Larvae of grayling, Thymallus thymallus (L.) were immersed in tetracycline hydrochloride (TC) and alizarin red S (AL) solutions for 3–4 h at concentrations of 300 and 70 ppm, respectively. Fluorescent marks on the otoliths from the marked fish were identified using a UV‐light microscope. Results obtained with AL were superior to TC in marking otoliths. Fish kept in an aquarium retained good marks for 842 days. Stocking of the Carpathian River Ochotnica with marked grayling larvae revealed good mark retention for 128 days and a survival rate of approximately 12.2%.
In the first food of pollan alevins, nauplii and copepodites dominated, but after the alevins had reached 20 mg, copepods appeared to be more frequent food items. I n the middle of May, Daphnia Zongispina was found in the food of pollan fry with a n individual weight over 45 mg. Benthic invertebrate fauna were taken after the fish weighed more than 1.4 g. Chironomus anthracinus and Chironomus sp. larvae were among the food item dominants.
Institute of Ichthobiology and Fisheries Olsztyn Tetracycline (TC), when consumed along with zoo plankton by the young-of-the-year whitefish, is deposited in the skeleton as calcium-tetracycline compounds, which-in the UV light-form yellow-gold fluorophores. The fluo rescent mark is particularly distinct in vertebrae and otoliths, remaining in those skeletal elements for 24 months and presumably longer. An attempt to utilise artificial feed, based on frcezedried krill substituting live zooplankton used so far, as a TC carrier was made.
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