A species you would not think to be invasive

[Silurus]

Mazzoni, R, RC da Silva & MP Pinto, 2015. Invasion and colonisation of a tropical stream by an exotic loricariid fish: indices of gradual displacement of the native common Pleco (Hypostomus punctatus) by the Red Fin Dwarf Pleco (Parotocinclus maculicauda) over fifteen years. PLoS ONE 10(10): e0139968. doi:10.1371/journal.pone.0139968

Abstract

The introduction of invasive species represents a major threat to the integrity of stream-dwelling fish populations worldwide, and this issue is receiving increasing attention from scientists, in particular because of potential impact on biodiversity. In this study, we analysed the dispersal of an exotic loricariid fish the red fin dwarf pleco (Parotocinclus maculicauda) in a stream of the Atlantic Forest biome in coastal south-eastern Brazil and evaluated the effects of this invasion on the native loricariid common pleco (Hypostomus punctatus). Specimens were collected at eight sites located along the course of the stream over a 15-year period. The distribution and density of the two species were determined by the Successive Removal Method. The introduction of P. maculicauda occurred in the medium sector of the stream, and during the course of the study, the species dispersed to new sites further upstream. By the end of the study, it was found at all points upstream from the original site. Hypostomus punctatus was registered at all sample sites both before and after the introduction of P. maculicauda, but its density decreased at all upstream sites after the arrival of the exotic species. Our analysis shows that colonisation by P. maculicauda seems to have a negative effect on H. punctatus densities. The maintenance of H. punctatus densities at the sites not colonised by P. maculicauda reinforces the conclusion that the colonisation of the stream by the exotic species had deleterious effects on the density of the resident H. punctatus populations, either by direct or indirect action.

[Bas Pels]

If someone would have suggested keeping them together in a tank, I would have worried about the Parotocinclus, not the Hypostomus. I still would

But in the wild things are often different. For instance, assuming Hypostomus is predated by birds, which only predate fish over a certain size, P maculicauda could well remain too small, thus be save, and able to spend more time feeding than H punctatus.

This would result in less food for, and therefore less H punctatus