Detachment and grading of the tropical sea cucumber sandfish, Holothuria scabra, juveniles from settlement substrates

The culture of the sea cucumber sandfish, Holothuria scabra, requires the regular detachment of juveniles. The use of physical methods to detach juveniles are time consuming, labor intensive and potentially harmful. This study demonstrates that 1% w/w potassium chloride (KCI) in sea water is an effective agent for detaching H. scabra from settlement surfaces without adverse effects. Experiments were conducted in static, 700 mi-glass flasks, at 28 +/- 1 degrees C and stocked with 8 to 10 juveniles. Survival was monitored for 1 to 6 days following treatment. Juveniles of 2.2 mm total length (TL) detached within 1 min when bathed in 1% KCI, but only 70 +/- 20% (mean +/-SD) were detached in 0.5% KCI. Re-attachment was determined after 1, 3, 5 and 10 min exposure to 1% KCl in separate experiments with juveniles of 2, 8 and 20 mm TL. Small juveniles detached more easily, and re-attached more rapidly than large juveniles. The ability of juvenile H. scabra, particularly small ones, to remain detached in 1% KCI baths for IO min facilitates counting, grading and adjustment of stocking densities during plate culture. Exposure to 1% KCI for 10 min resulted in evisceration in 7% of juveniles of 8 mm TL and 17% of juveniles of 20 mm TL. No juveniles eviscerated following exposures of < 10 min. More than 97% of juveniles exposed to baths of 0.5% to 5% KCI survived and re-attached. None of the juveniles exposed to 10% KCI survived for longer than 24 h. The practical application of using 1% KCI bathing was tested on juveniles attached to settlement plates and through a grading experiment using juveniles of 1 to 39 mm TL. Juveniles < 15 mm curled into spheres when detached and were easy to grade. In contrast, individuals > 25 mm did not form a sphere and were difficult to grade. Freshwater was not an effective alternative to KCI, since only 83.3 +/- 5.8% of juveniles detached and 67% survived after 1 min. (C) 1998 Published by Elsevier Science B.V.