Colossal Armored Suckermouth Catfishes!

I apologize to those who saw an accidentally published early draft of this post. Anyways:

Pseudacanthicus histrix reportedly measuring 0.91 m (total length?). Contra to the prior reference, this is not Acanthicus hystrix. Source unknown.

At some point in my childhood, I was awestruck by several very large loricariids at the Shedd Aquarium. I had a ~30 cm (TL) Hypostomus plecostomus at home, among the biggest I had seen up until then, but the largest individuals from those two species at least doubled that. Does anybody know if the fish are still there - and what species they are? The concept of colossal loricariids has been bumping around in my brain ever since...

As you probably noticed, in a couple recent posts I discussed how invasive armored suckermouth catfishes (Loricariidae) impact local ecologies. Several of the Pterygoplichthys species appear to be the cause of the most problematic "infestations"; their large body size is probably one of the traits responsible for their success, as it allows them to outcompete indigenous species and escape predation. Exactly how large these and other loricariids can grow is an interesting question, to me at least, hence this post.

Determining the sizes of loricariid species is a needlessly complicated affair - weight data is sparse, maximum lengths are given more frequently than averages, total length (TL - counting the caudal fin) is sometimes used instead of standard length (SL), confusion between cm and mm sometimes occurs, species are often confused, and there are wild rumors. The definition of a "colossal" loricariid should be something like 10+ kg on average, but given the current state of the data I'll consider any species which can exceed 50 cm SL "colossal".


The Colossi That Never Were

Attention researchers: If you see a loricariid listed at ~100 cm, please check to see if the original source is actually in mm!

Fishbase listed Peckoltia braueri at 88.6 cm maximum SL, which would make it larger than almost every other loricariid. A photograph from Fishbase gives the impression of a much smaller animal, and I subsequently noticed that while one other site gave a similar size, several others did not. I do not have access to the original description nor the paper that Fishbase cited, but I found that Armbruster and Werneke (2005) noted that the largest species of Peckoltia had a SL of 103 cm. My hunch turned out to be correct and the issue is currently being fixed.

Fishbase lists Lasiancistrus guacharote at an incredible 135 cm TL... and stated that it occurs in Puerto Rico. In the last post the notion that Puerto Rico had any native loricariids was discounted and consultation of the same source revealed that the L. guacharote was 119.5 mm SL (Armbruster 2005). It is possible that both records are in fact from the same specimen. Unfortunately, at least one source currently reports the erroneous locality and size.

While this erroneous information probably hasn't become too entrenched, I think it is still worth pointing out the errors and their likely cause.


Rumors of Mega-Colossi, Conflicting Math, and Pterygoplichthys

The blog NO FORM - NO SUBSTANCE reported a rather lively radio broadcast from the Philippines which claimed that invasive "janitor fish" (Pterygoplichthys disjunctivus) reached 2-3 meters and 30 kilograms! One telltale factor of a "fish story" is an implausible length-weight relationship, which was my first impression with the rumor.

The quickest way of roughly extrapolating mass (assuming isometric growth) is the square-cube law; if we use the 0.512 m/1.8 kg P. multiradiatus (?) from my last post as a template, this means that a 2 m P. disjunctivus would be 3.9 times longer and implies that it is (3.9³ =) 60 times more massive, which is over 100 kg. Liang et al. (2005) recorded the lengths and weights of over 500 invasive P. multiradiatus in Taiwan and extrapolating from their averages predicts about 2 kg for a 0.512 m specimen, suggesting that isometric growth is likely and that the 100+ kg prediction is not off the mark. But...

Growth is not necessarily isometric (i.e. proportions vary) so the equation W = aL^b is used, where L = total length (cm), W = weight (grams), b = exponent describing growth, a = a constant, for those interested, there's this. Using the equation from Liang et al. (2005) predicts 22-27 kg (depending on gender) for a 2 m (standard length) P. multiradiatus and Shukor et al. (2008) predicts 27.6 kg for a similarly sized P.  pardalis. Since laypeople generally use total length (including the caudal fin) when measuring fish and scientists use standard length (distance to caudal peduncle) this suggests that 30 kg is probably still too light for a 2 m Pterygoplichthys - but it is still probably close. To put that in perspective, a 2 m sturgeon weighs around 60 kg and a 1.8 m eel is over 20 kg - in other words the weight derived from W = aL^b is clearly off the mark. I'm assuming that while it is valuable as a tool for determining traits like condition, it has limited ability to predict length-weight relationships considerably outside the range of data used to calculate it. Or I could have screwed everything up somehow...

So how large can Pterygoplichthys species get? Fishbase lists the maximum size of P. pardalis at 42.3 cm SL; however Shukor et al. (2008) report that invasive individuals from the Malaysian peninsula are in their best condition between 30 and 40 cm and according to their Figure 1, 5 individuals out of 928 were ~50 cm in length. Invasive P. multiradiatus in Taiwan averaged about 30 cm for 537 specimens with a maximum length of 43.7 cm SL (Liang et al. 2005); Fishbase lists a cool 50 cm TL for the maximum, possibly equivalent to the SL. However, Bunkley-Williams et al. (1994) list a possible 51.2 cm specimen and cite Page and Burr 1991, which give 70 cm. Pterygoplichthys undecimalis reportedly gets up to 50 cm SL, but I cannot find (or read the language of) any corroborating sources. Quevedo and Reis (2002 - citing Schaefer 1986) state that Pterygoplichthys can reach one meter in length. Not knowing the species or any other details is certainly frustrating.


Other Colossal Loricariids

The same source states that Panaque and Acanthicus also can exceed 1 meter in length. According to Fishbase, P. nigrolineatus is the largest species at 43 cm TL - leaving me perplexed. The Acanthicus species are much more likely to reach 1 m; Fishbase and its source list A. hystrix at SL, this source from 1890 lists the length at 0.71 m, this aquarium atlas lists the length at 1.1 m, and this book lists the length at "over" 1.2 m. The Fishing World Records page also lists 1.2 m, although it does not lists sources and confuses Pseudacanthicus histrix for A. hystrix. That website and Planet Catfish also list A. adonis at 1 meter, strangely Fishbase puts it at a mere 20.6 cm SL.

As far as I can tell, Pseudacanthicus histrix is the largest loricariid for which there is reasonable evidence. The lack of peer-reviewed literature on the species, and the paucity of data on colossal loricariids in general, is a concern. It does not seem unreasonable to assume that some loricariids can reach about a meter and 20 kg in weight, although if the individuals belong to any of the species here or even some taxa yet to be described has yet to be seen.

References:

Armbruster, Jonathan W., and Werneke, David C. (2005) Peckoltia cavatica, a new loricariid catfish from Guyana and a redescription of P. braueri (Eigenmann 1912) (Siluriformes). Zootaxa 882, 1–14. Available.

Armbruster, Jonathan W. (2005). The loricariid catfish genus Lasiancistrus (Siluriformes) with descriptions of two new species. Neotropical Ichthyology 3(4), 549-569. Available.

Bunkley-Williams, Lucy, et al. (1994). The South American Sailfin Armored Catfish, Liposarcus multiradiatus (Hancock), a New Exotic Established in Puerto Rican Fresh Waters. Caribbean Journal of Science 30(1-2), 90-94. Available.

Liang, Shih-Hsiung, et al. (2005). Size Structure, Reproductive Phenology, and Sex Ratio of an Exotic Armored Catfish (Liposarcus multiradiatus) in the Kaoping River of Southern Taiwan. Zoological Studies 44(2), 252-259. Available.

Quevedo, Rodrigo and Reis, Roberto E. (2002). Pogonopoma obscurum: A New Species of Loricariid Catfish (Siluriformes: Loricariidae) from Southern Brazil, with Comments on the Genus Pogonopoma. Copeia 2002, 402-410.

Shukor, Samat A., et al. (2008). Length-weight Relationship and Condition Factor of Pterygoplichthys pardalis (Pisces: Loricariidae) in Malaysia Peninsula. Research Journal of Fisheries and Hydrobiology, 3(2), 48-53. Available.