The growth of the juvenile sea cucumber, Holothuria scabra, was studied under captivity to elucidate the growth variation pattern and determine the best-fit growth model to estimate age-and size-specific growth rates. Individual growth was extremely variable, with some individuals below the mean initial weight and some expanding their original body length (L) and weight (W) by up to 6.4 and 156 times, respectively; during 84 days of culture starting at 127 days of age. Some of the smallest individuals showed a higher condition factor than larger individuals in the presence of ample food, indicating that lack of food may not be the only impediment to growth. Among the three growth models compared (von Bertalanffy, Gompertz and logistic), the Gompertz model was considered optimal to express H. scabra growth; both in L and W. The age-and size-specific daily growth rate for L and W up to 365 days of age, as estimated by the Gompertz model, had a range of two and nine orders of magnitude in L (0.035 -0.96 mm/day) and W (3.4 × 10 -7 -3.5 g/day), respectively. Use of the Gompertz model over the linear model, which tends to overestimate growth rates, is encouraged to estimate the growth of H. scabra more accurately.
The ability of Holothuria scabra to digest nutrients, such as organic matter (OM), protein and carbohydrate from animal and plant feed ingredients was investigated. Four test feeds prepared by mixing sand with single ingredients from animal sources (shrimp and mussel) and plant sources (diatom and seaweed) were fed to H. scabra to estimate apparent digestibility coefficient (ADC). The total assimilated nutrient (TAN) increased with ADC, whereas ingestion rate (IR) varied slightly among the feeds suggesting that ADC might be a good indicator of nutrient availability to H. scabra. The ADC OM of shrimp and mussel was significantly higher than that diatom and seaweed: 86.2%, 77.1%, 55.1% and 32.3% respectively. ADC protein was similar for shrimp (88.7%), mussel (84.8%) and diatom (75.2%), but significantly lower in seaweed (34.4%). ADC carbohydrate was similar in mussel (58.5%) and diatom (58.3%) as well as in seaweed (31.6) and shrimp (28.0%). ADC protein was relatively higher than ADC carbohydrate suggesting that H. scabra generally digests more protein than carbohydrate. Furthermore, results indicated that nutrients from animal-based feeds are more efficiently digested by H. scabra; thus, animal ingredients rich in easily digestible protein could potentially provide an efficiently balanced diet for H. scabra fed with diatom containing high easily digestible carbohydrate.
The lucrative returns brought by abalone fisheries have caused overexploitation and decline of the wild population. In the Philippines, the Aquaculture Department of the Southeast Asian Fisheries Development Center has successfully produced Haliotis asinina seeds in the hatchery. Aside from utilizing these seeds in aquaculture, they are also being considered for future stock enhancement endeavors of the department. This study aimed to evaluate post release behavior, recapture and growth rates of hatchery-reared abalone juveniles released in the Sagay Marine Reserve. From the two release trials conducted, results showed that abalone of shell length >3.0 cm had lower mortality during onsite acclimation and utilized transport modules as temporary shelter for a shorter period after release. Both wild and hatchery-reared abalone preferred dead branching corals with encrusting algae as their habitat. Recapture rates were comparable between the wild (7.97%) and hatchery-reared (HR2) abalone (6.47%). Monthly growth rates were almost the same between wild (0.25 cm, 4.0 g), 4.6 g; HR2: 0.35 cm, 3.8 g) abalone. Moreover, hatchery-reared abalone were recaptured up to 513 days post-release, indicating viability of released stocks in the wild. Results of releases revealed that hatchery-reared abalone can grow and survive with their wild conspecifics.
Many species of tropical sea cucumbers in many countries in the Pacific and Indian Oceans are being over-exploited for processing into bêche-de-mer (dried form) 5,8,18 . As the demand for sea cucumbers increases and fishery stocks dwindle in many areas of these countries, there is a growing demand to produce sea cucumbers by aquaculture and stock enhancement using juveniles produced in the hatchery. There is also growing interest in co-culturing sea cucumbers alongside other organisms to utilize organic debris and thus mitigate eutrophication within and around the aquaculture facilities 4,22,33,37,46 . To this end, an increasing number of studies have recently been performed to develop techniques for hatchery, aquaculture and stock enhancement of sea cucumbers, especially sandfish, Holothuria scabra, the most valued species of tropical sea cucumbers 3,4,28,37 . The hatchery production of H. scabra seeds has got underway in countries, such as Vietnam, India, New Caledonia and the Philippines 1,11,36 , but the high mortality and slow growth rate of cultured juveniles have been problematic. Despite the various food items used in broodstock maintenance and juvenile production and grow-out of H. scabra, including Spirulina spp, Schizochytrium spp, Navicula spp, homogenized Sargassum spp, ground shrimp feed, shrimp head meal, soya bean powder, rice bran, chicken manure and seagrass powder 1,3,11,36 , juveniles often grow much faster in sea pens or earthen ponds where no artificial feeding is conducted. Information about H. scabra diets is indispensable in improving hatchery, aquaculture and reseeding techniques, as well as monitoring environmental conditions for wild stocks.H. scabra are benthic detritus feeders, which ingest muddy sandy sediment and assimilate the organic matter AbstractTo provide a basis for a stable carbon and nitrogen isotope ratio (δ 13 C / δ 15 N) analysis to determine the assimilated organic matter in sea cucumber, Holothuria scabra, diet-tissue fractionations were experimentally determined by mono-feeding rearing with diatom. While δ 15
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