Damselfish Observation Experiment

[NewbFish]

Hello!
I am kinda new to this whole forum thing, (i hope i didnt mess up and post this twice or in the wrong place!) but I figured I would come to the experts with my question.

I am a biology student in my senior year at college and currently am taking a class on animal behavior. Our end of semester assignment involves a project where we choose an animal and form a hypothesis about an aspect of its behavior and then spend time observing it in detail.

Basically the question I posed was: Are fish inclined to more aggressively chase other species rather than their own kind? I chose to work with three types of damsels: 10 Blue Damsel (Pomacentrus coeruleus), 5 Yellow-Tail Damsel (Chrysiptera parasema), and 10 three stripe damsels (Dascyllus aruanus).


The blue damsels (the larger fish in the tank) were HIGHLY aggressive to the yellow tails, but only mildly aggressive to their own species.

What I don't understand is that both the blue damsels and the yellow tails completely ignored the three stripe damsels (which tended to stay near the middle of the tank whereas the other two inhabited the lower areas).

I did a little research and found that the three stripes live in a slightly different area of the indo pacific as compared to the other two. Is this the reason why they are being ignored??

If anyone has any ideas they would be much appreciated!

God bless!

-Dan

PS: None of the fish were harmed AT ALL! We didn't even take pictures so as to not scare them with the flash

 

[littleme1969]

Most damsel fish in general are agressive to be honest. Alot depends on the age of the fish also as they grow the agression does increase with age. Once full adult they can be a real handfull and will have a go at anything in the tank including fish twice their size. If purchased together as a group of the same age they will tend to swim together in their own species as a shoal. This is true of the yellow tail as ive seen many people on here have them in groups and they get on well. The plain blues from what I know are one of the most agressive species of damsel so I would expect them to be trouble. The stripes as yougsters are really quite shy little guys prefering to hang out in safe spots away from the trouble, but this does change as the fish reaches adulthood and they too can become agressive.
I would think the behaviour of the fish to each other and to other species can not be determined in a short space of time. There are many variables to their behaviour including tank size how much if any cover/rock work there is. If they where all added at the same time, if they where all the same age etc. All of these things will effect the outcome. You would also have to factor in if the fish where tank raised or caught in the wild too
Lets face it placing 3 groups in a large tank and watching them is not a fair situation, as all the fish will be both stressed and frightened and not behaving as the would naturally in the wild, in a situation that they where born into.

This has probably been no help at all to you ...lol but its just my own observation as a fish keeper for 8 years and reef keeper for 1 year

 

[NewbFish]

hehe thanks! It actually does help a lot. yeah i really wish i was able to use a larger, established tank

The age factor of the fish totally escaped me! It actually clears a lot of trouble spots up. Much appreciated!

-Dan

 

[jeasko]

also dont overlook the fact that the blue damsels and the yellow tails are similar in shape where as the striped damsels are a slightly different shape, sounds odd I know but in my experience if fish look different they are less of a threat than those that are the same shaped hence the stiped damsels are less aggressive to the other damsels and are pretty much left alone by the other damsels in the tank, this is not unique to damsels as angel fish can be the same to.