Estimating fish sizes in captivity

[Aquarist007]

Estimating fish sizes in captivity:

Here is a great article/study an estimating maximum sizes of fish in captivity by Jay Hemdal:

http://microcosmaqx.typepad.com/jay...-of-fish-in-captivity-an-estimation-tool.html

His conclusion was:
I found the fish in the group had reached their maximum captive size in a range from 45% to 91% of the maximum FishBase size for each species. The average was 66% "


He also stated that in the past people relied soley on this database for fish:
http://www.fishbase.org/search.php


and suggests we use the 66 per cent formulae with it


I am anticipating that we can have a good discussion on this

 

[Aurora D.]

I've always wondered why the reef sellers only posted maximum size instead of both maximum and average size. Thanks for the link, it really helps in estimating bio-load.

EDIT: On the other hand, the sample size is a little smaller than I would like and I would assume that since this is one source it might depend highly upon the amount of food they tend to feed.

 

[Paul B]

This is interesting, I know many people do not think that fish are stunted in captivity but that is because many people do not dive. Most of the fish we commonly keep in a tank get huge in the sea.
I have had hippo tangs and yellow tangs for over ten years and they never get larger than about 6" in my 100 gallon tank. I had a hippo for about 5 years in a 40 gallon tank and he got to about 4". In the sea I have seen them about 10" long.
Look downs get huge as do panther groupers. Forget about moray eels. I have seen those over 10' long. One of them bit a guy I was diving with and he got the guys arm into his mouth almost to his elbow.
Even clownfish get huge. My 16 year old fire clown is very healthy and spawning but he is only about 3".

If a fish is spawning ,that fish is as healthy as he is going to get. If they are not spawning or attempting to spawn they are not very healthy and are subject to diseases and being stunted.
We as people can "spawn" a couple of times a day even if we sit around and eat potato chips all day. Fish do not work like that.
They need different food to become healthy but can "live" a long time in reduced health with other foods

 

[Aquarist007]

<a href=showthread.php?s=&postid=14937433#post14937433 target=_blank>Originally posted</a> by Paul B
This is interesting, I know many people do not think that fish are stunted in captivity but that is because many people do not dive. Most of the fish we commonly keep in a tank get huge in the sea.
I have had hippo tangs and yellow tangs for over ten years and they never get larger than about 6" in my 100 gallon tank. I had a hippo for about 5 years in a 40 gallon tank and he got to about 4". In the sea I have seen them about 10" long.
Look downs get huge as do panther groupers. Forget about moray eels. I have seen those over 10' long. One of them bit a guy I was diving with and he got the guys arm into his mouth almost to his elbow.
Even clownfish get huge. My 16 year old fire clown is very healthy and spawning but he is only about 3".

If a fish is spawning ,that fish is as healthy as he is going to get. If they are not spawning or attempting to spawn they are not very healthy and are subject to diseases and being stunted.
We as people can "spawn" a couple of times a day even if we sit around and eat potato chips all day. Fish do not work like that.
They need different food to become healthy but can "live" a long time in reduced health with other foods

thanks Paul--as always your posts are appreciated

The author sited above also made a similar comment to yours

"If the fish shows no signs of chronic disease or abnormality, exhibits normal feeding and reproductive behaviors and most importantly, exhibits a normal lifespan compared to that of wild counterparts (minus the predation that wild fish incur of course!), then there is no other metric we can use to determine if a certain suite of husbandry techniques are suitable or not."
http://microcosmaqx.typepad.com/jay_hemdal/2009/01/beware-the-tang-police.html

 

[Aurora D.]

I still think that size has a lot to do with what we feed our fish.

 

[sikpupy]

I am going with "amount". Muscle builders do not get thier bulk from breathing air, nor does Michael Moore. Well, then again, he is kind of full of hot air.

 

[LobsterOfJustice]

It seems like people are taking this as "they dont get as big in our tanks, so it's okay to keep them in smaller tanks".

To me, this is indicating "they have stunted growth in our tanks, we should be striving to keep them in proper sized tanks to avoid this."

As far as I know, we don't really see this happening often in smaller fish like dwarf angels, gobies, etc. Or at least, it isnt discussed. Could it be because we keep these fish in appropriately sized tanks which avoids, or minimizes, stunting their growth?

I can speak from experience, I kept a majestic angel, mimic tang, and scribbled rabbit all for at least 2 years (some as long as 4) and none of them grew a cm in my 75/90 gallon tank during that time. They all remained about 4"-5". I KNOW in the wild these fish do not stay this size for years at a time. If you have ever seen any of these fish in a huge tank, or in the wild, you would understand how big they get. They obviously aren't going to get that big in a small tank - they will just dwarf themselves and live a strange, dwarf, stunted life. The other problem is many species of tangs are naturally found in groups - and I personally HATE keeping fish in conditions far from their natural state. Butterflies are another example - always found in pairs in nature.

I just think we have a responsibility to provide the fish we keep with the BEST conditions we can, afterall, we are ripping them out of the perfect conditions. People will disagree with me, whatever. But I just like to see fish kept in close to natural conditions. I try to consider how much ground a fish would naturally cover in a given time period. Considering this, almost every fish we keep is not appropriate for the average home tank. But, considering tangs will cover 10' with one flick of the tail, in 5 seconds, and a hogfish will slowly scoot around, looking in all the nooks and crannies, etc, maybe that's a more appropriate fish for home aquariums. Just a different swimming pattern and body size. I sold the fish I mentioned earlier and restocked the tank with numerous, small fish. Looks much more natural, lets me have more fish, the tank looks more "in proportion," the list goes on.

All this said - I have a desjardini in my 90. I've only had him about a year (and, as the fish mentioned earlier, hasnt grown at all) - and I was planning an upgrade. Plans have changed, and I am currently actively seeking a new, proper home for him (I know a maintenance company with accounts that have 300+ gallon tanks).

If you take a 4"-5" tang, angel, rabbit, or butterfly and put it in a 4' tank you will likely notice little to no growth indefinitely. Put the same fish in a 8' tank and it will probably reach 10" within two years. That indicates an issue to me.

I have a problem with the study - going off the same basis, giving my example of the three fish mentioned earlier. Are we just going to call the home sizing for majestic angels, rabbitfish, and mimic tangs 5"? And then be happy with that? They haven't grown in 2,3,4 years. But they would have if they were put in a 300g originally. And possibly growth would resume if placed in a larger tank after a period of stunting.

Anyway, I don't know what it all means. All four of the fish mentioned seemed/seem healthy and happy. But I just have an aversion to knowing I'm causing problems like stunting my fish... we don't know what it does. I just feel like I'm responsible for giving the fish the best conditions possible, and to me that means most like the environment they come from. If we are doing something to cause these fish to stray form their natural condition, I think it's wrong, wether it be size, coloration, behavior, etc.

 

[Aquarist007]

<a href=showthread.php?s=&postid=14938398#post14938398 target=_blank>Originally posted</a> by LobsterOfJustice
It seems like people are taking this as "they dont get as big in our tanks, so it's okay to keep them in smaller tanks".

To me, this is indicating "they have stunted growth in our tanks, we should be striving to keep them in proper sized tanks to avoid this."

As far as I know, we don't really see this happening often in smaller fish like dwarf angels, gobies, etc. Or at least, it isnt discussed. Could it be because we keep these fish in appropriately sized tanks which avoids, or minimizes, stunting their growth?

I can speak from experience, I kept a majestic angel, mimic tang, and scribbled rabbit all for at least 2 years (some as long as 4) and none of them grew a cm in my 75/90 gallon tank during that time. They all remained about 4"-5". I KNOW in the wild these fish do not stay this size for years at a time. If you have ever seen any of these fish in a huge tank, or in the wild, you would understand how big they get. They obviously aren't going to get that big in a small tank - they will just dwarf themselves and live a strange, dwarf, stunted life. The other problem is many species of tangs are naturally found in groups - and I personally HATE keeping fish in conditions far from their natural state. Butterflies are another example - always found in pairs in nature.

I just think we have a responsibility to provide the fish we keep with the BEST conditions we can, afterall, we are ripping them out of the perfect conditions. People will disagree with me, whatever. But I just like to see fish kept in close to natural conditions. I try to consider how much ground a fish would naturally cover in a given time period. Considering this, almost every fish we keep is not appropriate for the average home tank. But, considering tangs will cover 10' with one flick of the tail, in 5 seconds, and a hogfish will slowly scoot around, looking in all the nooks and crannies, etc, maybe that's a more appropriate fish for home aquariums. Just a different swimming pattern and body size. I sold the fish I mentioned earlier and restocked the tank with numerous, small fish. Looks much more natural, lets me have more fish, the tank looks more "in proportion," the list goes on.

All this said - I have a desjardini in my 90. I've only had him about a year (and, as the fish mentioned earlier, hasnt grown at all) - and I was planning an upgrade. Plans have changed, and I am currently actively seeking a new, proper home for him (I know a maintenance company with accounts that have 300+ gallon tanks).

If you take a 4"-5" tang, angel, rabbit, or butterfly and put it in a 4' tank you will likely notice little to no growth indefinitely. Put the same fish in a 8' tank and it will probably reach 10" within two years. That indicates an issue to me.

I have a problem with the study - going off the same basis, giving my example of the three fish mentioned earlier. Are we just going to call the home sizing for majestic angels, rabbitfish, and mimic tangs 5"? And then be happy with that? They haven't grown in 2,3,4 years. But they would have if they were put in a 300g originally. And possibly growth would resume if placed in a larger tank after a period of stunting.

Anyway, I don't know what it all means. All four of the fish mentioned seemed/seem healthy and happy. But I just have an aversion to knowing I'm causing problems like stunting my fish... we don't know what it does. I just feel like I'm responsible for giving the fish the best conditions possible, and to me that means most like the environment they come from. If we are doing something to cause these fish to stray form their natural condition, I think it's wrong, wether it be size, coloration, behavior, etc.

I lobster of justice--its a pleasure to have you on this thread I hope your career is going well. I am thrilled when a marine biologist, chemist, or someone with the years of experience like Paul B or Water Keeper takes the time to post and help poor peon reefers like myself.

I was interpreting his articles to be more on the line that if the fish appear healthy active, are spawing ect(as Paul B) mentioned that we shouldn't make inferences that we are causing harm to the fish we keep.

I ask you, being a marine biologist, if there is any evidence reported that a fish that has grown only to 66% of its natural adult size is indeed not healthy or their has been some damage done to its internal organs.
One of the cautions that Jay Hemdal mentioned was to be careful and define the word happy in human terms when it comes to describing fish

 

[Paul B]

The author sited above also made a similar comment to yours

Yes Capn, but he stated much more elequently.

As for fish with stunted growth being in a less healthy state, I don't think so. A mammal I think if it were stunted by confinement would have a problem but not a fish in certain circomstances. (That word just does not look correct)

As I said, as long as a fish is spawning, it is healthy. Only fish in the best health which are not stressed will spawn. It is hard to tell with a fish like a tang which will probably not spawn in a tank but if your tangs are living for 10 years or more and they look like they have all their scales and clear eyes, and not suseptable to maladys like ich they are also probably healthy even if dwarfed. I am sure they would be better off if they were in the sea but then we would not have a hobby. No tank is larger enough for a tang. If you follow these things in the sea, you will not be able to keep up with any of them on their 100 yard jaunts around the reef.

 

[Aurora D.]

<a href=showthread.php?s=&postid=14938803#post14938803 target=_blank>Originally posted</a> by Paul B
Yes Capn, but he stated much more elequently.

As for fish with stunted growth being in a less healthy state, I don't think so. A mammal I think if it were stunted by confinement would have a problem but not a fish in certain circomstances. (That work just does not look correct)

As I said, as long as a fish is spawning, it is healthy. Only fish in the best health which are not stressed will spawn. It is hard to tell with a fish like a tang which will probably not spawn in a tank but if your tangs are living for 10 years or more and they look like they have all their scales and clear eyes, and not suseptable to maladys like ich they are also probably healthy even if dwarfed. I am sure they would be better off if they were in the sea but then we would not have a hobby. No tank is larger enough for a tang. If you follow these things in the sea, you will not be able to keep up with any of them on their 100 yard jaunts around the reef.

I agree.

 

[jenglish]

<a href=showthread.php?s=&postid=14938803#post14938803 target=_blank>Originally posted</a> by Paul B
Yes Capn, but he stated much more elequently.

As for fish with stunted growth being in a less healthy state, I don't think so. A mammal I think if it were stunted by confinement would have a problem but not a fish in certain circomstances. (That word just does not look correct)

As I said, as long as a fish is spawning, it is healthy. Only fish in the best health which are not stressed will spawn.

I have to question if spawning = health. We have stated it does not have to for humans. Some simpler organisms can be "scared" into reproducing such as anemones or apple trees. In this way less than optimum conditions are seen as a reason to try to pass on DNA. Could spawning be a sign that conditions are prime for the offspring.... and not mean the adult is at optimum health. Obviously there has to be a certain level of health for them to have the energy to breed, but I am not sure a stunted fish can be said to be healthy simply by breeding.

Then we can get into a discussion of the definition of health. Animals will live longer in captivity... but is longer life the definition of health? Are they less stressed when easily fed and free from predation? probably. Ok.. now I am just rambling off topic.

 

[Aquarist007]

<a href=showthread.php?s=&postid=14938935#post14938935 target=_blank>Originally posted</a> by jenglish
I have to question if spawning = health. We have stated it does not have to for humans. Some simpler organisms can be "scared" into reproducing such as anemones or apple trees. In this way less than optimum conditions are seen as a reason to try to pass on DNA. Could spawning be a sign that conditions are prime for the offspring.... and not mean the adult is at optimum health. Obviously there has to be a certain level of health for them to have the energy to breed, but I am not sure a stunted fish can be said to be healthy simply by breeding.

Then we can get into a discussion of the definition of health. Animals will live longer in captivity... but is longer life the definition of health? Are they less stressed when easily fed and free from predation? probably. Ok.. now I am just rambling off topic.

you didn't finish the quote
"It is hard to tell with a fish like a tang which will probably not spawn in a tank but if your tangs are living for 10 years or more and they look like they have all their scales and clear eyes, and not suseptable to maladys like ich they are also probably healthy even if dwarfed."

which makes perfect sense to me
(PaulB always makes sense when individually postings as does his companion the water keeper. Get the two together however and who knows what the heck they are saying:lol: :rollface: :lol: )

 

[DamnPepShrimp]

<a href=showthread.php?s=&postid=14938398#post14938398 target=_blank>Originally posted</a> by LobsterOfJustice
It seems like people are taking this as "they dont get as big in our tanks, so it's okay to keep them in smaller tanks".

My biggest problem with this "study" and why I don't like it. This is just asking for people to keep tangs in 30g tanks. If I remember correctly, Jay was working on figuring out proper tank sizes for fish, and what he came up with was way undersized. There are way to many people over stocking their tanks with fish that belong in tanks 3-10x bigger then what they have, this "study" just gives them more reason to do so and I believe its horrible for the hobby and the animals we keep. Not trying to be a downer/flame anyone, I just hate seeing fish that get huge, cramped in tiny tanks, like powder blues in 75gs etc. Its ridiculous.

 

[jenglish]

<a href=showthread.php?s=&postid=14938970#post14938970 target=_blank>Originally posted</a> by capn_hylinur
you didn't finish the quote
"It is hard to tell with a fish like a tang which will probably not spawn in a tank but if your tangs are living for 10 years or more and they look like they have all their scales and clear eyes, and not suseptable to maladys like ich they are also probably healthy even if dwarfed."

which makes perfect sense to me
(PaulB always makes sense when individually postings as does his companion the water keeper. Get the two together however and who knows what the heck they are saying:lol: :rollface: :lol: )

I was just trying to save space, the rest of the quote doesn't do any more to back up the assumption that any fish that is breeding is healthy. I can't say that it isn't true either but I think we should at least state that it is an assumption. In all likelihood it is mostly true at the very least but plenty of things besides fish will reproduce in less than ideal conditions if they get the right triggering events.

 

[Aquarist007]

<a href=showthread.php?s=&postid=14939006#post14939006 target=_blank>Originally posted</a> by DamnPepShrimp
My biggest problem with this "study" and why I don't like it. This is just asking for people to keep tangs in 30g tanks. If I remember correctly, Jay was working on figuring out proper tank sizes for fish, and what he came up with was way undersized. There are way to many people over stocking their tanks with fish that belong in tanks 3-10x bigger then what they have, this "study" just gives them more reason to do so and I believe its horrible for the hobby and the animals we keep. Not trying to be a downer/flame anyone, I just hate seeing fish that get huge, cramped in tiny tanks, like powder blues in 75gs etc. Its ridiculous.

I know there are idiots in this hobby that do inane things just are there are in other hobbies and sports ect. When I used to long distance run I would come across these obviously over weight guys struggling to stay in a race--wearing a plastic garbage back with the idea it would help lose weight:eek2:

One has to hope that anyone who has been successfull in this hobby for a few years that they would make them selves informed on key issues of coral and fish husbandry. And that the norm of them would not try a stunt like keeping a 12 inch blue in a 30 gal tank.

The discussion I am trying to encourage on this thread is more the signs we should notice that are fish are stressing out and some of the reasons for it. --for my self and others to be informed.
To me this is a key concept to know and it should limit the questions like can I keep x fish in y size of tank.

My 4 tangs are extremly colourful, active and there has never been any noticable ich in my display tank(touch wood )
I would personally like to keep them this way.

 

[Aquarist007]

<a href=showthread.php?s=&postid=14939073#post14939073 target=_blank>Originally posted</a> by jenglish
I was just trying to save space, the rest of the quote doesn't do any more to back up the assumption that any fish that is breeding is healthy. I can't say that it isn't true either but I think we should at least state that it is an assumption. In all likelihood it is mostly true at the very least but plenty of things besides fish will reproduce in less than ideal conditions if they get the right triggering events.

we both have different interpretations of Paul's post I guess.
Hopefully he will be back to enlighten

 

[Aurora D.]

I think we could just rant on and on in this particular subject (particulary determing what is happiness) and never come to a conclusion. Most of us can't even reach true happiness never the less our fish. Although, because I would deem them incapable of complex thought perhaps a safe place and plenty of food is true happiness.

 

[Paul B]

but I am not sure a stunted fish can be said to be healthy simply by breeding.

Fish are not apple trees or anemones, or urchins for that matter who will also spawn in response to envirnmental conditions, Fish are much higher up on the evolutionary scale and will not spawn due to conditions other than optimum health. A pregnant fish may release eggs early due to stress but I do not consider that spawning. Spawning is when a fish is compatable with another fish, builds a nest, lays eggs and protects them. Of course some fish do it differently but only fish in perfect condition can do this. Eggs can take up a large portion of a fishes body and a large proportion of food and energy must go into producing eggs. Most captive fish have enough trouble staying alive much less produce eggs. Have you ever heard of a fish spawning that was fed flakes or is kept in a too small tank where it is stressed or a fish with ich spawning?
Spawning in "fish" means optimum health.
Many of my fish are currently spawning, they will not do that if I stopped their nutritious live foods and substitute flakes or pellets.
I just came back from a Speaking trip to California where we were away for a week. I had someone take care of the tank and I gave them frozen food in measured portions to feed the fish.
A pair of gobies which were ready to spawn when I left lost the urge on this diet and she even seems to have re absorbed her eggs. Now that I am back and the fish will be back on a much better diet of worms and live shrimp I am quite sure in a few weeks she will again start spawning as she has been doing for a couple of years. Fish do not seem to have much capacity to store up nutrients like we do in fat.
Also it is very easy to get fish into breeding condition even in a smaller tank if you can get certain nutrients into them.
Many fish will adjust to a smaller tank if they do not feel threatened and are fed proper foods, not flakes and pellets which will certainly keep them alive but they will be suseptable to ich, bacterial infections and a host of other things.
Dwarfing fish slightly IMO does not affect ther health as I have had fish before larger tanks were common. In the seventees a 20 gallon tank was considered large. I spawned clownfish in a 10 gallon tank. Even after 12 years the clownfish remained smaller than they should have been but it did not seem to effect their health.
I am not a fish biologist and can only go by my fifty years of experience keeping, collecting and breeding fish. I could be wrong but you can't compare fish to apple trees, urchins, birds, dogs or humans. Fish are a totally different animal with different needs. If you have a breeding fish, you have a healthy fish.

I think we could just rant on and on in this particular subject (particulary determing what is happiness) and never come to a conclusion. Most of us can't even reach true happiness never the less our fish.

Actually, I am almost always happy, especially when no one is shooting at me

 

[jenglish]

It does get back to what the definition of health is on a certian level. I think breeding is 1 sign of a very short time period of health, where stunted growth some would argue could be seen as a long term sign of health. WOuld a fish that was stunted have survived and gotten a mate if it had been in the wild? I have heard people say they had a fish that still likely had ich in it's mucous membranes and gills but was breeding. Some would say it is a healthy specimen because it is breeding and others would say it is not because it has an infection that could be fought off or could under the wrong conditions be fatal.

As far as fish nutrition, I know some FW fish can store fat but cannot access it well. SOme cichlids fed the wrong diet get fat but putting them on a fishy diet will starve them to death but will not burn any significant portion of that fat. So nutritionally the health of a fish is essentially a here and now factor. I'm sure chronic malnutriont could have some poor effects as well, but that would just be speculation.

 

[NexDog]

Paul, my Bangaiis are spawning regularly and I have 3 babies from 3 different spawns and I feed flake, pellet and frozen mysis. But then again I never saw my Clarkii pair spawn (and then the male jumped) and they were together 4 years.