This study aimed at improving the reproduction effectiveness and synchronization of ovulation in the pikeperch, Sander lucioperca (L.), during induced spawning, which is one of the main bottlenecks in the aquaculture of this species. For this purpose, a new categorization of maturation stages in pre-ovulatory oocytes was applied. It is generally based on two morphological indicators: germinal vesicle migration or its breakdown (GVBD) and different oil droplet coalescence rates. This categorization covered seven stages (from I to VII) – from the end of vitellogenesis to ovulation. The categorization was verified by controlled reproduction with the use of hormonal stimulation (500 IU of hCG per kg of female body weight) and low spawning temperature (12 °C), which extended the latency time. In addition, some morphological indicators (pseudo-gonadosomatic index, Fulton's condition coefficient) of females were calculated in order to determine their usability in determining the maturation stage. However, these indicators proved to be ineffective for this purpose, further highlighting the need to determine the maturational stages in pre-ovulatory oocytes to synchronize ovulation in pikeperch. During the experiment, ovulation seemed to be synchronized among the experimental treatments. Statistical differences were found in terms of latency time between experimental groups at different maturity stages (II – 78–98 h; III – 57–78 h; IV – 48–58 h; V – 32–49 h; VI – 5–30 h) according to the proposed classification. This classification and the results presented in the study significantly improved the synchronization of ovulation, which may positively affect the effectiveness of pikeperch production under controlled conditions.

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This study analyzed the morphological development and allometric growth patterns of Lota lota L. (burbot) larvae reared under controlled laboratory conditions. From hatching to day 50, twenty larvae were sampled each [between 1 and 14 days post-hatch (DPH)] or every second day (between 14 and 50 DPH) and measured under a stereoscopic microscope using analytic software. Based on the external morphology, the different stages during early development of burbot were identified: yolk sac larva 0–8 DPH [3.92–4.37 mm total length (TL)]; preflexion larva 9–26 DPH (4.57–12.06 mm TL); flexion larva (between notochord degradation and its replacement with rays) 28–34 DPH (14.00–16.34 mm TL) and postflexion larva/juvenile 36–50 DPH (18.20–29.27 mm TL). Allometric growth patterns of some parameters (e.g., total length, head length, body length, tail length, head depth, body depth, eye diameter) were modeled by a power function and described by the growth coefficient. Organogenesis and changes of body proportions in burbot larvae were more rapid and complex during the yolk sac and preflexion phase of development as larvae developed most of their sensorial, feeding, respiratory and swimming systems and after notochord flexion, when most morphological changes were related to the progressive transformation from pelagic larva to demersal larva/juvenile.