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1.
《Fisheries Research》2007,85(3):285-290
Avoidance reactions of young-of-the-year fish assemblages were investigated in the offshore zone of three reservoirs in the Czech Republic during late summer. Pikeperch (Stizostedion lucioperca) strongly dominated in the Lipno Reservoir in 2003, bream (Abramis brama) and bleak (Alburnus alburnus) were the most abundant species in the Slapy Reservoir in 2004 and roach (Rutilus rutilus) and bleak dominated in the Želivka Reservoir in 2004 and 2005. Densities of fry ranged between 1.09 ind./100 m3 in the Lipno Reservoir and 2.95 ind./100 m3 in the Slapy Reservoir. In each reservoir, three trawl nets of different widths (dimensions 1.5 m × 3 m, 3 m × 3 m, 6 m × 3 m) were used in the pelagic area at night. For each trawl the estimated fish density was determined as the catch per 100 m3 of water and was compared between all three trawls. The fish length–frequency distribution was also compared between all the trawls. Day catches were much lower compared with those taken at night. Adult fish showed very clear avoidance of fry trawls. At night, no important differences in estimated fry density, obtained by these trawls, were observed in any locality for any fish species, nor in the length distribution of important species between trawls. According to these results, the avoidance reactions of fry in the late summer (August, September), at night, are unimportant. At this time of year, nighttime pelagic trawling appears to be an effective method for quantitative fry sampling. We recommend the 3 m × 3 m trawl for quantitative night sampling of the fry community as a good compromise between assured efficiency and relatively easy handling.  相似文献   

2.
Substantial loss of fry to cannibalism by brood-fish occurs in live-bearing ornamental fish farms. Previous results demonstrated that fry yields in breeding tanks of the guppy fish (Poecilia reticulata) can be increased by attracting the newborns by a light stimulus into net baskets from which they are collected. In the present study the effects of the number of daily collections and timing of lighting on fry yield in breeding tanks in the laboratory were tested. No difference in fry yield was found between one and two daily collections, and no effect of the timing of lighting (lighting during the day versus during the night). Contrasting of the morning and afternoon collections within the two-collection treatment under day lighting versus night lighting revealed that more fry were collected when the collection followed the lighting period than the no-lighting period. Experiments conducted in commercial farms revealed no difference in fry yields between one and two daily collections when the baskets were illuminated, concurring with the laboratory results. The farm experiments demonstrated that without illumination there is an advantage for two collections over one collection. Taken together, the results showed that the novel method of using light to attract newborn guppies into mesh baskets have a double benefit; it increases fry yields and concurrently lessens the labor required to harvest maximal fry yields in guppy breeding tanks.  相似文献   

3.
Pink salmon fry, Oncorhynchus gorbuscha, were held in a small floating net pen for nearly 7 weeks. The pen was moored in a narrow channel where tidal current velocities reach values near 0.4 m/s. The fry were maintained solely by marine zooplankton carried into the enclosure by surface currents.Samples of approximately 100 fry were removed weekly from the pen to monitor growth and diet. For the 1049 fry which began the experiment, fork length (FL) averaged 32.7 mm and wet weight (W) 0.23 g. Forty-eight days later 330 fry remained in the pen; FL had increased to 44.1 mm and W to 0.76 g. Natural mortality in the pen was less than 2% during this period.  相似文献   

4.
Gonadally undifferentiated Oreochromis niloticus × O. aureus hybrid fry (F2 generation), were fed a single level of androgen-treated diet (60 mg/kg 17-α-ethynyltestosterone), in earthen pond cages, an indoor tank and outdoor concrete tanks. All fry fed androgen-treated diets had populations consisting of ≥ 96% males, whilst those populations fed control diets had sex ratios which were not significantly different from an expected 1:1. No all-male broods were obtained, but populations composed of 96% and 99% males were produced in earthen pond cages following 25- and 28-day treatment periods, respectively, at a mean temperature of 30°C. Fry in outdoor pond cage treatments appeared to grow faster than those inside. Additional, naturally occurring food in the ponds is considered partly responsible for this. Survival of fry during androgen treatments depended upon size and density at stocking. Larger and more vital fry survived better than newly hatched fry.  相似文献   

5.
Phytoplankton cultures of Chlorella sp., Tetraselmis sp. and Isochrysis galbana were used alone as feed to rear separate batches of newly caught milkfish (Chanos chanos) fry (about 21 days old). Ultrastructural studies of fry hepatocytes and pancreatic acinar cells indicated that they cannot directly utilize Chlorella, which has a rigid cell wall. The fry can directly utilize Tetraselmis and Isochrysis, but neither is nutritionally adequate for growth and survival if used as the only feed. Tetraselmis is nutritionally inferior to Isochrysis.  相似文献   

6.
The variation in egg size within and between egg clutches of O. mossambicus, and the subsequent influence of mean egg size on growth, feeding incidence and survival of unfed fry were investigated.The individual egg sizes within 90% of the egg clutches examined were normally distributed and the coefficient of variation of egg size within clutches ranged from 7.4% to 15.4%. Fry emerging from the small, medium and large egg size groups reached their maximum length and weight at 9, 9 and 12 days after hatching, respectively. Maximum attainable fry length and weight were significantly correlated with egg size (r = 0.885 and 0.947, respectively, with P < 0.01).Egg size had little influence on the onset of feeding. Fry were capable of exogenous feeding within 6 to 7 days of hatching. Fry originating from small and medium egg size classes reached the point-of-no-return at 15–16 days after hatching compared to 21 days for fry from the large egg size class. The mean survival time (ST50) of fry on their yolk reserves was significantly correlated (r = 0.923; P < 0.01) with their original mean egg weight and ranged from 9.5 days for fry hatching from 0.91-mg eggs to 21 days for fry from 1.93-mg eggs.  相似文献   

7.
The fry industry of the milkfish (Chanos chanos Forskal) in the Philippines is alleged to suffer from certain inefficiencies, principal among which are an annual shortage to meet the stock requirements of the 176 000 ha of fishponds in the country, and the failure of the pricing system to direct and allocate the fry resources geographically. Contrary to these and other allegations, this paper presents a preliminary analysis that indicates a higher level of performance for the industry than hitherto supposed. Specifically, fry catch is estimated to be 1.35 billion, sufficiently high to meet present stocking requirements; less than 3% of trade flows between regions overlap; and monthly average fry prices between trading regions are significantly correlated, indicating the system responds to supply and demand changes and other stimuli.  相似文献   

8.
Young Nile tilapia (12 mg mean body weight and 11 mm total length) were stocked at a density of 5 fish/l in twelve 50-l aquaria filled with 30 l of tap water. They were fed pellet crumbles containing 35% crude protein at various daily feeding rates expressed as percentages of fish biomass. Mean increases in body weight after 5 weeks were 63, 198, 232 and 228 mg for the 15, 30, 45 and 60% feeding rates, respectively, when ambient temperature ranged from 19 to 21°C. Corresponding survival rates were 53, 85, 87 and 84%. Growth and survival rates were enhanced significantly (P < 0.01) at the 30, 45 and 60% feeding rates.Two feeding trials were conducted to compare the growth and survival of fry fed pellet crumbles and an unpelleted form of the same diet. Results showed that growth and feed conversion were similar for both forms of diet. However, the survival rate of fry fed pellet crumbles was significantly higher (P < 0.01) than the survival rate of fry fed the unpelleted diet. Prior pelleting of the formulated diet for the tilapia fry given at 30% to 45% of fish biomass daily ensured high survival, fast growth and efficient feed conversion.  相似文献   

9.
Schnabel's mark and recapture abundance estimates of perch fry in Kli?ava Reservoir (Czech Republic), differentially marked in autumn and in spring, partly failed due to the existence of groups of individuals which behaved differently. There were three groupings. 1) a group of fry caught by shore seining from autumn of the first year (O+) to summer of the second year of life (1+), the only group in the littoral during late autumn and early spring and the fry with the slowest growth rate; 2) a group of perch fry that consisted of males maturing at 1 year and that dominated the trap catches in reservoir; 3) a group of fry that avoided the littoral in late autumn and during March-May 1983, which appeared in the littoral in May and June 1983, thus diluting the previously marked littoral fry. These 3 groupings of fry were relatively stable and separable throughout 1–2 years, apart for the mixing of groups 1 and 3 that took place in the littoral during the summer. The density of perch fry of 1982 year class in spring 1983 was estimated to be about 0.094 individuals per m2.  相似文献   

10.
This study was conducted to investigate the effects of different levels of dietary vitamin C on some skin mucus immune parameters, mucus antimicrobial activity and growth performance of Caspian roach (Rutilus rutilus caspicus) fry. Six hundred sixty Caspian roach (1.4 ± 0.02 g) fry were allocated to 12 tanks (55 fish per tank), and triplicate groups were fed diets containing 0, 1,000, 1,500 and 2,000 mg kg?1 vitamin C for 60 days. At the end of the trial, the epidermal mucus protein level, alkaline phosphatase and antimicrobial activity against two gram-positive bacteria (Streptococcus faecium and Micrococcus luteus) and gram-negative bacteria (Escherichia coli and Serratia marcescens) as well as growth performance were measured. The results demonstrated that feeding on vitamin C significantly elevated skin mucus alkaline phosphatase and protein levels compared to the control group (P < 0.05). However, lysozyme activity was undetectable in both the vitamin C-fed roach fry and the control group. Skin mucus antimicrobial activity was increased following vitamin C administration, and the bacterial growth inhibition zones were significantly elevated in vitamin C-fed roach (P < 0.05). Similar results were obtained in case of the minimum inhibitory concentration of skin mucus. Also fish fed the control diet had a significantly lower weight gain, specific growth rate and condition factor compared to the other treatments (P < 0.05). These results revealed that dietary vitamin C beneficially affects the skin mucus immune parameters and growth performance of Caspian roach fry.  相似文献   

11.
A bacterium belonging to the genus Vibrio was isolated from sheatfish (Silurus glanis L.) fry during an epizootic in week-old fish. Due to the characteristic signs of illness the new symptom-complex was named “red head” disease. The Vibrio sp. bacterium causing disease of freshwater fish, the symptoms of the disease, and its histopathology are discussed. The mode of infection is unknown. It probably spreads with the eggs from the parent host fish, in which case iodophoric treatment of the fertilized eggs could give good disease control.  相似文献   

12.
Fertilized eggs of the Nile tilapia (Oreochromis niloticus L.) spawned in freshwater, were removed from mouthbrooding females, 1 day post-spawning and artificially incubated at elevated salinities. At 6 days post-hatching, mean survivals of 85.5, 84.4, 82.5, 56.3, 37.9, 20.0 and 0% were recorded for broods incubated at salinities of 0, 5, 10, 15, 20, 25 and 32 ppt, respectively. Fertilized eggs exhibited a 96-h median lethal salinity (MLS-96) of 18.9 ppt, a value identical to that of 7- to 120-day-old fry and fingerlings. Fertilized eggs exhibited a higher median survival time (ST50 = 978 min) than 7- to 395-day-old fry and fingerlings (ST50 = 28.8–179.0 min).The salinity tolerances of fry spawned at various salinities and fry spawned in freshwater but hatched at various salinities, were determined using the median survival time (ST50), mean survival time (MST) and 96 h-median lethal salinity (MLS-96) indices. For comparative purposes, fry spawned and hatched in freshwater were acclimatized to various salinities and their salinity tolerance determined. Fry salinity tolerance progressively increased with increasing salinity of spawning, hatching, or acclimatization. However, at equivalent salinity, early exposure (spawning) produced progeny of comparatively higher salinity tolerance than those spawned in freshwater and hatched at elevated salinity. Similarly, at equivalent salinity, progeny spawned in freshwater but hatched at elevated salinity exhibited higher salinity tolerance than those spawned and hatched in freshwater, then acclimatized to an elevated salinity.The utility of these methods of early salinity exposure toward the saltwater culture of tilapias is discussed.  相似文献   

13.
One of the bottlenecks in Israel's cold water ornamental fish industry is the large loss of fish during the post-larval stage. As a first step towards increasing survival rates, the optimal stocking density in earthen ponds for fry of each species should be determined. The results of five consecutive experiments with fry of goldfish (Carassius auratus), common carp and koi (respectively, edible and ornamental morphotypes of Cyprinus carpio) are presented here. The experiments were run in 18 cages of 1 m3 and 0.8 mm mesh size placed in a 0.02 ha earthen pond, stocked at 50,100 and 200 fry per cage. The variables analyzed were growth rate, harvesting weight, biomass and survival. Equations to estimate growth rates under different conditions are given. The three fish types present different growth rates and survival patterns in relation to stocking density and season, which lead to different management implications. Koi can be stocked up to 2 million fry per ha without showing negative density effects. Goldfish should be stocked at low density (500,000–1 million fry per ha) in spring and at higher rate (2 million fry per ha) in summer. Common carp stocking density should be adjusted to obtain the required fish size at harvest.  相似文献   

14.
Abstract. Laboratory examinations of pond-reared common carp, Cyprinus carpio L., revealed a close correlation between the prevalence of swimbladder inflammation (SBI), renal sphaerosporosis and infection by C-blood-protozoan among the carp fry. In impression smears as well as light and electron microscopic preparations we detected developmental stages of intercellular protozoa, mainly in the loose fibrous tissue of the swimbladder. The parasites multiplied by internal budding so that 20–46 secondary cells were formed in each primary cell and two tertiary cells were formed in each secondary cell. The final stage of development was a unit consisting of a secondary cell enclosing two tertiary cells, i.e. a so-called triple formation, which bore a close resemblance to the early sporogonic stages of the renal sphaerosporan Sphaerospora angulata Fujita, 1912. Certain morphological similarities and the frequent simultaneous presence of the swimbladder protozoan, C-bloodprotozoan, and S. angulata in hosts with clinical SBI have led us to postulate that the former two parasites could represent the hitherto unknown presporogonic stages of S. angulata. In view of the pathological changes caused by the parasites in the hosts with clinical SBI, and negative bacteriological and virological findings we have postulated that the swimbladder protozoan is the primary cause of SBI in carp fry.  相似文献   

15.
Groups of Atlantic salmon (Salmo salar) eggs were incubated at 12, 10 and 8° C. At 12° C mortality was high and fry averaged little more than half the weight of those hatched at 10 or 8° C. Development of alevins to the ‘swim-up’ stage was also abnormal at 12° C. The results suggest that 10° C is optimal for incubating Atlantic salmon eggs. For the period between hatching and swim-up, the most favourable temperature varies according to the temperature used during incubation. Mortality rate during the first 6 weeks of feeding was correlated with mortality during earlier development. Total numbers of day-degrees required by the eggs and fry to reach the eyed, hatching, and swim-up stages of development were significantly less at 12° C than at 10 or 8° C. However, total day-degrees required to reach an average weight of 0.5 or 0.6 g were almost the same regardless of temperature during hatching.  相似文献   

16.
First-feeding stage tilapia fry were reared for 40 or 50 days in 20-l capacity aquaria at six stocking densities (2, 4, 6, 8, 10, 12 l?1) and three feeding levels (6, 12, 24% of body weight daily). Fry survival and growth were improved at the higher feeding levels, but the percentage of fry surviving showed no consistent relationship to stocking density. Cannibalism accounted for a mortality rate of 10–35% in each experimental group and was inversely related to the level of feeding. Under equivalent conditions, O. niloticus female × O. aureus male fry had a higher rate of survival, better food conversion and were more uniform in size than O. mossambicus fry.  相似文献   

17.
Rearing of rohu spawn to fry size was carried out at high density (2000 spawn m?2) in large concrete nursery tanks (10 m × 5 m × 1.2 m) to standardize the daily ration of supplementary feed and to assess the impact of soil base on the fry performance. In Set‐1, supplementary feed was provided at 100% (control), 75% and 50% of the daily ration that is commonly used in earthen carp nursery ponds and named as the three treatments T‐1, T‐2 and T‐3 respectively. Although in Set‐II, performance of fry were evaluated in tanks provided with and without soil base. The fry survival was to the tune of 45–59% at this high density of 2000 spawn m?2, indicating the efficacy of the concrete nursery system for high density seed rearing. In Set‐I, T‐2 receiving 75% of the control ration exhibited similar fry growth as that of T‐1, but its fry survival (58.8%) was 10% higher than the latter. This indicated that supplementary feed in a concrete nursery can be reduced up to 25% of that provided in earthen nursery system while ensuring a higher fry yield. However, further reduction up to 50% of the control ration in T‐3 yielded lower fry survival and growth (P < 0.05) revealing inadequacy of the available feed. In Set‐II, treatment without soil base (T‐ns) yielded similar fry growth but 10% higher survival compared to that with the soil base (T‐s) revealing non‐essentiality of soil base in concrete tanks for such short‐term nursery rearing of rohu.  相似文献   

18.
采用静水压法处理半滑舌鳎(Cynoglossus semiliaevis)受精卵以抑制其卵裂并进行染色体加倍,筛选出有效的静水压处理起始时间、处理强度及其持续时间。结果表明,孵化水温(23±0.2)℃时,授精后21.5 min,采用40 MPa的静水压压力,休克处理4.5 min,四倍体诱导效果最好,鱼苗四倍体率达到68.3%。采用流式细胞仪分析了四倍体鱼苗细胞DNA含量,表明四倍体鱼苗细胞DNA含量为二倍体对照鱼苗的2倍。通过染色体制作分析表明四倍体鱼苗的染色体数为84条,而二倍体对照鱼苗的染色体数为42条。本研究采用静水压方法,在国内外首次建立了半滑舌鳎四倍体诱导方法。本项技术的建立旨在为大量生产半滑舌鳎三倍体不育群体奠定基础。  相似文献   

19.
Heritability of mortality in eggs, alevins and fry were estimated using data from salmon, sea trout and rainbow trout. The highest value (average for all species and both estimation methods) based on the sire component was obtained for the eyed egg stage, h2 = 0.08, followed by the alevin stage, h2 = 0.05, while estimates for fry mortality did not differ significantly from zero.The maternal effect was rather large for uneyed eggs and eyed eggs, while it was low for alevin mortality. Maternal effects were also found to have a significant influence on the mortality of salmon fry. It was, however, not possible to separate maternal effects from tank effects.  相似文献   

20.
Sternecker K, Geist J. The effects of stream substratum composition on the emergence of salmonid fry.
Ecology of Freshwater Fish 2010: 19: 537–544. © 2010 John Wiley & Sons A/S Abstract – Salmonid fishes are target species for the conservation of freshwater habitats, but their natural reproduction is often insufficient. The emergence of fry is a crucial phase in the life cycle of salmonids and the stream substratum is the key habitat which regulates the emergence success. In this study, brown trout (Salmo trutta) and Danube salmon (Hucho hucho) eggs were exposed to different sediment textures and the emergence and the postemergence survival and growth were observed under constant water chemical conditions in the laboratory. In both species, textural effects on emergence rate, chronology of emergence, survival rate after emergence and growth after emergence were detected. Fine‐textured substratum (5–8 mm) formed a physical barrier to the posthatch migration of salmonids from the interstitial zone to the open water. The time period between the first and the last emerged fish was shorter in treatments with fine texture compared with coarse substratum. The survival rate was higher in treatments of coarser sediment. The effects of different textures on the growth of fry after emergence differed between brown trout and Danube salmon, which can be explained by different life history strategies. These results suggest that physical characteristics of substratum texture can have strong effects on salmonid emergence, and ultimately on the persistence of salmonid populations. They also suggest that biodiversity conservation in stream ecosystems can greatly benefit from an inclusion of the physical characteristics of the stream bed into catchment‐based management plans.  相似文献   

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