Nursery growth, survival and chemical composition of great scallop Pecten maximus (L.) spat from different larval settlement groups

Scallop Pecten maximus spat (1.3–2.1 mm shell height) from different settlement groups were transferred from hatchery to land‐based nursery at different ages and sizes. Chemical content, growth and survival were compared at transfer time and after 1 and 8 weeks of nursery growth. Growth was lowest and mortality highest in the first week after transfer. Mean shell height growth was 21.5–71.4 μm day^?1 and ash‐free dry weight (AFDW) growth ?2.7 to 10.3 μg day^?1. Spat from the first settlement group attained a larger size and weight than spat from larvae settled 3 days later, but had a lower daily growth rate (%). Keeping the late‐settled spat a longer time in the hatchery to reach a bigger size before transfer seemed not to improve subsequent nursery growth. Survival showed a large variation with mean survival ranging from 32% to 74%. A substantial reduction in lipid content was found after transfer to the nursery. Sterol content at transfer was the only lipid class correlating with survival in the nursery. Based on the results, it is justified that spat groups of different settlement age are included in production of 15‐mm great scallop spat if they are transferred from the hatchery at the same age.     

Larval and post‐larval growth,spat production and off‐bottom cultivation of the smooth venus clam Chionista fluctifraga

Harvesting practices of the clam Chionista fluctifraga show a decline in commercial size and densities, but no strategies have been developed to maintain clam beds. Aquaculture represents an alternative for preserving this resource. Adult clams from commercial grounds were used as broodstock. Conditioning, induction of spawning, cultivation of larvae, settlement of eyed larvae and nursing of postlarvae were performed in the hatchery for producing spat. Larvae and postlarvae were used to measure increase in shell height and data were fitted to exponential growth models. Spat were placed in floating trays and maintained in off‐bottom cultivation for 9 months. Samples of clams and tissues were collected monthly to measure absolute growth, shell height increase and a condition index. Larvae, postlarvae and juveniles showed exponential growth patterns. Mean shell height increased about 0.030 mm day^?1 during larval and post‐larval stages and 0.049 mm day^?1 during field cultivation. Pediveligers (height 215 ± 83 μm) entered metamorphosis at days 9–13 after fertilization, and postlarvae reached 3011.7 ± 325.5 μm (height) at day 60. After field cultivation, survival was about 95%; juvenile shell height was 20.6 ± 2.2 mm, and total weight was 5.3 ± 0.7 g. Growth rates were superior to natural conditions and the condition index was high throughout the study. Our results show that spat of C. fluctifraga can be produced in the hatchery, and that field production can be maintained in off‐bottom trays until reaching commercial size. Aquaculture activities for this species need to be established and evaluated.     

Growth and survival of the Calafia mother-of-pearl oyster Pinctada mazatlanica (Hanley 1856) under different sequences of nursery culture–late culture at Bahía de La Paz, Baja California Sur, México

The Calafia mother‐of‐pearl oyster, Pinctada mazatlanica (Hanley), and the Rainbow nacre shell, Pteria sterna (Gould), represent an important resource for México because of their potential in pearl production. The present work deals with the effect of different sequences of nursery culture‐late culture on growth and survival of P. mazatlanica, from September 1993 to October 1994. The collected spat presented two main size groups: small (mean shell height of 7 mm), and large (13 mm). They were arranged into four experimental batches for each size group at a constant stocking density of 40–45 juvenile pearl oysters per Nestier cage. Three batches remained in nursery culture for 2, 4 and 6 months respectively, after which they were transferred to late culture in rail cages. A control group remained in nursery culture for 12 months. Growth was evaluated monthly and compared through anova and HSD Tukey tests. In addition to the shell height, width, depth (mm) and weight (g), data of shell volume (height × width × depth, in mm³) was also introduced to estimate and compare growth among the experimental groups. Mortality was estimated by counting the dead specimens every month and obtaining the percentage from a 100% initial survival at the start of the experiment. The juveniles showed different responses to the change from nursery culture to late culture; the level of each response varied significantly among the experimental groups at the end of the study. It seemed that a 6‐month period for nursery culture was propitious for P. mazatlanica.     

Nutritional value of Pavlova spp. (Prymnesiophyceae) for spat of the Cortez oyster Crassostrea corteziensis during late-nursery culturing at the hatchery

Three Pavlova species were evaluated for their nutritional value as diets for growth and survival of the Cortez oyster Crassostrea corteziensis spat during late‐nursery cultivation at a hatchery. Microalgae were provided as monospecific diets (Pavlova salina, P. sp. C50 and P. sp. C53) and in binary combinations of diets 1+2, 1+3 and 2+3 at 80–90 × 10³ cells mL^?1 for 21 days. Juveniles experienced high survival rates and grew well with all dietary treatments, but binary diets yielded greater survival and growth of spat. From the three binary treatments, Diet 6 (P. sp. C50 and P. sp. C53) promoted significantly (P<0.001) fastest growth of juveniles in shell height (0.19 mm day^?1), shell length (0.14 mm day^?1), total wet weight (0.04 g day^?1) and dry weight of meat biomass (0.024 g day^?1). For all shell dimensions, the lowest growth rates occurred with Diets 2 (P. sp. C56 alone) and 3 (P. sp. C50 alone). These results highlight the importance of testing microalgal diets for bivalve spat rather than just relying on published nutritional values.     

Development of nursery culture techniques for the mud crab Scylla paramamosain (Estampador)

Cannibalism is one of the main causes of mortality in the culture of the mud crab Scylla paramamosain, particularly in the early post‐larval and juvenile stages when the densities of hatchery‐reared crabs may be very high before stocking into ponds or release into the wild for stock enhancement. In a series of experiments investigating cannibalism mitigation, the influence of stocking density, the effectiveness of sand substrate, brick and shell shelters and feed type were compared in culture of crabs from instar 1 for short nursery periods of 15–30 days. Inclusion of brick and shell shelters significantly increased survival over sand substrate alone. However, inclusion of shelters did not affect growth rates. In scaled‐up nursery production in lined‐ponds, with shelters, live Artemia biomass and fresh chopped shrimp or tilapia were found to be equally effective feeds for juvenile crabs stocked at a density of 70 m⁻² from instar 1 and grown for 30 days [52–66% survival, 21.6–24.6 mm carapace width (CW)]. In an extended nursery period for a further 30 days, crabs of 22 mm CW, stocked at 30 m⁻² in the same ponds, attained a final size of 34.5–36.2 mm CW with a survival of 64.3–67.0% using the same feeds.     

Effects of alternate starvation and refeeding cycles on food consumption and compensatory growth of abalone, Haliotis asinina (Linnaeus)

The effects of alternate starvation and refeeding on food consumption and compensatory growth of hatchery‐bred abalone, Haliotis asinina (Linnaeus), were determined. Two groups of abalone juveniles (mean shell length = 29 mm, body weight = 5 g) were alternately starved and refed a macro‐alga, Gracilariopsis bailinae at equal duration (5/5 or 10/10) over 140 days. A control group (FR) was fed the seaweed ad libitum throughout a 200‐day experimental period. Starved and refed abalone showed slower growth rates (DGR, 63 and 70 mg/day in the 5/5 and 10/10 groups respectively), as a result of reduced food intake (DFI 15% and 16% day^?1 respectively), after repeated starvation and refeeding cycles. Percentage weight gains (5/5 = 196%, 10/10 = 177%) were significantly lower than that of the control (397%). When refed continuously over 60 days, the starved groups exhibited increased DFI and fed at the rate of 24% and 25% day^?1, which were not significantly different from that of the control at 26% day^?1. At the end of the experiment, no significant differences were observed among three treatments in terms of shell length (range: 46–48 mm), body weight (range 25–28 g), % weight gain (392–465%) and per cent survival (range 87–98%). The results indicated that H. asinina had a complete compensatory growth following a return to full rations after a series of intermittent starvation and refeeding cycles.     

Lion's paw scallop (Nodipecten subnodosus, Sowerby 1835) aquaculture in Bahía Magdalena, Mexico: effects of population density and season on juvenile growth and mortality

This study examined the effects of density and growing season on growth and survival of juvenile lion's paw scallops (Nodipecten subnodosus) in Estero San Buto, a mangrove channel in Bahía Magdalena, Mexico. Scallops were kept in plastic mesh bags in oyster trays at three population densities (500, 1000 and 2000 organisms per tray, or low medium and high density respectively) over a period of 2 months from October to December 2001 and from February to April 2002. Growth (shell height increment) was measured every 7–12 days and mortality was evaluated at the end of the experiment (dead shell count). Overall growth was fast (0.24–0.38 mm day^?1) in comparison with other pectinids. Significant differences were found for both, density and season, with faster growth occurring at lower densities and during the fall season when the water temperature was higher. Mortality was low (0.5–3.0% 60 day^?1) except for the high‐density treatment in the fall (44% 60 day^?1). Crowding together with high water temperatures and increased metabolic oxygen demand of the scallops and possibly competition for food were the probable reasons for this high mortality. Overall, mortality was lower in the spring, when temperatures were lower, O₂ values were higher and food was more abundant.     

Analysis of growth and first reproduction of hatchery‐reared juvenile Cortez oyster (Crassostrea corteziensis) in northwestern Mexico: proposal of a minimal fishing size

This study presents complimentary data of early growth and age/size of first reproduction of hatchery‐reared Crassostrea corteziensis juveniles cultivated in the field for 9 months. Samples of oysters and gonads were collected monthly to determine absolute growth and growth rates, as well as overall gonad development. At the end, adult oysters ranging 75.6 ± 0.62 mm shell height (SH) yielded a mean growth rate of 0.308 mm day⁻¹, which is among the highest reported for the species. Gametogenesis began in March–April and spawning occurred during August and September. Males outnumbered females at smaller sizes, but female were more abundant at larger sizes. From planting time in the field, the age/size of first maturity was 3.25 months for males (42 mm SH) and 4.5 months for females (54 mm SH), with a mean population age of 4.75 months for males (size range 55–59 mm) and 5.25 months for females (60–64 mm). Based on these results, and the time needed for hatchery care prior planting juveniles in the field (2.25 months), we propose limiting fishing of wild oysters to sizes >65 mm height to allow them to breed at least once and contribute to restoring wild populations.     

Effect of ammonia-N on growth and feeding of juvenile Macrobrachium rosenbergii (De-Man)

Survival rate, growth and feed intake were determined for late juveniles (4.31 ± 0.18 g) of river prawn Macrobrachium rosenbergii in freshwater with total ammonia‐N (NH₃‐N+NH₄‐N) concentrations of 0.015 (control), 0.5, 1.0 and 1.5 mg L⁻¹ for 60 days at pH 7.53 ± 0.04 and temperature 24.0 ± 2.5°C. Survival rate was significantly (P<0.05) lower (54 ± 4.2–70 ± 5.4%) for total ammonia concentrations from 0.5 to 1.5 mg L⁻¹ [0.0139–0.0419 mg L⁻¹ of unionized ammonia (NH₃)]. Growth (0.026–0.030 g day⁻¹ range) of the prawns did not differ for the different NH₃ levels but were significantly (P<0.05) lower compared with control (0.056 g day⁻¹). Feed intake rates also diminished significantly (P<0.05) from 77.60 ± 2.45% at control (0.015 mg L⁻¹ NH₃‐N) to 48.69 ± 2.13% at 1.5 mg L⁻¹ NH₃‐N (0.0419 mg L⁻¹ of unionized NH₃).     

Complete and partial replacement of Artemia nauplii by Moina micrura during early postlarval culture of white shrimp (Litopenaeus schmitti)

Growth rate, soluble protein content, osmotic stress and digestive enzyme activity were studied in early Litopenaeus schmitti postlarvae under different feeding regimens, by partially or completely replacing Artemia nauplii with Moina micrura. Growth was significantly higher in the postlarvae fed with a mixture of M. micrura, Artemia nauplii and algae (0.030 mg dry weight (dw) larva^?1 day^?1, 17.4 ± 2.1% day^?1), together with the postlarvae fed on Artemia nauplii and algae (0.027 mg dw larva^?1 day^?1, 18.3 ± 1.9% day^?1). Complete replacement of Artemia nauplii by M. micrura produced the lowest growth rate (0.018 mg dw larva^?1 day^?1, 14.3 ± 1.6% day^?1) and induced the highest protease and α‐amylase activities and lower soluble protein contents. No significant difference among the treatments could be detected in postlarval resistance to osmotic stress. Based on the growth results, soluble protein content, enzymatic activity and osmotic stress resistance, we determined that the partial replacement of Artemia nauplii by M. micrura did not affect the growth, the soluble protein content and the nutritional state in the postlarvae of L. schmitti. To our knowledge, this is the first reported use of M.micrura as feed for early postlarvae of L. schmitti.     

Prey availability and daily growth rate of juvenile Japanese flounder Paralichthys olivaceus at a sandy beach in the central Seto Inland Sea,Japan

The aim of this study was to characterize a nursery ground (Ohama Beach, Hiuchi-nada) for the Japanese flounder Paralichthys olivaceus in the central Seto Inland Sea having insufficient availability of mysids, Nipponomysis ornata and Iiella oshimai. We examined daily growth rates of wild juveniles; this measure can be used as an index of quality of a nursery. Juveniles consumed not only mysids, but also Crangon uritai and fishes. Mysid availability was lower at the study beach than in the nursery in the Sea of Japan; however, mean growth rates (MGRs) from May to June varied from 0.75 to 1.84 mm day^?1 and equaled that in the nursery with sufficient availability of mysids in the Sea of Japan. Prey availability was high from May to June and decreased after July. Additionally, water temperatures after late July were higher than the optimal temperature. Multiple regression analysis suggested that the low availability of prey and high water temperatures reduced the MGR after July. The results indicate that the optimal season for releasing hatchery-reared juveniles is from May to June, a period characterized by high availability of prey.     

Economic performance of mechanised trawlers in the state of Kerala,India

The rapid growth in the fleet of small mechanised shrimp trawlers in Kerala from 769 trawlers day⁻¹ in 1973 to 3500 trawlers day⁻¹ in 1980 resulted in considerable erosion in the estimated annual net profit trawler⁻¹ from a maximum of Rs 537.5 × 10³ im 1976 to a minimum of Rs 5805 in 1982. This study proposes to optimise the fleet at 1460 trawlers day⁻¹ at which the net profit day⁻¹ for the trawler sector in Kerala would be Rs 2.127 × 10⁶ (or Rs 457.305 × 10⁶ year⁻¹ of 215 fishing days). At this economically optimum level of fishing effort, the yield from trawl fishery is estimated at 91 323 tons, comprising 44 931 tons of shrimps and 46 392 tons of finfish. The optimum number of trawlers may be chosen each year by about March or April by lot. The surplus vessels may be deployed in alternative fisheries such as for whitebait, rock perches, red snappers, breams, cephalopods, sharks and larger pelagics.     

Habitat preference,distribution and growth of postlarvae,juvenile and pre-adult Indian white shrimp,Penaeus indicus H. Milne Edwards,in Ghubat Hasish Bay,Gulf of Masirah,Sultanate of Oman

Abstract An investigation of postlarvae, early juveniles and pre-adult Indian white shrimp, Penaeus indicus H. Milne Edwards, in Ghubat Hasish Bay around Mahawt Island in the Gulf of Masirah was carried out from January 1991 to December 1992. Peak abundance of postlarvae and juveniles was observed during March and April. The size of newly recruited postlarvae ranged from 9 to 11 mm total length. The highest concentration of postlarvae and early juveniles occurred in muddy substratum covered by mangrove detritus. Postlarvae and juvenile densities varied significantly between years, seasons and habitats. The main fishery recruitment observed in late August and early September resulted from the major postlarval abundance peaks in March and April. Growth rates of postlarvae, juveniles and pre-adult shrimp of the main cohort recruited in March were calculated. During the peak fishing season (September to November), pre-adults were concentrated at depths of 3–5 m in muddy substrata south-west of Mahawt Island. An environmental impact study is recommended in this area prior to the proposed harbour development at Mahawt.     

Age determination,growth, mortality and age of first reproduction in adult Queen Conch,Strombus gigas L., off Puerto Rico

Growth and mortality of adult Strombus gigas L. was studied in a population offshore of La Parguera, Puerto Rico. Adult queen conchs do not grow in shell length, but only in shell thickness. Growth in thickness of the flared shell-lip was measured during a 2-year mark-recapture study and modelled using the von Bertalanffy growth function. Model parameters were K=0.3706 year⁻¹ and L_∞ (asymptotic lip-thickness) =54.9 mm; the third von Bertalanffy parameter, t₀, cannot be obtained from mark-recapture data alone. Growth in tissue, meat and shell weights of adults were determined using the von Bertalanffy growth function in conjunction with regression equations for weights versus shell length and/or lip thickness. Total instantaneous mortality in adults, determined using von Bertalanffy parameters and lip-thickness frequency analysis, was 1.66 year⁻¹. Subtracting a previous estimate of fishing mortality (F=1.14 year⁻¹) yielded a natural mortality (M) of 0.52 year⁻¹. Given an average age at maturation, defined by the formation of the flared shell-lip, of 3.2 years, the age of first reproduction was estimated at 3.6 years, but could be as much as 4 years.     

Litopenaeus vannamei (Boone) post-larval survival related to age, temperature, pH and ammonium concentration

Transport of post‐larvae shrimp used in aquaculture is an important element of successful cultivation because of the potential for stress during stocking procedures. To find optimum transport conditions, several bioassays were performed in the laboratory to evaluate survival of whiteleg shrimp Litopenaeus vannamei 5–30‐day‐old postlarvae under conditions similar to those encountered during transport from the hatchery to nursery and shrimp ponds. Postlarvae were exposed for 4 h to different temperatures and pH levels ammonia concentrations. Survival was significantly reduced after a 4 h exposure to pH 9 and was inversely related to temperature with or without 7 mg L^?1 of ammonia. The 15‐ and 20‐day‐old postlarvae had higher survival rates than other ages. The lowest survival occurred in alkali conditions (pH 9), with 7 mg L^?1ammonia at 30 and 32°C. To assure optimal survival of postlarvae during transfer from the hatchery to the nursery and shrimp ponds, we recommend temperatures below 28°C, pH no higher than 8, no ammonia and post‐larval age at least 15 days.     

Effect of microencapsulated diets supplemented with genetically modified bacteria on the growth and survival of Fenneropenaeus indicus postlarvae

Microencapsulated diets were prepared and supplemented with two genetically modified bacteria that produced digestive enzymes. One produced a protease (strain Escherichia coli XL1Bluep635), and the other a lipase and a protease (strain E. coli XL1Bluep7). Fenneropenaeus indicus at the postlarval 1 stage (PL1) were fed these diets for 16 days, and their total length and survival were recorded every 2 days. The results were analyzed by anova and sequential Turkey–Kramer analysis. Shrimp fed on the diet supplemented with strain E. coli XL1Bluep635 (diet 635) exhibited the fastest growth rate of 0.26 mm day⁻¹, followed by shrimp fed on the control commercial unsupplemented diet CD2 – 0.21 mm day⁻¹, and shrimp fed on diet supplemented with strain E. coli XL1Bluep7 (diet 7) – 0.20 mm day⁻¹. The growth rates of shrimp fed on diet supplemented with control strain E. coli XL1BluepUC19 (diet XL1), and those fed on unsupplemented diet prepared in our laboratory (D2), were 0.15 and 0.14 mm day⁻¹, respectively. The survival of shrimp fed on diets CD2 and 635 showed the same level of survival of 83.3%, followed by those fed on diet D2 with 76.6%. Shrimp fed on diet 7, showed 71.6% survival, and those fed on diet XL1, 55%.     

Effects of single and combined microalgae on larval growth, development and survival of the commercial sea cucumber Holothuria spinifera Theel

The results of the study on the suitable algal feed for the mass rearing of holothurian larvae through hatchery system are presented. Auricularia larvae, after 48 h of fertilization, obtained from induced spawning of Holothuria spinifera, were fed with different algae Isochrysis galbana, Nanochloropsis salina, Pavlova lutheri, Tetraselmis chuii and Chaetoceros calcitrans as well as I. galbana+C. calcitrans to ascertain the effect of single and combined microalgal diet. The rate of feeding was 2 × 10⁴ cells larvae^–1 day^–1 for a period of 9–12 days. The growth rate of 59 μm day⁻¹ with 90% and 43 μm day⁻¹ with 100% occurrence of late auricularia in the larvae fed with C. calcitrans alone and I. galbana+C. calcitrans, respectively, indicated that C.calcitrans itself or in combination with I. galbana is the effective feed for the larvae of H. spinifera.     

Effects of temperature and salinity on survival and growth of juvenile ark shell <Emphasis Type="Italic">Anadara broughtonii</Emphasis>

We investigated the combined effects of temperature (23, 26, 29 and 32 °C) and salinity [15, 18, 21, 24, 27 and 30 practical salinity units (PSU)] on the growth and survival of juvenile ark shell Anadara broughtonii under hatchery conditions. Mortality, shell length and shell height were monitored for a period of 25 days in all exposure groups. Survival greater than 98% was observed in all treatment groups with no significant difference among treatment combinations. Absolute growth and specific shell length and height growth rate were significantly influenced by temperature and salinity. Growth of juvenile A. broughtonii increased with higher salinity and peaked at an intermediate temperature (26 °C). Optimal specific growth rates of 4.64 ± 0.04% day^?1 by shell length and 4.76 ± 0.11% day^?1 by shell height were observed at a combination of 26 °C and 30 PSU. This study enhances our understanding of the biology of A. broughtonii and determines ideal environmental conditions for pre-planting culture operations.     

Effects of starvation on larval growth,survival and metamorphosis of Ivory shell Babylonia formosae habei Altena et al., 1981 (Neogastropoda: Buccinidae)

The impact of starvation on larvae of Ivory shell Babylonia formosae habei was studied in a laboratory experiment. Newly hatched veligers showed considerable tolerance to starvation due to their endogenous yolk material, and time to the point-of-no-return (PNR; the threshold point during starvation after which larvae can longer metamorphose even if food is provided) was calculated to be 104.5 h. However, starvation still affected larval growth, survival, and metamorphosis. Mean shell length of larvae increased 49.77 μm day⁻¹ for nonstarved, but only 11.13 μm day⁻¹ for larvae starved for 108 h. After larvae began feeding, their growth rates rapidly recovered to the level of the nonstarved following short periods of starvation (less than 48 h), but were inhibited and unable to ever reach the level of the nonstarved when being starved beyond 48 h. Percent metamorphosis was 53.75% for the nonstarved, but all larvae died before 10 days for those starved for 108 h. Starvation not only affected larval time to reach metamorphosis, but also caused the delay in the time to metamorphosis. For the nonstarved, larvae took only 11.5 days to reach spontaneous metamorphosis, but they took 20 days to reach spontaneous metamorphosis when starved for 96 h, and this duration of delayed metamorphosis reached 8.5 days. Furthermore, the importance of yolk material for maintaining larval survival of B. formosae habei during starvation periods is also discussed.     

Relationship between daily survival rates of larval Japanese anchovy (Engraulis japonicus) and concentrations of copepod nauplii in the Seto Inland Sea, Japan

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.