Growth of two invasive cichlids (Perciformes: Cichlidae) in a natural thermal water habitat of temperate Central Europe (Lake Hévíz, Hungary).

The outflow of the natural thermal Lake of Hévíz is habitat of several fish species, with conservation relevance. In the past few years, numerous thermophile (tropically originated) fishes were reported in this waterbody, from which two species Parachromis managuensis (Günther, 1867), Vieja melanurus (Günther, 1862) characterized with strong, self-sustaining population. The aim of our research was to provide basic population data and to study their individual growth. The standard length of jaguar cichlid ranged from 37 to 283 mm (mean SL = 110.21 ± 65.4 mm), the redhead cichlid standard length varied between 30 and 203 mm (mean SL = 93.91 ± 40.0 mm). Slightly positive allometry (b > 3) was found in the case of both species. The von Bertalanffy Growth Function can be described as the following L t  = 343.6[1 - e -0.196(t+0.973) ] in jaguar cichlid and L t  = 298.9[1 - e -0.113(t+0.997) ] in the case of redhead cichlid. The Bertalanffy growth equations show slow growth for both species. Fulton's condition factor (K) values varied between 1.376 and 2.11 (mean K = 1.701 ± 0.17) in the case of jaguar cichlid, and between 1.391 and 3.033 (mean K = 2.237 ± 0.24) for redhead cichlid. These baseline population biology data from the first known self-sustaining, temperate-zone populations of two tropical cichlids provide information e.g., for future ecological risk assessments or comparative growth analyzes.