Purcell SW and Agudo NS (2013), Optimisation of mesh enclosures for nursery rea...

ECB-ART-47945

PLoS One 2013 Jan 01;85:e64103. doi: 10.1371/journal.pone.0064103.

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Optimisation of mesh enclosures for nursery rearing of juvenile sea cucumbers.

Purcell SW , Agudo NS .

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Mariculture of tropical sea cucumbers is promising, but the nursery rearing of juveniles is a bottleneck for farming and sea ranching. We conducted four medium-scale experiments lasting 3-6 weeks, using thousands of cultured juvenile sandfish Holothuria scabra, to optimise nursery rearing in mesh enclosures in earthen seawater ponds and to test rearing in enclosures in the sea. In one experiment, survival in fine-mesh enclosures (1 m(3); 660-µm mesh) related nonlinearly to juvenile size, revealing a threshold body length of 5-8 mm for initial transfer from hatchery tanks. Survival in enclosures within ponds in the other experiments ranged from 78-97%, and differences in growth rates among experiments were explained largely by seasonal differences in seawater temperatures in ponds. Stripped shadecloth units within fine-mesh enclosures increased feeding surfaces and improved growth rates by >15%. On the other hand, shading over the enclosures may lower growth rates. Following the rearing in fine-mesh enclosures, small juveniles (0.5 to 1 g) were grown to stocking size (3-10 g) in coarse-mesh enclosures of 1-mm mesh. Sand or mud added to coarse-mesh enclosures did not significantly improve growth compared to controls without sediment. Survival of sandfish juveniles in coarse-mesh enclosures set on the benthos within seagrass beds differed between two sheltered bays and growth was slow compared to groups within the same type of enclosures in an earthen pond. Our findings should lead to significant improvement in the cost-effectiveness of rearing sandfish juveniles to a stocking size compared to established methods and highlight the need for further research into nursery systems in the sea.

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Genes referenced: LOC100887844 LOC583082 srpl

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References :

Mercier, Settlement preferences and early migration of the tropical sea cucumber Holothuria scabra. 2000, Pubmed, Echinobase

	Figure 1. Stripped shadecloth unit.Photograph of the end of a stripped shadecloth unit used to increase the surface area of mesh inside fine-mesh enclosures. The sand-filled polypropylene tubes at the bottom of the photograph weigh down the woven polyethylene fabric while the foam pieces at the top kept the strips upright in the water.
	Figure 2. Fine-mesh enclosures.Photograph of 1-m3 fine-mesh enclosures (660 µm mesh) in the earthen pond during the first experiment (Effects of increasing mesh surfaces and shading), showing some replicates shaded with dark shadecloth and some with stripped shadecloth inside.
	Figure 3. Coarse-mesh enclosures.Photograph of some 2 m×2 m×1-m-high coarse-mesh enclosures (1-mm mesh) in an earthen pond.
	Figure 4. Body length vs body weight of juveniles sandfish.Scatterplot shows relationship (growth curve) of body length with body weight for sandfish juveniles of 6–70 mm in length. Juveniles were drained and blotted dry on a damp cloth for 30 sec before being measured and weighed.
	Figure 5. Effects of increasing mesh surfaces and shading.Bar graphs of (A) average individual body weights and (B) average survival of sandfish in fine-mesh enclosures with and without stripped shadecloth, and with (shaded) and without (open) shade; n = 6. Error bars are 1 standard error of the mean.
	Figure 6. Effects of sediment type and sediment depth.Scatterplot of survival of juvenile sandfish in fine-mesh enclosures across various initial mean group body lengths, three weeks after transfer from hatchery tanks; n = 20 fine-mesh enclosures. The fitted curve is the most appropriate nonlinear function by AIC selection.
	Figure 7. Enclosures at sea vs. pond.Bar graphs comparing (A) average growth rates and (B) average survival of sandfish in coarse-mesh enclosures at two sites at sea and those in an earthen pond; n = 4. Error bars are 1 standard error of the mean.