Estimating fish sizes in captivity

[Aquarist007]

<a href=showthread.php?s=&postid=15023118#post15023118 target=_blank>Originally posted</a> by JHemdal
I would like to expound a bit on my work on maximum fish sizes in captivity. There seems to be some confusion about the study. Although only 19 fish met the criteria as outlined in the project, fully 2300 fish were analyzed as candidates, it is just that 2281 of them did not meet the strict criteria:

"None of them has grown appreciably in the past two years, and all have been in captivity at least 5 years (the range was 5 to 20 years)."

Also, the ONLY conclusion that I drew from this is that the maximum size of fish on FISHBASE tends to run larger than what is seen as a maximum size in captivity - to the extent of it being 66% of that value. Remember that FISHBASE lists the maximum recorded size for a fish - not the normal adult size. Their sample size (taken from the literature) is just ONE fish. They also tend to "round up" their numbers. Think of their max size as the record size for that species.

This was just a starting point. The problem is getting enough additional data. How many fish in your own aquariums would meet the criteria? Still, I think we can safely say that stating the Fishbase maximum size as being the "adult size" for fish (as is often done on message boards) will be less precise than using a figure of say, 75% of that value.

Finally, there is still no real way (yet) to use the size of a fish and calculate what size aquarium that fish will need....so what does it really matter if you say that a particular fish will reach the Fishbase max. size or only 66% of that value, you still don't have any real way to objectively apply that information...


Thanks,

Jay

Thank you Jay--it's a honour to have you join this thread.

In your expertise what observations should one use to decide then a particular tang for eg is too big for its current home and you either need to upgrade or find the tang a new home?

 

[JHemdal]

Capn'

Well, that's the "64 thousand dollar question", isn't it? As you've read, I have certain minimum health / well-being criteria that I look for in captive fishes, but those may not be the only metrics to use; I'm still searching for others. I've only seen a couple of real-world examples where a fish died DIRECTLY because it was housed in too small of an aquarium. Less obvious would be those fish housed in too small of an aquarium, and then suffer from "quality of life" issues, but don't actually die as a result. As I've said, if "quality of life" is the sole driving issue for people, then perhaps the safest course of action might be to leave the fish in the wild. (But then what about predation?) Since as aquarists, we do not leave fish in the wild, what is the "next best thing"? I'm not sure I know....but I'm working hard every day, to try and understand what it is...

Jay

 

[Aquarist007]

<a href=showthread.php?s=&postid=15023825#post15023825 target=_blank>Originally posted</a> by JHemdal
Capn'

Well, that's the "64 thousand dollar question", isn't it? As you've read, I have certain minimum health / well-being criteria that I look for in captive fishes, but those may not be the only metrics to use; I'm still searching for others. I've only seen a couple of real-world examples where a fish died DIRECTLY because it was housed in too small of an aquarium. Less obvious would be those fish housed in too small of an aquarium, and then suffer from "quality of life" issues, but don't actually die as a result. As I've said, if "quality of life" is the sole driving issue for people, then perhaps the safest course of action might be to leave the fish in the wild. (But then what about predation?) Since as aquarists, we do not leave fish in the wild, what is the "next best thing"? I'm not sure I know....but I'm working hard every day, to try and understand what it is...

Jay

it's the double edged sword of this hobby---reefers are always searching and asking for absolutes when there are probably few if any.

I just happy now that the mimimum size criteria is being challenged.

 

[sufunk]

<a href=showthread.php?s=&postid=15024648#post15024648 target=_blank>Originally posted</a> by capn_hylinur
it's the double edged sword of this hobby---reefers are always searching and asking for absolutes when there are probably few if any.

I just happy now that the mimimum size criteria is being challenged.

I find it odd that you are so willing to "challenge" the minimum size criteria

Is this because you dont believe it and are therefore not following it and love the idea of "challenging" it???

When i tried to "challenge" your notion that hyposalinity is 100% necessary for EVERY case of ich or most likely ALL of your fish would die, you and waterkeeper dismissed that as complete nonsense. So much so that my posts with an alternative view were actually removed from the thread and buried in a different thread. Then, "challenging" your established viewpoint was dangerous and not valid in your view.

Then your argument was basically that this is the accepted way and you view challenging it is not valid or appropriate. Now, your argument is completely different. Seems you dont practice what you preach unless it is YOUR belief.

Keeping tangs in tanks smaller than the established minimums is dangerous at best. You and maybe some others might get away with it but you are just encouraging people who probably dont have the necessary experience or tank to think it is fine to cram it full of tangs. The odds are NOT with those people

 

[JHemdal]

All,

For what its worth, (and I understand that I'm bringing back a two month old thread, that is pretty much dead here) I've developed a more accurate means to measure the length of fish in-situ using twin laser pointers and a digital camera. This process does away with the issue of refraction, which causes fish in aquariums to appear 30% larger than they really are when viewed outside the aquarium.

While I don't expect every home aquarist to rig up something like this just to measure their fish, it may have applications for public aquarists and some advanced hobbyists. The link to the information is here:

http://microcosmaqx.typepad.com/jay_hemdal/


Thanks,

Jay

 

[jadeguppy]

I'm glad someone mentioned growth surpressing hormones. This was something often spoken of when discussing the breeding of fw fish. Perhaps because of the shorter lifespan of many of the fw fish that were looked at it was easier to determine. However, the one thing that stuck out in my mind was that crouded fish will release a stress hormone that surpresses growth. In the short term this is helpful to keep the fish from overgoring a limited space. When the next rain comes the fish are free to grow larger. One of the side effects of keeping such fish in small tanks long term was spinal admoralities such as curvatures. I have to seriously wonder if this is also what is happening to sw fish, just on a slower time schedule due to the longevity of the sw fish we keep as compared to many of the fw fish that are kept and studied by breeders.

Also, the idea that we can't provide tangs with constant grazing doesn't make sense. I grow macro algaes for nutrient uptake, but also for tang food. My tang loves to graze on a ball of cheato or other algae all day long. Eventually she manages to eat it at a rate that outpaces the growth and I have to add more, but it keeps her fat and healthy. I have noticed some behavior changes when I don't keep a constant source of food int he tank for her. Particularly what could be described as an increase in begging for food.

 

[Aquarist007]

<a href=showthread.php?s=&postid=15370681#post15370681 target=_blank>Originally posted</a> by JHemdal
All,

For what its worth, (and I understand that I'm bringing back a two month old thread, that is pretty much dead here) I've developed a more accurate means to measure the length of fish in-situ using twin laser pointers and a digital camera. This process does away with the issue of refraction, which causes fish in aquariums to appear 30% larger than they really are when viewed outside the aquarium.

While I don't expect every home aquarist to rig up something like this just to measure their fish, it may have applications for public aquarists and some advanced hobbyists. The link to the information is here:

http://microcosmaqx.typepad.com/jay_hemdal/


Thanks,

Jay

Very interesting invention and article Jay, thanks for posting and revising the thread. I am sure others will find this interesting and pratical also.

 

[Aquarist007]

<a href=showthread.php?s=&postid=15370943#post15370943 target=_blank>Originally posted</a> by jadeguppy
I'm glad someone mentioned growth surpressing hormones. This was something often spoken of when discussing the breeding of fw fish. Perhaps because of the shorter lifespan of many of the fw fish that were looked at it was easier to determine. However, the one thing that stuck out in my mind was that crouded fish will release a stress hormone that surpresses growth. In the short term this is helpful to keep the fish from overgoring a limited space. When the next rain comes the fish are free to grow larger. One of the side effects of keeping such fish in small tanks long term was spinal admoralities such as curvatures. I have to seriously wonder if this is also what is happening to sw fish, just on a slower time schedule due to the longevity of the sw fish we keep as compared to many of the fw fish that are kept and studied by breeders.

Also, the idea that we can't provide tangs with constant grazing doesn't make sense. I grow macro algaes for nutrient uptake, but also for tang food. My tang loves to graze on a ball of cheato or other algae all day long. Eventually she manages to eat it at a rate that outpaces the growth and I have to add more, but it keeps her fat and healthy. I have noticed some behavior changes when I don't keep a constant source of food int he tank for her. Particularly what could be described as an increase in begging for food.

I use a pole feeder to provide constant grazing for my tangs. Very simply it consists of a piece of pvc with two elastics. I use romaine lettuce, nori, kelp, broccoli ect which they love to go at all day.
I never thought of using the chaeto however because I had read somewhere that it can affect the digestive system of some fish.
But with your success using it I'll try it again--thanks

A pole feeder:
http://www.reefcentral.com/wp/?p=291