Potential effects of Pterygoplichthys spp. include alteration of bank structure and erosion, disruption of aquatic food chains, competition with native species, mortality of endangered shore birds, changes in aquatic plant communities, and damage to fishing gear and industry.
Environmental impacts of Pterygoplichthys spp. are not fully understood, but in locations where they are introduced and abundant, their feeding behaviours and burrowing activities can cause considerable disturbance. Their burrows have been reported as contributing to siltation problems and bank erosion and instability (Nico et al, 2009b). Pterygoplichthys spp. forage along the bottoms of streams and lakes, occasionally burying their heads in the substrate and lashing their tails. These behaviours can uproot or shear aquatic plants and reduce the abundance of beds of submersed aquatic vegetation, creating floating mats that shade the benthos from sunlight. By grazing on benthic algae and detritus, they may alter or reduce food availability and the physical cover available for aquatic insects eaten by other native and non-native fishes where they are introduced (Mendoza et al, 2009; Hossain et al, 2008). Pterygoplichthys spp. may also compete with native fish. They are believed to displace several species of minnow in Texas including the Federally threatened and 'Vulnerable (VU)' Devils River minnow (see Dionda diaboli ) (Mendoza et al, 2009).
Pterygoplichthys spp. are thought to create large, novel nutrient sinks in invaded streams of southern Mexico. They sequester the majority of nitrogen and phosphorus of systems in their body armor. These impacts on nutrient systems may also exacerbate the nutrient limitation of primary productivity in invaded streams (Capps et al, 2009).
Thousands of nesting tunnels excavated by P. multiradiatus have contributed to siltation problems in Hawai'i. Because of their abundance in Hawai'i, P. multiradiatus may compete with native stream species for food and space (Nico, 2006). The burrowing behaviour and overpopulation of P. multiradiatus may also displace native fish in Puerto Rico where they have been reported as detrimental to reservoir fishes (Bunkley-Williams et al, 1994). At least 20 brown pelicans have choked to death while trying to swallow the armored P. multiradiatus (Bunkley-Williams et al, 1994; Levin et al, 2008). In Lake Okeechobee, Florida P. multiradiatus feeds and burrows at the bottom and destroys submerged vegetation, essentially displacing native fishes that would otherwise use the aquatic vegetation for spawning and refuge and interfering with their reproduction (Mendoza et al, 2009). P. multiradiatus is known to cause economic losses to fisherman by damaging equipment such as cast and gill nets in India and displacing native fish (Krishnakumar et al, 2009).
P. multiradiatus and P. pardalis damage fishing gear and gill nets in various locations of Mexico (Wakida-Kusunoki et al, 2007).
P. disjunctivus and P. pardalis are reportedly destroying cages and nets and causing a decline in native, more desirable fish in Laguna de Bay, Philippines (Chavez et al, 2006). P. disjunctivus attaches to the skin of the 'Endangered (EN)' native Florida manatee (see Trichechus manatus ssp. latirostris ) and feeds on their epibiota. In some instances dozens of P. disjunctivus and manatees appeared agitated. This interaction may be detrimental to manatee but remains unclear (Nico et al, 2009a).