Zebrafish Study Help - Food

[shrimply]

OK I know this might not be the more suitable place, but I know you guys know your fish better than anyone else. And I'm hoping this is a case of experience beating literature ( which is proving useless).

Basically my honours project involves zebrafish, or zebra danio, or Danio rerio. But what I could really do with to finish it off is a dominance rank for each fish, and due to the setup the only feasible trial is a feeding one.

The problem is, even in groups when taken out of their home tank they are very reluctant to feed, regardless of accumulation time, or how dark the tank is etc. So I'm hoping some of you can share what foods your danios go crazy for. Either in the form of processed food or otherwise.

So far we've tried brine shrimp ( they'll take smaller ones of these in the home tank), bloodworm ( which they won't take in any case), aquarian flake (but they are not really surface feeders)and some other small sinking pellets. Already on the list to try is live daphnia which couldn't be sourced today but this may be too hard to see.

Any help greatly appreciated.
Cheers

 

[thereverendturtle]

I don't know if its available in Scotland, but cyclops-eze is bright red and irresistible to most fish.

 

[shrimply]

Thanks, a quick google search suggests I probably won't be able to source these, at least not in the time I need to.

I sort of thought I'd get more suggestions, but maybe there is no hope that anything will work *sigh*

 

[ZoddyZod]

crushed peas?

my zebra danios used to love them.

 

[thereverendturtle]

Yeah I read it and thought it weird you didn't have a bunch of responses.
The only other thing I can think of would be live brine shrimp or black worms.

 

[TwoTankAmin]

As a psych major who did the traditional rat experiments, I can tell you there is a little trick involved. In order to make fish want to eat, you need to starve them some first. Nothing motivates an animal to eat like being hungry. Simply do not feed them for a couple of days before you move them into the experimental tank.

The one potential problem is that when a fish is hungry, it may not behave normally in its quest to eat. I keep a school of rummy nose tetras in with my altum angels. The rummys always keep well clear of the angels until its feeding time. Then all caution is thrown to the wind and they are darting in and around the angels grabbing food. Hunger trumps fear. So a hungry fish, normally less dominant, may throw caution to the wind when it comes to food and will ignore the fact that another fish is higher in the normal pecking order. This could throw off your results.

 

[shrimply]

Thanks guys, but we gave up.

They wouldn't eat outside the home tank, at least not in the acclimation time we have available, and in the home tank they really only take food from the water column, which makes it hard to score.

Excuse the anthropomorphism in this explanation...
Starving the fish is all very well, but you are equally likely to identify the greediest fish, or hungriest fish, or one that needs the most food, rather than the most dominant. Sure the fish need to be hungry but starving would lead to dodgy results. In much the same way the experiment was decided to be a failure because the fish won't feed as normal out of their home tank, and therefore the first fish to feed is more likely to be the boldest and first to overcome the novel environment rather than a good measure of dominance.

 

[TwoTankAmin]

I may have been unclear in how I put things. In research terms starve doesn't mean quite the same thing it might mean in a non research setting. It refers to the process of withholding food make the fish hungry, this way hunger serves as the motivational factor. And I did say in the setup you described this might have undesirable consequences that make the results uncontrolled.

What I should have added is your design was faulty for exactly the reasons you indicated. Hunger is more effective when it is used to observe the behavior in single subjects or when you want to compare the behavior of a well fed subject vs a hungry one.

Good food wont make a fish who is not hungry eat. Hunger, however, will make most fish eat things they normally might not.

I could suggest a few way to design an experiment to measure dominance, but the biggest challenge would be in designing a way to differentiate the fish from each other as it would require keeping them in a group rather than pairs. Then there are specific behaviors you could observe over some time which would clearly indicate the pecking order.

 

[shrimply]

I'm gonna tell you know that we could argue/discuss this all day, you're a psychologist, I'm a behavioural ecologist. And the views, while over lapping are distinct. Trust me I know, its been a big issue while doing my research.

Dominance rankings were really to supplement the study, and they are not essential. And I know plenty about the ways that researchers traditionally run dominance trails on fish, many of which are not possible for numerous reasons. Running dyads on all the fish is not practical time wise, especially given the acclimatisation period. There are numerous issues involved such as whether aggression=dominance, which it probably doesn't for zebra danios. In theory, feeding is a good, sex inspecific way of measuring dominance, in a group which has an established hierarchy the more dominant fish should get the pick of the food. Or at least we could soundly argue that to be the case.

It really comes down to time which I don't have enough of, but there is also the case of avoiding a subjective study where an ethogram is used to score different behaviours. Which usually require less powerful non-parametric analysis.

I understand what you are saying about starving, but what we want is a healthy feeding response as we would get in a home tank, not an artificially created hunger driven one. Something that should technically be possible if the fish calmed down enough, but they are not playing ball.

 

[TwoTankAmin]

Well, in the wild fish do not eat daily. So they are normally wired to eat as much as they can when the opportunity arises. Of course they do get full when there is more food available than they can eat. Moreover, many fishkeepers will normally do one starve day a week or more in their tanks. I am one. The only fish not subjected to this are relatively new fry. It does not harm the fish and many of us feel is it actually is good for them. And what about fish who live under seasonal conditions where food is more available at certain times of the year while at other times it is much scarcer? I would suggest that your argument of test almost guarantees results which are not based on what is natural but rather an artificial construct created by the researcher.

what we want is a healthy feeding response as we would get in a home tank, not an artificially created hunger driven one

I never realized that fish ate when they were not hungry. Please educate me as to what motivates any living creature to eat if it is not hunger? Does it matter if the fish is hungry because it can not find food in the wild or if it is hungry in a tank because it has not been fed for the same amount of time? How do you know a fish is hungry? The answer is really simple, don't feed it (aka starve time where starve means no food given, not that the fish has been deprived of food to the point where it is causing health type issues).

When it comes to dominance in fish groups the conventional wisdom is often that the fish with the most body mass tends to be the most dominant. I have been spawning plecos for a number of years and I do so in groups rather than pairs or trios. My main focus has been on zebra plecos. One of the things I learned over the years and which I have confirmed with conversations with other breeders was a surprise initially. The alpha male of our groups was usually not the biggest one. It was usually the second biggest.

For me is was clear from spawning behavior. I had two males spawning every 30 days or so but two weeks apart. What I was able to observe was that the smaller alpha male was the first to spawn when the season began and then he also would spawn a couple of time at the end of the season while the slightly larger male stopped. Also, the smallest females rarely got to spawn with anybody.

Moreover, there are actually three distinct groupings. First there is the whole colony, which included both sexes. Who gets to occupy a given space or to eat will be based more on the whole group dynamic regardless of sex. But then there are the two sexual sub groups. Males compete for the best spots to spawn. But the females also develop their own pecking order in terms of who will get to spawn with the most desirable males. So which way is best for trying to measure a group dynamic in terms of dominance?

Finally, when it comes to the dynamics of fish. I feel in many areas of study is is almost impossible to observe natural behavior in a tank. Fish are not real smart, but they do learn. In the wild, fish are not going to come to the surface and beg for food when they see a human, but they will learn to do this in a tank. Finally, how does one even begin to study fish which are so small, active and live in good sized groups.

Pardon my sense of humor, but who is in charge here (not my video)?

I wish you good luck in your future research. I am decades away from mine and am now merely a fish keeper who learns by casual observation not experimentation.