Incubation and Larval Development Durations of Sterlet (A. ruthenus LINNAEUS 1758) in River Water Rearing under Near-Natural Conditions

Abstract

Day-degrees [°D], also known as accumulated thermal units (ATUs), have been used to predict the duration of early development for fish. For most sturgeon species, the available data in the literature were determined under temperature-constant conditions. However, there is a lack of information on ATUs of early development for sturgeons under natural or near-natural temperature conditions. The aim of this study was to observe the duration of incubation and the duration from hatch until feeding of sterlets (Acipenser ruthenus) under near-natural conditions. This study was embedded within the LIFE-Sterlet and LIFE-Boat 4 Sturgeon project and data were gathered from the year 2017 to 2023. The rearing of fish larvae took place in the project hatchery container with Danube water without biological, chemical, or thermal water treatment to simulate natural conditions. Temperatures [°C] were monitored on a daily basis and day-degrees were calculated by summing the temperature over time. Results indicated slower larval development than described in the literature. Hatching started earliest after 7 days at 106 °D and latest after 151 °D. Feeding started between 155 and 271 °D. The findings of this study provide valuable insights into the temperature-dependent development of sterlet larvae under near-natural conditions and can assist in the design of optimal rearing of sturgeons for conservation efforts.