Effects of salinity on distribution, growth and survival of three neotropical armoured catfishes (Siluriformes—Callichthyidae)

Three species of closely related armoured catfishes, Hoplosternum littorale, H. thoracatum and Callichthys callichtkys , are widely distributed throughout (sub)tropical South America, but a detailed inspection of collection localities in both Suriname and the South American continent reveals a clear pattern. Hoplosternum littorale is not found in rainforest creeks and clear-water rivers draining the Precambrium Guiana and Brazilian Shields. Here, waters are extremely poor in dissolved minerals. In salinity tolerance experiments, 1-week-old larvae of H. littorale were found to be incapable of surviving in rainwater that is also very poor in electrolytes. Probably for the same reason, H. littorale is not collected in black-water rivers like the Rio Negro. Within the Amazon river-system H. litiorale is found in sediment-laden white-water rivers originating in the Andes. Larvae of H. thoracatum and C. caiiichthys are able to survive and develop further in rainwater and consequently have a less restricted distribution than H. littorale . Both species are found in clear water and black water. All three species tolerate salinities up to 2000 mg Cl/1, and show a marked decrease in growth at low salinities.