Effect of water temperature on egg incubation time and quality of newly hatched larvae of northern pike (Esox lucius L., 1758) Summary This study examined the effect of temperature on egg incubation, survival of eggs during embryonic development and quality of newly hatched larvae of northern pike (Esox lucius L.) under laboratory conditions. Eggs of similar size (diameter 2.7 AE 0.16 mm and weight 6.11 AE 0.35 mg) from five females were incubated at 3, 6, 10, 14, and 18°C (groups A, B, C, D, and E, respectively). The lowest fertilization (FR) and hatching rates (HR) were observed in larvae incubated in group A, 44.6 AE 3.2% and 18.26 AE 2.25%, respectively. The highest FR and HR were found in group B (FR, 71.3 AE 4.3%; HR, 56.2 AE 3.21%) and C (FR, 65.6 AE 3.1%; HR, 65.5 AE 5.41%). Time of incubation period varied from 38 AE 0.33 days (120 AE 1.03°d) when 5% larvae were hatched to 46 AE 0.42 days (144 AE 1.31°d) when 95% larvae were hatched in group A and 2.5 AE 0.08 days (44.67 AE 1.42°d) when 5% larvae were hatched to 3.42 AE 0.06 days (61.11 AE 1.07°d) when 95% larvae were hatched in group E. Larvae from groups A, D, and E were characterized by the lowest values of variables such as resistance to osmotic stress after 90 min of exposure of saline solution (OS = 54 AE 3-76 AE 3%), frequency of normally developed larvae (FNL = 23.8 AE 4.14-87. 1 AE 2.42%), and yolk sac volume (YsV = 3.41 AE 0.44-3.89 AE 0.45 ll 3 ). The highest quality larvae were recorded in groups B and C: OS = 92 AE 3% and 80 AE 4%, FNL = 89.7 AE 3.62% and 93.8 AE 3.17, YsV = 3.3 AE 0.66 ll 3 and 3.04 AE 0.42 ll 3 ). Fertilization and hatching rates and quality of larvae showed optimal temperature for successful egg incubation and production of high quality larvae to be 6 to 10°C. Relationship of ontogenic rate to temperature showed development of the pike embryo to be hypothetically stopped at 3.3°C.U.S.

Effect of incubation temperature (range: 9-36 °C; interval: 3 °C) on artificially propagated weatherfish (Misgurnus fossilis) early ontogeny (during interval from egg fertilization to the finish of hatching) was investigated. Both, the amplitude of the incubation period (evaluated in four crucial moments), the total hatching period duration was inversely proportional to the incubation temperature and ranged from 17.5 days at 9 °C to 1.8 days at 24 °C (expressed at H 50 ) or from 137 hours at 9 °C to 9 hours at 24 °C, respectively. There were no influence of rising temperature on the total length of newly hatched larvae (T L = 4.23-4.67 mm), in contrast to negative correlation with developmental stage (9-18 °C: stage 37; 21-24 °C: stage 36), i.e. the length might determine the age at hatching, rather than the age at hatching determines the hatching length. The thermal tolerance range in term of survival lies between 9 and 24 °C (the thermal optimum 15-24 °C, i.e. weatherfish is a warm-mesothermic species). Temperatures above 24 °C (in our study 27-36 °C) are considered the lethal temperatures already during embryonic period. It is highly recommended to distinguish an impact of suboptimal temperatures 9-12 °C on development during explored interval only, in contrast to possible other effect of these lower temperatures in context of the whole early ontogeny. RÉSUMÉEffets de la température sur les premiers stades de vie de la loche d'étang, Misgurnus fossilis (L. 1758) L'effet de la température d'incubation (gamme : 9-36 °C, intervalles : 3 °C) sur les premiers stades ontogéniques de loches d'étang (Misgurnus fossilis) (de la fécon-dation à la fin de l'éclosion) a été étudié. La durée de la période d'incubation (évaluée à quatre moments clés) et la durée de la période d'éclosion des oeufs d'un lot sont inversement proportionnelles à la température d'incubation et s'étalent de 17,5 jours à 9 °C à 1,8 jour à 24 °C (pour l'indice H 50 ) et de 137 heures à 9 °C à 9 heures à 24 °C, respectivement. Il n'y a pas d'influence d'une élévation de température sur la longueur totale des larves à l'éclosion (T L = 4,23-4,67 mm), alors qu'il y a une corrélation négative avec le stade de développement (9-18 °C : stade 37 ; 21-24 °C : stade 36), i.e. la longueur semble déterminer l'âge à l'éclo-sion, plutôt que l'âge à l'éclosion déterminerait la longueur à l'éclosion. La gamme

The study investigated the combined effect of weaning from live feed to a commercial dry pellet at 10, 15, 20, 25 or 30 days posthatching (dph) and co‐feeding for 1, 3 or 6 days on survival and growth of Coregonus peled larvae. Additional groups fed only live Artemia sp. nauplii (ART), and only Biomar LARVIVA ProWean 100 (DRY) were included. A final survival rate of 66.4%–85.5% was observed in groups weaned after 20 dph. Final body weight (BW) and total length (TL) were significantly lower in groups weaned at 10 and 15 dph, regardless of the duration of co‐feeding. Larvae reached 29–37 mg BW and TL of 17.7–19.0 mm in groups weaned at 20, 25 and 30 dph. The recommended minimum duration of feeding with live food, based on these results, is 20 days. Based on the significantly higher yield of larvae weaned after 20 dph irrespective of co‐feeding duration, it can be concluded that abrupt weaning to dry food after 20 days of feeding with live prey can provide adequate production while reducing the effort and costs associated with live feed.

Rapid expansion of round goby (Neogobius melanostomus) and western tubenose goby (Proterorhinus semilunaris) beyond their native ranges calls for urgent management action, particularly in localities with high introduction possibility of the species. We used a comparative functional response (FR) approach to forecast invader ecological impact. We compared their foraging efficiency in three habitat structures: sand, coarse gravel, and coarse gravel with an artificial plant. Both Neogobius melanostomus and Proterorhinus semilunaris showed type II FR in all habitats. Interspecific comparison showed similar handling times in both the gravel and gravel with artificial plant habitats, suggesting similar per capita impact. Intraspecific comparison showed significantly lower handling times of both predators on gravel substrates. Therefore, their ecological impact in such an environment could be higher. Neogobius melanostomus showed higher attack rates on sandy substrates compared with Proterorhinus semilunaris, while no significant differences were observed on other substrates. Our results highlight the importance of interacting factors in management of ecosystems with multiple invaders, as the elimination of invasive Neogobius melanostomus may lead to utilization of the empty niche by alien Proterorhinus semilunaris with similar ecological impact.

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