Invasion of the Armored Suckermouths!

Alternate title: Endangered pelicans try to swallow invasive catfish. Pelicans suffocate. Die.

Due to the probability of a cease-and-desist letter from England, I'll weave the hinted-at tale above into the tapestry of woe that the armored suckermouth catfishes have caused.

My highly derivative alternate title refers to a phenomenon that occurred in Oct. 1992* in the lower Loiza and Gurabo Rivers of Puerto Rico: at least twenty Brown Pelicans (Pelecanus occidentalis, a locally endangered species at the time) were found strangled to death with large armored suckermouth catfish (over 40 cm, 16" in length) lodged in their throats (Bunkley-Williams et al. 1994). It is worth pointing out that Brown Pelicans typically take prey under 25 cm in length (ref.), do not have bills over 16"/40 cm in length (according to this), and weigh 2-5 kg compared to the ~1 kg that the catfish weighed**. The possibility that Brown Pelicans can successfully swallow prey of that size cannot be precluded, so the extensive armor and unusual morphology*** of the catfish may have been the fatal factors. As to why the phenomenon was so widespread, the catfish became established in Puerto Rico only a few years before and their ease of capture may have prompted curiosity towards a new potential food source. No more reports have been published, so it is possible that the local Brown Pelican population has learned to avoid the catfish, which are probably now permanently established. And sorry to those seeking out morbid photos of the failed loricariid consumption, photographs do not seem to have been published, or even taken as far as I know.

* The table actually says "Ott 1992", I'm fairly certain it's a typo and not some hyper-obscure Latin abbreviation.

** The first recorded loricariid from Puerto Rico was a 1.8 kg, 51.2 cm "Hypostomus plecostomus" - this identification is dubious and the (lost) specimen was presumably the same species as the ones the pelicans swallowed (Bunkley-Williams et al. 1994). Anyways, extrapolating from that record gives 0.86 kg for a 40 cm specimen - I stated ~1 kg due to uncertainty and the implication that 40 cm was a minimum. 
*** Hoover et al. (2004) suggest that the dorsal and pectoral defensive spines were the cause of the mortalities.

Bunkley-Williams et al. (1994) identified the invasive loricariid catfish species as Liposarcus multiradiatus, which is now (again, actually) known as Pterygoplichthys multiradiatus. Puerto Rico has no native loricariids* and while a report occurred as early as 1983 (a likely accidental), P. multiradiatus became established in eight rivers and two reservoirs in the early 1990's, with numbers significant enough to support a local fishery in one area (Bunkley-Williams et al. 1994). While there are markets for the fish in the food and pet industries (at least one fish farm existed on the island for the latter purpose), Bunkley-Williams et al. (1994) suggested that the unexpectedly large size reached by the species led to amateur aquarists discarding them. The catfish appear to be incredibly tolerant of handling stress and can even reportedly survive out of the water for hours** (Bunkley-Williams et al. 1994).


* The type locality of Lasiancistrus guacharote (formerly Hypostomus) was Puerto Rico, but it turns out that this is in error, the species is actually from Venezuela and Columbia (Armbruster 2005). 
** Over 30 hours, in fact (Armbruster 1998 citing Val and De Almeida-Val 1995). They accomplish this by breathing air into an enlarged and highly vascularized stomach, which primarily functions to survive low-oxygen conditions in water (Armbruster 1998). Hoover et al. (2004) documented Pterygoplichthys specimens which apparently entered a period of estivation in burrows, from which they recovered as soon as they returned to water. The implication is that they can survive considerably longer than 30 hours out of the water. Oh, and they can also move on land during extreme environmental conditions.


If the trouble caused by Pterygoplichthys multiradiatus seems familiar, that's because a couple posts ago I discussed how P. disjunctivus (and/or hybrid descendants) specimens in Florida grazed on manatees to a likely deleterious effect. I didn't properly introduce the loricariid catfishes then, and I'm not sure how I passed on such a succulent tangent. So here's a scenic detour through the world of these bizarre armored suckermouth catfishes.

P. multiradiatus from the Wikipedia Commons.

Ideally, the common name "armored suckermouth catfishes" should be used for Loricariidae since they are not the only clade with extensive armor (Callichthyidae) nor are they the only ones with a sucker mouth (Astroblepidae). Loricariidae and Astroblepidae are sister clades (indicating the suckermouth is a shared derived character) and Callichthyidae is a more distant relative (indicating the extensive armor is convergent, unless lost numerous times) in the greater clade Loricarioidea, which includes everything from parasites to a monotypic oddity. Loricariidae itself has a staggering array of morphological variability: Panaque nigrolineatus (Ancistrinae) has an incredibly large head, Tim Burton-esque stripes, and the ability to digest wood with the aid of bacteria; some species (e.g. Farlowella amazonum - Loricariinae) have a body shape reminiscent of pipefish (likely for similar camouflage needs); the Sturisoma species and relatives (Loricariinae as well) look similar except with very exaggerated fins; dwarf suckermouths (Otocinclus et al. - Hypoptopomatinae) look more like generic tetra-like fishes than highly derived catfishes at first glance; one Ancistrus species is a blind cave-dweller, others have bizarre facial tentacles (Ancistrinae); Chaetostoma sovichthys (Ancistrinae) and relatives hardly look like fish at all in dorsal view - more like a revisitation of Cephalaspis or even the ichthyological answer to Triops. The point is, with 700+ species, Loricariidae is a very successful clade - considering they're mostly freshwater* and restricted to one continent. Adriaens et al. (2009) discussed the highly derived jaw morphology** which apparently allowed the loricariids to radiate into the algae-scraped niche; exactly how the numerous species differ niche-wise has not had much discussion.The species Adriaens et al. (2009) used as a model for their study of loricariid jaw mechanics? - Pterygoplichthys disjunctivus.

* Although sources like Fishbase state that they are strictly freshwater, Hoover et al. (2004) report that they occur in brackish water. 
** Catfish jaw morphology is normally conservative, but loricariid jaws have a uniquely mobile upper jaw (as in, it typically doesn't move at all in other catfishes) and the bones of the lower jaw are decoupled to allow for asymmetric scraping movement. 


Back to the invasive loricariids. As it appears that the most widespread and damaging taxa are a few related Pterygoplichthys species (e.g. within the genus), I'll be focusing on those sailfin catfishes - distinguishable by their large dorsal fins consisting of more than 10 rays. In addition to Puerto Rico and Florida, Hawaii has a particularly noteworthy population of Pterygoplichthys and several other genera of loricariids (Bunkley-Williams et al. 1994 - citing various). In the Philippines, P. disjunctivus and P. pardalis were present in the Laguna Lake region since the 1950's and in the early 2000's were found in the Agusan marsh, one of the largest in Asia (Hubilla et al. 2007). Members of Pterygoplichthys are also established in Taiwan, Singapore, Malaysia, Indonesia, and Mexico (Page and Robins 2006, Armando et al. 2007). While Pterygoplichthys spp. are reported from a few states in the mainland USA, there is a chance that like could go from localized to very widespread and wreak havoc (Hoover et al. 2004). So what makes these loricariids particularly damaging invasive species?

The Pterygoplichthys species are capable of far more severe impacts than choking pelicans and cleaning manatees. In fact, Hoover (2004) states that the variety and severity of the ecological impacts from the catfish are unprecedented. I can't emphasize that enough. Loricariids burrow into the banks of streams and lakes in order to spawn and take refuge from droughts and cold temperatures; this behavior can erode away 4 meters of bank annually and cause increased silt loads and turbidity (Hoover et al. 2004, Hubilla et al. 2007). The increased turbidity slows down photosynthesis and likely has negative effects on the food web and energy flow (Hubilla et al. 2007). The catfishes also plow into the substrate and uproot plants, which likely reduces the abundance of native plants and may even aid in the spread of invasive plants (Hoover 2004). Invasive Pterygoplichthys, being large and bewilderingly resilient species, likely outcompete the native algae consumers, aggressively drive them away, and consume the eggs of those species and others (Hoover 2004). The presence of a ravenous algae grazer may also reduce cover for aquatic insects and disrupt the food chain by prematurely diverting nutrients into feces Hoover 2004). Having owned Hypostomus plecostomus specimens in my life, I can't help but wonder if the prodigious amount of feces that loricariids produce has some sort of impact as well.

So what can be done to prevent the potential ravaging of aquatic freshwater ecosystems by invasive loricariids? Bunkley-Williams (1994) discussed the possibility of large predatory fish controlling Pterygoplichthys numbers (Peacock bass, Cichla ocellaris, and Largemouth bass, Micropterus salmoides), however they concluded that there was no known effective predator, disease, or parasite. The Philippines populations also do not appear to have any significant predation, even from native fishermen gillnets as they are damaged from the large fish (Hubilla et al. 2007). Hoover et al. (2004) and Hubilla (2007) suggest that fisheries, possibly with government incentive, could be a way of controlling populations (presumably with better equipment) as the fish are valued for their flesh and eggs. Hoover et al. (2004) also suggested protecting banks from burrowing and isolating the "infected" areas as method for preventing the problem from becoming very widespread. Hoover et al. (2004) and Bunkley-Williams et al. (1994) suggest public education to the prevent further release of loricariids and the latter publication proposed a program to return unwanted fish from amateur aquariums. Those two papers and Hubilla (2007) all suggest that environmental laws should be strengthened in order to prevent multiple Pterygoplichthys species or even multiple loricariid genera from being established. Bunkley-Williams (1994) doubt that the invasive species can ever be eradicated, but the chances of controlling the spread of the catfishes are still good if people recognize the problem before it gets completely out of control.

I'll admit that when I was a kid I released a large loricariid into a quarry before I moved. Even though it had no chances of becoming widespread, it was still a very dumb decision. So please, if you own these catfishes, whatever you do, don't release them into the wild!

References:

Adriaens, Dominique, et al. (2009). Extensive Jaw Mobility in Suckermouth Armored Catfishes (Loricariidae): A Morphological and Kinematic Analysis of Substrate Scraping Mode of Feeding. Journal of Experimental Biology 212, 116-125. Available.

Armando, T. et al. (2007). Amazon Sailfin Catfish Pterygoplichthys pardalis (Castelnau, 1855) (Loricariidae), another exotic species established in Southeastern Mexico. The Southwestern Naturalist 52(1), 141-144.

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

Armbruster, Jonathan W. (1998). Modifications of the Digestive Tract for Holding Air in Loricariid and Scoloplacid Catfishes. Copeia 1998(3), 663-675. 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.

Hoover, Jan Jeffrey, et al. (2004). Suckermouth Catfishes: Threats to Aquatic Ecosystems of the United States? ANSRP Bulletin 04(1). Available.

Hubilla, Marianne, et al. (2007). Janitor Fishes Pterygoplichthys disjunctivus in the Agusan Marsh: a Thread to Freshwater Biodiversity. Journal of Environmental Science and Management 10(1), 10-21. Available.

Page, Lawrence W. and Robins, Robert H. (2006). Identification of Sailfin Catfishes (Teleostei: Loricariidae) in Southeastern Asia. The Raffles Bulletin of Zoology 54(2), 455-457. Available.