Fisheries & Aquatic Life

Formerly: Archives of Polish Fisheries

Vol. 26 Fasc. 2

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Fish. Aquat. Life                  Vol. 26 Fasc. 2                  2018         p. 101-109

DOI 10.2478/aopf-2018-0011


Triiodothyronine and thyroxine changes in yearling sea trout (Salmo trutta L.) during spring

Ilze Rutkovska, Ruta Medne

ABSTRACT. Triiodothyronine and thyroxine levels and morphological parameters of fish were studied from January to May to evaluate the smoltification of yearling sea trout (Salmo trutta L.) raised in two different rearing systems (recirculating and flow-through) in three different hatcheries in Latvia. Thyroid hormone levels increased from January to May in both rearing systems in fish of different sizes. There was positive correlation between the degree of silvering and fish fork length and thyroid hormone levels, but there was no correlation between condition facor and thyroid hormone levels. Fish reared in recirculating systems were significantly larger (p < 0.05) and exhibited more visible signs of smoltification earlier than those reared in flow-through systems. The thyroid hormone levels and degree of silvering gradually became nearly the same by May in the sea trout from both rearing systems. Changes in thyroid hormone levels or fish size in spring cannot be evaluated separately from other signs to determine smoltification.

Keywords: morphology, salmonids, silvering, smoltification, thyroid hormones.

CORRESPONDING AUTHOR:

I. Rutkovska [+], R. Medne
Latvia University of Life Sciences and Technologies,
Faculty of Veterinary Medicine, Latvia
e-mail: ilze.rutkovska@gmail.com

Ruta Medne
Institute of Food Safety, Animal Health and Environment BIOR, Latvia