior to capture. Prey capture manoeuver characteristics were very similar for both species, including positive relationships between water depth and both prey detection distance and prey interception swimming speed, and no relationship between depth and speed of return to the focal point. Because prey encounter rate is expected to increase with increasing water depth, we used capture probabilities to predict capture rates for coho and steelhead, which increased linearly with water depth. We conclude that any benefit of foraging in deeper water is more likely due to increased encounter rate rather than to increased capture probability.  相似文献   

7.
A towed 330 kHz sector scanning sonar was evaluated for surveys of near-surface migratory salmonids (Oncorhynchus sp.) and other fish in the Strait of Georgia near the mouth of the Fraser River near Vancouver, BC (Canada). Detection of large near-surface fish presents a serious challenge to conventional net trawls or echo-sounder surveys due to vessel avoidance behaviour by the fish. The sonar was towed beside a research vessel on a custom-built towfish at a nominal depth of 18 m. The optimum configuration was determined to be with the sonar scanning a 30° vertical sector oriented perpendicular to the tow direction, at a ping rate of 5 Hz and a sector scan period of 5 s. Fish were detected up to a range of 100 m, limited by systemic noise and backscattered reverberation from the sea surface. Some evidence of vessel-avoidance behaviour by the fish was observed. Near surface temperature and salinity gradients are shown to induce downwards refraction of the sonar beam, resulting in biases in apparent depth and target strength of the fish. A simple model of the sonar performance in this scanning mode, including beam-pattern effects, is used to generate curves of fish target detectability and beam-pattern induced bias as a function of range and fish target strength. After correction for refraction effects, beam-pattern bias, and detectability, the survey results show reasonable agreement with net trawl and riverine escapement data.  相似文献   

8.
Channel catfish, Ictalurus punctatus (Rafinesque), goldfish, Carassius auratus (L.), striped bass, Morone saxatilis (Walbaum), and Gulf sturgeon, Acipenser oxyrinchus desotoi Vladykov, were acclimatized to fresh water or salinities of 9.0‰ or less and then exposed to Flavobacterium columnare (formerly known as Flexibacter columnaris ), the bacterial pathogen that causes columnaris disease. None of the fish acclimatized to 3.0 or 9.0‰ salinity died, and all deaths in lower salinities occurred between 1 and 5 days after exposure to F. columnare . Mortality was 97.7% in fresh water and 67.1% in 1.0‰ salinity for channel catfish (model SE, 1.8) and 66.5% in fresh water and 40.8% in 1.0‰ salinity for goldfish (model SE, 1.2); and 96.9% in fresh water and 61.7% in 1.0‰ salinity for striped bass (model SE, 1.8). After exposure to F. columnare , none of the Gulf sturgeon died. Flavobacterium columnare was isolated from the skin and gills of all fish dying during the experiments, but was not isolated from survivors in fresh water and 1.0‰ salinity 21 days after bacterial exposure. In vitro growth of bacteria was significantly higher in 1.0 or 3.0‰ salinity than in control medium (0.3‰ salinity). However, in vitro adhesion of bacteria was reduced with increasing salinity, which could explain the lower mortality of fish at higher salinities.  相似文献   

9.
Rapid sand filtration was explored as a means of removing Triactinomyxon actinospores (Tams), the waterborne infective stage of the salmonid parasite Myxobolus cerebralis that causes whirling disease, from contaminated water. Preliminarily, a batch of sand was sieved to create 12 size ranges from 180 to 2000 μm. These individual ranges were tested for their efficacy of removing Tams through sand beds either 2 cm or 4 cm deep. The critical size at which no Tams passed through the sand bed was 300 μm at 2 cm depth and 425 μm for 4 cm bed depth. Additional tests evaluated the passage of Tams through filter beds comprised of sand that had all particles smaller than 180 μm removed. With this sand, 0.2±0.5% of Tams passed through a 2 cm bed, and 0.0±0.0% with a 4 cm sand bed. Based on these preliminary results, small (61 cm×15 cm) rapid sand filters were placed in-line with aquaria containing rainbow trout fry. The sand bed depth was 10 cm under which lay 10 cm of aquarium gravel. Four treatments were (1) negative control, (2) positive control, (3) sand of >180 μm, (4) sand of >300 μm. Tams were regularly introduced to the rearing systems above the sand filters. After 60 days, clinical signs of whirling behavior and black tails were seen among the positive controls. A polymerase chain reaction assay for Myxobolus cerebralis 1 month after exposure proved negative for negative controls and the >180 μm group, whereas 10% of the >300 μm group and 71% of the positive controls were infected. Results from the PCR assay at the study’s conclusion indicated the negative controls and >180 μm group were still disease free. All positive control fish were infected, and 49% of >300 μm fish were infected. These results were mirrored by those obtained from a pepsin–trypsin digest assay, except one fish among the >180 μm group was found to be infected. These results demonstrate that sand filtration may be a viable option in treating hatchery water supplies that are contaminated with whirling disease.  相似文献   

10.
红水河岩滩水库鱼类资源声学评估   总被引：1，自引：0，他引：1  
为评估梯级开发下渔业资源变化情况,2015年9月采用分裂波束鱼探仪EY60(120 kHz,250 W)对红水河岩滩水库库区及上游江段鱼类资源进行声学调查,并结合渔获物统计和地理统计分析对鱼类时空分布进行分析,评估鱼类资源量。结果显示整个调查区域的鱼类资源密度为(0.53±2.11)尾·m~(-2)(±SD),从水坝上游至库区呈增长趋势,鱼类资源密度水平分布与水深无显著相关关系。垂直分布方面,鱼类主要分布在30 m以内水层;不同大小个体对水深有一定的选择性,小个体鱼类(10 cm)约86.2%分布在30 m水层之内;大个体(30 cm)有44.7%分布在40 m以下水层。基于鱼类分布GIS建模,估算调查区域鱼类资源量为6.57×10~7尾。  相似文献   

11.
The bottom culture of southward‐transplanted sea cucumber Apostichopus japonicus in a subtropical fish farm was investigated in a field study at Dapeng Cove, Daya Bay, from January 5–August 5 2011, with the aim of finding the ideal period for culturing A. japonicus in fish farms, and developing an integrated multi‐trophic aquaculture (IMTA) in southern China. Results showed that the bottom‐cultured sea cucumbers survived well (100%) before summer, survival rates decreased to 65.00 ± 21.21% in July, and all animals had died at the end of the study. Specific growth rates of the sea cucumbers were high during winter (1.05 ± 0.03% d?1), decreased in early spring (0.44 ± 0.11% d?1) and became negative in the following months. Growth rate was mainly influenced by water temperature, dissolved oxygen and sulphide content; the anoxia caused by water column stratification at the seafloor in the summer were the main causes of mass mortality. Our results indicate that bottom culture in the temperate season (winter and spring, optimally from late November to early April) is a viable way to rear the deposit feeder A. japonicus underneath a subtropical fish farm.  相似文献   

12.
John Stewart   《Fisheries Research》2008,90(1-3):289-295
Variables affecting the short-term survival of snapper (Pagrus auratus) captured using commercial fish traps and subsequently released were investigated by holding the fish in cages. A logistic regression model showed that capture depth had the greatest affect on short-term survival of snapper, with no mortalities observed from depths of less than 21 m and 2% from depths of less than 30 m. Mortality of snapper increased rapidly after 30 m and was 39% between capture depths of 30 and 44 m and 55% between capture depths of 45 and 59 m. Survival was also effected by fish length, with smaller fish being more likely to die. The rate of ascent of captured snapper and the density of fish in cages were kept reasonably constant and did not appear to affect survival. The number of snapper swimming upside-down prior to being returned to the sea floor in cages was not a good predictor of mortality. Future studies that use cages to assess discard mortality rates would benefit from underwater video observations of fish behaviour. The results demonstrate that the discard mortality of snapper should be considered when managing the fishery in New South Wales, Australia.  相似文献   

13.
Abstract –  The vertical distribution pattern (VDP) of fish at shallow sites in eutrophic lake – Lake IJssel, the Netherlands – as affected by water transparency, was examined. The pattern was assessed by pair trawling at three depths and by hydroacoustics from June to August. Water transparency was estimated by light intensity and Secchi depth measurements. Hydroacoustics showed that fish were more dispersed at night than during the day. European smelt, ( Osmerus eperlanus ) and young-of-the-year Eurasian perch ( Perca fluviatilis ) comprised 97% of the fish in numbers. European smelt concentrated near the surface, at light intensities of >200 µW · cm−2 when the water was turbid, and near the bottom when the water was clear (Secchi depth > 1.2 m). We concluded that low water transparency over-ruled the light sensitivity of European smelt, and caused European smelt to stay higher in the water column.  相似文献   

14.
ORIO  YAMAMURA 《Fisheries Science》2003,69(3):445-455
ABSTRACT:   The species composition of demersal fish was studied in nearshore waters (33–116 m depth) of south-eastern Hokkaido, the coldest area around the Japan Archipelago due to the influence of the cold Oyashio Current, using bottom gillnet samples collected during October 1996, August 1997, May 1998 and September 1999. The water temperature just above the sea bottom in the study area was lowest (< 2°C) during May and then rose through autumn (> 14°C). Cottids were the most abundant family in terms of both overall biomass and number, but their gravimetric dominance decreased from May (84%) through October (14%), whereas pleuronectids and stichaeids increased. Of the 57 fish species sampled, plain sculpin Myoxocephalus jaok was the dominant species in terms of overall biomass, accounting for 29.0% of the total biomass, followed by horned sculpin Enophrys diceraus (19.5%), Kamchatka flounder Atheresthes evermanni (6.5%) and blackline prickleback Acantholumpenus mackayi (4.9%). Plain sculpin dominated during May and September, but its predominance was low during October (9.6%), when witch flounder Glyptocephalus stelleri (22.7%) and blackline prickleback (10.8%) became important. This seasonal change appears to reflect the annual life cycle events of the fish, such as spawning.  相似文献   

15.
The design and operation of aquaculture tanks should minimize stagnant areas especially in the immediate vicinity of the fish. In tanks with pelagic fish, mixing caused by the water flow and by fish swimming is sufficient to maintain dissolved oxygen and metabolite concentrations in the immediate vicinity of the fish that are similar to those in the main water body. Given the behavior of sedentary benthic species, such as the California halibut (Paralichthys californicus), and their tendency to remain motionless on the bottom of aquaculture tanks, often in layers that are several fish deep, water quality may stratify with the worse conditions occurring in the area where they fish are lying. The purpose of this study was to evaluate the influence that California halibut (450 g average weight) may have on the vertical profile of oxygen concentration in a raceway (239 cm long, 28 cm wide) and a circular tank (92 cm diameter) operated at two water depths (10 and 20 cm). Oxygen was measured at each centimeter of the vertical profile both in an area with fish and without fish to assess their influence.

Results showed a lower oxygen concentration in the near-bottom region of the raceway and circular tanks. The phenomenon was most pronounced in the raceway operated at a 20 cm depth, but was also observed in the circular tank operated at 20 cm and in the raceway at 10 cm.

Measurements were also taken in samples collected just in front of or directly from a fish's mouth. A zone of depressed oxygen concentration in the immediate vicinity of the fish was documented, with oxygen concentrations as low as 50% of the measured tank effluent concentration. The magnitude of the depression was greater in raceways than in circular tanks and in 20 cm water depth than in 10 cm depth. The fish remained sedentary in these zones of depressed oxygen concentration for extended periods of time and frequently exhibited hyperventilation. The oxygen concentrations in the vicinity of the fish were consistently lower than the concentrations measured in the tank effluent. Therefore, effluent measurements did not provide an accurate representation of conditions to which the fish were exposed.  相似文献   


16.
珠江首次禁渔西江段鱼类资源声学跟踪监测分析   总被引：1，自引：0，他引：1  
2011年珠江开始实行禁渔期制度。该研究采用 Simrad EY60鱼探仪,分别于2010年5月19日和2011年5月22日对珠江西江段进行了走航式探测。结果显示,珠江禁渔期期间西江段鱼类资源密度增加,2010年和2011年鱼类平均密度分别为0.0513尾·m -3和0.1068尾·m -3,根据渔获物调查数据,推算增幅分别为广东鲂（Megalo-brama terminalis）47.85％、赤眼鳟（Squaliobarbus curriculus）18.54％、鲮（Cirrhina moitorella）10.87％和鳊（Parabra-mis pekinensis）6.25％;两年西江段深水区域鱼类密度均较大,尤其是水底结构为凹形区域,鱼类有明显的聚集现象;浅水区域且底部较平整的水域,鱼类分布分散且密度较低;垂直分布方面,鱼类主要分布4--10 m 中下层水层。珠江禁渔期的实施,在一定程度上保护了鱼类的产卵亲体繁殖,对鱼类资源数量的补充起到了增殖作用,同时在很大程度上护养了鱼类的自然生长,起到了资源增重作用。  相似文献   

17.
Abstract –  Induced morphological defences, where individuals develop morphological structures as a response to signals from sympatric predators, are common among invertebrates. Such defences have also been reported in a freshwater fish, the crucian carp Carassius carassius . In crucian carp, the presence of piscivorous fish presumably induces the development of a deep body as a defence mechanism. We tested how the growth rate (in body depth, length and mass) of individually tagged crucian carp responds to pike Esox lucius odours and control water. In general, crucian carp exposed to pike odour grew better (both in length and mass) than control fish. The treatment crucian carp also developed deeper bodies than control crucian carp. Further, there was a strong positive relationship between individual growth rate and the rate of change in body depth and this relationship did not differ between control and treatment fish.  相似文献   

18.
According to the Ideal Free Distribution theory, individual fish are distributed where environmental conditions are optimal, and the occupied area may vary with population abundance. Thus, observed distributions are a combination of habitat suitability and density-dependent effects. Data from an annual bottom trawl survey taking place in autumn were used to assess associations between the distributions of eight demersal fish species, separately for juveniles and adults, and habitat characteristics (depth, temperature and salinity) in the Bay of Biscay and Celtic Sea. Cumulative distribution functions were used to describe the general frequency distributions of environmental variables and their relationships with fish density. During the period 1992–2006, observed bottom temperatures fluctuated with no time trend (ΔT = 8°C in the first 80 m) and population abundances varied significantly. Juvenile hake, poor cod, blue whiting, adult red gurnard, adult megrim, and lesser-spotted dogfish were found to be significantly associated with specific depth ranges. Associations with bottom temperature and salinity were weaker. For some species, preferred environmental conditions changed over time, independently of variations in environmental conditions. In general, most species seemed to be able to cope with the experienced range of conditions. Habitat associations were not influenced by abundance variations. Fluctuating abundances had an impact on spatial occupation only for red gurnard adults, lesser-spotted dogfish and blue whiting juveniles, independent of absolute densities.  相似文献   

19.
Abstract– Habitat use and population dynamics in brown trout Salmo trutta and Arctic charr Salvelinus alpinus were studied in an oligotrophic lake over a period of 10 years. Previous studies showed that the species segregated by habitat during summer. While brown trout occupied the surface water down to a depth of 10 m, Arctic charr were found deeper with a maximum occurrence at depth 10–15 m. Following the removal of a large number of intermediate sized fish in 1988–89, habitat segregation between the species broke down and Arctic charr were found in upper waters, while brown trout descended to deeper waters. The following year, both species were most frequently found in surface waters at depths of 0–5 m. During the last four years, the species reestablished their original habitat segregation despite another removal experiment of intermediate-sized fish in 1992–1994. The removal of fish resulted in an increased proportion of large (≥ 25 cm) fish in both species. Furthermore, the charr stock responded by reduced abundance and increased size-at-age. The results revealed plasticity and strong resistance to harvest populations of brown trout and Arctic charr. This is probably due to internal mechanisms of intraspecific competition within each population, which result in differential mortality among size classes.  相似文献   

20.
Abstract  The distribution and overall biomass of an underfished vendace, Coregonus albula L., population in the mesotrophic Henne Reservoir (Germany) was studied using hydroacoustics and gill nets. Additionally, midwater trawling was carried out. Overall fish biomass, based on five hydroacoustic surveys (June to September 2002), ranged from 188 kg ha−1 in early August to 302 kg ha−1 in September 2002. The overall mean fish biomass was 256 kg ha−1 (±48 kg ha−1 SD). Biomass of fish smaller than 25 cm total length (mostly vendace) varied from 56 kg ha−1 in August to 99 kg ha−1 in September, with an overall mean fish biomass of 74 kg ha−1 (±17 kg ha−1 SD). The echograms showed temporal variation in fish distribution in Henne Reservoir. In June, fish were fairly evenly distributed over the whole reservoir but in September a dense aggregation of fish (mostly vendace) was found in the deeper water layers near the dam. The distribution of vendace stock, its impact on water quality and fisheries management, biomanipulation and effort for mass removal are discussed.  相似文献   

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