Effect of Stock Density and Ploidy in Jundia,Rhamdia quelen,Larvae Performance

The performance (growth and survival) of diploid and triploid jundia, Rhamdia quelen, was evaluated at six different stocking densities (10, 60, 110, 160, 210, 260 larvae/liter) during 31 days after rearing in an intensive larviculture system. Triploid fish exhibited a significantly higher survival rate than diploids at all stocking densities (27.1 ± 4.3% vs. 12.1 ± 3.3%; P < 0.01). Survival was not affected by stocking density (P > 0.05). Length gain was not affected by either ploidy or stocking density. Diploid fish gained more weight than triploids (P < 0.05), though this difference could result from lower fish densities in diploid treatments resulting from the higher mortality rate of diploid fish. This hypothesis is strengthened by the higher biomass present in triploid treatments (P < 0.01).     

Effects of Stocking Density, Salinity, and Light Intensity on Growth and Survival of Southern Flounder Paralichthys lethostigma Larvae

Four separate studies were done on Southern flounder Paralichthys lethostigma larvae during first feeding and metamorphosis to determine the effects of stocking density, salinity, and light intensity on growth and survival. One study used stocking densities of 10, 20, 40, and 80 fish/L during first feeding; the second study compared the growth and survival of larvae stocked at 20 and 33 ppt; and a third experiment evaluated stocking densities of 1/L and 3/L under two different light intensities (1,600 lux vs 340 lux) during metamorphosis. The fourth experiment tested the effects of different salinities (0, 10, 20 and 30 ppt) on larval growth and survival during metamorphosis. Growth and survival (overall 6.9%) were not significantly different ( P > 0.05) for stocking rates up to 80/L. Larvae placed into 20 ppt salinity had survival through first feeding similar to that of larvae raised at 33 ppt. During metamorphosis, light intensity had no effect ( P > 0.05) on growth or survival, but fish stocked at 3/L had significantly lower ( P < 0.05) survival than fish at 1/L. Complete mortality of larvae occurred at 0 ppt. Growth and survival past metamorphosis were not significantly different ( P > 0.05) at 10, 20 and 30 ppt, but unmetamorphosed fish did not survive to day 60 at 10 ppt. Based on these results, practical larviculture of Southern flounder may require a two-step process with high stocking rates (80 fish/L) through first feeding and lower densities (1/L) through metamorphosis. Fingerling production in fertilized nursery ponds might he possible at salinity as low as 20 ppt.     

饵料和养殖密度对中国对虾幼虾生长及存活率的影响

在实验用虾遗传背景一致的情况下,分析了3种饵料(配合饲料、冰冻鲜鱼肉和活卤虫)和4个不同的养殖密度对小水体中国对虾幼虾生长和存活率的影响。结果表明,饵料和饲养密度对中国对虾幼虾生长及存活率有显著影响。在饵料、养殖密度单因子实验及饵料和养殖密度相结合的双因子实验中,幼虾的生长均表现出极其显著的差异(P<0.01),活卤虫对幼虾生长的效应尤为突出。而养殖密度对中国对虾的行为生物学、个体间体重增量均有影响。随着养殖密度的提高,中国对虾增重变慢;同时,个体间体重增量差异变大。随着养殖密度的增加,中国对虾幼虾的存活率呈下降趋势,但不同饵料对存活率影响变化幅度较大,波动在58.1%～85.2%之间,其中投喂活卤虫养殖密度为50尾/桶的存活率最高(85.2%);投喂配合饵料4个养殖密度梯度的存活率变化不明显;而投喂冰冻鱼肉4个养殖密度梯度的存活率变化较大。因此,采用合适的饵料和养殖密度,能够提高中国对虾的生长速度,提高对虾养成存活率,改善生长过程中对虾群体体长、体重的整齐度。     

Effect of Stocking Density on Growth,Physiological Responses,and Body Composition of Juvenile Blunt Snout Bream,Megalobrama amblycephala

The impact of stocking density on growth performance, physiological indicators, and body composition of juvenile blunt snout bream in recirculating aquaculture system was investigated in this study. Juvenile blunt snout bream were raised at stocking densities of 75, 150, 225, 300, and 450 fish/m³ for 12 wk with three replicate tanks at each density. All treatment tanks were supplied with water from the same recirculating system to ensure uniformity of water quality across groups. This study has shown that higher stocking densities had a negative effect on individual growth performance. Final body mass, specific growth rate (SGR), and weight gain decreased significantly as stocking density increased. Individual body mass as well as body length were more uniform in fish stocked at densities of 75 and 150 fish/m³ than in other groups. Stocking densities of 225 and 300 fish/m³ resulted in significant increases in serum total protein, triglyceride, lactate, and cholesterol levels, whereas blood glucose concentrations decreased significantly. In addition, decreased body lipid content and increased body moisture content were observed at stocking densities of 300 and 450 fish/m³. Overall, a density of 150 fish/m³ resulted in higher SGR and more uniform size among juvenile blunt snout bream.     

Effects of stocking density on haematological parameters,growth and fin erosion of great sturgeon (Huso huso) juveniles

The influence of stocking density (1, 2, 4, 6 and 8 kg m^?2) was investigated on haematological parameters, growth and fin erosion of great sturgeon (Huso huso) juveniles for a period of 8 weeks. The mean weight of fish at the start of trial was 93.13±1.04 g. After 8 weeks of rearing, the mean weight was 362.4, 319.7, 267, 242.1 and 211.1 in densities 1–8 kg m^?2 respectively. The results of this study showed that growth parameters, including condition factor, weight, weight gain, feed conversion ratio, specific growth rate and body weight increase, had a statistically significant difference among treatments (P<0.05). A significant difference (P<0.05) was observed in haematocrit, but the other haematological parameters, including red blood cells, white blood cells (WBC), haemoglobin concentration, mean corpuscular haemoglobin, mean corpuscular volume, mean corpuscular haemoglobin concentration and differential WBC count, showed no significant effect with stocking density (P>0.05). At the end of the experiment, stocking density had no significant effect on plasma cortisol and glucose concentration. The fin length (dorsal, anal, ventral, pectoral and caudal) of fish was measured to calculate the fin index. According to this index, dorsal, anal, ventral and pectoral fins showed no significant difference among treatments (P>0.05), but the erosion of the caudal fin was significantly different between fish held on 6 and 8 kg m^?2 (P<0.05). These results showed that rearing density has a major effect on the growth indices of H. huso. Unlike many other fish, great sturgeon exhibited lower stress responses to high stocking density. This indicates that they are more tolerable to rearing conditions in high stocking densities. With respect to the various effects that density causes on growth, fin erosion and physiological and haematological parameters, better understanding of these phenomena considering different levels of density could have a beneficial impact on many rearing steps of this species.     

Determining an effective density regime for rearing juvenile Austropotamobius pallipes in a small‐scale closed system hatchery

With recent advances in aquaculture techniques, captive‐breeding of the endangered white‐clawed crayfish Austropotamobius pallipes for restocking is becoming a widespread conservation method. Establishing optimal stocking densities for aquaculture is essential in maximizing productivity, and increases the likelihood of crayfish survival when released. A 240‐day experiment took place using 2‐month‐old juvenile, captive‐born, A. pallipes, within a small‐scale, closed‐circuit hatchery to investigate survival, growth and aggression at three treatment densities, low (100/m²), medium (200/m²) and high (300/m²). Crayfish were counted and measured every 60 days between August 2015 and April 2016. Mean survival rates were high across all three densities (87.7% ± 2.8%). Carapace length was significantly longer at low density than at medium and high densities. While growth rate was not significantly different between treatments, it was significantly higher in the first 2 months, across all three treatments (47.1% ± 6.6%) than in subsequent periods (14.1% ± 5.8%). Size variation within groups increased with density, suggesting that social dominance hierarchies are established with increasing stocking density: dominant individuals are larger and competitively exclude smaller individuals from food resources. Males were significantly larger than females from 6 months of age, (when they could be reliably sexed), in all three treatments. The larger male size suggests that sexual dimorphism begins prior to sexual maturity, with males growing faster and being more dominant and aggressive than females. In conclusion, young‐of‐the‐year A. pallipes can be reared at high densities without compromising survival; however, the optimal stocking density that maximizes growth and health is 100/m².     

Effect of stocking density on the growth performance and yield of Nile tilapia [Oreochromis niloticus (L., 1758)] in a cage culture system in Lake Kuriftu,Ethiopia

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.     

Fin damage and growth parameters relative to stocking density and feeding method in intensively cultured European perch (Perca fluviatilis L.)

We evaluated the relationship of stocking density to survival, growth performance and fin condition of European perch Perca fluviatilis with hand feeding and self-feeders. Hand-fed perch (body weight 19.1 ± 5.1 g and total length 107 ± 9 mm) were reared at 0.5, 1.0, 1.5 and 2.0 fish/L. Self-feeding perch (body weight 25.4 ± 3.9 g and total length 128 ± 7 mm) were reared at stocking densities of 0.6, 1.0 and 1.4 fish/L. Pond-reared perch served as a comparison group for fin damage assessment. We found no differences in survival rate among stocking densities with either feeding method. Hand-fed fish displayed the highest weight gain and SGR at stocking density of 0.5 fish/L. The self-feeding fish showed a non-linear association of weight gain with stocking density with the highest growth at 1.0 fish/L. Fin length was noticeably greater in pond-reared fish compared with RAS-reared fish regardless of feeding method. In both experiments, fin length relative to standard length showed a negative relationship with stocking density, with pectoral fins showing the greatest effect. Fin condition deteriorated with increasing stocking density, and growth was highest at 0.5 and 1.0 fish/L in hand-fed and self-feeding fish, respectively.     

Preliminary study on the production of the tilapia, Oreochromis spilurus (Günther), cultured in seawater cages

Abstract. A preliminary study was conducted to assess the performance of the tilapia, Oreochromis spilurus (Günther), cultured in seawater cages at different stocking densities during the nursing and rearing phases. The stocking densities tested were 200, 400 and 600 fish/m³ during the nursing phase and 100, 200, and 300 fish/m³ during the rearing phase.
In both growth phases, no significant differences (P>0.05) were observed among the different stocking densities on the mean individual final weight, daily growth rate, feed conversion ratio and survival rate. Yields in cages stocked with 400 and 600 fish/m³ during the nursing phase, however, were significantly (P<0.05) higher compared with cages stocked with 200 fish/m³. No significant differences (P>0.05) were observed between 400 and 600 fish/m³. A density of 600/m³ is therefore considered to be optimum for the nursing phase.
Yields of cages during the rearing phase increased significantly (P<0.01) with the increase in stocking density. After grading the fish, however, no significant differences (P>0.05) were observed when only fish bigger than 150g were considered. The occurrence of exophthalmia (cataract) was observed in two of the four replicates at the highest stocking density (300 fish/m³) during the rearing stage. Therefore, a stocking density of 200 fish/m³ is considered optimum for the rearing phase.     

Enhanced growth and immuno‐physiological response of Genetically Improved Farmed Tilapia in indoor biofloc units at different stocking densities

An experimental trial was conducted for 90 days to evaluate the growth performance, immunophysiological response of GIFT strain of Tilapia in biofloc‐based rearing system and to assess the relative percentage survival in 3 days after challenging with the virulent strain of Aeromonas hydrophila. Fingerlings with an average body weight 0.98 ± 0.06 g were stocked in triplicate at different stocking densities of 200 (SD1), 250 (SD2), 300 (SD3) and 350 (SD4) m^?3 in biofloc‐based treatments and 150 (C) m^?3 in control (clear water). Biofloc‐based units (SD1 and SD2) obtained significantly better (P < 0.05) growth performances at the end of the experimental period. Mean body weight of fish in biofloc‐based units showed a decreasing trend with increase in stocking density with 100% survival in all units including control. The stress parameters were significantly lower in biofloc‐based rearing units especially in treatments SD1 and SD2 as compared to the control. The fish from the biofloc‐based units (SD1 and SD2) possessed significantly (P < 0.05) higher immune status as compared to control and other biofloc treatments in terms of respiratory burst, serum lysozyme and myeloperoxidase activity. Relative survival percentages were significantly better in biofloc treatments with highest in SD1 and SD2 (83.33%) after challenge study. GIFT strain of Tilapia at higher stocking densities 200–250 nos m^?3 can be taken as optimum stocking density whereas higher stocking densities up to 350 nos m^?3 can be reared in the biofloc systems without compromising the growth and immunity.     

Effects of stocking density on the survival, growth, size variation and condition index of juvenile rabbitfish Siganus rivulatus

Spinefoot rabbitfish, Siganus rivulatus, is an economically important species of herbivorous fish that is relatively easy to rear and thus considered to be suitable for aquaculture. Juveniles are generally reared in nursery systems before being stocked into growout cages or ponds. We report here our evaluation of the effects of stocking density on the survival, growth, feed efficiency and condition index of S. rivulatus juveniles in nursery tanks. The experiment was conducted in a recirculating system of twelve 52-l aquaria connected to a biological filter and a sand filter. Juvenile fish (average weight 6.5 g) were stocked into aquaria at four stocking densities (10, 20, 30, and 40 fish/aquarium) with three replicate aquaria per treatment. Diet was provided at 3% body weight daily divided into two feedings. Fish were weighed weekly for 8 weeks and the diet increased accordingly. Survival was greater than 95% in all treatments, with no significant differences observed among treatments. There were also no differences in specific growth rate (SGR 2.12–2.27) of the fish among treatments. Growth rate was linear during the 8 weeks in all treatments, and harvested biomass increased proportionally to stocking density (198, 401, 600 and 785 g per increasing stocking density, respectively). Feed efficiency (FE 0.67–0.71) of the fish did not vary significantly among treatments. The coefficient of variation was high (35–41%) among the harvested fish, but it also did not differ significantly among treatments. The final condition indices of the fish in all treatments were similar to each other but significantly greater than the initial values (P < 0.05). The results suggest that there is no apparent effect of stocking density at the levels tested on the survival and growth of juvenile rabbitfish.     

Comparison of stocking time and density on Gulf Killifish growth in freshwater ponds

The Gulf Killifish (Fundulus grandis) is a popular baitfish and a candidate for commercial‐scale production. For inland production, ponds may need to be stocked at different times and densities to meet market demands. Therefore, in Experiment 1, juveniles were stocked into freshwater ponds at a density of 25,000 fish/ha, with two cohorts (mean total length (TL) = 3.92; 3.52 cm) stocked 1 month apart and evaluated for 12 weeks. Cohort 1 had a lower overall survival (40%) than cohort 2 (79%); with no difference between mean final TL (8.46; 8.00 cm); reaching a market size of 6 cm in 22 days and 32 days respectively. In Experiment 2, juveniles (mean TL = 3.16; 3.23 cm) were stocked into freshwater ponds at two densities (25,000 fish/ha and 50,000 fish/ha). Mean final TL was greater in the lower stocking density (8.68 cm) than the higher stocking density (8.20 cm); with no differences in survival between treatments (75; 72%) respectively. Lower stocking and higher stocking densities reached a market size of 6 cm in 29 and 31 days respectively. These results suggest that multiple cohorts can be stocked and grown to market size in one season at a stocking density of 50,000 fish/ha.     

Effects of green wavelength light on antioxidant and non-specific immune responses of the olive flounder Paralichthys olivaceus maintained at different stocking densities

In the present study, we investigated the effects of green light illumination on antioxidant systems and immunity in the olive flounder Paralichthys olivaceus. Fish at three different stocking densities (900, 1350, and 2250 fish per 8-ton tank) were compared. The effects of green light illumination were assessed by measuring survival rates, mRNA expression activity of antioxidant enzymes (superoxide dismutase and catalase), an oxidative stress-related parameter (hydrogen peroxide, H₂O₂), and immune-related parameters (lysozyme and melatonin). Overall, fish survival rates decreased over the 30-day period of the experiment, but survival rates were significantly higher among the groups of fish exposed to green light. In high stocking densities groups, mRNA levels and activities of antioxidant enzymes and H₂O₂ concentrations had increased at 30 days; however, in fish under green light conditions, significantly lower levels of antioxidant enzyme expression were observed. By contrast, parameters indicating immune responses decreased in high stocking densities groups, although in fish under green light treatment, significantly higher levels of immune response were observed. A comet assay revealed that a high stocking density increased the rate of nuclear DNA damage; however, treatment with green wavelength light reduced the frequency of damage. These results indicate that although high density induces oxidative stress and reduces immune system responses in olive flounder, green wavelength light prevents oxidative stress and boosts the immune system.     

Effects of stocking density and water exchange regimes on growth and survival of juvenile spotted babylon, Babylona areolata (Link), cultured in experimental earthen ponds

The growth and survival of juvenile spotted babylon, Babylonia areolata , were determined at five stocking densities (100, 200, 300, 400 and 500 snails m⁻²) and three water exchange regimes (7-, 15- and 21-day intervals) in experimental earthen ponds over a 6-month experimental period. The results showed that the growth of spotted babylons was not significantly different among any density treatments ( P <0.05). At the end of the experiment, the average growth rates in body weights were 0.59, 0.59, 0.58, 0.42 and 0.41 g month⁻¹ respectively. Growth was significantly different among the different water-exchange treatments ( P <0.05). The higher body-weight gains were observed in snails held at water exchanges of 7- and 15-day intervals, when compared with those held at water exchange of 30-day intervals. At the end of the experiment, average body-weight gains were 4.22, 3.67 and 2.68 g for snails held in water-exchange treatments of 7-, 15- and 30-day intervals respectively. This study recommended that stocking densities ≤300 snails m⁻² and water exchange of 7–15-day intervals are suitable for cultured B. areolata juveniles in earthen pond.     

A comparison of growth, survival rate, and number of marketable fish produced of swordtails, Xiphophorus helleri Heckel (Family Poeciliidae), between two types of culture systems

To test the effect of stocking density on growth, survival rates and size distribution of juvenile swordtails, Xiphophorus helleri Heckel, under different environmental conditions, fish were stocked at rates of 1, 3 and 6 fish I^?1. Growth was monitored over a 14-week period. Fish were weighed in six groups of 20 fish per tank. Size variation was determined at the end of the growth period by measuring the total length of each fish to the nearest mm. Fish were stocked in two different systems at three stocking densities (1, 3, and 6 fish I^?1) in replicate. The systems were an indoor aquarium system and a tunnel system under semicommercial conditions. In each system, increasing stocking rates resulted in a significant reduction of growth rates. In the aquarium system, survival rate was not related to stocking density, whereas in the tunnel system, fish at the highest stocking density had a lower survival rate than those kept at the two lower stocking densities. The number of marketable fish above a set size limit of 40 mm total length was not higher in fish stocked at 6 fish I^?1 than at 3 fish I^?1 at the end of the study. Therefore, a stocking rate of 3 fish I^?1 would be optimal. At the end of the study, fish were categorized into males, females and immature fish. Fish with a clearly visible gonopodium were classified as males, those with typical female characteristics as females, and small fish that were not yet differentiated as immature fish. The ratio of females to males was highly skewed in both systems, favouring a higher percentage of females. As stocking density increased, the female:male ratio was significantly reduced, which would result in a greater number of saleable pairs at increased stocking density. The implications of these results for the management of intensive production of swordtails are discussed.     

密度对网箱养殖硬头鳟生长及经济效益的影响

本文主要研究密度对网箱养殖硬头鳟Oncorhynchus mykiss存活和生长的影响。在水温8.2~19.1℃下,将体质量1.02 kg的硬头鳟鱼种养殖在5m×10m×6m网箱中,网箱放置在松花江上游的松山水库中,密度分别为5尾/m~2(Ⅰ组)、8尾/m~2(Ⅱ组)、11尾/m~2(Ⅲ组)和14尾/m~2(Ⅳ组),投喂粗蛋白含量为42%、粗脂肪22%的颗粒饲料,常规养殖。145d的养殖表明:网箱养殖的放养密度对硬头鳟的生长有一定影响。第Ⅳ组鱼的存活率显著低于其他3组(P0.05);放养密度为5~11尾/m~2时硬头鳟的生长与密度呈正相关,大于此密度范围则呈负相关。第Ⅲ组鱼的终末体质量、日增重、增重率、利润和利润率显著高于其余3组(P0.05);4个密度组硬头鳟的产量随放养密度增加而递增。本试验表明:网箱养殖硬头鳟的放养密度为11尾/m~2较适宜。     

Physiological responses of juvenile wedge sole Dicologoglossa cuneata (Moreau) to high stocking density

Physiological responses to a high stocking density were tested in juvenile wedge sole Dicologoglossa cuneata (Moreau). Fish were kept at low (1 kg m⁻²), medium (3 kg m⁻²) and high (9 kg m⁻²) stocking densities for 22 days. No differences in the weight, length, survival and hepatosomatic index were observed among treatments. Basal plasma cortisol and osmolality were found to be directly and positively related to stocking density. A mild increase in plasma glucose was seen at medium density, and plasma protein was elevated at medium and high densities. The liver glucose and glycogen content was inversely related to stocking density. The liver triglyceride level was significantly elevated at the highest density, and the α-amino acid content decreased at the highest density. In muscle, glucose levels were significantly higher in fish kept at the lowest density; the α-amino acid content was elevated in fish kept at high density. In conclusion, plasma cortisol levels indicated an increasing stress level depending on the culture density, but significant changes in energy reserves did not occur in tissue (mainly liver and muscle glycogen and glucose reserves were significantly affected).     

Effect of Stocking Density on the Growth and Survival of Spotted Sand Bass Paralabrax maculatofasciatus Larvae in a Closed Recirculating System

Abstract.— The effect on growth and survival of the initial stocking density (50, 100, 150, and 200 larvae/ L) in larval rearing of spotted sand bass was evaluated over 30 d in a closed recirculating system. Larvae were fed with rotifers, copepods, nauplii and adult Artemia , and spotted sand bass yolk-sac larvae. Water quality was monitored daily. The notochordal or standard length of sampled larvae was measured by image analysis. Specific growth rates at each density were compared by covariance analysis. Survival was estimated from day 15 to the end of the experiment, when a resistance test was used to evaluate the juvenile quality among densities. At the end of the experiment, mean standard length of larvae at lower densities was significantly larger ( P < 0.05) than at higher densities. Higher specific growth rates were found at lower densities. Significantly higher survival ( P < 0.05) was recorded for the lowest density, but the highest number of harvested fish was obtained with the highest densities (150 and 200 larvae/L). The lowest density also showed the significantly ( P < 0.05) higher survival after using a resistance test. We conclude the highest density can be used in larval rearing of spotted sand bass. However, better survival, growth, and seed quality are obtained at the lowest density. To recommend an optimal density for this specie, it is necessary to improve the water quality in the culture system and to make a cost-benefit study.     

Prolonged photoperiod improves the growth performance for a hatchery reared right-eyed flatfish

Rearing winter flounder (Pseudopleuronectes americanus) in captivity for aquaculture and stock enhancement is a viable option to relieve fishing pressure and aid in ongoing recovery strategies. The objective of this study was to determine the effect of photoperiod on growth and survival of young-of-the-year juvenile winter flounder. Juveniles were reared for 12 weeks at three photoperiods: 24 light/0 dark, 18 light/6 dark, and 12 light/12 dark. Twenty fish were stocked into each of 18 enclosures with six enclosures per treatment. Fish in all treatments were fed to satiation every four hours. All fish were imaged at stocking and at three-week intervals. Growth was measured as changes in standard length (SL) and body area (BA). As early as Week 3, fish in all treatments were significantly different in terms of SL and BA. In general, fish grown under continuous 24 light were the largest and fish in the 12 light/12 dark regime were the smallest. Maximum specific growth rates of 0.41 % per day for SL and 0.83 % per day for BA were achieved in the 24 light/0 dark photoperiod. Average mortality rate over the course of the experiment was 9.17 % and there were no significant differences in the number of dead fish among the treatments. In conclusion, this study demonstrates that a longer day coupled with available food will increase growth rate for winter flounder juveniles, without affecting survival. By extending the photoperiod, growth in young-of-the year winter flounder is accelerated, bringing the growth rate of winter flounder close to that of other commercially produced flatfish.     

Extension of nursery culture of Scylla serrata (Forsskål) juveniles in net cages and ponds

To address the preference of mud crab farmers for larger size Scylla serrata juveniles (5.0–10 g body weight or BW; 3.0–5.0 cm internal carapace width or ICW), a study was conducted to compare the growth and survival of crab juveniles (2.0–5.0 g BW; 1.0–3.0 cm ICW) produced a month after stocking of megalopae in net cages when reared further in net cages installed in earthen ponds or when stocked directly in earthen ponds. In a 3 × 2 factorial experiment, three stocking densities (1, 3 and 5 ind m⁻²), two types of rearing units (net cages or earthen pond) were used. Megalopae were grown to juvenile stage for 30 days in net cages set inside a 4000 m² brackishwater pond and fed brown mussel (Modiolus metcalfei). Crab juveniles were then transferred to either net cages (mesh size of 1.0 mm) or earthen ponds at three stocking densities. After 1 month, no interaction between stocking density and rearing unit was detected so data were pooled for each stocking density and rearing unit. There were no significant differences in the growth or survival rate of crab juveniles across stocking density treatments. Regardless of stocking density, survival in net cages was higher (77.11±6.62%) than in ponds (40.41±3.59%). Growth, however, was significantly higher for crab juveniles reared in earthen ponds. The range of mean BW of 10.5–16.0 g and an ICW of 3.78–4.33 cm obtained are within the size range preferred by mud crab operators for stocking grow‐out ponds.