Expression of smoltification in reared yearling sea trout (Salmo trutta L.). Summary of the doctoral thesis for the scientific degree of Dr.med.vet. | Smoltifikācijas izpausmes audzētiem vienu gadu veciem taimiņiem (Salmo trutta L.). Promocijas darba kopsavilkums Dr.med.vet. zinātniskā grāda iegūšanai
2020
Rutkovska, I., Latvia Univ. of Life Sciences and Technologies, Jelgava (Latvia). Faculty of Veterinary Medicine. Inst. of Food and Environmental Hygiene
The aim of the thesis was to determine smoltification parameters of reared yearling sea trout, the influence of parasite infections on smoltification and to develop suggestion for implementation of Fish resource restocking plan. Objectives of the research: (1) to detect changes in sea trout morphological parameters in the first year of life depending on rearing biotechnology; (2) to detect a dynamics of blood morphological and biochemical parameters in the last five months prior to sea trout release in natural waters; (3) to evaluate sea trout hypo-osmoregulatory ability before and during smoltification; (4) to detect parasite infections and their influence on smoltification parameters; (5) to develop suggestion for release of sea trout juveniles for implementation of Fish resource restocking plan. In the research 1850 yearling sea trout were examined, fish weight and length was established, condition factor was calculated. Salt-water challenge test was performed for 520 sea trout. In total 1077 blood samples were obtained, 520 of them were assessed for haematological parameters, 520 of all blood samples were evaluated for thyroid hormones and 37 blood samples were assessed for chloride ion concentration after salt water challenge test. Section of 1523 sea trout was performed, hepatosomatic index and spleen somatic index was calculated. All sea trout were examined for parasite infections. Results showed that red blood cell count during research from January to March increased but form March to May red blood cell count decreased. The same situation could be seen with haemoglobin, which increased from January to March and from March to May decreased. Haematocrit did not change significantly during the research. Plasma thyroid hormone (triiodothironine and thyroxine) level gradually increased during spring and the highest level was reached in May.
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