Assessing the acclimatisation to the wild of stocked European graylings Thymallus thymallus by monitoring lipid dynamics and food consumption

This study investigated how 2+-year-old stocked pond-reared European graylings (Thymallus thymallus) acclimatised to a wild environment during six months (May–October 2019) after released. We examined the quantity and composition of lipids in the liver, muscles and visceral adipose tissues (VAT), as well as size parameters, condition factors and stomach contents. Our results showed a low post-stocking recapture rate (5.17%) of stocked fish after 6 months suggesting a poor acclimation to the wild environment. During the six months of monitoring, stocked fishes exhibited a sharp decrease in lipid content in all examined tissues, and, in the final month, lipid content was well below those of wild conspecifics. Stocked graylings preferred risky foraging behaviour and consumed numerous small drift preys with occasional hyperphagic events, thus experiencing strong bioenergetic challenges. Our study reveals that fish cultivated for extended periods struggle to acclimatise to the wild environment and that this commonly used stocking practice seems unsuccessful when aimed at strengthening wild grayling populations

Pharmaceutical pollution disrupts the behaviour and predator–prey interactions of two widespread aquatic insects

Pharmaceutical pollution represents a rapidly growing threat to ecosystems worldwide. Drugs are now commonly detected in the tissues of wildlife and have the potential to alter the natural expression of behavior, though relatively little is known about how pharmaceuticals impact predator-prey interactions. We conducted parallel laboratory experiments using larval odonates (dragonfly and damselfly nymphs) to investigate the effects of exposure to two pharmaceuticals, cetirizine and citalopram, and their mixture on the outcomes of predator-prey interactions. We found that exposure to both compounds elevated dragonfly activity and impacted their predation success and efficiency in complex ways. While exposure to citalopram reduced predation efficiency, exposure to cetirizine showed varied effects, with predation success being enhanced in some contexts but impaired in others. Our findings underscore the importance of evaluating pharmaceutical effects under multiple contexts and indicate that these compounds can affect predator-prey outcomes at sublethal concentrations

Pharmaceutical pollution disrupts the behavior and predator-prey interactions of two widespread aquatic insects

Pharmaceutical pollution represents a rapidly growing threat to ecosystems worldwide. Drugs are now commonly detected in the tissues of wildlife and have the potential to alter the natural expression of behavior, though relatively little is known about how pharmaceuticals impact predator-prey interactions. We conducted parallel laboratory experiments using larval odonates (dragonfly and damselfly nymphs) to investigate the effects of exposure to two pharmaceuticals, cetirizine and citalopram, and their mixture on the outcomes of predator-prey interactions. We found that exposure to both compounds elevated dragonfly activity and impacted their predation success and efficiency in complex ways. While exposure to citalopram reduced predation efficiency, exposure to cetirizine showed varied effects, with predation success being enhanced in some contexts but impaired in others. Our findings underscore the importance of evaluating pharmaceutical effects under multiple contexts and indicate that these compounds can affect predator-prey outcomes at sublethal concentrations.</p

Evaluation of large-scale marking with alizarin red S in different age rainbow trout fry for nonlethal field identification

Fry of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), was subjected to one-hour and four hours immersion in Alizarin red S (ARS) bath 150 mg · L–1. The experiment involved seven age groups (40, 50, 60, 70, 80, 90, and 100 days) and was conducted to estimate the minimal age of salmonids for mass marking with ARS bath enabling subsequent effective, simple field nonlethal identification, based on fin rays checking. The fish were examined at the ages of 200 and 300 days. The results showed a high retention level of ARS traces in caudal fin rays ensured satisfactory visibility and quick detection. A success rate of marking detection was >90% at 200 and 300 days of age and the fish were immersed in ARS solution from 60 days of age (685°D). This treatment provided better results in fish bathed for four hours. Recognition of marks using a laser pointer and protective glasses was successful even in fish, with a 3.5–5.0 times length increase compared to the marking time. The results indicate a high potential for ARS marking and its field identification for juvenile salmonids, which can significantly expand the possibilities of field experiments