5.4 TECHNIQUES – TRANSPORT OF JUVENILES

Scallops produced in hatcheries or collected from natural settlements normally require transportation to other sites for continued culture. Scallops are particularly difficult to transport as they are usually sub-littoral organisms, unlike oysters or mussels, and seldom encounter aerial exposure. In part, for this reason, stress associated with transport often causes mortalities.

Several methods of transport have been attempted; two of the most common are the use of insulated boxes with material soaked in seawater, referred to as dry transport, (Ventilla, 1982; Maguire, Cashmore and Burnell, 1999; Maeda-Martinez, Siscard and Reynoso-Granados, 2000), and vivier lorry, where animals are transported in seawater with a continuous oxygen flow (Maguire, Cashmore and Burnell, 1999). Although some success is obtained, survival reported in the literature does not exceed 61 percent immediately following 19 hours of simulated dry transport (Maeda-Martinez, Siscard and Reynoso-Granados, 1999), and increased mortality (up to 51 percent) is often seen in subsequent months during growout (Maguire, Cashmore and Burnell, 1999). As for transporting in seawater, high densities cause a rapid deterioration in quality of holding seawater by reducing dissolved oxygen and increasing ammonia and bacterial levels, leading to gill tissue damage (Maguire, Cashmore and Burnell, 1999).

In Bermuda, due to the small size of the island, transport to growout site can be easily conducted by holding scallops in seawater-filled containers on-board a boat. However, because of interest expressed by other Caribbean islands to rear tropical scallop species and consequent need for transport of spat or adults, procedures for optimal transport were investigated. These procedures were tested for both the sand scallop and the calico scallop, aiming for maximal survival following 24 hours transport time and following transfer to the field.
Details of the experiments conducted are reported in Sarkis, et al., 2005. The procedures are based on methods used for fish transport in the aquarium trade. The methodology developed has been used in two real life situations for the sand scallop. In both cases, scallop spat were taken by air to another site; the total duration of the trip – from packing of scallops to unloading of scallops in the receiving nursery – was of 16 hours. Survival rate upon arrival was >90 percent. It was found that for successful transport of scallop spat, care must be taken to minimize stress during transport, and enhance tolerance of spat to stress by acclimation prior and post transport. Starvation and gradual acclimation to lower temperature, prior to transport, allow for a reduction in metabolic rate, reducing oxygen consumption, amount of excretia and accumulation of acidity, carbon dioxide and ammonia during transport. Low temperatures during transport maintain a low metabolic rate, minimizing oxygen consumption throughout the duration. Following transport, gradual acclimation to ambient temperature minimizes recovery stress, possibly enhancing long term survival. Shell growth of scallops transferred to the natural environment was not affected by simulated transport. The protocol developed is given in detail below (Protocol–17). This procedure should become easily adaptable to various scallops species, with additional insight into some of the species-specific physiological requirements.

PROTOCOL–17
PROCEDURE FOR LONG TRANSPORT PERIODS OF JUVENILE SCALLOPS
1. Do not feed scallops to be transported for 24 hours prior.
2. Acclimatize juvenile scallops to cold water (14 °C) for a minimum period of 6 hours (without feeding).
3. Make a false bottom of polystyrene to fit the cooler, in order to avoid direct contact of scallops with gel packs. Drill several holes in false bottom to allow cooling of entire container.
4. Weigh 160 grams sub-samples of spat (in tarred mesh, blotted dry as in Protocol–14). 5. Fill 1 litre zip-lock bags with 600 ml of 1 µm filtered cold seawater (14 °C).
6. Add scallops to zip-lock bag. Partially close bag.
7. Fill zip-lock bag with oxygen using Pasteur pipette fitted to oxygen regulator and bottle. Close zip-lock bag.
8. Place zip-lock bag into second bag for additional security. Use duct tape to secure closure and avoid any potential tearing or opening.
9. Cool a polystyrene box (60x30x40 cm) to 14 °C using four gel packs. Install false bottom on top of the gel packs and place scallop bags on it.
10. Secure lid of polystyrene box with tape.
11. Following transport do a visual assessment of scallop behaviour and mortality. Record temperature in bag.
12. Transfer scallops into a cold water bath (14 °C) and gradually increase seawater temperature ambient over a 12-hour period.
13. Maintain spat in running seawater once ambient temperature is reached.
14. Following a minimum 3-day acclimation to ambient temperature spat can be transferred to the field.
15. If spat is kept for longer than 3 days, complimentary food supply should be added as described in Appendix 21.