Standard Length (SL)

[zenyfish]

Can someone enlighten me on the meaning of SL?
I know the definition is that from tip of head to base of tail minus caudal fin. But how does one arrive at the numbers in the catalog?

It can't be the absolute maximum because there are many fish that grow beyond the SL. For example, the common pleco (P. Pardalis) has a SL of 10" but I hear it can grow to 2 feet.

Does one go out into the field, catch a bunch of adult (breed-able) fish and measure SL? In which case it's an average breed-able length?

Thanks in advance.

[Silurus]

Many of the maximum sizes in the CAt-eLog are based on data from Fishbase. These data, in turn, are largely derived from museum specimens (for most of the species) and fisheries data or fishing records (for a few commercially important species).
In the case of museum-derived data, this is always a bit off, since there is no certainty that the largest specimen would be seen by scientists, much less collected.

[zenyfish]

Thanks. So it's meant to be an absolute maximum.

To me, it seems an average breed-able length would be more useful (the center of a Gaussian density). I mean how many people are NBA center height?

[Silurus]

It's much easier to get a maximum length than a length at sexual maturity. You just need to look at the number of species for which some info about basic biology exists and compare that to the total number to see why.

[MatsP]

Thanks. So it's meant to be an absolute maximum.

To me, it seems an average breed-able length would be more useful (the center of a Gaussian density). I mean how many people are NBA center height?

Both numbers can be useful, for different purposes...

The breedable size can easily be a lot less than the maximum size. For instance, my bristlenose male is about half of the MAX size. Certain fish, I'm sure, can breed at much smaller size (proportionally to their max size, at least). I think chubb are sexually mature at about 5-6", but they can easily grow beyond 15" (but a lot get eaten before that...)

Whilst knowing what size it breeds at is a useful thing to know for breeders, the maximum size is needed to know the size of tank and what tank-mates will be suitable, for instance.

--
Mats

[Shane]

Caudal fins are easily damaged in both nature and preserved fishes so it really does not make any sense to include them in accurate measurements. There are also fish with very long caudal filaments. If these were included we would give lengths of 12 inches plus for Farlowella and 16 inches for some Hemiloricaria. Since half the length of these animals is caudal fin, it really is not an accurate description of how big they get.
-Shane

[Coryman]

Looking at it very simply, SL = Standard length = Body length.

SL is not meant to be the maximum a species grows to, it is just a measurement, tip of snout to caudal peduncle, and if I am correct it is the measurment the all others used in taxonomy are bases around, i.e. head length = 2.6x into SL. body depth = 2.8x into SL.

I am sure HH will tell me if I have it wrong, but basically SL is not a reference as to what a fish should grow to, just waht it measures.

Ian

[bronzefry]

So then "TL" means total length, which would include the fins?

[Shane]

So then "TL" means total length, which would include the fins?

Yes it is.
-Shane

[zenyfish]

I am sure HH will tell me if I have it wrong, but basically SL is not a reference as to what a fish should grow to, just waht it measures.

Ian

Sorry, I'm a little confused now. If I go out and capture 10 common plecos and they measure from 6" to 12", then SL = 12"? So SL = max length of examined specimens?

[mummymonkey]

Sorry, I'm a little confused now. If I go out and capture 10 common pl*cos and they measure from 6" to 12", then SL = 12"? So SL = max length of examined specimens?

The SL is just a measurement. It's like saying inside leg. So in your example, the SL of the specimens you caught, varies from 6" to 12". Fishbase gives a max size in TL. So for Liposarcus pardalis it gives "Max size = 40cm TL"

[zenyfish]

The SL is just a measurement. It's like saying inside leg. So in your example, the SL of the specimens you caught, varies from 6" to 12".

There is only one number, and not a range, for SL of each species regardless of age, sex, and locality ... as far as I can tell.

[Shane]

SL has nothing to do with a range. If you caught the above loricariids they might measure:

Standard Length (SL) (length from tip of snout to caudal peduncle) 5.5 in., 6 in, 6.5 in, 7 in, 9 in, and 10 in.

Total Length (TL) (total length from snout to the end of the caudal fin) 7 in, 8 in, 8 in, 9 in, 11 in, and 13 in.

Fish number 3 is larger SL than fish number 2, but the same TL because 1/2 in. of fish number 3's caudal (tail) fin was eaten by a passing piranha.
-Shane

[Coryman]

No not really, SL is the body length measurment of one individual speciemen and not a standard for all of that particular species.

If you collected ten fish you have ten separate SL measurements.

Ian

[zenyfish]

But how does one arrive at the numbers in the catalog?

Thank you. I understand the definition, but my original post really concerns the SL numbers listed in the catalog. For example, how does one get 10" for the common pleco?

As there are no qualifications for that particular number.
Is that a max, average, or median adult fish? If I interpreted correctly, HH implies it's the max SL of all documented specimens?

[Silurus]

That's supposed to be the absolute maximum.

The common pleco is a really bad example, because everyone knows the max size in the Cat-eLog is wrong.

[sidguppy]

yup; 10" Common Pleco's (P pardalis) are common as dirt.....

it's the two-footers wich are rare; dunno the exact size of maxed-out pardalis, but I did see one specimen myself wich topped 20"

[Psy]

As for catelog sizes, I like what Cichlid-forum did for their cichlid sizes. There are too many values to do the entire list that way, but perhaps the most common types. They listed the most common adult size, what you would expect.

If the common pleco reaches 24 inches max, but 95% of them only reach 18 inches, list 18 inches as the "average max size." It makes it pretty clear what can go in what aquarium (until you grow a new record atleast).

[zenyfish]

For example, the common pl*co (P. Pardalis) has a SL of 10" but I hear it can grow to 2 feet.

Sorry, I see the source of the above confusion now. P. Pardalis is listed as having a size of 10" SL and not a SL of 10" ... my error. My subject heading is misleading.

[mummymonkey]

There is only one number, and not a range, for SL of each species regardless of age, sex, and locality ... as far as I can tell.

I never said anything about a range. Every fish in the world has its own SL. It's just the distance from the tip of its nose to the base of its tail fin rays. Nothing else.
I can see how the word 'standard' is a little ambiguous in this instance. I like Coryman's suggestion of body length as a reasonable alternative.

[MatsP]

But how does one arrive at the numbers in the catalog?

Thank you. I understand the definition, but my original post really concerns the SL numbers listed in the catalog. For example, how does one get 10" for the common pl*co?

As there are no qualifications for that particular number.
Is that a max, average, or median adult fish? If I interpreted correctly, HH implies it's the max SL of all documented specimens?

The cat-elog has an entry called "Max size", which is given in SL. So this is the largest well-documented size of the fish. It's not the world record for this fish, but it's the largest of, say, 100 fish that was caught and examined when they did the scientific description of the fish.

It gives you a decent idea of the size you can expect the fish to get, but if your fish grows another 10% larger, that wouldn't be entirely surprising.

The reason for using SL is as above, both that the caudal file can be destroyed, and long filaments can make the "total length" a bit misleading.

--
Mats

[Jools]

The catelog definition reads:

"This is the maximum standard length (SL). This is the length from the top of the snout to the caudal peduncle. The caudal peduncle is the muscle at the base of the caudal fin. So, SL, is the length of the fish minus the tail fin. This is given in mm in line with modern scientific work but an approximate conversion to imperial inches is also provided."

It's really an issue of available data.

If we're talking about a fish we have no other data on then something like the fishbase size is used. If we have a range of SL data (as discussed above) then the "maximum standard length" us used and this will include aquarium specimens and personal observations.

So, 10" for a common pleco is about the largest one we've seen but I don't carry around a ruler for measuring ones that might be 5mm larger...

Does that answer the question?

Jools

[zenyfish]

Yes, completely. Thanks.

I could've worded my question better if I didn't confuse SL with Max Size.

Though the last picture of P. Pardalis in the catalog looks larger than 10" to me ...