Maximum Sizes of Fishes in Captivity - an estimation tool

[jhemdal1]

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

 

[Anonymous]

Good to know, thanks Jay

 

[Anonymous]

Interesting post Jay. In my experience growth seems highly variable depending on what size category we're talking about, as well as some species or genus specific norms. This of course under home aquarium conditions, even tanks large by home aquarium standards.

For instance, we can count on many smaller species quite easily growing to maximum adult size in captivity. Just a few examples off the top of my head would be certain damselfish, clownfish, dottybacks, basslets and many dwarf angels. I’ve seen a few Dascyllus and even a Mandarin grown into absolute monsters! The list goes on, the point being that smaller fish often attain their max adult size in captivity. There are examples amongst the larger fish, with species such as Grammistes sexlineatus and a majority of the Pterois species happily reaching max size or close to in short order. Contrast this with certain other species, which you’ll be lucky if they reach half of their adult size – ever, especially if purchased as youngsters. This includes species such as the B. undulatuts, the Rhinecanthus species, and P. hepatus just to name a few. Most large angels, Pomacanthids and Holocanthids alike will not come anywhere close to 2/3 of their adult under most conditions either, public aquariums possibly accepting.

Anyoo, not writing this to contradict you Jay, your knowledge and research is much appreciated. I realize you're just making a broad stroke generalization. I just want to make sure that those looking for info and reading this realize that there are far too fish out there, and far too many variables out there to arrive at any hard and fast rules.

Cheers
Jim

 

[jhemdal1]

Jim,

Thanks for the input. A couple of things - it is important to note that this study was done using the FishBase maximum size records. Think of these more as "maximum angling records" than as normal adult size. So they list Arapaima as growing to 450 cm, almost 15 feet long. much larger than is normal for that species in the wild. Certainly taking 66% of that length is valid for captivity - 10 feet is still larger than any I've ever worked with. In another example, John Randall lists the maximum size of the vlamingii tang at 55cm and FishBase lists it as 60cm, or about 10% larger, and I've never had one in captivity exceed 45 cm.

The purpose of this study was to try and halt the blind use of FishBase records as the "gold standard" as to how large fish can grow to captivity. Too many people are going around saying things like Naso vlamingii will reach 24" in captivity - and they don't. I found that for the fish I looked at, there was a pretty consitent trend for them NOT to grow as large as their size listed on FishBase. I agree with your examples of the triggers and angelfish in home aquariums, I've seen that myself (less so in public aquariums). I didn't worry too much about that, because 66% of the FishBase maximum for those fish is still MORE accurate than the FishBase record itself.
I've also seen male mandarins get larger than the FishBase listing for 6cm, and I recall seeing a huge deformed Royal Gramma almost twice the 8cm FishBase length. Still, these exceptions are few and far between. I agree with you that there are some clownfish, dottybacks and the like that will reach their normal adult size in captivity. Pterois and Grammistes come close to the FishBase numbers for me, but don't exceed them.

So the bottom line is this: FishBase has become the standard for nomenclature for many people, and since people are visiting the site to look up names, they use a lot of the other data while there. My contention is that taking 66% of the FishBase maximum length is always going to be more accurate on average when talking about home aquarium fish. Getting a larger sample size would unlikely change this value much, but it would pick up more of the exceptions and outliers you mentioned. To tell you the truth, I was kind of surprised at the results of this - my hypothethis going in was that I would see an average of around 80% maximum growth reached.


Jay

 

[Anonymous]

Understood Jay, thanks for the clarification...especially regarding the "maximum angling record" bit. I wasn't thinking of it that way.

 

[Anonymous]

Great thread and input folks.

I tend to tell people the Fishbase max size of fish, with the caveat that it is in the wild.

Unfortunately I suspect that sharing with people the smaller max size in captivity means they're more likely to entertain the notion of cramming it in their 180 gallon tank.

 

[Anonymous]

Needless to say, this was not a large sample set, but I did find 20 good candidates.

and from this you can extrapolate anything ?

:lol: :roll:

 

[jhemdal1]

Vitz,

No, I am not going to get into the "sample size" discussion with you - been there / done that. Instead, why don't you look at the full data set:

http://microcosmaqx.typepad.com/jay_hem ... -tool.html

So the sample size was only 20 fish, but actually the total collection was over 2300 fish, but 2280 of them did not meet all the criteria - rest assured though, that all of these were at LESS than 66% of the maximum fishbase size.

We have found some exceptions. FishBase tends to list "record" sizes for fish that have been sampled a lot, like gamefish. The two thirds estimation works very well for those. For some smaller reef fishes, their sample size is smaller and therefore their "maximum" size is more along the lines of the normal maximum size. In these cases, captive full-grown fish tend to run at 80 to 90% of FishBase. I have a few instances where fish were reported to grow larger than the FishBase size - clownfish, killifish, and some tetras for example. In these cases, it looks like predation or other ecological pressure keeps them from attaining full size in the wild, and they actually live longer in captivity and can attain larger sizes.

Finally, the "two thirds figure" is just an average, so finding one fish that grew to 100% of the Fishbase size would be offset by one that grew to 50%. I've had people run tests on their own fish, and they agree that this figure is simply more accurate than using the Fishbase figure. Personally, I advocate for using 80% of the FishBase total...just to add a layer of safety.

Jay

 

[Anonymous]

Vitz,
they actually live longer in captivity and can attain larger sizes.
Jay

Also, larger captive size is often is related to diet, and we see this often in herbivorous fish. For instance you can grow a M. Zebra, or any Mbuna species quite easily beyond their maximum wild size by offering them a diet richer in protein rather then their natural diet of algea (and small amounts of protein), as many unwise keeper do. This isn't good for the fish, and most probably leads to a shorter live span, but much larger size. Stupid, but prevalent nonetheless.

 

[Anonymous]

Vitz, how many fish do you have that fit the following criteria?

none of them has grown appreciably in the past two years, and all have been in captivity at least 5 years.

That's a short list here as well, even with close to 3,000 fish in our tropical marine collection...