Fisheries & Aquatic Life

Age and growth of invasive alien fish species, Perccottus glenii and Lepomis gibbosus, in water bodies of Transcarpathia (Ukraine)

2026-02-06T08:15:13+01:00

The Transcarpathia region of Ukraine is one of the most vulnerable regions for bioinvasions. There are five invasive and nine native species in the artificial water bodies of plain Transcarpathia. This study focused on the life-history traits of the Chinese sleeper Perccottus glenii Dybowski and pumpkinseed Lepomis gibbosus (L.). The standard length of the Chinese sleeper varied from 14.40 to 94.85 mm, and the total weight varied from 0.11 to 20.05 g. The standard length of pumpkinseed varied from 12.31 to 75.81 mm, and the total weight varied from 0.04 to 17.26 g. Both species form five age group populations dominated by young individuals and reach sexual maturity in their second year of life with a standard length of more than 40 mm. The combination of early maturation, rapid population turnover, and a broad size structure likely enhances the invasive success of both species under local conditions. These findings highlight the high adaptive potential of P. glenii and L. gibbosus and emphasize their capacity to establish stable populations, posing a long-term threat to native fish assemblages in artificial freshwater ecosystems of Transcarpathia.

Length-weight relationship and condition factor of sea trout from the Słupia River (Poland), during the spawning migration

2026-02-06T08:15:19+01:00

Ulcerative dermal necrosis (UDN) has been observed in sea trout (Salmo trutta L.) entering the Słupia River to spawn. During this time, various biotic and abiotic factors can disrupt homeostatic balance, leading to severe pathological changes, including those on the skin surface. The aim of the study was to determine whether the symptoms of ulcerative dermal necrosis affect the growth and condition of sea trout migrating to spawning areas in the Słupia River. Between 2021 and 2024, 63 fish ascending the fish ladder in the Słupia River were tested. The length-weight relationship (LWR) and Fulton’s condition factor (Kc) were estimated. A comparison of the slopes and intercepts of the LWR regressions for both healthy and diseased males and females indicated no statistically significant differences among the groups examined. Consequently, this suggests that UDN infection does not have a relevant impact on linear regression. Additionally, a comparison of Kc values between the studied groups did not reveal a statistically significant effect of UDN in sea trout. The current study provides basic biometric data on spawning stocks of sea trout in the Słupia River, where UDN is observed, thereby expanding knowledge on this subject.

Assessing the potential for introducing resident brackish-water pike (Esox lucius) to restore depleted Baltic Sea populations

2026-02-06T08:15:24+01:00

The northern pike (Esox lucius L.) inhabits the Baltic Sea and has two reproductive strategies: spawning in freshwater wetlands (anadromous populations) and direct spawning in coastal marine waters (resident brackish populations). Resident brackish populations do not occur in Polish marine waters, and anadromous pike populations in Puck Bay are virtually extinct. This study assessed whether reproductive material from resident brackish pike populations could be used to obtain larvae under hatchery conditions for population restoration. Eggs were collected from resident brackish pike spawners in the coastal waters of Rügen (Germany) and transported 600 km (9 h) to a hatchery in Poland. The eggs were incubated in artificially prepared saline water at 0, 5, 7, and 8.5 PSU. In the 2023 trial, hatching success was 0% at 0 PSU, 0.7% at 5 PSU, 8.3% at 7 PSU, and 8.0% at 8.5 PSU. Larval survival to 18 days post hatching in salinities of 5–8.5 PSU was high (approximately 90%), and growth rates at 14°C ranged from 0.26 to 0.31 mm d^-1. No eggs hatched in 2024. The results indicate that this strategy is feasible, particularly given the high larval survival; however, the low and variable hatching success requires further optimization before application in restoration programs.

Unusual development of an accessory otolith in herring (Clupea harengus) larva

2026-02-06T08:15:30+01:00

Otoliths are key to reconstructing fish life history, as their structure records individual and environmental information. These inner ear structures grow incrementally, revealing growth rates, migration patterns, and environmental conditions. However, internal factors (e.g., genetic mutations and stress) and external factors (e.g., temperature changes and pollution) can cause structural anomalies, such as shape deformities, asymmetry, and altered composition. This study describes a unique anomaly, an unusual accessory otolith, in the sagittal otolith of an Atlantic herring (Clupea harengus L.) larva collected from the Vistula Lagoon in the southern Baltic Sea, a vital spawning area. A 40 mm larva exhibited a rare otolith anomaly (found in only one of ~2000 specimens analyzed) characterized by a main otolith measuring 0.47 × 0.39 mm with an average of 64 daily increments, and an attached accessory measuring 0.20 × 0.10 mm with an average of 25 daily increments. This anomaly, previously unreported in Baltic herring larvae, may reflect environmental stressors and is significant for understanding developmental abnormalities in fish.

Fish lice (Argulidae: Argulus spp.) infestations detected on freshwater fish in Türkiye: Argulus foliaceus (Linnaeus, 1758) and Argulus japonicus Thiele, 1900

2026-02-06T08:15:35+01:00

Argulus (Crustacea: Branchiura) species, also known as fish lice, are among the most important aquatic ectoparasites infesting fish in Türkiye and worldwide because of their low host specificity and widespread distribution. Approximately 130 species have been identified within this genus, which inhabit freshwater, marine, and estuarine environments. To date, only two species have been reported from Türkiye: Argulus foliaceus (Linnaeus, 1758) and A. japonicus Thiele, 1900. This study aimed to determine the host diversity of Argulus species reported in Türkiye through a literature review. Additionally, we aimed to report A. japonicus infestations detected in common carp (Cyprinus carpio L.) and Amur carp (Cyprinus rubrofuscus Lacepède) (ornamental form; koi) during routine parasitological surveys conducted at the Mediterranean Fisheries Research, Production, and Training Institute (Antalya, Türkiye). Argulus japonicus, a parasite found on common carp (C. carpio), represents a new host–parasite association for the parasitic fauna of Türkiye.