Spawning in captivity can be hard on abalone, as aquaculture operators have to periodically yank the molluscs off the insides of their tanks to inspect their gonads. Things could soon get kinder and gentler, however, thanks to the use of ultrasound.
Instead of just leaving everything to chance, abalone farmers typically collect sperm and eggs from captive male and female abalone, as soon as the animals release them. Those reproductive cells are then mixed together in a controlled environment, and in an ideal ratio – if too many sperm are present, they can destroy eggs in a process known as polyspermy.
In order to know when the abalone are about to release their eggs and sperm, farmers regularly check the size of their gonads. Unfortunately, doing so usually involves pulling the molluscs loose from the inner surface of their tank, then physically finger-probing their soft tissue. Needless to say, this can be quite stressful for the animals.
Led by Asst. Prof. Jackson Gross and postdoctoral student Sara Boles, scientists at the University of California-Davis decided to look to ultrasound as an alternative. Gross had previously used the technology to inspect the gonads of sturgeon and catfish, but wasn't sure if it would work on abalone (which are actually a type of snail).
For the study, individual abalone were kept either in clear plastic tubs, or in troughs lined with a removable sheet of transparent plastic. In both cases – after the creatures had suctioned themselves onto one side of the plastic – the researchers were easily able to image their gonads by placing an ultrasound transducer against the other side of the plastic, adjacent to the soft tissue of the molluscs' feet.
The tests were conducted on about 100 red abalone at the university's Bodega Marine Lab, over a seven-week period. Throughout that time, the scientists were successfully able to judge the increasing size of the molluscs' gonads, assigning each animal a score of 1 to 5 indicating its readiness to reproduce.
Although some physical handling of the abalone was still required when it came time to actually collect their sperm and eggs, no yanking or prodding was necessary up until that point.
Gross informs us that his team is now working with commercial abalone farmers, to evaluate the technology further.
"There are not a lot of animal welfare methods applied to invertebrate animals, let alone for aquatic species," he said. "Here’s a way to increase the welfare of an abalone without bringing added stress to them."
A paper on the research was recently published in the journal Frontiers in Marine Science.
Source: University of California-Davis
