• alcohol;
  • fish;
  • freezing;
  • preservation;
  • shrinkage

Preservation in 30% ethanol and freezing to a temperature of −20 ± 2° C is an appropriate method for measurement of fish eggs, larvae and juveniles. Egg diameter of the common carp Cyprinus carpio increased insignificantly by 1·32% after preservation compared with live size. The total length (LT) of 1 day post-hatching (dph) larvae as well as the standard length (LS) of 16 dph larvae of C. carpio increased significantly (2·95 and 1·50%, respectively) after preservation. Egg diameter as well as the LT of 1 dph larvae of barbel Barbus barbus increased significantly after preservation, by 1·74 and 1·96%, respectively over their original size. The standard length (LS) of 14 dph larvae of B. barbus as well as juveniles of B. barbus, crucian carp Carassius carassius, common nase Chondrostoma nasus and tench Tinca tinca decreased significantly after preservation (−0·56 to −5·54%), whereas their body mass increased significantly (11·46–18·57%). Preserved eggs of C. carpio and B. barbus were hard, round and transparent. The larvae and juveniles of examined fishes, preserved in frozen ethanol, were straight, flexible and easily measurable after 60 days. Integrity of body surface and fins, as well as preservation of colours were much better in larvae or juveniles frozen and thawed only once than in specimens frozen and thawed thrice. Cooling in 30% ethanol to a temperature of 6 ± 2° C and freezing in water to a temperature of −20 ± 2° C are not appropriate preservation methods for eggs and larvae of C. carpio (1 and 16 dph).