What do amphibians, reptiles and fish have in common? They are all ectotherms – cold blooded creatures. They are animals which cannot regulate their own body temperatures (like warm blooded animals can) and they rely on the external environment to change their internal temperatures.
For long scientists wondered if sickness like cold, flu and fever were the lot of warm blooded creatures . As it turns out – they aren’t. Cold blooded creatures can fall ill too.
How (?), you may ask. In order to understand this, we need to understand how fevers set in warm blooded creatures.
All warm blooded creatures have a particular body temperature, which for them is considered normal. For example:
- Humans – 98.6°F
- Dogs – 102.0°F
- Elephants – 97.7°F
- Horses – 100.4°F
- Goats – 103.4°F
If the body temperatures of these animals rises above this limit (as is the case during infections), the body tries to thermoregulate .i.e. bring the temperature back down, to normal. When the body fails to do this and the body temperature continues to rise, fever sets in.
What about cold blooded animals?
Based on this, it’s important to note that for fever to set in, there has to be a biologically-set body temperature. But cold blooded animals don’t have a fixed temperature. Their body temperature falls or rises depending on the temperature of the external environment.
So, how do they fall ill?
Well, cold blooded or warm blooded, all animals are susceptible to illness. Just as with their warm blooded cousins, cold blooded animals too may get infections from parasites or viruses, which can raise or drop their body temperatures abnormally. Just like warm blooded animals, ectotherm animals’ bodies too can handle only a certain level of heat and cold. If the change in temperature during the infection falls beyond this limit, illness similar to fever sets in.
But the biggest mystery here isn’t just about how these animals fall ill, but it also includes what these animals do to get back to health.
Changing behaviours for the sake of wellness
When fish, amphibians or reptiles fall ill, they indulge in what is known as a “behavioural fever“. If the animal is infected by a parasite or virus and experiences signs of ill health, it moves away towards areas which support warmer climates. For example, fish that normally prefer cold waters may swim towards warmer waters when they are ill.
Heat has the ability to deactivate viruses and destroy the proteins which assist in virus duplication. The same goes with parasites – heat can kill them too.
So, a cold blooded creature that falls ill, will instinctively move towards a warmer place, in order to increase its body temperature, which will in turn help in killing or deactivating the pathogen in their bodies.
This instinctive “behaviour“, which ectotherms exhibit when they have “fevers“, is called “behavioural fever“. Scientists speculate this behaviour could stem from the fact that the immune systems of cold blooded animals may actually function better when in warmer climates.
One of the best examples of cold blooded creatures who exhibit behavioural fever are Zebrafish. The moment they fall ill, Zebra fish will change their water-heat preferences and swim to warmer waters. The same goes for Guppies.
When behavioural fever benefits the host
For some time, it was assumed that behavioural fever was helpful only for ectotherms who were in the throes of infection & fever. But as it turns out, in some cases, the move to hotter areas benefits pathogens too.
Schistocephalus solidus, a tapeworm found in the gut of rodents, fish and fish-eating birds, actually thrive on heat. Once the parasite is in the hot climate, it grows stronger and changes the heat preferences of the fish and manipulate other atypical (and often self-destructive) behaviours in the animal.
Then there is the Cyprinid herpesvirus 3, which is a virus that attacks fish in the Carp family. This virus affects the genetic code of the fish it infects and overrides the genes which stimulate behavioural fever. So, the infected fish doesn’t move towards warmer waters (as it is supposed to), instead choosing to stay in colder waters, where the virus can gain in strength.
What happens if a feverish ectotherm cannot move to warmer climates?
Vicious parasites and mind-control viruses aside, the inability to indulge in behavioural fever can have a massive, negative impact on cold blooded animals. This is in fact, very true of pets.
In the wild, cold blooded creatures have a lot of freedom to move to different places, in order to rid themselves of their illness and infection. But pets stuck in aquariums and enclosures don’t have this luxury.
Cold blooded pets like fish, turtles, tortoises, iguanas, lizards and snakes are cooped up inside their temperature-controlled tanks/enclosures for almost their entire lives; where they are subjected to the same temperature day-in-and-day-out.
Now imagine these pets fall ill and have a fever. Biologically they are programmed to leave and move to a place that is warmer, to heal themselves. But because they are stuck in their tanks/enclosures, these animals do not get the opportunity to get their bodies at the right temperature to kill the infection.
When this happens, the fever and the infection only gets worse and in the worst cases, the pet dies. In fact, a large number of fish deaths in aquariums can be attributed to this.
So, what can pet owners do about this?
Fish owners can set aside a separate tank where they can change the temperature of the water as required. Owners of amphibians and reptiles can create heat spots in corners of the enclosure by using detachable heaters and small light sources. This can give the sick pet an opportunity to self-heal.
If however, your pet looks worse, it’s best to take him/her to a vet immediately.