Increasing the stocking density in Paracentrotus lividus larviculture: Effects on survival and metamorphosis rates

The development of sustainable methods for sea urchin juvenile production is currently constrained by high mortality rates during larval growth and the high costs of larval rearing systems management. With the aim of developing a method for the production of juveniles of the purple sea urchin Paracentrotus lividus in a medium‐scale recirculating system, the present study focused on the effects of high stocking densities on larval growth. Plutei larvae were reared at three different densities (up to 7 ind/ml) in a semi‐static culture system. Larval survival and metamorphosis success were evaluated in order to identify the most effective density range. The highest metamorphosis rates (80%–95%) were obtained at 4 and 7 larvae/ml. These results are comparable with (and in some cases higher than) those reported for the same species at much lower larval densities. In conclusion, the rearing conditions tested here show for the first time that a significantly higher (4 ind/ml) stocking density than those of traditional P. lividus rearing methods (based on large volumes and low densities) can be adopted, thus supporting the feasibility of an increase in the final output of competent larvae with no increase in rearing volumes.     

The effect of density in larval rearing of the pullet carpet shell Venerupis corrugata (Gmelin, 1791) in a recirculating aquaculture system

The pullet carpet shell Venerupis corrugata is an economically valuable species in several European countries, however, nowadays stocks are under high fishing pressure. Hatchery production of juveniles for release is a major contributor to strengthen the stock and consequently improve the sustainability of the natural stocks. This study aimed to determine the feasibility of rearing V. corrugata larvae with different larval densities (10, 40 and 200 larvae per mL) in a recirculating aquaculture system (RAS), compared with the traditional larval rearing methodology (Batch). The mean survival, growth and metamorphic rate of V. corrugata larvae in RAS was higher (11.1%; 71.3 μm; 21.6% respectively) than in the Batch system, in all tested densities. The larval growth was not affected by the initial density until 40 larvae per mL, however, 200 larvae per mL decreased the larval growth in length nearly 54 μm. The larval rearing time was shortened in 2 days in the RAS system. The physical, chemical and microbiologic parameters suggested that the tested densities were not excessive to disturb the biofilter stability of RAS. The V. corrugata larval rearing performed at high larval stocking densities in RAS system present a reduction in the operating costs to produce this species.     

Effects of two culturing techniques on the growth, survival and larval quality of Dentex dentex Linnaeus, 1758

Common dentex larvae were reared using two culturing techniques, mesocosms and intensive rearing, to determine the principal culture parameters involved in the differences observed in growth, skeletal deformations and survival between the two rearing techniques. In growth, only dry weight of larvae of 40 days post‐hatching (dph) from mesocosms was significantly higher than larvae from intensive rearing. Significant differences were observed in survival at 40 dph (6.58% in mesocosms and 1.58% in intensive rearing) and in the incidence of skeletal deformations, both for percentage of deformed larvae and for some deformation types such as those related to vertebral column and to the caudal complex. Initial larval density and initial prey density and quality are the factors suspected to affect growth and survival performance, while skeletal deformities might also be affected by tank hydrodynamics.     

Larval rearing of calico scallops, Argopecten gibbus, in a flow-through system

A flow-through (FT) culture system is described for calico scallop, Argopecten gibbus, larvae. Its performance was assessed by larval survival rate, shell growth, settlement rate and post-larval shell growth for the duration of larval life (13 days). Comparisons were made with larvae reared in standard static system (S). Effect of increased larval density on FT performance was also investigated. With comparable larval densities, survival rate of Day 2 larvae to pediveliger stage was similar in both larval rearing systems. Shell growth for FT-reared larvae was comparable or significantly higher than in the static system (P < 0.01). Settlement rate of pediveligers was comparable for both systems, averaging 30.7%, and no significant difference was seen in shell growth of FT- and static-reared pediveligers. Increased initial larval density did not affect survival rate in FT, but did negatively affect larval shell growth, settlement rate and post-larval shell growth yielding lower growth and minimal settlement rate (10.9 ± 2.8%) compared to the static system. This FT system was successful as larval rearing system, optimising space allocation in the hatchery, reducing labour, and eliminating the use of antibiotics. Optimising initial larval density within the system needs to be investigated in association with food ration.     

Effect of stocking density and feeding regime on larval growth,survival, and larval development of Japanese flounder,Paralichthys olivaceus,using live feeds

This research examined the effect of initial stocking density and feeding regime on larval growth and survival of Japanese flounder, Paralichthys olivaceus. Larval rearing trials were conducted in nine 50‐L tanks with different initial stocking densities combined with different feed rations (20 larvae/L with standard feed ration [LD], 80 larvae/L with standard feed ration [HD], and 80 larvae/L with four times the standard feed ration [HD+]). Larvae were stocked on 0 days posthatch (DPH) following hatching of the fertilized embryos. Larval total length (TL), survival rates, and final densities were observed on larval settlement (32 DPH) to evaluate larval rearing performance. At 32 DPH, there were no significant differences (p > .05) in TL or survival rates between the LD (46.5 ± 17.0%) and HD+ (40.3 ± 9.4%). The TL and survival rate of HD (23.1 ± 3.5%) were significantly lower than that of LD and HD+ (p < .05). However, the larval density of HD was significantly higher than that of LD (p < .05). HD+ achieved the best larvae production (32.27 ± 7.51 larvae/L), supported by sufficient food source, high water exchange, and proper water quality management (routine siphoning, surface skimming). The larval‐rearing protocols and larval development from hatching to metamorphosis is described in detail, with corresponding photographs taken during the experiment.     

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).     

盐度与pH对花鲈孵化、初孵仔鱼成活及早期幼鱼生长性能的影响

为探究我国北方海域花鲈繁育适宜盐度和pH处理的设定,及促进早期花鲈苗种推广,本研究针对不同盐度(0、15、20、25、30、35和40)与pH(5.5、6.5、7.5、8.5和9.5)条件下,北方人工繁殖花鲈受精卵的孵化率、畸形率及饥饿10 d后的存活情况进行了分析,并对花鲈初孵仔鱼进行不投饵耐饥饿实验,记录每日存活率(SR)及最终生存活力指数(SAI)。最后观测低盐0、养殖盐度30与高盐45对花鲈早期幼鱼生长性能的影响。结果显示,北方海域花鲈受精卵适宜孵化盐度为20~35,以盐度25组孵化率最高,适宜pH为6.5~7.5,以pH 6.5组孵化率最高。低盐15组中,具最低的孵化率及最高的畸形率,但在最终饥饿SR的统计中,低盐15组的SR及SAI明显高于盐度30与35组,推测低盐15接近花鲈体液等渗点,降低了渗透调节中的能量消耗,更利于存活。初孵仔鱼饥饿实验中,盐度20组SR下降相对平缓,在第8天仍有12.66%的SR(其他组已为0)。饥饿1 d时,各pH组SR均小于90%,以pH 6.5组SR最高,为89.11%。与盐度处理组相比,花鲈初孵仔鱼对pH变化较为敏感,其孵化率及最终SR显著低于盐度处理组。花鲈早期幼鱼盐度处理组中,低盐0与高盐45将对此规格花鲈幼鱼产生较大损伤,以高盐45抑制最显著,应为苗种盐度推广的上限,而花鲈生长盐度30与各处理盐度相比,较适合花鲈早期幼鱼的生长。研究结果将为北方海域花鲈繁育适宜盐度和pH处理的设定,及提高花鲈孵化率、育苗成活率与早期苗种推广提供基础资料。     

Effect of Stocking Density on the Growth,Survival, and Behavior of Postpuerulus Western Rock Lobster,Panulirus cygnus (George) (Decapoda: Palinuridae)

The effect of four stocking densities (30, 60, 100, and 150 lobsters/m²) on the growth and survival of Panulirus cygnus postpueruli was determined over a 112‐d grow‐out trial. Agonistic behavior at each experimental density was recorded using infrared filming. Survival and growth decreased with increasing density, although this trend was only significant between the lowest (30/m²) and the highest densities (150/m²) (P < 0.05) at the conclusion of the grow‐out trial. Density had no significant effect on apparent feed intake but significantly affected food conversion ratios (FCR) across all four densities, with FCR being best at 30/m² and worst at 150/m². The number and frequency of agonistic encounters per tank differed significantly with density, with agonistic encounters being highest at 150/m² and lowest at 30/m². Agonistic encounters coincided with the crepuscular foraging pattern of postpueruli. The reduction in survival and growth of postpueruli at the highest density (150/m²) can be attributed to the significant increase in the number of agonistic encounters. This study supports that P. cygnus postpueruli should be stocked at densities less than 100/m² in order to minimize the negative effect of density on growth and survival.     

Effect of stocking density and addition of proteins on larval survival in Japanese flounder, Paralichthys olivaceus

The effects of larval density, rearing media, and protein additions on fish larval survival were tested by rearing larvae in small containers. Yolk-sac larvae of Japanese flounder, Paralichthys olivaceus, were transferred 1 day after hatching to plastic dishes and cell-culture microplates by Pasture pipette at densities ranging from 0.3 to 30 individuals/ml and incubated at 16 °C without food. Dead larvae were removed and counted every 12 h. Three peaks of larval mortality were observed: the first peak appeared just after the transfer, the second corresponded to the completion of yolk absorption, and the third occurred 10–12 days after the transfer. Since about 50% of larvae survived until the third peak, it was clear that mortality at the second peak (completion of yolk absorption; equivalent to the first feeding) was not due to starvation. At the first mortality peak, better survival was unexpectedly recorded at higher larval densities (30 individuals/ml), suggesting that some material beneficial for survival is derived from the larvae. This idea was further supported by the improved survival in media previously used to rear larvae at high densities. The addition of bovine serum albumin (BSA) at 10 μg/ml effectively reduced mortality in microplates and in 30-l tanks. To reduce the larval mortality just after handling, addition of egg white at a dilution rate of 1/30,000 (vol/vol) or less is recommended as a practical alternative to BSA. Since the addition of polyethylene glycol 6000 (1 μg/ml) also effectively reduced mortality, reduction in mortality could not be attributed to a specific mechanism. The precise determination of the magnitude and timing of larval mortality was attained through the use of small containers, and a method to prevent mortality due to handling was identified in this study. These types of tests may allow the logical evaluation and establishment of better rearing procedures for seed production in aquaculture.     

Growth trials for polyculture of hatchery-reared juvenile spotted babylon (Babylonia areolata) and sea bass (Lates calcarifer) in a flow-through sea water system

Juvenile spotted babylon (Babylonia areolata) and sea bass (Lates calcarifer) were cultured in 11.5‐m³ indoor rearing tanks supplied with flow‐through of ambient natural sea water over a 120‐day experiment. Each species, stocked at the following densities for the following treatments, was tested with three replicates per treatment: 5000 B. areolata per tank (Treatment 1); 200 L. calcarifer per tank (Treatment 2); and 5000 B. areolata plus 200 L. calcarifer per tank (Treatment 3),. The average growth (length and weight), feed conversion ratio and total production of spotted babylon and sea bass from Treatment 3 were not significantly different from those of Treatment 1 and 2 (P > 0.05). Average survival rates for both spotted babylon and sea bass exceeded 95% for all treatments.     

Effects of temperature, density and early weaning on the survival and growth of Atlantic ditch shrimp Palaemonetes varians larvae

This investigation examined the effects of temperature, density and early weaning on the survival and growth of Palaemonetes varians larvae. Survival of larvae raised at 17.5 °C was not significantly different (average + standard deviation) (94 ± 5%) from the survival of those raised at 19.5 °C (95 ± 5%) and at 21.5 °C (94 ± 4%). However, the duration of the larval stage was significantly longer for shrimp reared at 17.5 °C (17.3 ± 0.8 days) compared with shrimp reared at 19.5 °C (14.3 ± 0.7 days) and at 21.5 °C (11.3 ± 0.6 days). No significant differences ( P >0.05) were found in the survival rate, final weight and length of larvae reared at the densities of 5, 10, 20 and 50 larvae L⁻¹. The survival of P. varians larvae fed solely on Artemia was significantly higher ( P <0.05) than larvae weaned with an artificial practical diet from Zoea II stage (94 ± 4% and 82 ± 1%, respectively, for Artemia and artificial diet-fed larvae), but no significant differences ( P >0.05) were observed in the final larval weight or length between these two treatments. The survival and growth of the larvae fed with the practical diet tested is a promising step ahead in the development of the culture of this species as it eliminates both the need for Artemia throughout all larval stages, and the need for more expensive artificial diets.     

A closed water recirculation system for ecological studies in marine fish larvae: growth and survival of sea bass larvae fed with live prey

This paper describes the suitability of a closed recirculation system to study the development of fish larvae in a strictly controlled environment, where only feeding was varied (fed, starved, delayed and late fast treatments). The system served both as an incubator and hatchery. The time variation of physical and chemical parameters together with survival and growth of reared sea bass larvae (Dicentrarchus labrax) were studied over the first month of life. The recirculation design allowed for the maintenance of levels of ammonia, nitrite and nitrate below those cited as responsible for mortality or decreased feeding ability in other marine fish larvae. Almost no larval mortality occurred in the fed larvae from day 9 after hatching. The starved group of larvae showed a sharp decline in survival after 16 days of food deprivation. Larvae for which feeding was delayed until day 13 ceased dying 4 days after food was supplied. Fast feeding on days 24 and 25 had no effect on larval survival. Growth in length was similar during the first 2 weeks of larval life regardless of feeding treatment. Two days of late fast had no effect on larval growth. Growth patterns of fed larvae in this study were similar to those reported for larvae reared in flow through systems. We believe that survival and growth of the reared larvae was a direct function of diet, and that the type of rearing system did not adversely affect these parameters. The rearing design and the results obtained suggest that future nutritional studies of field-collected larvae will benefit from this kind of rearing experiment.     

Improved survival and growth performances with stocking density manipulation and shelter availability in bagrid catfish Mystus nemurus (Cuvier & Valenciennes 1840) larvae

Manipulation of stocking densities (10, 20, 30, 40 and 50 larvae L^?1), each with or without the presence of shelter was conducted to determine the effects on survival, cannibalism and growth performances of larval bagrid catfish Mystus nemurus (Valenciennes 1840) from 2 to 14 days after hatching. This study revealed that stocking density significantly affected survival, cannibalism, total length, feed intake, specific growth rate and final weight of bagrid catfish larvae. Significantly higher survival was observed at moderate stocking density of more than 20 but less than 50 larvae L^?1. Survival was significantly low beyond this threshold and was the lowest at 10 larvae L^?1, coincides with the highest cannibalism. Total length, feed intake, specific growth rate and final weight were significantly higher at 10 larvae L^?1. Shelter significantly improved total length and feed intake. No significant effects of stocking density and shelter were observed on the apparent feed conversion ratio and coefficient of variation. There was also no significant interaction between stocking density and shelter in all parameters. This study suggests that bagrid catfish larvae could be cultured at more than 20 but less than 50 larvae L^?1 with the availability of shelter for optimal larviculture condition.     

Effect of Stocking Density on Growth and Water Quality for Largemouth Bass Micropterus salmoides Growout in Ponds

Juvenile largemouth bass Micropterus salmoides , trained to accept artificial diets, were stocked into six 0.04-ha ponds at stocking densities of either 6,175 or 12,350 fish/ha. Fish were fed a floating custom-formulated diet, containing 44% protein, once daily to satiation for 12 mo (May 1994–May 1995). At final harvest, the total yield of fish was significantly greater (P < 0.05) and feed conversion ratio (FCR) was significantly lower, for bass stocked at the higher density (4,598 kg/ha and 2.3, respectively) than when stocked at the lower density (2,354 kg/ha and 3.3, respectively). There was no significant difference (P > 0.05) in average weight, length, or survival of bass stocked at the two densities. Averaged over the study period, there were no significant differences (P > 0.05) in total ammonia-nitrogen (TAN), nitrite-nitrogen, or un-ionized ammonia concentrations in ponds in which bass were stocked at the two densities. These data indicate that largemouth bass of the size used in this study are amenable to pond culture at densities of at least 12,350 fish/ha and that higher stocking densities may be possible.     

Effect of larval stocking density on growth,survival and whole body cortisol of the Mediterranean mussel Mytilus galloprovincialis (Lamarck, 1819) larvae reared under laboratory conditions

Interest of mussel hatchery development has increased during the last years as natural seed collection does not always satisfy the demand of producers. Success on larval bivalve culture depends on several factors such as diet, temperature or stocking density. In this study, the effect of larval density in mussel culture success has been assessed testing three larval densities: high (50 larvae mL^?1), medium (25 larvae mL^?1) and low (5 larvae mL^?1). Results showed higher growth and survival at low density but the amount of postlarvae was low. The highest number of settled larvae was observed at high density but mortality was also high and a delay on the larval development was detected producing a prolongation on the culture length. However, medium density resulted in a good survival and growth and also in a considerable amount of postlarvae, as this density could be adequate for massive mussel seed production. Cortisol content on the larvae and postlarvae was also analysed and significant differences were obtained among groups probably due to the stress associated to settlement and metamorphosis.     

Effects of stocking density and algal concentration on the survival,growth and metamorphosis of Bobu Ivory shell,Babylonia formosae habei (Neogastropoda: Buccinidae) larvae

Independent and combined effects of stocking density and algal concentration on the survival, growth and metamorphosis of the Bobu Ivory shell Babylonia formosae habei larvae were assessed using a 5 × 5 factorial design with densities of 0.25, 0.5, 0.75, 1.00 and 1.50 larvae mL⁻¹ and algal concentrations of 5, 10, 15, 20 and 25 × 10⁴ cells mL⁻¹ in the laboratory. Larval growth, survival and metamorphosis were significantly affected by both the independent effects of stocking density and algal concentration and by their interaction. The highest per cent survival (72.5%) and metamorphosis (49.5%), fastest growth (41.57 μm day⁻¹) and shortest time to initial metamorphosis (10 days) all occurred at the lowest stocking density and the highest algal concentration. Both crowding and food limitation had independently negative impacts on the survival, growth and metamorphosis of larvae, and these negative impacts were further strengthened by the interaction of a higher stocking density and a lower algal concentration. Moreover, the results suggest that stocking density and algal concentration obviously played different roles in determining larval survival and growth. To maximize survival and growth, B. formosae habei larvae should be reared at a lower stoking density of 0.25 larvae mL⁻¹ and fed a higher algal concentration of 25 × 10⁴ cells mL⁻¹ in large-scale hatchery seed culture.     

Evaluation of plankton surface pushnets and oblique tows for comparing the catch of diadromous larval fish

A bow-mounted surface pushnet and an obliquely towed plankton net were compared to evaluate gear efficiency and effectiveness in collecting larval fishes under daytime and nighttime conditions. The diadromous species targeted were striped bass Morone saxatilis, white perch, Morone americana, and river herring Alosa sp. We sampled the lower Roanoke River, North Carolina, from March through June of 2002 and 2003. Striped bass, white perch and river herring represented over 90% of the larvae collected during the study period. Mean larval densities (number/100 m³) were 63.4 for striped bass, 26.4 for river herring, and 17.7 for white perch. Striped bass larval densities were significantly higher in the surface pushnet for both years (P ≤ 0.05). In 2002, white perch mean larval density was significantly higher at night in the surface pushnet samples, but in 2003 there were no differences between day and night samples. River herring mean densities were significantly higher in the surface pushnets for both years, but showed no clear patterns between day and night samples. Larger larvae were consistently collected in the surface pushnets for all species. Overall, the surface pushnet was easier to operate. The pushnet was mounted on the bow of a small jon boat and required less specialized gear and fewer personnel than oblique sampling. The method also allows for sampling in shallow water or vegetated habitats. Because larvae were significantly larger in the surface samples, using surface pushnets may not allow for detection of the smaller-sized larvae therefore underestimating the abundance of smaller fish. Depending on the question being asked, we recommend that sampling programs should use both gear types to reduce any gear biases.     

微生态制剂对提高漠斑牙鲆育苗成活率的作用

对漠斑牙鲆育苗过程中添加微生态制剂以提高育苗成活率进行了比对实验。结果表明:采用育苗水体中添加微生态制剂的方法,能明显提高漠斑牙鲆育苗的成活率,改善水质,降低育苗用水量约30%~40%。在初孵仔鱼1×104ind/m3密度的条件下,添加微生态制剂的育苗池中不同阶段的仔稚鱼成活率高于对照组5%~10%;但随密度增加至2×104ind/m3时,实验组和对照组相互殘杀增加,仔稚鱼成活率都呈下降趋势;密度增加至3×104ind/m3时,实验组与对照组之间差异不显著(P<0.05)。     

厚壳贻贝早期幼虫低温保存的影响研究

探讨低温(4 ℃)条件下的厚壳贻贝早期幼虫保存可能性,同时调查了不同培育密度对低温保存的影响。在正常条件下,继续培育低温保存后的幼虫,并调查其存活率和生长的变化。 结果表明,在低温保存后,早期幼虫存活率较高,超过95%;厚壳贻贝早期幼虫的壳长和壳高出现显著性的增长。不同培育组间,培育密度对厚壳贻贝早期幼虫的存活和生长影响不同,表明密度是幼虫低温保存的一个重要因素。在正常培育条件下,低温保存后的幼虫,3周后其存活率明显低于对照组,但仍超过50%,且其生长速度明显高于对照组。因此,低温培育是保存厚壳贻贝早期幼虫的有效方法,可用于今后贝类幼虫生物学实验和人工育苗技术的改善研究。     

Larval rearing of hilsa shad,Tenualosa ilisha (Hamilton 1822)

Hilsa, Tenualosa ilisha has received much attention for culture due to decline of the natural population. Lack of knowledge on larval rearing is the bottleneck for its culture. This study was aimed at developing larval rearing protocols for hilsa shad. Hilsa larvae (4 days old, 4.76 ± 0.06 mm/0.49 ± 0.01 mg) were stocked in fibreglass‐reinforced plastic tanks (1.7 m³ water volume) at 300, 600 and 1,200 nos/m³ in triplicates in three experimental systems viz., E‐I (circular, 0.567 m water depth), E‐II (circular, 0.962 m water depth) and E‐III (rectangular, 0.567 m water depth) and reared for 46 days. The larvae were supplied with Chlorella vulgaris, Brachionus calyciflorus, mixed phytoplankton and mixed zooplankton during 4–50, 6–25, 8–50 and 26–50 days of their age respectively. In each system, higher (p < 0.05) fry survival at 300 nos/m³ than in higher densities indicates density dependent stress. Circular tanks showed higher survival (13.3%–61.31%) than in rectangular tanks (6.88%–27.26%) in each stocking density, indicating the importance of tank shape for rearing. Water depth affected fry survival in circular tanks (E‐I and E‐II) at 300 nos/m³; at 0.962 m depth, survival was higher (61.31%, p < 0.05) than that of 0.567 m depth (49.93%). Good fry survival was achieved through feeding the larvae initially with Chlorella followed by co‐feeding with Brachionus, mixed phytoplankton and zooplankton and rearing in circular tanks at 300 nos/m³ densities at 1 m depth. This first‐ever larval rearing protocol is useful for mass production of fry to support hilsa aquaculture in future.