Model organisms have been used in scientific research. A model organism can be defined as a specie that has been widely studied, usually because it is easy to maintain and breed in a laboratory setting and has particular experimental advantages. The most common model organism used in labs are rats and mouse because the rats have similarity to humans in terms of genetics, physiology and anatomy and more than 95% of the mouse genome is similar to humans. On the other hands rats also provide numerous advantages like the physiology in the rats are easier to monitor and also the cognitive abilities of a rat are more superior than any other models. Besides rats are more intelligent and are able to perform a wide variety of memory related tasks.
But since 1990s fish also have been used as model organisms in research and they also have a high success rate as compared to rats and mouse. They are used in every kind of research starting from Toxicology, Neuroscience, cancer research and so on. There are more than 25,000 fish species and have developed many physiological, behavioral and ecological specialization. From research point of view fish provides numerous advantages like fish provide simpler systems for the study of complex processes; they are small, inexpensive, and relatively easy to house, they have become a ‘convenient’ test subject for many scientists; there is a reduction in animal costs by using a ‘phylogenetically lower species.’
The most common fish used is the Zebrafish, a freshwater fish found in the Ganges river in India. It is noted for its regenerative capability, reproductive cycle and small size. They are used in cancer research, addiction research and neuroscience. The larvae of the Zebrafish have also been used to study neural circuits and adult Zebrafish have been used to study circuit mechanisms of memory and stress. Fish are also used to study social interaction stress and to study hermaphroditism.
This reminds me of the movie “Finding Nemo” wherein after the female fish dies, the male fish takes care of the young ones. Well, when the female in the colony dies or disappears, the dominant male will change into the dominant female, and the fish who was waiting in line behind him takes over as the new top guy. If the story had to be biologically accurate then it should be something like this: Nemo hatches as an undifferentiated hermaphrodite (as all clownfish are born) while his father transforms into a female now that his female mate is dead. Since Nemo is the only other clownfish around, he becomes a male and mates with his father (who is now a female). Should his father die, Nemo would change into a female and mate with another male.
Fish have also been used to study pain and a recent study concludes that fish don’t feel pain just like humans do. They do have the nociception system but the presence of the receptors did not mean the animals felt pain, but only triggered a unconscious reaction to the threat.
Recent studies have shown that fish are clever than we think. A link to BBC audio:
I have used fish for studying activation of immediate early genes (IEG) c-Fos and EGR-1 due to stress and aggressive behavior. Believe me, they are excellent to work with. They don’t bite but you have to put your hands in cold water to net them 😉 The fish species i used was Rainbow trout which is a freshwater salmonid fish. When you put a pair of rainbow trout together they would fight for food, mating with the females, occupying territory and maintaing their social hierarchy. The dominant male usually gets a chance to mate with the females. Due to social interaction, the fish were stressed and one of them became dominant and the other subordinate. After 5 days of social interaction the fish were sacrificed and it was found that the subordinate fish expressed more amount of both the IEG in the telencephalon and optic tectum region of the brain.
I also wanted to see if there exists any behavioral difference between juvenile males and females. Therefore, i did another social interaction study and found the dominant-subordinate relation existed from juvenile stage. Any guess who was more dominant (male or female)? Well, the males were more dominant than the females winning more no. of social interaction or fish fights as compared to females.
To conclude, i would like to say fish are growing as model organisms and many scientists have started considering to used fish in research over rats and mouse. The only question i always think of is how can we transform the data that has been generated using fish into humans? But nevertheless, if you get a chance to work with fish then go for it.
Some of the famous fish biologists are Prof. Svante Winberg (Uppsala University), Prof. Lynne Sneddon (University of Liverpool), Prof. Wendelaar Bonga (Radboud University), Prof. Wolfang Driver (University of Freiburg) and Prof. Rui Olivera (Champalimaud University). If you get a chance then do read the stress response in fish by Prof. Bonga (Link given below)