I’m looking into whether there are portable X-ray devices that would
allow us to detect and measure the swimbladder of fish during surveys at
sea. I’m completely inexperienced in this area and was wondering if
anyone in the WGFAST community has attempted something similar. If so, I
would greatly appreciate it if they could get in touch and share their
experience.
In particular, I’m looking for advice on existing models available on
the market, their performance in detecting and measuring swimbladders,
whether the procedure can be carried out efficiently and safely at sea,
and ultimately, whether such observations on fresh animals are
worthwhile compared to what could be done in the lab with preserved
or thawed specimens.
Many thanks in advance, and warm regards to the WGFAST community.
Hi Alejandro, I know that Chu used a more or less portable X-ray machine at sea. I think he mainly used it to take pictures of relatively large fish. I think to remember that the one Chu used did not have a particularly high resolution. If you are looking to take images of smaller organisms, maybe look into small X-Ray machines for Vets or even dentists. These are generally more portable and cheaper, also they might have a lower radiation load.
I think the usability of an X-Ray machine at sea depends on what you want to achieve.
will you be able to create a safe environment a sea using X-Rays?
What kind of fish are you trying to scan? Do you expect them to degrade quickly or can you get them in a lab where you can do the scans safer and easier?
If they have swimbladders, can you et them to the surface without damaging the swimbladder?
Do you need X-Ray or can you maybe just take pictures (fish from the side and from top and then opened up to reveal relevant inernal structures). Will the insights you get from the X-Ray improve your modelling or would simple pictures suffice?
Will densiy and soundspeed measurements of body parts be important?
You can also send me an email and we can have a quick meetin if you think that would be useful.
I can answer some but not all the questions! So let’s keep the conversation open here. Hopefully someone else could jump in and provide more details on the subject.
X-rays are intended for small mesopeagic fish (mostly lanternfishes and Cyclothone species). I’ve done x-rays at land, samples were taken in two different cruises at a variety of depths, time of day, and body lenghts. I got surprised by the few number of gas-filled swimbladders found. I expected regressed swimbladders in larger specimens, but they were also undetectable in small fishes, most of the times. Individuals lacking a swimbladder often showed gas pockets distributed throughout the digestive area and mouth. This led us to consider barotrauma during ascent, but the truth is that it was also common in fish caught near the surface. The specimens were frozen immediately after capture and thawed before the X-ray session. Basically, we are unsure whether swimbladders can deteriorate during the freezing and thawing process. We wonder if X-ray swimbladder detection is more successful when done fresh, just minutes after capture. Perhaps someone has an answer to this? I hope so!
On another note, there is also interest in having this type of equipment to facilitate taxonomic identification through the observation of skeletal structures. Let’s say the question is beginning to circulate in France as to whether it would be worthwhile to have this device onboard during mesopelagic surveys.
Also, if X-ray detection proves effective, I believe swimbladder measurements would be faster, more accurate, and the specimens would not be damaged.
But honestly, we are not decided on acquiring this kind of equipment. Rather, we’d like to explore with the FAST community whether this is a good option.