Fisheries & Aquatic Life

Fish communities in Baltic Sea coastal bays; using eDNA metabarcoding to assess vertical profile and traditional method comparison

Neele Schmidt — 2025-06-30

Fish communities in the coastal Baltic Sea are currently monitored using passive fishing gears, such as gillnets. In recent years, eDNA approaches have gained popularity for fish detection thanks to their non-invasive nature, faster processing, and more precise identification, although such methods have been underutilized in comprehensive fish community assessments in the Baltic Sea. This study reports fish diversity using eDNA metabarcoding within different depth profiles for the first time in
temperature-stratified coastal bays in the Baltic Sea, while also offering some comparison with traditional net-based approaches. Comparing samples above and below the thermocline revealed exclusivity in fish species at both depths, emphasizing the importance of vertical sampling in capturing a comprehensive understanding of fish distribution patterns in such systems. Results indicated that eDNA captured more fish taxa per sample compared to gillnet sampling, with similar or higher fish diversity, although variations occurred between bays. This study highlights the importance of incorporating eDNA metabarcoding, alongside traditional survey methods, to aid assessment of fish communities in aquatic environments.

Length-weight relationship and condition factors of European perch, Perca fluviatilis, from 38 lakes in northeastern Poland

Michał Kozłowski — 2025-06-30

Length-weight relationships and condition factors of various fish species depend on food resources, habitat, season, water quality, and the size, age, and sexual maturity of fishes. The aim of this study was to determine the length-weight relationships (LWR) and the values of the Fulton condition factor (K_f), the allometric condition factor (K_a), and the relative condition factor (K_r) of European perch Perca fluvatilis from 38 lakes located in northeastern Poland. The total length (TL) of the perch ranged from 3.9 to 41.4 cm. The body weight of the fish caught ranged from 0.4 to 1,162.1 g. The linear regression coefficient of the LWR was highly significant (r²=0.99). Parameter b (3.1859) indicated positive allometric growth. The mean values of K_f (0.996 ± 0.154) and K_r (1.003 ± 0.121) indicated that the fish from the Polish lakes were in good condition. None of the condition coefficients differed significantly among the various maximum depth ranges of the lakes (P > 0.05). RDA analysis indicated a weak positive correlation between K_r and morphometric parameters of lakes. K_a was strongly correlated with lake surface area, while K_f was weakly correlated with the depth of the lakes studied. The results of this study are very important for updating data regarding the fish fauna of Polish lakes and for the management of commercial and recreational fisheries.

Effects of active protection of the endangered fish lake minnow, Eupallasella (Rhynchocypris) percnurus (Pallas, 1814), on its occurrence in Mazowieckie Voivodeship in Poland

Justyna Sikorska — 2025-06-30

Mazowieckie Voivodeship was the first region in Poland to widely apply fish translocations for the active protection of the lake minnow, Eupallasella (Rhynchocypris) percnurus, a species of the family Leuciscidae at serious risk of extinction. These efforts began in 2002 and concluded in 2018, during which time over 21,000 juvenile fish from aquaculture were translocated to 13 water bodies. As a result, five new viable populations were established with the use of 17,000 fish. Three of these were confirmed to be viable in 2024, and one other probably also still exists. The failure of all the other translocations were habitat loss from drying up or population extinction caused by introductions of predatory fish species. The three or four new lake minnow populations contribute considerably to the present status of this species in the voivodeship, because the total number of all sites in 2024 did not exceed seven. These new populations also play a notable role in Poland, as there are likely not more than 80 lake minnow sites at present.

Relative growth and morphometry of otolith sagittae of Pseudotolithus senegalensis (Val.) along the coastline of Cameroon

Matouke Matouke Moise — 2025-06-30

Pseudotolithus senegalensis is among the most important commercial fishes in Cameroon. However, data on the life history of P. senegalensis are limited. This study analyzed the length-weight relationship (LWR) and condition factor of the fish, the relationship between the length and weight of fish and the length and weight of otolith sagittae. The fish (123) were collected for a period of three months (March-May) from the coastline region of Down Beach, Limbé, Cameroon. There was a significant (P<0.05) positive allometric relationship between the length and weight of the fish. However, no significant (P>0.05) relationship between the length class frequency of males and females was noted. Relationships between fish length and weight and otolith length and weight were described by linear regression models and significant correlations were obtained for all relationships. The highest correlation (r² = 0.55) was between otolith length and fish weight and the lowest correlation (r² = 0.14) was between otolith weight and fish weight. The results of this study demonstrate that fish length and weight and otolith dimensions have a positive allometric relationship; therefore, they could be a useful instrument for the assessment and evaluation of fish growth in stock and fisheries management.

Morphological characteristics of smoothbelly sardinella, Amblygaster leiogaster (Val.) in the Bay of Bengal

Md. Ashekur Rahman — 2025-06-30

Species identification, classification, and the genetic studies of fishes rely principally on meristic counts and morphometric characteristics. The current study was designed to provide the first comprehensive, instructive description of the meristic counts and morphometric relationships (length-weight relationship [LWR] and length-length relationship [LLR]) of Amblygaster leiogaster (Val.) from Bangladesh waters. Using various traditional fishing gears, 250 individuals were collected from the Bay of Bengal, Bangladesh between December 2019 and November 2020. A magnifying glass was used for the meristic counts, including several fin rays. Nine lengths were measured to the nearest 0.1 cm using a measurement board, and body weight (BW) was determined to the nearest 0.01 g with a digital electronic balance. The fin formula was: D. 17–18 (2/15–16); P. 15–16 (1/14–15); Pv. 8 (1/7); A. 18–20; C. 19–20 (2/17–18). Total length (TL) range was 13.3–20.0 cm, and BW range was 25.72–79.69 g. All LWRs demonstrated a high level of significance (P < 0.0001) with r² values ≥ 0.946. The best fitted models were BW vs TL in LWRs, and TL vs FL in LLRs, as shown by the highest r² values. This study serves as a baseline for identifying this species that will help fisheries scientists in further research.