Determination of fish age and growth through otolith growth rings (otoliths)

Main area:Aquatic biology
Target group:Biology
Educational level:Bachelor, Outside course scope
Project description:
Otoliths are hard, calcium carbonate structures located directly behind the brain of bony fishes. Otoliths (also called ear stones) are part of the sensory organs, which help the fish determine their position and speed in the water. Since fish otoliths are formed by deposits of layers of calcium carbonate and organic matter throughout the lifespan, studying the otoliths may reveal the age of the fish and the amount it has grown in each year of its life. The deposition rate varies with food intake, temperature and day length. Each year two rings are formed which in trans-illumination appears dark (formed during summer) and light (formed during winter). By comparing data for age and growth of individual fish to e.g. climatic data (precipitation, temperature, ice cover) and biotic conditions (e.g. food availability) from the same locality or area, it is possible to estimate how a fish population has responded to outer conditions over a number of years. Such studies have relevance in many contexts where considerable changes take place due to for instance climate change, lake restorations, changes in hydrological conditions or the use of chemicals such as pesticides. In other words, there are many options to study fish physiology and ecology through the use of otoliths. The art of reading otoliths can be mastered after some training and involves microscopy coupled with image analyses. The project can be based either on: 1) otoliths that are already sampled and where the relevant environmental data exist (see a list below with available samples), or 2) otoliths that will be sampled as part of the project. For the latter options, the sampling location can be any lake or stream in Denmark where it time wise and logistically is possible to harvest enough specimen. Existing samples: Introduced (and landlocked) lake trout from six Andean lakes (Ecuador) Landlocked and migrating Arctic charr from a lake and two ponds in Greenland
Methods used:Microscopy, data analysis
Keywords:Freshwater fish, Othlith, Growth, Climate change
Supervisor(s):  Kirsten S. Christoffersen