Stojmir Stojanovski

Aquaculture in Europe has experienced significant growth in recent decades, driven by rising demand for sustainable production and strong policy frameworks promoting environmentally responsible aquaculture practices. Biomarkers, defined as measurable biological indicators reflecting physiological, biochemical, or molecular responses to environmental and biological stressors, have greatly expanded their use in aquaculture applications. In this regard, biomarker-based approaches are increasingly applied in multiple areas of aquaculture, including health and disease monitoring, welfare as-sessment, environmental toxicology, reproductive biology, population management, and the optimization of cryopreservation protocols. This review provides a compre-hensive overview of current biomarker applications in European aquaculture, highlig-hting recent technological advances, methodological challenges, and emerging rese-arch directions. By synthesizing current knowledge and identifying future research priorities, this review aims to contribute to the development of biomarker-driven mo-nitoring strategies that enhance the resilience, efficiency, and sustainability of aqua-culture in Europe.

Large freshwater mussels, also known as naiads, are important organisms that provide crucial ecosystem functions and services but are experiencing significant declines across Europe. To ensure effective conservation, it is essential to have a well‐coordinated monitoring scheme. Therefore, we analyzed the functioning of naiad monitoring systems in 31 European countries. Monitoring of naiad populations is not coordinated in Europe, is largely unrelated to monitoring of water quality or host fish species, and receives irregular funding. Raw data on monitored species are typically unavailable, which hampers independent and/or large‐scale analyses. The quality of EU monitoring schemes according to Article 17 of the Habitats Directive is poor for the most threatened species. To improve this, a new scheme is recommended with raw data stored in publicly available repositories to enable instant analysis and rapid, appropriate, evidence‐based responses that can support the conservation of this imperilled taxon.

During a parasitological survey of Squalius squalus from Belčišta Wetland (Republic of North Macedonia), six parasite species found. These were Dactylogyrus sphyrna, Paradiplozoon ergensi, Gyrodactylus sp., Allocreadium isoporum, Proteocephalus torulosus and Pomphorhynchus bosniacus. The total helminth prevalence was 90.91%. The species with the highest prevalence were P. bosniacus (59.09%) and D. sphyrna (54.55%). The average intensity of infection was 6.08, with the highest values of D. sphyrna (7.83) and P. bosniacus (5.92). The present study is the first record of Proteocephalus torulosus in S. squalus in the Republic of North Macedonia. Among the parasite species found, the greatest pathological impact was associated with D. sphyrna, P. ergensi and P. bosniacus.

Eight out of the eleven indigenous fish species of Prespa are endemic, i.e. they exist only in the Lake Prespa. One of these endemic fish species is Prespa bleak (Alburnus belvica). The parasitological examination from the Macedonian part of the Lake Prespa in 2023 showed that all of 14 examined specimens of Prespa bleak fishes were infested (100.0%). In our case study the presence of 8 parasite species was established: Gyrodactylus sp., Dactylogyrus alatus f. typica, Dactylogyrus fraternus, Dactylogyrus sphyrna, Posthodiplostomum cuticola (larva), Cestoda gen. sp. (larva), Raphidascaris acus (larva) and Ergasilus sieboldi. Individually, by the parasite species, the highest prevalence was with Dactylogyrus fraternus, Dactylogyrus sphyrna and Posthodiplostomum cuticola (larva) (71.43%). The lowest one was with Cestoda gen. sp. (larva) (7.14%). In our case study the parasites Gyrodactylus sp., Dactylogyrus fraternus and Cestoda gen. sp. (larva), are recorded for the first time in the ichthyoparasitofauna of Lake Prespa and Macedonia.

Belčišta wetland is the largest wetland habitat in R. of North Macedonia, located 20 km distance from Ohrid Lake and it is a relict remnant of the ancient Desaret Lake, which existed in this area since the Pliocene. This region hosts an endemic freshwater species of the Balcan Penninsula, Pelasgus minutus, which is threatened by habitat loss. There are intentions of artificial introduction of salmonid fishes in Belčišta wetland to develop the recreative fishery and tourism in this area. Introduction and spread of salmonids is a great risk factor to the survival of the ohrid minnows (Pelasgus minutus).

In our study, a total of 33 specimens of three cyprinid fish (Squalius squalus, Phoxinus lumaireul, and Pelasgus minutus) from Belčišta wetland (south-west Macedonia) were subjected to a parasitological investigation, by season. One specimen of Acanthocephalus lucii was found in autumn, in intestines of minnow (Phoxinus lumaireul Linnaeus, 1758). The record of Acanthocephalus lucii in minnow is considered as the first in N. Macedonia. At the same time, minnow represent a new host for this parasite worldwide.

Large freshwater mussels (Unionida) are long-lived, have large bodies, and produce thousands to millions of larvae (glochidia) that usually must attach to host fish tissue to complete their life cycle. This is an obligate parasitic stage of mussel larvae. However, less than one in onemillion find a suitable host and survive. The degree of host specificity varies among unionid species, from specialists that can successfully parasitize only one or a few closely related fish species to generalists that can complete development on a taxonomically broad range of fish species. In addition, freshwater mussels are among the most threatened groups of animals. This is due to habitat destruction, the introduction of non-native species, and the loss of host fish on which their larvae (glochidia) are obligate parasites. Glochidiosis harms fish by affecting their growth; on the other hand, freshwater mussels play an important role in freshwaters by improving water quality and ridding the water of bacteria, algae, and pollutants, they are an indicator species of water quality. During our parasitological survey of fish from the Macedonian part of Lake Prespa in April 2022, many glochidia were found on the gills, skin, and fins of two endemic fishes, Prespa roach (Rutilus prespensis) and Prespa nase (Chondrostoma prespense), in the range of tens to thousands on one host. We thus recorded these two endemic species as new hosts of A. cygnea.

The representatives of the class Monogenea are of great importance in fish pathology. Dactylogyrus vastator (Nybelin 1924) (Monogenea: Dactylogyridae) is a common pathogenic monogenean parasite in common carp (Cyprinus carpio Linnaeus, 1758) from freshwater lakes and cyprinid ponds, worldwide. In our study, a total of 133 specimens of common carp from the cage culture system on Mladost Reservoir (N. Macedonia) were subjected to a parasitological investigation, by seasons. Only fresh fish were subjected to routine identification, dissection, and observation methods. Parasite identification was performed morphologically, based on the character of significant organs, using referent keys for determination. Dactylogyrus vastator was found in winter, on gills of 27 specimens of common carp, with a prevalence of 2.818%, and mean intensity of 6.850. During our research, the presence of Dactylogyrus vastator was found in an aquaculture facility with a very high fish stock density. This parasite species would lead to fish mortality and it depends primarily on the mean intensity, the fish condition, and size, as well as the water temperature and oxygen content. The records of Dactylogyrus vastator in common carp in the present study are considered as the first records in N. Macedonia. The common carp is regarded as a new host for these parasite species in Macedonian aquaculture.