Fisheries & Aquatic Life

How endocrine disruptors affect fish reproduction on multiple levels: A review

2025-01-02T14:13:56+01:00

This review paper presents fish reproductive toxicology studies with a specific focus on endocrine-disrupting chemicals (EDCs) present in the aquatic environment. These substances, including bisphenols, heavy metals, pesticides, phthalates, and polychlorinated biphenyls (PCBs), act as hormone mimics, receptor blockers, or enzyme inhibitors that affect hormonal regulation in the hypothalamic-pituitary-gonadal (HPG) axis. In this review, we provide an overview of the adverse effects of these pollutants on both female and male fish reproduction (i.e., hormonal disruption in the HPG axis, gametogenesis disorders, disturbed embryogenesis, etc.). Even at low concentrations, EDCs can exhibit reproductive toxicity in fishes. They can affect the functioning of certain systems within the hypothalamus (Kiss/GPR54, GnRH) and can also impact luteinizing hormone (LH) secretion in the pituitary. These compounds have negative impacts on gonads, oocyte maturation, steroidogenesis, and gametes. Early-life exposure to these substances not only affects embryonic development, resulting in increased mortality and body malformations, but this also induces genetic changes in newly hatched larvae. All these observations underscore the need for monitoring the aquatic environment for EDCs and implementing protective measures to preserve the health and welfare of fishes and safeguard water ecosystems.

Fishery stock dynamics in the Baltic Sea: The dichotomy between total allowable catch limits and spawning stock biomass

2025-01-02T14:14:01+01:00

When managing heavily exploited fisheries, the primary objective is ensuring the long-term sustainability of stocks. Policy makers employ various measures to achieve this, with one important approach being the establishment of total allowable catch (TAC) limits for commercial fish stocks. These limits are set to maintain a target level that can sustain or rebuild the spawning stock biomass (SSB), which is an indicator of a stock’s reproductive capacity. Ideally, a strong correlation between TAC quotas and SSB exists, indicating that reductions in TAC are positively impacting SSB. However, in practice, the influence of TAC quotas on fish populations is diminished by other factors affecting reproductive capabilities. This study conducted on the eight most commercially valuable stocks in the Baltic Sea examined this relationship using statistical analysis. The findings revealed that five stocks exhibited a strong-to-moderate positive association between variables, while data for the remaining three stocks were insufficient. The results indicated that stocks with a strong correlation between TAC limits and SSB can be managed more effectively, offering greater potential for sustainability. In contrast, those without this correlation need a more holistic approach that incorporates external ecological factors, as management alone may not suffice to prevent declines. Future strategies should balance TAC and SSB while considering broader environmental factors to ensure sustainable stock dynamics.

Assessing the probiotic potential of Lactococcus lactis isolated from the intestine and gill of rainbow trout (Oncorhynchus mykiss) through in vitro analysis

2025-01-02T14:14:07+01:00

The emergence of diseases and the indiscriminate use of antibiotics have had deleterious consequences in the aquaculture industry. Consequently, the growing emphasis on eco-friendly alternatives has taken center stage, and probiotics have emerged as a notable solution. This investigation aimed to identify and characterize potential probiotic bacteria present in the gills and intestine of rainbow trout (Oncorhynchus mykiss (Walbaum)). A total of 29 isolates were selected for in vitro evaluation. The assays included morphological evaluation, catalase, oxidase, hemolysis, pathogen antagonism, antimicrobial susceptibility, protease, and amylase tests. Seven isolates exhibited antagonism against one of the three pathogens tested (Aeromonas hydrophila, Streptococcus agalactiae, and Lactococcus garvieae). None of the isolates showed resistance to the antibiotics ampicillin, florfenicol, or tetracycline. Furthermore, all isolates showed proteolytic but not amylolytic activity. The isolates with the best characteristics were identified as Lactococcus lactis (n=7) by 16S rRNA gene sequencing.

An investigation on the population parameters of freshwater crayfish (Pontastacus leptodactylus Eschscholtz, 1823) in Lake Yeniçağa (Bolu)

2025-01-02T14:14:12+01:00

This study examines the monthly population parameters of Pontastacus leptodactylus in Lake Yeniçağa, including sex, length, and weight compositions, length-weight relationship, fecundity, morphometry, meat yield, and crayfish plague ratio. For this purpose, 641 crayfish were collected using fyke nets with a 34 mm mesh size. The females carrying eggs were observed between February and May. The female specimens carried between 103 and 841 eggs each, with a diameter ranging from 2.03 to 2.82 mm. The research revealed a size range of 80–168 mm and weight range of 15–133 g for crayfish specimens. As a result of regression analyses, the length-weight relationship was calculated as W = 0.0392L^2.9148 for males and W = 0.0701L^2.6139 for females. The population exhibited negative allometric growth based on the length and weight data. The evaluation of meat yield was based on the total meat yield, which comprises cheliped meat yield and abdomen meat yield. The study found that 14.35% of the P. leptodactylus population in Yeniçağa Lake was affected by crayfish disease. The results indicate that the P. leptodactylus population in Lake Yeniçağa has an overall healthy population structure, with a size suitable for fishing, and should be considered from an economic standpoint.

Assessment of selected indicators of physicochemical conditions in the Rega River from 2018 to 2022 in accordance with EU regulations

2025-01-02T14:14:17+01:00

The aim of this study, conducted in accordance with both European Union and national legislation, was to evaluate the physicochemical conditions of the Rega River in northern Poland, where efforts are underway to restore its watershed for migratory fish. From 2018 to 2022, water temperature, dissolved oxygen (DO), pH, total suspended solids (TSS), conductivity, alkalinity, total hardness (TH), biochemical oxygen demand (BOD₅), chemical oxygen demand (COD_Cr), nitrite nitrogen (NO_2-N), ammonium nitrogen (NH_4-N), and total phosphorus (TP) were measured at nine monitoring sites. The results showed that TSS and nitrite nitrogen (NO_2-N) were the main factors threatening the suitability of the Rega River as a habitat for salmonid fishes. Additionally, maximum water temperatures occasionally exceeded the tolerance limits for these fishes. Seasonal variations in nitrogen and phosphorus forms, and the dependency of nitrogen forms on DO, indicated disruptions in natural biochemical processes due to surface runoff pollutants from the watershed. This includes fertilizer runoff from agricultural fields and municipal pollution from the towns through which the river flows. The findings underscore the need for continuous monitoring of Rega River waters to safeguard the habitat conditions required by environmentally sensitive fish species.

The first data from non-commercial monitoring of the occurrence and range of river lamprey, Lampetra fluviatilis, in selected rivers in northern Poland

2025-01-02T14:14:23+01:00

Human impact on fish populations extends beyond mere exploitation. Rivers and streams, essential conduits for these fish migrations, have undergone substantial anthropogenic modifications driven by navigation, hydropower generation, and water regulation imperatives. An example of one species that has been affected from the anadromous lampreys is river lamprey, Lampetra fluviatilis (L.). Populations of anadromous lampreys have declined dramatically in European rivers, including in Poland, because of the loss of river connectivity and habitat modification that prevents adult lamprey from reaching their original spawning grounds. The present study was conducted on 11 rivers located in northern Poland in the southern Baltic Sea catchment area. River lamprey spawners were sampled with dedicated traps, and 3,026 specimens of 29 fish species were caught at all the sites investigated. The most abundant, frequent species was river lamprey (n = 1,062), which was recorded in 10 of 11 rivers. Only in one case, were river lamprey specimens recorded above a barrage with a fish pass in a tributary of the Rega River. In all other rivers, lamprey was recorded only at sampling sites below the first barrier. Since most fish passes are not designed to provide passage for weaker swimming or non-jumping species, they are not suitable for non-salmonid species like river lamprey.

Main life history traits of the largehead hairtail, Trichiurus lepturus (Linnaeus, 1758) from the Senegalese North coast

2025-01-02T14:14:28+01:00

Trichiurus lepturus is a benthopelagic species of socio-economic importance in Senegal. Despite its intensive exploitation, there is a lack of studies on its life traits in West African waters, particularly in Senegal. This study aims to determine the biological parameters of this species in the northern coastal zone of Senegal. Samples were collected monthly from April 2015 to March 2016 in Cayar, one of the main landing sites in Senegal. A total of 354 specimens were caught with longlines. Condition factor varied between the years with a peak in May. Positive allometric growth (b = 3.24) was found for this species. The reproductive period mainly occurred from April to July, and the sizes at first sexual maturity were 831 mm and 766 mm for females and males, respectively. Absolute fecundity was highly variable (39,976.88 ± 19,793.02 oocytes). The growth parameters estimated were asymptotic length (L∞) = 134 cm and the growth coefficient (K) = 0.0016. The maximum observed age was 1 year and 7 months. These parameters could be integrated into stock assessment models, providing a better estimate of the exploitation level of this resource and aiding in the formulation of more scientifically informed management measures for sustainable exploitation.