If this sounds like a medical story, it is not. The pills in this case are stomach temperature pills. Stomach temperature pill (STPs) are telemetry devices we use to record or transmit the stomach temperature in an animal.
But why would we want to know the temperature in an animal’s stomach?
When the host animal is not feeding, the stomach temperature is the same as the deep body core temperature. This can tell us about the health status of an animal, but it can also tell us something about the reproductive cycle of female mammals. In most mammals, females exhibit characteristic temperature changes associated with specific reproductive events such as ovulation and parturition. By monitoring body core temperature remotely, we can find out when a female is ovulating, and when she gives birth.
In this case, stomach temperature pills may be a convenient and non-invasive way to collect such data. You can simply feed an STP to an animal in a fish. It will then remain in the stomach for some time after the fish is digested, and will eventually be either passed or regurgitated. Here at the ASLC we use recording STPs that require us to recover the device to gain access to stored temperature data. In the wild, we use transmitting STPs that link to an external tag that in turn records or relays the data, for example via satellite transmissions.
So where does x-ray come into play here?
We may occasionally use x-ray imaging for diagnostic purposes on one of our resident research animals. We wanted to know if such x-ray procedures might interfere with the correct operation of our STPs. Worst case scenario, the x-rays could wipe the data from the memory chip. So, ASLC Veterinary Technician Jane Belovarac took an x-ray radiograph of an STP at comparable energy settings to what would be used to image the abdomen of an adult sea lion.
The good news: the STP was completely unfazed by multiple x-ray exposures. In part, that could be the result of using modern digital imaging systems that require far lower energy levels than old style imaging systems based on x-ray film.
There is another really cool application of stomach temperature pills: in homeotherm animals that eat cold-bodied prey (let’s say a sea lion eating a squid), we can detect a drop in the stomach temperature whenever the cold prey is ingested. Now we have a record of when the sea lion is eating something. Even more, the magnitude and duration of the temperature drop may be somewhat proportional to the ingested mass. This can be tricky though as many other factors can affect this temperature drop, including how much the animal has already eaten, and how much that mass has warmed up. This of course would not work in cold-blooded predators such as fish. For poikilotherm organisms, we are looking into pH-sensing pills instead.
So, standby for another blog post coming soon with actual data from an stomach temperature pill!
Written by: Dr. Markus Horning