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1.
Understanding the factors limiting copepod productivity in dense cultures is a prerequisite for the partial or entire replacement of Artemia and rotifers as live feed for finfish larvae. In dense cultures, high encounter rates between individuals may increase stress, cannibalism incidents and potentially trigger resting egg production. We conducted an experiment to evaluate the potential egg production and egg quality of Acartia tonsa stocked at densities ranging from 10 to >5000 ind. L?1. Egg Production (EP), Delayed Hatching Eggs production (DHE), hatching success (HS), egg mortality and water quality were used as end points. In the present system, A. tonsa was raised at >5000 ind. L?1 without affecting the mortality, confirming that attaining this high density in culture is possible. However, egg harvest reached an optimum of 12 000 egg L?1 day?1 at ~2500 ind. L?1 indicating that increasing stocking density above this level is not of practical interest. Calculations showed that the loss in egg harvest at stocking densities <2500 ind. L?1 is of 1.3% for every additional 100 adult copepods L?1. The increasing adult density did not affected the proportion of DHE produced (~10% of harvest) but decreased significantly the HS, though not to a point that would be problematic in a commercial production. Understanding the biology of copepods when stocked at high density is important to improve copepod culture systems and increase egg harvest yields. Technical solutions such as the continuous separation of eggs from adults in the water column, recirculation and the continuous provision of food are seen as potential solutions.  相似文献   

2.
In this study, we analysed the effect of population density and food concentration on the fecundity of a Mediterranean strain of Acartia tonsa to maximize egg production. During 4‐day feeding experiments, egg hatching success and faecal pellet production were also followed. The algae Rhinomonas reticulata was supplied at different concentrations corresponding to 250, 500, 1000, 1500, 2000 and 3000 μg C L?1 day?1 at the following adult copepod density: 40, 80 and 160 ind. L?1. Our results show a positive relationship between algal concentration and egg production under all experimental conditions confirming that the quantity of food strongly limits A. tonsa fecundity. Maximum egg production (57 eggs per female) was reached at the lowest density and at the maximum food concentration. Percentage of egg hatching success was not dependent on the quantity of food used. At the same food concentration, an increase in population density from 40 to 80 ind. L?1 induced an increase in faecal pellet production per couple which did not correspond to an increase in egg production, suggesting that higher energetic costs were shifted to swimming activity. Productivity of the A. tonsa Mediterranean strain is mainly limited by the quantity of food rather than by crowding conditions.  相似文献   

3.
Pinfish (Lagodon rhomboides Linnaeus) and pigfish (Orthopristis chrysoptera L.) are relatively new, cultured species commonly used as marine baitfish in the south‐eastern United States and currently have no defined protocols for egg incubation. Thus, experiments were conducted to determine efficient egg stocking densities during static and flow‐through incubation that yielded higher quality larvae. Eggs of each species were incubated statically at 250, 500, 1000 and 2000 eggs L?1, and after incubation, egg hatching success, larval survival to first feeding, larval morphometrics and water quality were assessed. Stocking densities above 250 eggs L?1 led to significant reductions in pinfish hatching success and water quality degradation, evident from decreased dissolved oxygen and pH levels and increased nitrogenous wastes. Increased stocking densities for pigfish also resulted in significant water quality degradation, although hatching success was unaffected up to a density of 1000 eggs L?1. A high flow‐through water exchange rate of 2000% daily resulted in significant reductions in nitrogenous wastes and greater stability in dissolved oxygen and pH levels during incubation when compared to static treatments of the same egg density. Additionally, the high exchange rate of 2000% was critical in maintaining high hatching success and larval survival to first feeding at stocking densities of 1000 eggs L?1 for pinfish and up to 4000 eggs L?1 for pigfish. No clear patterns in larval morphometrics were observed among stocking densities. Static incubation densities of 250 and 1000 eggs L?1 are recommended for pinfish and pigfish, respectively.  相似文献   

4.
Cannibalism in copepod culture may limit its production yield and therefore affect the economic interests associated with the use of copepods as live feed in aquaculture. The effects of adult density, egg density, and algal availability were tested on the calanoid copepod Acartia tonsa to understand how these parameters affect cannibalism rates on eggs. The overall cannibalism within the range of adult densities tested (120–1,000 adult L?1) was solely influenced by the egg and algal density, and not by the adult density. The increased densities of eggs lead to higher occurrences of cannibalism. Increasing the availability of alternative diets (e.g., algae) significantly diminished the adults’ cannibalistic behavior. The highest cannibalistic rates per adult were observed at low densities of adults and high densities of eggs (120 ind L?1 and 20,000 eggs L?1, respectively) and resulted in consumption rates >20 eggs ind?1 h?1. In this experiment, cannibalistic behavior reached 20 % of adult weight ind?1 h?1 under the aforementioned parameters. Additionally, the present study suggests that at high adult copepod density, the interactions between adults result in a decreased “time to feed.” Finally, it is argued that the separations of eggs from adult copepods, as well as the continuous access to an alternative food source, are necessary for decreasing the effects of cannibalism in copepod cultures.  相似文献   

5.
Copepods are the optimal live feed for hatcheries and improvement of cultivation techniques, to provide a constant food source, is crucial for the expansion of the industry. However, studies based on experimental work and real observations can be labour intensive and expensive. A simple model was developed based on the well‐known life history traits of Acartia tonsa to describe batch cultures and their productivity. Model results were compared to observations from real cultures. For maximizing egg production yields, the optimal stocking density of copepods should be adapted to the design (depth) of the culture tanks. At high densities, stress due to encountering conspecifics, as well as cannibalism of eggs by adults, limits egg production yields. Using this model, the potential selection efficacy of copepod strains was also evaluated in order to increase production yields. Selecting larger copepods increases the egg production per litre of culture, but decreases the optimal stocking density and the range of densities at which egg production yield is high, and vice‐versa. Selecting copepods that are less affected by stress due to conspecifics only affect production yields at very high adult densities. However, selecting copepods with a high Specific Growth Rate (SGR), or improving their SGR, was found to be an alternative which did not affect the optimal cultivation densities but improved egg production yields.  相似文献   

6.
Two consecutive experiments were conducted to study the effects of stocking density on growth, food utilization, production and farming profitability of Nile tilapia (Oreochromis niloticus) fingerlings (initial mean weight: 16.2 ± 0.2 g) fed Azolla, as a main component in diet. In experiment 1, fish were hand‐fed twice daily with three isonitrogenous (28.5% crude protein) and isocaloric (14.5 kJ g−1) diets A30, A35 and A40 containing 30%, 35% and 40%Azolla, respectively, for 90 days. Diets were formulated by mixing Azolla with locally available by‐products. No significant differences were found in growth parameters and production (P>0.05). Total investment cost was significantly higher with A30 (P<0.05), but same profitability values were obtained with all diets (P>0.05). In experiment 2, three stocking densities, 1, 3 and 5 m−2, were assigned to three treatments T1, T2 and T3 respectively. Fish were hand‐fed twice daily with diet A40. The final mean weight (89.53–115.12 g), the mean weight gain (0.81–1.10 g day−1), the specific growth rate (1.90–2.20% day−1) and the apparent food conversion ratio (1.29–1.58) were affected by stocking density, with significant difference (P<0.05) at 5 m−2, compared with the other densities. Stocking density did not affect survival rate (P>0.05). Yield and annual production increased with increasing stocking density, ranging from 7.10 ± 0.90 to 25.01 ± 1.84 kg are−1 and 28.79 ± 3.66 to 101.42 ± 7.48 kg are−1 year−1, respectively, with significant differences between all densities (P<0.05). Higher stocking density resulted in higher gross return and lower cost of fish production, with significant variations (P<0.05). The net return increased with increasing stocking density (P<0.05). However, both densities of 3 and 5 m−2 produced the same profitability values. On the basis of growth values and economic return, it was concluded that Nile tilapia could be raised at a density of 3 fish m−2 with A40 to improve production and generate profit for nutritional security and poverty alleviation in rural areas.  相似文献   

7.
The understanding of the biological responses of copepods under crowding conditions contributes to establish their stable cultures at high densities for aquaculture industry, which are preferred live feeds for fish larvae. The present study investigated survivorship, fecundity, hatching success and respiration rate, of Acartia steueri raised under five densities, from 100 to 2,000 ind. L?1, to clarify the biological responses of the copepod under dense culture. There were no significant differences in survival, fecundity and hatching success among all density conditions, whereas the respiration rate at 2,000 ind. L?1 decreased by 80% as compared with a condition at 100 ind. L?1. The female copepods raised under a copepod density of >500 ind. L?1 probably invested a larger proportion of energy in reproduction in relation to total assimilated energy as compared with females under lower copepod densities. This change of energy allocation may allow A. steueri under high densities to maintain high fecundity. Acartia steueri might be a promising species for dense culture because its mortality and fecundity were independent of the effect of crowding, and the density‐dependent reduction in the metabolic rate might increase reproductive investment to maintain a constant rate of reproduction even under high densities.  相似文献   

8.
Two experiments were conducted in order to determine the appropriate age and stocking density of vundu catfish Heterobranchus longifilis at the weaning time. In the first experiment, five triplicate groups of 100 larvae (initial mean weight=3.4 mg) per aquaria were stocked from first feeding [day 3 post‐hatch (p.h.)] to day 30 p.h., and then weaned, on days 3 (W3), 5 (W5), 8 (W8) and 14 (W14), and an unweaned group (An). Significant differences were observed in growth, survival, cannibalism, coefficient of weight variation and body composition among larvae weaned at different ages and the control group. The later the larvae were weaned, the better were the growth performances [final mean weight: from 65.1 to 201.1 mg and specific growth rate (SGR): from 11.0 to 15.2% day?1] and the survival (from 36.5% to 74.3%). The experiment with stocking densities of 5, 10, 25 and 50 larvae L?1 showed that increasing the stocking density decreased growth performances and weight variation but improved the survival rate of larvae. The best growth performances (SGR=13.4 and 11.4% day?1) with the lowest survival rates (70.3% and 77.3%) were observed in larvae stocked at densities of 5 and 10 larvae L?1 respectively.  相似文献   

9.
The lined seahorse, Hippocampus erectus (Perry), is an important species in both medicinal and aquarium trades. The aim of this study was to evaluate the effects of stocking density (1, 3 and 5 individuals L−1) on the growth performance and survival of the early-stage juvenile H. erectus. The height (HT), wet weight, weight gain (WG) and specific growth rate (SGR) were affected significantly by the stocking density during the 40-day study. The HT, WG and SGR of the seahorse at 1 and 3 juveniles L−1 were significantly higher than that at 5 juveniles L−1. The survival of juveniles at the three stocking densities was not significantly different at day 25 (90.3 ± 4.5%, 86.7 ± 4.2% and 86.2 ± 3.8% for 1, 3 and 5 juveniles L−1 respectively), but was significantly different at day 40 (87.8 ± 3.9%, 69.6 ± 4.2% and 52.9 ± 2.8% for 1, 3 and 5 juveniles L−1 respectively). For the early-stage juvenile H. erectus, we recommend a stocking density of 3 juveniles L−1, but the density should be reduced to 1–2 juveniles L−1 to avoid reduced and variable growth and high mortality after 25 days.  相似文献   

10.
Growout production of the camouflage grouper, Epinephelus polyphekadion (Bleeker), in a 10-m3-capacity fibreglass tank culture system was evaluated, using hatchery-produced fingerlings (56-59 g initial weight) at stocking densities of five, 15 and 45 fish m?3. During the first 9 months of a 12-month growout period, the fish were fed twice a day with a moist pellet feed containing 40.9% protein. From month 10 onwards until harvest, the fish were fed moist pellets in the morning and trash fish in the evening at a 1:1 ratio. The final weight of fish at harvest was up to 900 g, with mean weights of 544.6 ± 170.72 g at five fish m?3, 540.2 ± 150.82 g at 15 fish m-?3 and 513.3 ± 134.52 g at 45 fish m?3. The results showed no significant differences (P > 0.05) in growth rate and fish size between the different stocking densities tested. The average daily growth rate ranged from 0.62 to 3.38 g fish?1 day?1, with mean weights of 1.49 ± 0.74 g fish?1 day?1 at five fish m?3 through 0.53 to 2.38 g fish?1 day?1, 1.32 ± 0.57 g fish?1 day?1 at 15 fish m?3 to 0.48-3.32 g fish?1 day?1 and 1.31 g fish?1 day?1 at 45 fish m?3 stocking density. Although up to 100% survival was observed at the lowest stocking density, the survival rate significantly decreased (P < 0.05) with increasing stocking density. The food conversion ratio (FCR) significantly decreased (P <0.05) with increasing stocking densities, showing efficient feed utilization with increasing stocking densities of E. polyphekadion. The FCR averaged 2.1 at a stocking density of 45 fish m?3. The yield in terms of kg fish produced m?3 of water used in the culture system significantly increased (P < 0.001) from five to 45 fish m?3. The yield averaged 17.3 ±0.53 kg m?3 at a stocking density of 45 fish m?3. The present results show that the present tank culture system could sustain more biomass in terms of increasing fish stocking densities. The growth performance of E. polyphekadion observed during this investigation has been reviewed with other grouper species.  相似文献   

11.
The growth and survival of kalbasu, Labeo calbasu, was evaluated at stocking densities of 5, 10 and 15 million spawn ha−1 in nursery rearing in concrete tanks of 50 m2, each for a period of 25 days. Survival of fry was density dependent and significantly higher (54.5%) at 5 million ha−1 than those at 10 million ha−1 (50.1%) and 15 million ha−1 (46.9%). Similarly, growth and specific growth rate were inversely related to the stocking density and varied significantly among the three densities.  相似文献   

12.
Copepods are crucial source of live feeds in the aquaculture industry. In particular, several species of the genus Acartia are considered optimal prey for fish larvae. The species Acartia bilobata has excellent potential for marine larvae culture, as it is easy for mass culture. This study investigated the effects of various algal diets on the egg production and egg‐hatching rate of A. bilobata. The results indicated that the single‐species diet Isochrysis galbana was the most supportive diet for A. bilobata egg production and female life span in all treatments (egg production: 23.85 ± 0.70 eggs female?1 day?1 and female life span: 18.00 ± 1.45 days). Nannochloropsis oculata and Tetraselmis chui treatments gave markedly lower egg production and female life span as both single‐species and multiple‐species diets. For the egg hatching‐rate experiment, except for the T. chui treatment, which yielded a considerably lower hatching rate than the other diets, the hatching rate was only slightly affected by the algal diets. These results confirm that A. bilobata, a tropical brackish‐water copepod species, develops rapidly at 28°C and can produce a large number of eggs; therefore, it has considerable potential for larvae culture.  相似文献   

13.
This research was conducted to investigate the effect of stocking density on the growth performance and yield of Oreochromis niloticus in cage culture in Lake Kuriftu. The treatments had stocking densities of 50 (50F), 100 (100F), 150 (150F), and 200 (200F) fish per m?3. All treatments were in duplicate. Juveniles with an average weight of 45. 76±0.25 g were stocked in the treatments. The fish were fed a composite mixture of mill sweeping, cotton seed, and Bora food complex at 2% of their body weight twice per day using feeding trays for 150 days in powdered form. The growth performance of O. niloticus was density dependent. The final mean weight of O. niloticus ranged 147.76±0.28–219.71±1.42 g and the mean daily weight gain was 0.69±0.01–1.15±0.02 g day?1. Fish held in cages with lower density were heavier than the ones held at higher densities, and showed higher weight gain and daily weight gain. The most effective stocking density, in terms of growth parameters, was 50 fish m?3. The gross yield (4.5–20.55 kg cage?1) showed a significant difference with increasing stocking density (P<0.05). Moreover, the apparent food conversion ratio (2.48–7.22) was significantly affected by stocking density (P<0.05). However, survival rate was not affected by stocking density (P>0.05). It can be concluded that the most effective stocking densities were at 50 fish m?3 cage for larger size fish demand in a short period and 200 fish m?3 for higher gross production with supplementary feed.  相似文献   

14.
The present research investigated the effect of stocking density on pond (75 m2, depth 1.2 m) production of Nile tilapia (Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) stocked at a fixed 3:1 tilapia:prawn ratio. Three stocking densities were tried in triplicate: 20 000 ha−1 (treatment TP‐20), 30 000 ha−1 (TP‐30) and 40 000 ha−1 (TP‐40). The ponds were provided with bamboo as substrate for periphyton development. Bamboo poles (mean diameter 5.5 cm and 5.0 poles m−2) were posted vertically into pond bottoms, resulting in 60% additional substrate area in each pond. On average, 43 genera of algae and 17 genera of zooplankton were identified from pond water, whereas 42 genera of algae and six genera of microfauna were attached to bamboo substrates. No differences were observed between treatments in the ash‐free dry matter (AFDM), chlorophyll a and phaeophytin a content of periphyton (P>0.05). Survival of tilapia and prawn and individual weight gain of tilapia were lower (P<0.05) in treatment TP‐40. The net yields were higher (P<0.05) in treatments TP‐30 (2209 and 163 kg ha−1 105 day−1 of tilapia and prawn respectively) and TP‐40 (2162 and 141 kg ha−1 of tilapia and prawn respectively) than in treatment TP‐20 (1505 and 136 kg ha−1 of tilapia and prawn respectively). The net tilapia yields were quadratic correlated (R2=0.92) with fish stocking density. The cost–benefit analysis shows that the net profit margin was highest in treatment TP‐30 (69%), followed by TP‐20 (50%) and TP‐40 (44%).  相似文献   

15.
We attempted to estimate the survival rates of larval cohorts (3–15 mm in body length) of the Japanese anchovy Engraulis japonicus population in Hiuchi‐nada, Seto Inland Sea, Japan, and examined the relationship to their food availability. The survival rates were directly calculated from the change in larval density during the survey. The estimated daily survival rate ranged between 0 and 89% d−1, but increased with the increase in the mean concentration of small‐sized copepod nauplii (<100 μm in body length) sampled at 10 m depth. When the food concentration was higher than about 5 nauplii L−1, the daily survival rate of larval anchovy reached an asymptote of approximately 89% day−1. It might be possible to provide a framework for the forecast for larval abundance immediately prior to recruitment size (10–15 mm SL), based on larval abundance of the monitored size (3–8 mm SL) and the survival rate which is estimated from the concentration of small‐sized nauplii.  相似文献   

16.
The effects of tank colour, larval stocking density, antibiotic administration and water exchange on survival and moulting of blue swimming crab, Portunus pelagicus, were determined. Circular 4‐m3 experimental larval‐rearing tanks were used in triplicate for all treatments. White, dark grey, blue and brown were tested as tank background colours. The stocking densities tested were 10, 20, 40, 60, 80 and 100 larvae L?1. The effect of oxytetracycline was estimated by comparing a treatment with oxytetracycline to a treatment without oxytetracycline administration. The daily water exchange rates tested were 0%, 25%, 50% and 100% of the tank volume. In all treatments, the larvae were fed with Artemia nauplii, rotifers and encapsulated Spirulina. The highest percentage survival was observed in the dark‐grey tanks when the stocking density of larvae was 20 larvae L?1. No larva reached the juvenile crab size in white tanks. No significant difference in survival was found between treated and non‐treated larvae with oxytetracycline when the daily water exchange rate was more than 50%.  相似文献   

17.
The nematode Panagrellus redivivus (Linné) has been suggested as a source of live food in the rearing of larval fish and shrimp species. This study tested the use of P. redivivus in the early rearing of the bottom‐feeding catfish Synodontis petricola (Matthes). A comparison of feeding rates of 5000–10 000 nematodes larva−1 day−1 showed that fish receiving 5000 nematodes larva−1 day−1 grew faster than those fed a dry diet, but slower than treatments fed 200 and 600 Artemia larva−1 day−1. Enrichment of nematodes with SuperSelco® improved fish growth relative to a non‐enriched control treatment, with both treatments receiving 5000 nematodes larva−1 day−1. In the first two trials, feeding commenced 2 days after hatching. In the third study, fish were fed nematodes 6 days after hatching and there was no difference in growth between Artemia‐fed fish (600 Artemia larva−1 day−1) and fish fed 5000 nematodes larva−1 day−1. Thus, it is suggested to feed S. petricola at a nematode density of at least 10 000nematodes larva−1 day−1 in order to achieve growth comparable to that of fish fed Artemia, or, alternatively, to feed 5000 nematodes larva−1 day−1 to improve growth relative to that achieved with a dry diet. Furthermore, nematodes may be enriched with essential fatty acids to improve the growth of S. petricola larvae.  相似文献   

18.
Copepods are candidates with great potential as live prey for rearing fish larvae and juveniles in aquaculture; however, the techniques for a large‐scale culture of copepods are yet to be developed. In this study, we examined the effects of water temperature, salinity, prey concentration and algal species on the grazing and egg production rates of a calanoid copepod Schmackeria poplesia (Copepoda: Calanoida). The results showed that the grazing rate of S. poplesia was the highest when the copepods were cultured in seawater with temperature of 25 °C, salinity of 20 g L?1, prey concentration at 105 cells mL?1 and supplied with Platymonas helgolandica as the prey. The egg production rates, however, was the highest when copepods were fed with a mixed prey of Isochrysis galbana and Phaeodactylum tricornutum (cell ratio 1:1, prey concentration 105 cells mL?1) at 25 °C, 20 g L?1 of salinity. A 100 L cultural system was established to culture S. poplesia under the condition optimized for egg production. The total number of copepods increased 40–43‐fold with the production rates of 87–290 copepods L?1 day?1 in 14 days. This research was the first attempt for a large‐scale culture of S. poplesia and the technique established can be further applied in aquaculture.  相似文献   

19.
Macrobrachium rosenbergii (de Man 1879) juveniles (0.4 g) were cultured in experimental cages (L × W × H: 2.5 × 1 × 1 m) in Laguna de Bay, the largest lake in the Philippines. The following stocking densities at four replicates each were used: 15, 30, 60 and 90 prawns m−2 of cage bottom. The mean sizes at harvest after 5 months of culture ranged from 14.3 g for the highest stocking density to 26.3 g for the lowest. The mean size at harvest, daily growth rate and size class distribution were significantly influenced by stocking density, with those at the lowest stocking density showing significantly better growth and overall proportion of larger prawns. Heterogeneous individual growth (HIG) was fairly evident in all treatments. The percentage of blue‐clawed males was not influenced by treatment but the mean weight was significantly higher in the lower stocking densities. Both the percentage and mean weight of berried females were significantly higher in the lowest stocking density. Survival was the highest in the lower stocking densities (55.3%, 54.0%, 52.7% and 36.9% for 15, 30, 60 and 90 prawns m−2 respectively). Feed conversion ratio (FCR) improved with decreasing stocking density, ranging from 2.1 to 3. As expected, yield per cropping increased with stocking density and ranged from 450 to 1089 g m−2 yr−1 of actual cage area. Production values obtained in the cage cultured M. rosenbergii were comparable to or even higher than those reported from pond culture, given that the stocking densities used in this study were generally higher than in ponds. The results show that the farming of M. rosenbergii in cages in lakes is a viable alternative to pond culture and has the potential of improve aquaculture production in lakeshore fish farming communities.  相似文献   

20.
The effects of stocking density and feeding levels on larval survival, growth rates, feed utilization efficiency and body composition of Nile tilapia (Oreochromis niloticus L.) fry were investigated in two consecutive experiments. In experiment 1, swimup fry (0.016 g average body weight) were stocked in 20‐L fibreglass tanks, in a closed, recirculating indoor system, at five stocking densities (3, 5, 10, 15 and 20 fry L?1) and fed a larval test diet (40% crude protein) to apparent satiation, three times a day, for 40 days. Fish survival, percentage weight gain and specific growth rate (% SGR) were negatively correlated with stocking density. The best performance was achieved at 3 fry L?1. However, no significant differences in growth parameters were found between 3 and 5 fry L?1. Body composition was not significantly affected by stocking density. In experiment 2, fry (0.016 g average body weight) were stocked at 5 fry L?1, and fed a larval test diet (40% crude protein) at six feeding levels (10%, 20%, 25%, 30% and 35% BW day?1) and to satiation, three times a day for 40 days. Fish growth rates and survival were extremely poor at 10% feeding level, and improved significantly with increasing feeding levels up to 30%, and levelled off with further increase in feeding levels. On the contrary, feed conversion ratio (FCR) and protein production value (PPV) were negatively correlated with feeding level. The lowest feeding level (10%) produced significantly lower body lipid and higher protein and ash than other feeding levels. The present results suggest that the optimum stocking density and feeding level of Nile tilapia fry are 5 fry L?1 and 30% per day respectively.  相似文献   

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