Terms for subject Ichthyology containing in

English	Russian
decrease in scale size, decremental change	уменьшение размера чешуи (Malysheva)
fish eggs enclosed in the ovarian membrane	ястык
in a belly-up position	вверх брюхом (о рыбах и рептилиях: While they are in a belly-up position, the strong righting reflex will induce them to strain and struggle. Гевар)
in a regular fashion	в обычной манере (Malysheva)
in whitefish populations	в популяциях сига (Malysheva)
place in a river where cartilaginous fish hibernate	ятовье (= ятовь)
place in a river where cartilaginous fish hibernate	ятовь