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1.
Abstract  The in situ avoidance reaction of vendace, Coregonus albula L., in relation to continuous artificial light in terms of a scaring device was tested by split-beam echosounding. The tests were carried out in the mesotrophic Bigge Reservoir (Germany) in November 2007 and 2008 using a Simrad EK 60 echosounder (120 kHz). An underwater lamp with light turned on and off was lowered to 30 m water depth at four sampling sites. No reaction of vendace was observed for the sampled references (light off), but strong avoidance behaviour by swimming mainly downwards was observed when the light was turned on. The light avoidance reaction was confirmed by the volume backscattering strength ( S v) and calculated fish densities (fish ha−1). The mean fish densities for the samples carried out with light turned on were lower (268 fish ha−1, ±409 SD, n  =   32) than for the references with light turned off (5028 fish ha−1, ±2317 SD, n  =   56). The related median values (33 and 3726 fish ha−1, respectively, n  =   88) differed significantly (Mann–Whitney test, P  = <0.001). In conclusion, artificial light has great potential to scare pelagic vendace from areas near the bottom outlets of reservoirs to prevent entrainment losses.  相似文献   

2.
Abstract – Production of cannibalistic Arctic char ( Salvelinus alpinus (L.)) and their prey conspecifics were estimated in an allopatric population, situated in an alpine ultraoligotrophic lake in central Norway. Estimates of population abundance were obtained by mark recapture and successive removal experiments. Assuming stable age distribution, we estimated mean yearly biomass (±95% CL) of char in sampled size groups vulnerable to predation (60 to 150 mm) to 7.93 (5.11–14.30) kg · ha−1. Similarly, mean yearly biomass (±95% CL) of cannibalistic char (> 250 mm) was estimated to 0.62 (0.50–1.06) kg · ha−1. Annual production (±95% CL) of char in length groups 60 to 150 mm was estimated to be 4.31 (2.74–8.03) kg · ha−1 · year−1, and production (±95% CL) of cannibalistic char to 0.19 (0.15–0.33) kg · ha−1 · year−1. Depending on the food conversion factor (set to vary from 0.1 to 0.4), the cannibalistic char removed from 10% to 40% of the production of char in sampled size-classes vulnerable to predation yearly. The overall ecological efficiency in energy transfer between the prey and predator population was 4.4%.  相似文献   

3.
The recreational catfish harvest was classified in 349 reservoirs larger than 200 ha distributed over 40 states of the contiguous USA. Harvesting occurred in 282 reservoirs, averaged 2.8 kg ha−1 year−1 and represented 15.6% of the total fish yield. The genus Ictalurus contributed most to catfish fisheries (mean = 2.0 kg ha−1), followed by Ameiurus (1.1 kg ha−1) and Pylodictis (0.4 kg ha−1). Five distinct clusters of reservoirs were identified, differing relative to geographical distribution, catfish harvests, angler favouritism towards catfish and physicochemical characteristics. Reservoir clusters across the northern USA had low harvests and essentially featured reservoirs in the upper periphery of the native range of catfish. Harvesting in reservoirs in the south-west of the country, where catfish have been introduced, was higher than in the north, yet yield remained low. Within their native range, three overlapping clusters included one with medium and another with high harvests, both types dominated by Ictalurus, and a cluster with very high harvest dominated by Ameiurus . Variability in harvests was attributed to zoogeography, reservoir physicochemical characteristics and fishing effort. Management of catfish fisheries of the three less-productive clusters may focus on enhancement through habitat manipulation and stocking; the two more productive clusters offer the greatest flexibility for management through regulation of harvest.  相似文献   

4.
Abstract  Removal of piscivores may affect population size structure, abundance and growth rates of the remaining fish community. A total of 572 northern pike, Esox lucius L., was removed from 25-ha West Long Lake, Nebraska from 2003 to 2006. The northern pike population was reduced from 36 fish ha−1 and 22 kg ha−1 in 2002 to 20 fish ha−1 and 9 kg ha−1 in 2006. The northern pike population shifted to dominance by smaller individuals. Relative abundance increased for bluegill, Lepomis macrochirus Rafinesque, but remained similar between years for largemouth bass, Micropterus salmoides (Lacepède), and yellow perch, Perca flavescens (Mitchill). Bluegill and yellow perch size structure increased probably because of reduced predation by northern pike. The effects of reduced northern pike density on largemouth bass were less evident. The largemouth bass population may be returning to higher density with smaller size structure observed before pike were introduced. The sport fish community responded positively to the removal of northern pike in this small lake.  相似文献   

5.
An on-farm trial was carried out from February to June 2006 to evaluate the growth and production performance of catla ( Catla catla ) and tilapia ( Oreochromis niloticus ) with freshwater prawn ( Macrobrachium rosenbergii ) and mola ( Amblypharyngodon mola ) in farmer's rice fields. In all treatments, 20 000 mola ha−1 and 20 000 prawn ha−1 were stocked. Besides, stocking included 2500 catla ha−1 in treatment-I, 2500 tilapia ha−1 in treatment-II and catla and tilapia at 1250 ha−1 each in treatment-III . Prawns were fed in the evening with pellets at a feeding rate of 3–8% body weight (initially 8% and gradually decreased to 3%). Catla and tilapia were fed in the morning with a paste of mustard oil cake and rice bran at a feeding rate of 3% body weight. Significantly higher combined production of fish and prawn observed was 2142 kg ha−1 in treatment-I. The benefit:cost ratio was found to be significantly higher in treatment-I than in treatment-II and there were no differences between treatments I and III. From the production and economic point of view, treatment-I was found to be the best proposition for the rotational rice–fish culture systems.  相似文献   

6.
The present paper describes the fishery of the Ea Kao reservoir in south Vietnam. Historical data on the total production and total numbers of fish stocked were available from 1983 to 1996, and this information, together with the results of monthly monitoring of the fishery from June 1996 to December 1998, was used in the present study. A number of gears are used in the Ea Kao fishery, the most important being gill, lift and integrated nets, and beach seines. The fishery of Ea Kao is based on the annual stocking of advanced fry/early fingerlings of 0.3–1.0-g bighead carp, Hypophthalmichthys nobilis (Richardson), silver carp, Hypophthalmichthys molitrix (Cuvier & Valenciennes) and rohu, Labeo rohita Hamilton, as well as the self-recruiting indigenous species Toxabramis houdemeri Pellegrin and two exotic species, i.e. Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. On average, the regularly stocked species contribute to 78% of total production, which has been around 400–450 kg ha−1 in the last few years. The monthly peak catches of stocked species tend to coincide with the rainy season from May to October and the catches of self-recruiting species peak between February and April. A significant relationship ( P < 0.001) exists between the stocking density in year n (SD, n ha−1) and the yield of stocked fish in year n + 1 ( Y , kg ha−1):  相似文献   

7.
Abstract – Mesotrophic Lake Pohjalampi in eastern Finland was fished intensively from 1992 to 1996. In 1996, the biomasses of the dominant fish species, roach and bream, were reduced to 14% and 6%, respectively, of that in 1992. The total biomass of percids was, however, unchanged or slightly increased. The proportion of benthic invertebrates in the total food of the fish decreased from 57% to 36% during the study period, whereas the proportion of zooplankton increased from 31% to 56%. At the same time the number of young planktivorous fish increased. Thus, the main object of fish predation turned from benthic invertebrates to zooplankton due to change in fish population structure. At the beginning of the study the amount of detritus eaten by cyprinids was about 620 kg  ·  ha−1  ·  year−1, but this decreased by 82% due to the intensive fishing. Thus, by recycling nutrients from the sediment, the detrivorous-benthivorous feeding of cyprinids is an important factor in the nutrient balance of the lake. Note  相似文献   

8.
Abstract  Culture-based fish yield in non-perennial reservoirs of Sri Lanka was related to reservoir morphometry and stocking density. The reservoirs were stocked mainly with fingerlings of one Chinese and three Indian major carp species, common carp, Cyprinus carpio L., and the genetically improved farmed tilapia strain of Nile tilapia, Oreochromis niloticus (L.), at four pre-determined species combinations and a range of stocking densities [ SD (fingerlings ha−1)]. Twenty-three reservoirs were harvested successfully at the end of the culture period of 2002–2003. Basic limnological and morphometric parameters, including shoreline development ( D L ) and shoreline area ratio ( R LA ), were estimated for each of the 23 reservoirs. Bray–Curtis similarity and non-metric multidimensional scaling using mean values of limnological data revealed that reservoirs could be ordinated into two major clusters, one with intact sample distribution due to similar trophic characteristics and the other with scattered sample distribution. Reservoirs in the cluster with similar trophic characteristics showed significant correlation ( P  < 0.05) between R LA and total fish yield ( Y ). A multiple regression equation, Y  = −693 + 4810  R LA  + 0.484 SD , was generated to estimate fish harvest in relation to SD .  相似文献   

9.
Abstract  Changes in catch-per-unit-effort (CPUE) were evaluated when all the sluice gates on the Pak Mun Dam, Mun River, Thailand, were opened between July 2001 and June 2002. CPUE ranged from 0.38 to 1.70 and 0.61 to 2.71 kg fisherman−1 night−1, downstream and upstream of the dam, respectively. No statistical differences ( P  > 0.05) among months were observed in both areas. The monthly percentage index of relative importance (%IRI) of the fish species caught varied between months.  相似文献   

10.
One of the three iso-nitrogenous (30% crude protein) and iso-energetic (15.0 MJ kg−1 diet) oil cake-based diets (groundnut, D-1; soybean, D-2 and mustard, D-3) was fed to the fingerlings (6.61 ± 0.06 g) of silver barb ( Puntius gonionotus ) for 120 days in triplicate fertilized ponds (0.04 ha) with a stocking density of 9000 fish ha−1. Fish were fed at 10% of their body weight for the first month, followed by 3% in the second and 2.5% in the third and fourth months of the culture period. The fish fed diets D-1, D-2 and D-3 grew from initial weights of 6.67, 6.67 and 6.50 g to 320.23, 298.23 and 305.13 g respectively. No significant variation ( P >0.05) was found in the growth and nutrient utilization of fish fed different dietary treatments. Net profits of Indian Rupees 67 385, 59 535 and 65 790 ha−1 were obtained in fish fed D-1, D-2 and D-3, respectively, within 120 days of culture. The results of this study suggest the possibility of the use of mustard oil cake as a dietary protein source for pond culture of silver barb in addition to groundnut and soybean oil cakes without compromising the growth, nutrient utilization, production performance and economics of culture of this fish.  相似文献   

11.
In August 2007, as part of the NOAA National Marine Fisheries Service (NMFS) West Coast Groundfish Bottom Trawl Survey, we examined the biomass of demersal organisms in a known hypoxic area off the Oregon coast. Although observed each summer, the intensity of hypoxia has varied annually (2002–2007) with the greatest temporal and spatial extent noted in 2006. In 2007 we identified the geographic extent of the hypoxic zone and sampled 17 stations along two depth contours (50 and 70 m) within the area. A Sea-Bird SBE 19 plus equipped with a dissolved oxygen (DO) sensor was attached to the bottom trawl to monitor oxygen concentration during each tow. Bottom DO concentrations at all stations were hypoxic with means along the tow tracts ranging from 0.43 to 1.27 mL L−1. Total catch per unit effort (ln CPUE, kg hectare−1) and species diversity (number of species, N ) were significantly and positively related to oxygen concentration along the hypoxic gradient. In addition, CPUE (natural log-transformed) for eight fish species and five benthic invertebrate species were significantly and positively related to bottom oxygen concentration within the hypoxic region. Condition factors for five fish species, as well as Dungeness crab ( Cancer magister ) increased with increased bottom oxygen levels along the hypoxic gradient. Historical catch (2003–2006) within the hypoxic zone indicates that biomass was significantly lower in 2006, the year with the lowest bottom DO levels, relative to other years.  相似文献   

12.
This study was conducted to determine the effects of feeding increasing lipid concentrations (310, 380 and 470 g kg–1 lipid on dry weight) in diets based mainly on herring byproducts to Atlantic salmon Salmo salar . The diets were isonitrogenous, varying in dietary lipid content at the expense dietary starch. Average fish weight increased from 1.2 kg in April to 2.2–2.7 kg at the end of the feeding trial in September. Significantly greater growth was found in fish fed either the 380 g kg−1 or the 470 g kg−1 lipid diets compared with the 310 g kg−1 lipid diet. Muscle lipid content increased in all dietary groups on a wet weight basis from 7.7 ± 1.4% to 12 ± 3% in salmon fed the 310 g kg−1 lipid diet, and to 16 ± 2% in salmon fed the 380 g kg−1 and 470 g kg−1 lipid diets. In fish of similar weight there was a positive correlation between dietary lipid and muscle lipid concentrations. Low concentrations of muscle glycogen were detected in fish fed each of the diets, while muscle vitamin E concentrations slowly decreased as muscle lipid increased. Muscle fatty acid composition reflected dietary fatty acid profiles, containing similar percentages of total saturated, monoenic and n-3 fatty acids (20:5n-3 and 22:6n-3) in fish from all dietary treatment groups. However, a higher ratio of n-3/n-6 was found in muscle from fish fed the 470 g kg−1 lipid diet compared with the other two groups. Blood chemistry values varied somewhat, but all values were within normal ranges for Atlantic salmon of these sizes.  相似文献   

13.
The effects of temperature on growth, food-conversion ratio (FCR) and feeding intensity of juvenile dusky kob Argyrosomus japonicus (23.7±2.6 g fish−1) were assessed over the temperature range 17.5–28.5 °C in a 42-day growth trial. Growth increased with increasing temperature up to an optimum after which it declined. Specific growth rates were 2.05% and 1.2% day−1 for the fastest (25.3 °C) and the slowest (17.5 °C) treatments respectively. Food-conversion ratio peaked at a lower temperature than growth. Optimal (0.72 kg kg gain−1) and least efficient (1.40 kg kg gain−1) FCR were found at 21.7 and 17.5 °C respectively. Feeding intensity was linearly related to temperature within the range of 17.5–28.5 °C. These results corresponded to the thermal preference (25–26.4 °C) and natural temperature distribution (12–28 °C) of South African dusky kob. Determination of the temperature range that does not limit growth is a prerequisite to assess the relationship between growth and environmental variables such as light intensity, feeding regime and stocking density. Consequently, experiments to determine the effects of these environmental variables on growth and aquaculture potential of dusky kob should be conducted at 24–26 °C.  相似文献   

14.
ABSTRACT:   The life cycle of Dilophus okamurae and the associated benthic invertebrate fauna were studied monthly or bimonthly from June 1998 to September 1999 at a depth of 4–7 m in Onagawa Bay along the Pacific coast of north-eastern Honshu, Japan (38°28'N, 149°29'E). Dry biomass ranged from 230 g/m2 in June to 10 g/m2 in October. Sporophytes with tetrasporangia appeared during July to September 1998. Gametophytes with oogonia or antheridia were observed for the first time in May 1999 during observation. The absence of mature sporophytes in 1999 suggests that the life cycle is completed over two years. The sympatric gastropods Lirularia iridescens , Homalopoma sangrarense, Conotalopia minima and Cantharidus callichroa synchronized with seasonal changes in biomass of this algae. In contrast, Barleeia angustata and B. trifasciata fluctuated independently. The juvenile sea urchin Strongylocentrotus nudus appeared in the algal population starting in October at 0.7 mm mean test diameter at high density, and disappeared after March.  相似文献   

15.
This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass ( Morone chrysops female ×  Morone saxatilis male). Semi-purified diets supplemented with 0.2 mg Se kg−1 from Na2SeO3 and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg−1 as  DL -α-tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α-tocopherol kg−1 dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg−1 had significantly ( P  < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg−1. Dietary supplementation of vitamin E caused incremental increases in the concentration of α-tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid-stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken-line model indicated a minimum vitamin E requirement ( ±  SE) of 28 ( ±  3) mg kg−1 dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.  相似文献   

16.
The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g−1) were formulated incorporating WDM at 0, 100, 200 and 300 g kg−1 levels as partial substitutes for soybean meal (SBM). These were designated D0 [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg−1 diet], D1 (279 g CP and 446 g CHO kg−1 diet), D2 (207 g CP and 495 g CHO kg−1 diet) and D3 (175 g CP and 578 g CHO kg−1 diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different ( P  > 0.05). Protein efficiency rate (PER) was lowest in diet D0 and increased with decrease of SBM content (D1–D3). A significant increase in whole body lipid content was recorded in fish fed diets D2 and D3. Results showed that WDM could be a substitute for SBM up to 300 g kg−1 in practical Nile tilapia diets without compromising growth.  相似文献   

17.
Abstract– The population dynamics of perch, Perca fluviatilis L., in the absence of a top piscivore, pike Esox lucius L., were examined in simple fish communities in shallow lakes (mean depth < 1.5 m) in northeast Scotland. Perch in Sand and Lower Lochs were unexploited, whereas perch in Loirston were exploited. Population characteristics were fast growth rates, short life span (< 6 years) and no dominant year classes in Sand and Lower Lochs. The strong 1974 year class in Loirston may have been due to intensive exploitation of older age groups. Abundance of perch, expressed as biomass, was low for European waters, namely 30 kg. ha−1 in Loirston (comprising mainly 1 - to 2-year-old-fish), and biomass of adults (≥ 2 years) was 8.9 kg and 4.7 kg. ha−1 in Sand and Lower Lochs respectively. Recruitment in Sand and Lower Lochs appeared to be governed by water temperature, but the overall low abundance and population stability of perch in the 3 lochs was attributed to cannibalism.  相似文献   

18.
The objective of management of Polish lakes is to fulfil the needs of commercial and recreational fishermen that developed after the political changes of the last decade. The effectiveness of the policies and practices adopted has never been studied. Six lake enterprises were selected, two in each of the lake districts: Mazuria, Pomerania and Great Poland. The two Mazurian enterprises manage a total of 13 325 ha of lakes, the Pomeranian ones 6130 ha and those of Great Poland 4156 ha. All data on commercial fisheries were collected and studies of anglers' activities were carried out through 550 questionnaires. The six enterprises were analysed as a whole and separately, with attention being paid to commercial landings and stockings in 1995–1999, and anglers' catches in 1998. Two enterprises and lakes were chosen for closer analysis. It was estimated that an average lake angler caught 59.2 kg of fish in 1998, and the overall landings by anglers was 35.0 kg ha–1 yr–1. Fish yield from lakes was 50.0 kg ha–1 yr–1 without considering poachers' catches.  相似文献   

19.
A 12-week feeding trial was conducted to establish the minimum dietary vitamin E requirement of juvenile red drum by broken-line regression analysis. The semi-purified basal diet was supplemented with 10, 20, 30, 40, 60 or 80 IU vitamin E kg−1 as all-rac -α-tocopheryl acetate. Juvenile red drum were conditioned by feeding the basal diet for 8 weeks prior to the feeding trial to reduce whole-body vitamin E levels. Then, fish initially averaging 12.2 ± 0.4 g fish−1 (mean ± SD) were fed the experimental diets at a rate approaching apparent satiation for 12 weeks. Weight gain and feed efficiency responses of fish fed diets were significantly ( P  < 0.01) altered by the level of vitamin E supplementation but not strictly in a dose-dependent manner. Vitamin E concentrations in liver and plasma also were significantly ( P  < 0.001) influenced by dietary vitamin E level. Plasma ascorbic acid in fish fed the basal diet tended ( P  = 0.066) to be lower than in fish fed diets containing the various levels of vitamin E. In addition, fish fed the basal diet showed edema in the heart, while fish fed all other diets were normal. Fish fed 60 or 80 IU all-rac -α-tocopheryl acetate kg−1 diet had significantly higher respiratory burst of head kidney macrophages than fish fed all other diets, although dietary effects on hematocrit and neutrophil oxidative radical production were not significant. The minimum dietary vitamin E requirement of juvenile red drum was established based on broken-line regression of liver thiobarbituric acid reactive substances to be 31 mg all-rac -α-tocopheryl acetate kg−1 diet.  相似文献   

20.
ABSTRACT:   By using a seine net, fish samples were taken from the nonestuarine Chwaka Bay (Zanzibar, Tanzania) from the mangroves, mud/sand flats and seagrass beds. Sampling was done twice per month between November 2001 and October 2002. In total, 150 fish species belonging to 55 families were identified. Diversity ( H' ) ranged from 1.9 in mud/sand flats to 3.4 within the Chwaka seagrass beds. Mean density of fishes was significantly higher in the mangrove creeks than in any other habitat (mean = 238.7 ind./1000 m2). Highest, but non-significantly different mean biomasses were recorded in the mangrove creeks (1.7 kg/1000 m2) and in the Marumbi seagrass beds (1.6 kg/1000 m2). The mangrove channel had the lowest biomass (0.6 kg/1000 m2). A high overlap in species composition (as high as 93.4% similarity) was found for adjoining habitats (i.e. mangrove creeks and mangrove channel), while habitats that were far apart showed low overlap (6.6% similarity for the Marumbi seagrass beds and mangrove creeks). On average, 58.4 and 63.2% in terms of abundance and biomass, respectively, of the fish assemblage of Chwaka Bay were of commercial fishery importance. Thus, Chwaka Bay appears to be an important juvenile habitat for various commercially important fish species.  相似文献   

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