Most artificial fish passes have been developed in Northern temperate rivers and are designed to serve large, migratory sport fish species (mostly salmonids). Experience in construction and maintenance of fish passes show that salmon-criteria are not adequate for flat-land rivers and non-sport fishes. Consequently, over the last decade, design criteria have changed to take requirements of target species into account. Extrapolation of these concepts to rivers in the Southern Hemisphere with different hydrological conditions and fish community composition is not straight forward. This review focuses on requirements for an adequate hydraulic design of passes for non-sport fish species bodied (< 15 cm) threatened by small hydropower dams (with a typical head of 3-5 m). First, fragmentation of fish populations due to river obstructions that impede longitudinal movements is introduced from the perspective of environmental sustainability, taking the Chilean indigenous freshwater fish species as a study case. Subsequently, relevant properties of fish passages are reviewed, and experimental issues for maintenance in captivity and determination of swimming abilities in the laboratory are presented. Following dimensional considerations controlling scales for an adequate hydraulic design of fish passes, involving fluid, flow, fish, and pass properties are discussed. Finally, we postulate that successful passage design should consider habitat connectivity as the key concept for preservation of this highly threatened native fish fauna.