The Laboratory of Fish Age Analysis at the Institute of Freshwater Research

Last changed: 11 December 2018

Ageing of fish can provide detailed knowledge of fish stocks and show how fish react when the environment changes. At the Institute of Freshwater Research we primarily age determine fish from freshwater lakes, but also migratory fish such as salmon, sea trout and eel.

The Laboratory of Fish Age Analysis at the Institute of Freshwater Research performs age analyzes within three main areas:

• Environmental monitoring of small and medium-sized lakes
• The Great Lakes Vänern, Vättern, Mälaren and Hjälmaren
• EU Data Collection Directive ( DCF)

We also carry out assignments on behalf of the provincial governments, municipalities, fishing associations and others. Over 10 000 samples per year are beeing age determined at the Laboratory of Fish Age Analysis. Eight specialists work with age analysis, beeing experts in one or more species. Our specialists also share knowledge on the same species in order to maintain continuity and quality.

Species

The majority of the samples analyzed consists of perch and roach from small and medium-sized lakes. Pikeperch, whitefish and vendace dominates age analyzes of fish from the four largest lakes of Sweden. Salmon and eel make up the bulk of the analyzes carried out within the framework of the EU Data Collection Directive. In addition we also age determine trout, charr, smelt, ruffe, bream and grayling.

Method

Depending on the species, various methods are used in age determination. Otoliths (ear stones) are used to determine the age of most species, except for salmon and sea trout for wich only the scales are used. The otoliths are prepared in various ways. Depending on the species, the otoliths are analyzed whole/unprepared (e.g. trout and char), burnt and cracked (e.g. perch and whitefish) or mounted in plastic and sliced with a precision saw (roach) .

Depending on species, the growth is measured by studying additional tissues. In roach, whitefish and walleye we anlalyze otoliths as well as fish scales. In perch both the operculum bone and otoliths are studied.

The otholiths and other structures are studied in a microscope, stereo microscope or in an electronic magnifier type microfiche.

Age database and scales archives

The results of the age analysis are stored in a database, beeing part of the National Register of survey test-fishing - NORS. Currently, the database includes data from more than 112 000 age determined individuals of 17 species from more than 190 lakes throughout the whole country . The database is an important instrument for comparisons of growth and recruitment among lakes and years.

Samples are archived in the Institute of Freshwater Research scale archive. The archive contains more than 1 million samples, collected from 1901 and onwards. In recent years, the collection has also gained interest from a genetic perspective, since the scales give information on indigenous fish populations. Research on comparisons with contemporary fish populations are currently beein done.

Quality Accreditation

• We work according to the guidelines recommended in TACADAR 's (Towards Accreditation and Certification of Age Determination of Aquatic Resources) final report.
• A training program is used for our employees, following Methodological manual for age determination of fish at SLU’s laboratories.
• We always use otoliths for age determination, except for salmon and sea trout. When possible or if necessar, each perch, roach, whitefish, grayling and walleye is analyzed using two tissue samples (otoliths – opercular bones, otoliths - scales). This increases the quality of the analyzes.
• We make annual intercomparisons of the analyses on perch and roach to see if our age analysts are consistent. For analyses of whitefish, vendace, pikeperch, salmon and sea trout intercalibration is performed every two to three years.
• We analyse time series within programs for environmental monitoring. These includes samples of perch, roach, whitefish and vendace. By analysing strong or weak year classes, we get valuable information on the fish population in lakes. Accordingly, time series of fish populations gives us age analyzes of better quality.
• We document the characters of the analyzed age material for each lake. These characters are used when analyzing other new materials. Charachters and experieces are summarized in species-specific documents. The documents are part of Methodological manual for age determination of fish at SLU’s laboratories.
• A reference library is under construction, it will contain material with specific characteristics. An image archive will complement the reference library.
• We participate in SLU's knowledge sharing network Centre for Ageing analysis (CFA).
• We share our experiences in a Nordic group: Nordic Freshwater Fish Group (NOFF) .
• We participated in the EU project TACADAR (Towards Accreditation and Certification of Age Determination of Aquatic Resources), and regularly participates in ICES workshops for age analysis of salmon.
• External appointments: We carry out assignments on behalf of the provincial governments, municipalities, fishing associations and fishery conservation associations. Contact us for details and prices.


Contact

Magnus Kokkin, Research assistant
Department of Aquatic Resources, Institute of Freshwater Research, SLU
magnus.kokkin@slu.se, +46 (0)10-478 42 35