Maximum Size of Fishes

[JHemdal]

All,

As a side project to one that I'm working on to quantify swimming room required by fishes, I looked into the predicted maximum size to which fish will grow in captivity. Many of us use FishBase for their maximum size records, and extrapolate captive size estimates from that data. The problem is two-fold, first their records are for maximum sizes recorded, not normal adult size - and second, I had a strong feeling that many fish do not grow as large in captivity as they can in the wild.

What I did was measure the current size of a group of fish in a public aquarium collection. These fish were selected for the criteria that 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). Needless to say, this was not a large sample set, but I did find 20 good candidates.

The next step was simple, express the current length of each fish as a percentage of the listed maximum adult size on FishBase. I found the 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%

So, if people are using the FishBase size to estimate how large a fish will grow in an aquarium, it is likely more accurate to use two thirds of that value as the captive maximum size.


Jay

[Recty]

That sounds about right to me :)

[regina574]

Thats some interesting information. I will keep that in mind when looking at fish.

[MrTuskfish]

IMO, LA does a fair job listing the "maximum size in captivity."

[JHemdal]

MrTuskfish,
I checked a few fish on LA and it looks to me that they are using the FishBase listing as their max. size, or in a few cases, about 90% of that. There is absolutely nothing wrong with doing that - erring on the side of caution is always better IMO. Too many dealers underestimate the adult size of fish in order to make the sale - pacu only grow to 8" is a common statement I hear from pet stores (grin).


Recty,
I should point out that I always would use about 75% of the maximum adult size in the wild as what I would expect the fish to grow to in captivity - and despite this group of fish being only at 66%, I doubt that I'll change my future estimations - better safe than sorry, right?

Jay

[MrTuskfish]

..........then there's the issue of "recommended tank size". According to some dealers, I think the answer is always "whatever size you have is fine". And then there's always the "sure, these fish will get along" generic answer.

[fender4string]

Very cool. This is good info to know. Thanks alot for taking the time to post this!

[S4lt Lif3]

the moray I have (gymnothorax moringa) they say on fish base that the max size is 200 cm, what would 2/3 of that be...?

[hotrodolds]

<a href=showthread.php?s=&postid=14459281#post14459281 target=_blank>Originally posted</a> by S4lt Lif3
the moray I have (gymnothorax moringa) they say on fish base that the max size is 200 cm, what would 2/3 of that be...?

200cm*.66=132cm=52"=4'4"

[AquaKnight]

What about the flip side of the coin? Ergh....I'm having a brain fart at the moment, but there was just talk on here, maybe reef fish, about fish growing larger in captivity then in the wild. Any one else remember that?

[LisaD]

I have a zebra moray that I've kept for about 8 years. I got it from Flying Fish express at under 24".

It has been in either a 5' 120 gallon or 6' 210 for most of that time. It hasn't appeared to grow for several years. It is just 3 feet long. Maximum size in Fishbase for Gymnomuraena zebra is 150 cm TL. My eel is 91 cm, or 60.7 % of fishbase maximum length.

For several years I overestimated the size of my eel, because it was hardly ever out all the way.

I'd be very interested in knowing what is the maximum size to expect my emperor angel (currently ~6") and blueface angel (currently ~4") to attain. These fish are in a 210, and I'd like to have them there for life, if feasible. If not, I'll either upgrade or rehome them to a larger tank when it's time. Have you found using 2/3 to 3/4 of fishbase length holds well as a rule for angelfish?

[JHemdal]

LisaD,

Using the FishBase records for the two angels, 66% of their maximum reported size would be around 10", which might a bit less than what I think they could attain in captivity. Your eel seemed to follow the rule....

AquaKnight407,
I can only remember seeing one fish that grew substantially larger than its wild counterparts. Back in the late 1970's a guy called the store I worked at and asked to bring in a large royal gramma to trade in. I said sure (BTW - max. size of this fish is 3.15" on FishBase). This guy comes in with a Royal Gramma, all faded, with deformed fins, but it was at least 6" long - maybe more. It was a real freak...


Jay

[LisaD]

That was definitely a freak gramma!

I'd think fishbase lengths also would depend on the number of fish measured. If only a few were recorded, then the size may not be representative. With more common fish, I'd expect the size reported on fishbase to be closer to a true maximum.

[S4lt Lif3]

thanks for the reply, so does that mean I can keep the spotted moray by himself in a 75g for life?

[Stuart60611]

Although this information is useful, I think it has one major flaw. Fish growth will be stunted depending upon the fish and the size system it is housed in. For example, from what I have read, it seems that omnivore or herbivore fish seem to stunt less than carnivores. As such, if you have a fish in smaller system, it will not grow to its maximum size to a degree, depending on the fish, its tankmates, and the size system it is housed in. Some fish stunt more than others. And some fish survive well in a stunted form, while others do not.

For example, triggers adult size seem to be very affected by the size system they are housed in. Also, triggers who are stunted seem to adapt well and live long lives. In contrast, large angels, such as emperors, do not stunt as much and seem to do very poorly when in a stunted form. However, the passer angel, according to Fenner, is greatly affected by the tank size. I recall recently reading a post he made to someone about housing a passer in a 125, and Fenner opined that because of the tank size the passer will likely never exceed 5 iniches.

[JHemdal]

S4lt Lif3,
As was pointed out, the data would indicate a potnetial maximum size in captivity of 52" for your eel. The data however, does not tell what size tank you need for that fish (that will be the second part of my project). Just "off the cuff", I do not think that a 52" G. moringa would be suitable for a 75 gallon tank.

Stuart60611,
Actually, I think this data DOES show the effects of stunting quite well - the fact that the captive fish in this group did not on average, exceed two thirds of their wild maximum size points to that.
Stunting, as a syndrome, has many variables, and as you point out, it can vary greatly between species. Smaller tanks stunt some fish, (triggers) but not all (sharks). Small tank size can be offset by water changes to some degree. Fish housed in overally small tanks as juveniles can remain stunted even when they are moved to a larger tank, etc.
The only real flaw in this data is the small sample size. More data, collected for more species, would show these trends a bit better.

IMO, people should not count on their fish becoming stunted and being able to survive (thrive) in that condition...you just never know.


Jay

[Gotsoup]

I would be curious to know if diet plays into this and by how much. Also if the growth is stunted and 66% to 75% of the size is a more acurate account, then is it possible that perhaps a "long livid" fish may only be attaining 66-75% of its actual life expectancy? Just some thoughts, this has been an incredibly interesting topic IMO.

[MrTuskfish]

I believe "stunting" is much more common with FW fish. FW habitats can easily become over-crowded, especially as predators are fished-out. The FW fish have learned to live in these situations by limiting growth. This is not a problem in the ocean, so I'm guessing the SW fish hasn't had a chance to make this adaptation. Unfortunately, many hobbiests, encouraged by many lfs, make the mistake of assuming stunting will enable keeping fish in a tank that is much too small.

[Stuart60611]

Well, I think saltwater fish also do stunt. My experience has been that triggers in particular seem to attain their maximum size largely dependent on the size of the tank. I have seen quite a bit of variation in the adult size of triggers that people have had for many years where I have observed those triggers housed in large tanks attain a much larger adult size than the same species of trigger housed in a smaller system.

[MrTuskfish]

<a href=showthread.php?s=&postid=14464283#post14464283 target=_blank>Originally posted</a> by Stuart60611
Well, I think saltwater fish also do stunt. My experience has been that triggers in particular seem to attain their maximum size largely dependent on the size of the tank. I have seen quite a bit of variation in the adult size of triggers that people have had for many years where I have observed those triggers housed in large tanks attain a much larger adult size than the same species of trigger housed in a smaller system.
Common sense seems to say (at least to me) that you're probably right. This topic has come up from time to time since I can remember; but I can't remember seeing any documented info. Maybe someone will find some research in this area; I'll put it on my to-do list, which means I'll get around to searching when I'm about 95.

[LisaD]

This is a very interesting topic. It would be useful to have average or median adult size in the wild, vs. maximums, to look at size in captivity vs. the ocean.

[aquaman67]

Thank you!

I got into a heated debate (that resulted in someone getting banned from RC) that a niger trigger would not get to the fish base max size of 19 inches in an aquarium.

[kirkaz]

How about diet Jay? When I first got into the hobby, I relied far too much on brine shrimp, I would think now that probably affected the growth of my fish. No fish in captivity will likely have as good a diet as they would in the wild, no matter what we give them.

[Mentat]

The following observations IRT stunting were drawn from FW large cichlids experience, but some might apply to SW fish.

Tanks lenght needs to be around 2.5 to 3 times the fish lenght (sans tail); a smaller tank can induce stunting. One early sign of stunting is a fish swimming in circles on the small tank. Lack of swimming space can cause muscular atrophy and weakening of vertebral spine resulting in curvatures and broken backs. Also, among negative effects, is internal organ malformation (they keep growing inside stunted fish) and damage.

Would be nice to produce a table with data LisaD mentioned for most common species (just an idea).

QUOTE]<a href=showthread.php?s=&postid=14465762#post14465762 target=_blank>Originally posted</a> by LisaD
This is a very interesting topic. It would be useful to have average or median adult size in the wild, vs. maximums, to look at size in captivity vs. the ocean. [/QUOTE]

Such table could be flagged and the thread originator would need to have full edit capabilities. As other members submit data it would be incorporated to table. The "sample" size should be included if available. For example, table heading could read like this (where slashes represent columns):

Species Name - Average Size Wild (sample #)/Maximum Size Wild/Average Size Captive (sample #)/Maximum Size Captive (tank size).

[kaiboshi]

I'm not sure how this applies to the topic but I think it might be worth considering...

I had an african cichlid tank 2 years ago (75 gallons), one of the first fish I picked up was a little female yellow lab. From what I could tell she was the bottom of the dominance structure in the tank she came from and she was DEFINITELY the bottom of the ladder in my tank. Not to say that she was harassed but the pecking order was obvious. All of my fish started small but I fed them very well and they all grew like weeds (some easily doubling in size) but the yellow lab didn't really grow much at all. I still have her and she hasn't grown noticably at all. She is still fed well but now she is the top of the ladder in a community tank. Did her place in the social structure stunt her growth? She had plenty of space and a great diet. Is she a runt, was she malnourished early on resulting in permanently stunted size?

Anywho, does the forced agression in captivity (fw or sw) have some kind of effect on growth potential / rate? My train of thought just farted out of my brain but I'm intrigued and shall tag along.

[reefergeorge]

PAGE TWO :D

Great thread. I here people quoteing max size way too much. Like my fish is going to grow to 20" in a year then just stop.

OT, but my old yellow lab bullied the entire tank. He went for a swim in the pipes.

[JHemdal]

So, yellow lab = yellow labeotropheus? That, or I'm envisioning these big 'ol yellow dogs paddling around in people's tanks.

I have a group of Haplochromis cichlids that we've been breeding since 1993, five generations now. They get all the nutritious food they need, but we do need to keep them a bit crowded (but the systems are flow-throughs, so the water quality is good). The problem is that they are maturing at smaller sizes each subsequent generation. I don't know if it is environmental stunting, or inbreeding depression. We have a university running DNA samples on fin clips from the fish to try to help us find out which.

Long story short, I don't know all of the possible causes of stunting, nor the degree to which certain species will stunt...and I don't think many people have looked into it before. Lots of variables I imagine.


Jay

[Elysia]

<a href=showthread.php?s=&postid=14482052#post14482052 target=_blank>Originally posted</a> by kaiboshi
Anywho, does the forced agression in captivity (fw or sw) have some kind of effect on growth potential / rate?

I have wondered this about fish such as clownfish. In a lot of animals, genes for growth are chiefly turned on during youth, and thus nutrition at this time is paramount. In a species that changes genders based on social position, and whose growth is affected by these changes and whether or not they are expressing gender, who grows to be the largest animal? Is it a larval fish who finds an anemone, and slowly progresses up to the level of top (i.e. female) fish over the period of a few years? Or is it the larval fish that rapidly finds itself in the top position? Either way, I suppose it is remaining in that top position that really allows one to show their stuff.


As for the size of captive fish vs. wild... I would guess it would depend on how well we are able to recreate the wild habitat that the species in question comes from, and to what degree that species relies on its wild habitat... its unlikely that every thing that happens out on the reef needs to be reconstructed in captivity in order to create a habitat where healthy growth will occur. But figuring out which things must be recreated... there's the rub!

[Mentat]

<a href=showthread.php?s=&postid=14482052#post14482052 target=_blank>Originally posted</a> by kaiboshi
...was she malnourished early on resulting in permanently stunted size?...

The growth phase of most organisms (childhood for humans) is very dependent upon nourishment. If incorrect, it will cause permanent negative effects.

<a href=showthread.php?s=&postid=14482052#post14482052 target=_blank>Originally posted</a> by kaiboshi
...does the forced agression in captivity (fw or sw) have some kind of effect on growth potential / rate?...

Stress is part of every organism life. If it goes long term (stress factor remains unresolved) it messes up the immune system and can even kill the organism. Don't think much growth will happen if fish is stressed out and using all it's energy to survive.

[seahorsedreams]

There is a HUGE difference in WC verses CB seahorses. Remember the good ole days of the HUGE Reidis being the norm. I was just looking at my CBs last night and was saying how dinky they are in size.

No doubt in my mind it's a nutritional thing and we are not hitting the mark in identifying the missing link... yet.

[Gary Majchrzak]

No doubt in my mind it's a nutritional thing and we are not hitting the mark in identifying the missing link... yet.
x2

This applies to many species of fishes in captivity IME.

this isn't to say that aquarium size can't effect the final adult size but IME I've seen plenty of examples where diet is clearly to blame for the final outcome.

[sacremon]

I believe Bob Fenner has written that the mechanism for stunting that occurs in FW fish does not happen with SW. FW fish are often in an environment where space is limited. They continually produce a chemical signal, and are sensitive to the concentration of it in the surrounding water. The smaller the space or more of the species present, the higher the concentration, which leads to more stunting. The ocean would infinitely dilute any such signal, except in tidal pool/shallow lagoon environments, so SW fish would not have evolved such a mechanism in the first place.

Nutrition is certainly an element to the size the fish will attain. However, I think we should also consider natural selection in the captive vs. wild environment. The fish we keep might start out in the wild, but are generally very young. They are in a fairly protected environment in our tanks. Often if we see a fish being targeted by another fish for aggression, we separate them. In the wild, the fish would very likely die. What we see as the maximum size individuals in the wild might be that size because perhaps smaller adult individuals are less fit and are selected against (i.e. eaten). A fish that might not have made it in the wild due to size might live a long life in the tank.

Another point is variation in size within the species, and the sample that we are taking when we look at the ones in captivity. First, we don't know what the maximum size of any particular species is in captivity, because not everyone reports the size of their fish. We just have the group of people who have posted, hopefully accurately, the size of their fish. Second, however many of a particular species has been kept in captivity, that is nothing compared to the numbers in the wild. You are most likely going to have a much wider range of sizes in the wild simply because of the larger population present to be sampled.

[scchase]

I think that something commonly disregarded is that different populations of the same species often have different growth potentials. This is both die to genetics and food sources for instance it is known that the Florida strain of largemouth bass has much greater size potential than the northern strain. Even within populations each fish has different size potential not every fish born even has the genetic capability to reach the max size or even average size recorded an average is just that an average.

Some people are 7'2" some people are 3'5" both are outside average for humans but in general neither is dependant on nutrition but a result of genetics.

Even if fish aren't reaching their max size potential in captivity if they are living longer than they would in the wild I consider this a success at least in some terms now we just need to get better at breeding.

Something to consider in the problem that succesive generations are getting smaller is that in capitivity pretty much all the selective pressures for an animal to stay a certain size are removed. We commonly breed individuals that would never be able to breed in the wild due to smaller adults sizes leads to inabilities to protect a territory for breeding and ensures that the fish with the correct genetics for survival in an area sucessfully reproduce.

[Gary Majchrzak]

great overall posts. One thing worth pointing out IMO:
You are most likely going to have a much wider range of sizes in the wild simply because of the larger population present to be sampled.

eliminate the huge difference in populations to be sampled by using percentages.

I'm sure that the percentage of stunted captive fishes is much greater than the percentage of wild fishes in any given species.

[sacremon]

great overall posts. One thing worth pointing out IMO:


eliminate the huge difference in populations to be sampled by using percentages.

I'm sure that the percentage of stunted captive fishes is much greater than the percentage of wild fishes in any given species.

Sorry, but that does not address the errors that occur from trying to compare what has been reported for captive fish sizes vs. what has been observed in the wild. Never mind that no one has yet proposed a mechanism for this supposed stunting, which occurs in FW fish by a known mechanism that is absent in SW fish. The closest I have seen is nutrition, for which I have no doubt will stunt any fish, freshwater or marine.

We have too many biases, many of which we cannot control for, when looking at the statistics of the size of fish in captivity. We don't have control over the fish that the collectors catch in the first place, and that is the real population we are dealing with. What we have in our tanks are only the fish too slow to evade the collectors.

[Gary Majchrzak]

good point.

FWIW I've seen captive marine fishes that were fed an excellent diet fail to even approach the normal adult size for the species. So to reiterate: I've seen both diet and aquarium size effect the final size of several species of marine fishes.
I'm sure that others have witnessed similar.

[Gary Majchrzak]

Long story short, I don't know all of the possible causes of stunting, nor the degree to which certain species will stunt...and I don't think many people have looked into it before. Lots of variables I imagine.
any idea who might be reseaching something like this, Jay?

[LisaD]

from scchase:

Something to consider in the problem that succesive generations are getting smaller is that in capitivity pretty much all the selective pressures for an animal to stay a certain size are removed. We commonly breed individuals that would never be able to breed in the wild due to smaller adults sizes leads to inabilities to protect a territory for breeding and ensures that the fish with the correct genetics for survival in an area sucessfully reproduce.

But most of the marine fish we are discussing are collected from the wild, so there is no selective pressure if the fish do not leave offpsring for selection to act upon.

I agree, captive bred animals of any kind undergo different selective pressures in captivity. Even if we don't consciously select for certain traits, there will be "unconscious" selection for fitness under whatever the captive conditions might be. But this assumes there are sufficient progeny and generations. We aren't there yet with most marine fish. Freshwater fish are a different story...

BTW, a common effect of inbreeding depression is smaller size. This can be an issue with breeding populations that are too restricted.

[scchase]

That part of my response was directly in response so the comments made about freshwater fish earlier in the discussion.

[LisaD]

sorry, I didn't catch that.