Fish Population Dynamics Research Articles

The impact of climate change on the reproductive biology and population dynamics of fishes: Implications for fisheries and food security

The purpose of this paper is to review and evaluate published literature on the impact of climate change on the reproductive biology and population dynamics of fishes. A systematic method was utilized to access published literature on “Impacts of Climate Change on fishes and fisheries”. A total of fifty-two (52) research papers published between the years 1973 to 2024 were accumulated and used for this review. A subjective approach was used to select the topics: impact of climate change and fishes and fisheries. The physical and biological impacts of climate change on fisheries were evaluated. In addition, the role of fisheries in food security to combat the global hunger index of human beings was assessed in this review paper. Strategies to be implemented by fisheries to mitigate the effect of climate change was also presented in this review. The literature accessed revealed that fish is an important resource to the economies of many countries and a source of natural protein. As the average per capita food supply from fish and fisheries products continue to rise in developing nations, it is falling in underdeveloped nations. The published works of literature established that the global fisheries and fish population dynamics, reproductive biology, abundance and distribution are all affected by climate change. This review highlights the fact that more extensive studies on the impact of climate change on fishes and fisheries should be done in neotropical countries since there are gaps of such information on research and published data in these biodiversity rich regions.

Age-Dependent Enhancement in Fecundity and Ova Diameter of <i>Schizopyge niger</i> (Heckel, 1838) in Dal Lake, Kashmir

Understanding the reproduction and recruitment pattern is essential for successful conservation of a species. Accurate estimates of fecundity plays acrucial role in comprehending fish population dynamics. The snowtrout, Schizopyge niger, is a Cyprinid fish widely distributed throughout the lakes of Kashmir valley and is one of the most important commercial fish species. In this study, we examined the age-dependent reproductive perfor-mance of female S. niger, aiming to gain insights into its breeding characteristics for the development of an optimal brood-stock management plan. The study involved 78 female S. niger specimens collected from Dal Lake during the spawning season, representing age groups of 2+, 3+, 4+, 5+, and 6+ years. Fecundity and ova diameter showed an increasing trend from age 2+ (3,971 eggs; 1.45 mm) to age 6+ (10,501 eggs; 2.00 mm). Total fecundity exhibited positive correlations with age, total weight, ovary weight, and ova diameter. Additionally, there was a positive correlation between ova diameter and fish age, with the highest fecundity and largest ova diameter observed in the 6+ years age group. Among each age group, fecundity and ova diameter varied significantly (p <0.05). Based onthese findings, for optimal broodstock management of S. niger, it is recommended to use females of the6+ years age group after assessing the quality of eggs.

Population dynamics of resident fish in a coastal lagoon under eutrophication-mediated habitat changes

Coastal lagoons, as transitional ecosystems, are crucial for providing ecosystem services and preserving fish communities, yet they face increasing pressures from anthropogenic activities. The Mar Menor coastal lagoon in the western Mediterranean exemplifies this challenge, as it suffers from severe eutrophication driven by agricultural and urban influences. In this study, we assess changes in the population dynamics of three resident fish species (Apricaphanius iberus, Pomatoschistus marmoratus, and Syngnathus abaster) in the context of human-induced impacts in the Mar Menor. Using long-term monitoring data (the reference period of 2002-2004 vs. the eutrophication period of 2015-2019), we analyze temporal variations in their population dynamics and their relationships with eutrophication-mediated structural changes in shallow waters. Our results suggest that these resident species, which are closely associated with shallow areas, show population dynamics that reflect habitat alterations, underscoring their potential as indicators of eutrophication impacts. This study enhances our understanding of the dynamics within transitional ecosystems and provides a basis for integrated management strategies aimed at promoting effective fish conservation.

Evaluating intra- and inter-life stage density-dependent dynamics for management of perennial amphidromous fish.

Compensatory density-dependent (DD) processes play an integral role in fisheries management by underpinning fundamental population demographics. However, DD processes are often assessed only for specific life stages, likely resulting in misleading evaluations of population limitations. Here, we assessed the relative roles of intra- and inter-life stage DD interactions in shaping the population dynamics of perennial freshwater fish with demographically open populations. Specifically, we monitored populations of amphidromous banded kōkopu (Galaxias fasciatus), giant kōkopu (Galaxias argenteus), and shortjaw kōkopu (Galaxias postvectis) in five streams where migratory post-larvae are fished and in three no-take ("closed") streams located on New Zealand's South Island for two years. Using mark-recapture data, we investigated whether fishing altered densities of "small" (non-territorial recruits ≤1-year-old) and "large" (territorial fish >1-year-old) kōkopu size classes, and how subsequent density shifts affected the apparent survival and growth of each class while controlling for other confounding factors (e.g., habitat characteristics). We found that closed areas had substantially greater biomass of small kōkopu, particularly following the two-month fishing season. Despite this greater influx of recruits, there was no difference in the biomass of large kōkopu at the species level, or as a combined assemblage between stream types. This indicated that although fishing of post-larvae reduced recruit influxes into adult habitats, there was no subsequent evidence of recruitment-limitation within adult populations. Instead, kōkopu demographics were underpinned by intra- and inter-life stage DD competition and predation. Greater large fish densities played a key role in regulating the survival, growth, and/or presence of various kōkopu classes. In contrast, greater small fish densities had positive effects on the growth of opportunistic and insectivorous congeners, likely due to cannibalism and altered foraging behaviors, respectively. Our study details the prominent role of intra- and inter-life stage DD interactions in regulating the population dynamics of perennial migratory freshwater fishes, even in populations with inhibited recruit and juvenile availability. We emphasize the importance for fisheries management to implement recruitment dependencies and complex interactions between distinct life stages to avoid deleterious DD responses and ensure population persistence.

Ecological Connectivity of River‐Lake Ecosystem: Evidence From Fish Population Dynamics in a Connecting Channel

AbstractClimate change and human activities, for example, dam construction, largely affect hydrologic and hydrodynamic processes of river‐lake system, and hence exerted serious pressure on its aquatic ecology. It's challenging to restore its ecological environment without systematic investigation and knowledge about the features of hydrodynamics, water quality, and aquatic ecology. This study conducted field surveys of hydrodynamic, water quality, and fish distribution in the Yangtze‐Poyang system, the largest river and largest fresh lake in China, to investigate the effects of hydrologic and hydrodynamic variations on fish population dynamics, especially the extreme drought and its effects were largely concerned. In two surveys, discharge decreased from 12,000 m3/s to less than 1,000 m3/s. Distinct differences on fish density, species composition, and populations connectivity between two surveys were observed. During high‐water, connecting channel secured effective transition of river‐lake habitats, its strong hydrological connectivity and flow heterogeneity supported great biodiversity and bidirectional populations connectivity. Limited flow space and elevated turbidity during low‐water confined fish to a few channel units with sufficient depth and width, increasing fish density up to 7 times greater than during high‐water, and seriously weakening ecological connectivity of the system. Furthermore, species interaction was intensified due to limited environmental capacity, periodic strategists were favored while opportunistic strategists visibly diminished, leading to a dramatic decline in species by nearly half. In the future with increasingly frequent extreme climate, engineering measures, for example, effective ecological project regulation, are needful to alleviate the drought problem, being of great significance for maintaining ecological connectivity within the river‐lake system.

Investigating the impact of cross-shelf transport and local retention in the Black Sea Rim Current system on small pelagic fishes

Advection of pelagic fish larvae through ocean currents is a source of dispersal that is known to structure marine populations by directly impacting population success and persistence. To be able to understand fish population dynamics and manage existing fisheries it is therefore of importance to assess the extent of exchange between populations and determine the factors that drive it, which is still a challenge in fisheries research today. In this study, the output of a high-resolution basin-scale circulation model is used to calculate the dispersal probability from spawning areas and the remaining Black Sea for a range of commercially important fish such as anchovy, sprat, turbot, red mullet, and bluefish under different environmental conditions. The common trait of many commercially important species in the Black Sea is that they have pelagic larval stages of different time scales which are simulated by tracking virtual drifters in the simulated surface circulation of the Black Sea. Simulation results show that the dynamic current structure of the Black Sea causes low local retention of larvae. During spring and summer lower offshore transport and higher local retention is observed than in fall and winter, which is directly related to the Rim Current strength. The lowest offshore transport is observed on the northern northwestern shelf, the main spawning area for pelagic fish with still 24-32% of larvae transported offshore. Simulations show that pelagic fish species such as anchovy and sprat adopted different reproductive strategies through their species-specific traits. For the summer spawning species anchovy, timing, and location of spawning together with its short pelagic larval stage is shown to enhance retention on the northwestern shelf. Sprat with its long pelagic larval stage and winter spawning is more adapted to high offshore transport, making it unlikely that sprat is recruited to the same area as where it is spawned. This modeling framework provides a basis for investigating recruitment variability of pelagic fish species in the Black Sea specifically considering the impact of climate variability and provides a useful guide to the potential connectivity of marine populations or the spread of invasive pests in the Black Sea.

Linking functional habitat and fish population dynamics modeling to improve river rehabilitation planning and assessment

In-stream habitat enhancement is widely used to improve ecological conditions in rivers, often prioritizing key fish life stages such as spawning and juvenile development. However, no standard approaches exist to predict their effects on fish recruitment and populations. Here, we use a spatially-explicit population dynamics model that integrates functional habitat dynamics to assess the impact of two rehabilitation measures in a hydropower-impacted section of the Inn River (SE Germany) on the recruitment potential of four rheophilic and lithophilic fish species — grayling, nase, barbel, and chub. Rehabilitation measures implemented included the construction of a bypass channel and an island side-channel system to improve both longitudinal connectivity and habitat conditions. In addition, we analyzed two alternatives, which would enhance functional availability of nursery habitats from actual 33.2% to 66.8% and 95.3%, respectively. The results suggest that the improved habitat conditions will yield on average additional 14.9 individuals/ha (5.6 kg/ha) of the target species. However, the limited accessibility of usable nursery habitat constitutes a significant recruitment bottleneck for all species. In the alternative scenarios, the increase of functional connectivity will result in average densities of 17.9 and 25.8 individuals/ha, respectively. However, potential further improvements are species-specific, because of distinct population responses to spawning-to-nursery habitat ratios, with density changes varying between -11.7% for grayling and +172.6% for chub. This study not only demonstrates the applicability of the modeling approach for assessing and planning rehabilitation measures but also emphasizes the importance of considering habitat ratios and their functional connectivity to optimize recruitment potential.

Multi-method survey rediscovers critically endangered species and strengthens Madagascar's freshwater fish conservation

Freshwater ecosystems are crucial for global biodiversity through supporting plant and animal species and providing essential resources. These ecosystems are under significant threat, particularly in island environments such as Madagascar. Our study focuses on the Amboaboa River basin, home to the rare and endemic fish species Rheocles derhami, last recorded in 2013. To assess the status of this and other threatened fish species including Ptychochromis insolitus and Paretroplus gymnopreopercularis, and to understand freshwater fish population dynamics in this biodiversity hotspot, we conducted a comprehensive survey using both environmental DNA (eDNA) and traditional fishing methods. While traditional methods effectively captured a diverse range of species, including several invasive aliens and the critically endangered endemic species that were the focus of this study, the eDNA approach detected only a fraction of these introduced species and struggled to identify some critically endangered endemics at the species level. This highlights the value of combining methods to enhance species detection. We also investigated the trade-offs associated with multi-primer assessments in eDNA analysis, focusing on three different primer combinations targeting the 12S mitochondrial gene: MiFish, Tele02, and Riaz. Additionally, we provided 12S reference barcodes for 10 species across 9 genera of fishes from the region to increase the coverage of the public reference databases. Overall, our study elucidates the current state of freshwater biodiversity in the Amboaboa River basin and underscores the value of employing multiple methods for effective conservation strategies.

Hindcasting Estuarine Bottom Salinity Using Observing Systems Data and Nonlinear Regression, as Applied to Oysters in Delaware Bay

Salinity is a major environmental factor that influences the population dynamics of fish and shellfish along coasts and estuaries, yet empirical methods for hindcasting salinity at specific sampling stations are not widely available. The specific aim of this research was to predict the salinity experienced by juvenile and adult oysters (Crassostrea virginica) collected at sampling stations in Delaware Bay. To do so, empirical relationships were created to predict salinity at five oyster bed stations using observing systems data. These relationships were then applied to construct indices of salinity exposure over an oyster’s lifetime. Three independent salinity data sources were used in conjunction with observing systems data to construct and validate the predictive relationships. The root mean square error (RMSE) of the models ranged from 0.5 to 1.6 psu when model predictions were compared with the three independent data sets. Results demonstrated that data from an observing system near the head of Delaware Bay could be used to predict salinity within ± 2 psu at oyster bed stations as far down-estuary as 39 km. When these models were applied to estimate low salinity exposure of 2-year-old oysters via the metric of consecutive days below 5 psu, the indices suggested that there could be as much as a 42-day difference in low salinity exposure for oysters at stations just 31 km apart. The approach of using observing systems data to hindcast salinity could be applied to advance understanding of salt distribution and the effect of low salinity exposure on organisms in other estuaries, especially bottom-associated species.

Modeling fisheries and carbon sequestration ecosystem services under deep uncertainty in the ocean twilight zone

Mesopelagic fishes are a vital component of the biological carbon pump and are, to date, largely unexploited. In recent years, there has been an increased interest in harvesting the mesopelagic zone to produce fish feed for aquaculture. However, great uncertainties exist in how the mesopelagic zone interacts with the climate and food webs, presenting a dilemma for policy. Here, we investigate the consequences of potential policies relating to mesopelagic harvest quotas with a dynamic social-ecological modeling approach, combining system dynamics and global sensitivity analyses informed by participatory modeling. Our analyses reveal that, in simulations of mesopelagic fishing scenarios, uncertainties about mesopelagic fish population dynamics have the most pronounced influence on potential outcomes. The analysis also shows that prioritizing the development of the fishing industry over environmental protection would lead to a significantly higher social cost of climate change to society. Given the large uncertainties and the potential large impacts on oceanic carbon sequestration, a precautionary approach to developing mesopelagic fisheries is warranted.

Early-life dispersal traits of coastal fishes: an extensive database combining observations and growth models

Abstract. Early-life stages play a key role in the dynamics of bipartite life cycle marine fish populations. Difficult to monitor, observations of these stages are often scattered in space and time. While Mediterranean coastlines have often been surveyed, no effort has been made to assemble historical observations. Here we build an exhaustive compilation of dispersal traits for coastal fish species, considering in situ observations and growth models (Di Stefano et al., 2023; https://doi.org/10.17882/91148). Our database contains over 110 000 entries collected from 1993 to 2021 in various subregions. All observations are harmonized to provide information on dates and geolocations of both spawning and settlement, along with pelagic larval durations. When applicable, missing data and associated confidence intervals are reconstructed from dynamic energy budget theory. Statistical analyses allow traits’ variability to be revisited and sampling biases to be revealed across taxa, space and time, hence providing recommendations for future studies and sampling. Comparison of observed and modelled entries provides suggestions to improve the feed of observations into models. Overall, this extensive database is a crucial step to investigate how marine fish populations respond to global changes across environmental gradients.

About mathematical modeling in limnology, oceanology, ecology and economics in the works of V.V. Menchutkin

The article gives a brief review of the works of Doctor of Biological Sciences, Prof. V.V. Menshutkin for the 65-year period of scientific activity, which began in the 60s of the XX century with experimental works on the hydrophisics of Lake Baikal and the first mathematical models of the perch population of the small lake Kherya-Yarvi (Karelian Isthmus) and fish community in Lake Dalneye (Kamchatka). The latter was of great practical importance when concluding an agreement with Japan on catch quotas for sockeye salmon.V.V. Menshutkin’s range of interests was very wide and included mathematical modeling in biology, physiology, limnology, oceanology, demography, economics, ecology and rational nature management. The works on research of water objects and processes in them include modeling of dynamics of fish and aquatic invertebrate populations, Antarctic krill. He created mathematical models of ecosystems of Ladoga and Onega lakes, and during oceanic expeditions of the Academy of Sciences — of the Sea of Japan and the Peruvian upwelling area.His research in the field of physiology of blood circulation and water-salt metabolism, works related to space subjects, modeling of diagnostics and treatment of mental diseases are interesting. V.V. Menshutkin paid special attention to the issues of biological evolution. V.V. Menshutkin paid special attention to the issues of biological evolution and modeling of evolutionary process. The mathematical apparatus used by V.V. Menshutkin is very broad. The mathematical apparatus used by V.V. Menshutkin is very wide: from systems of differential equations to finite automata, neural networks, fuzzy logic and cognitive modeling (a new direction in artificial intelligence), with which the studies of ecological-socio-economic systems of water bodies catchments were connected.O.P. Savchuk and V.V. Menshutkin united research methods — mathematical modeling and objects under study: oceans, seas and lakes. However, their only joint work was the collective monograph on the results of “Nevskaya Guba” project, which conclusions became the basis for the important decision to complete the construction of the dam in St. Petersburg.

Length-Weight relationship and condition factor of Lutjanus peru and L. guttatus from the Gulf of California Mexico.

Fulton’s condition factor (k) and the length-weight relationship (LWR) are the most important biological tools with respect to basic aspects of fish population dynamics; they are applicable to strategic plans for the conservation and management of fisheries. A total of 478 snappers Lutjanus peru and L. guttatus were analyzed in Santa Rosalía, Baja California Sur, in the Gulf of California. The total length of Lutjanus peru ranged from 21 to 55 cm, and weight ranged from 215 to 1,920 g, whereas total length of L. guttatus ranged from 21 to 59 cm, and weight ranged from 290 to 1,675 g. The LWR and condition factor were estimated for the two species and intraspecific factors were analyzed (sex, season, maturity stage) using Bayesian hierarchical models with random effects. The parameters of the LWR equation were similar for the two snapper species (α≈0.026 and β ≈ 2.8); they both presented negative allometric growth (p(β<3)>85%). The L. peru growth rate was greater in the warm season (p(βwarm>βcold)≈97%), whereas this difference was not as evident in L. guttatus (p(βwarm<βcold)≈72%). The condition factor k was greater than 1 for all categories in the two species (p(μk)=100%), which suggests that they keep a good body condition. This indicates that L. peru and L. guttatus in Santa Rosalía experience environmental conditions that benefit their body condition, as a function of year-round food availability. This information is useful for future conservation studies and for monitoring snapper captures, as most L. peru individuals caught were sexually immature.

David Henry Cushing. 14 March 1920 — 14 March 2008

David Cushing was Britain's foremost twentieth-century marine fisheries ecologist, who did more than anyone else to develop the subject into a distinctive science over a career of more than 50 years. He was born and raised in Northumberland, and took both his first degree and a DPhil at Oxford, separated by war service in the Royal Artillery. He married Diana Antona-Traversi in 1943, and they had one daughter, Camilla. He worked for the whole of his career at the Fisheries Laboratory, Lowestoft, where he started in 1946 as a scientific officer, studying plankton off the northeast coast of England, and eventually becoming deputy director and head of the Fish Population Dynamics Divi­sion until his retirement in 1980. He published around 200 papers and reports, and wrote 11 books on marine ecology and fisheries, with four principal areas of interest: fisheries acoustics; planktonic biological production in the sea; the causes of the collapse of the North Sea herring; and the factors controlling recruitment of young fish, notably the influences of stock size and of climate. He famously proposed the match/mismatch hypothesis to explain how the great variability of fish recruitment arises from minor variations in climate from year to year. He died on 14 March 2008, on his eighty-eighth birthday.

The interplay of group size and flow velocity modulates fish exploratory behaviour

Social facilitation is a well-known phenomenon where the presence of organisms belonging to the same species enhances an individual organism’s performance in a specific task. As far as fishes are concerned, most studies on social facilitation have been conducted in standing-water conditions. However, for riverine species, fish are most commonly located in moving waters, and the effects of hydrodynamics on social facilitation remain largely unknown. To bridge this knowledge gap, we designed and performed flume experiments where the behaviour of wild juvenile Italian riffle dace (Telestes muticellus) in varying group sizes and at different mean flow velocities, was studied. An artificial intelligence (AI) deep learning algorithm was developed and employed to track fish positions in time and subsequently assess their exploration, swimming activity, and space use. Results indicate that energy-saving strategies dictated space use in flowing waters regardless of group size. Instead, exploration and swimming activity increased by increasing group size, but the magnitude of this enhancement (which quantifies social facilitation) was modulated by flow velocity. These results have implications for how future research efforts should be designed to understand the social dynamics of riverine fish populations, which can no longer ignore the contribution of hydrodynamics.

Reproductive biology and nuptial coloration of Trachinus draco (Trachinidae) from Atlantic Spanish waters (SW Europe)

Studies focusing on reproductive biology play a key role in deciphering fish population dynamics. We studied the main features of the reproductive biology of the greater weever Trachinus draco based on gonad histology and digital image analysis techniques and the main hypothesis of the study is that males of T. draco exhibit a nuptial colouration. The biological samples of 311 individuals along the Atlantic coast of Spain, covering the twelve months of the year (from 2020 to 2022), in combination with the gonadosomatic index trend revealed a spawning season from May to August, consistent with similar studies in different geographical areas. Length-weight relationship presented differences by sex (females reach higher weight at the same length). The maturity ogive for females indicated that 50 % were mature at a length of 182 mm. Histological analysis confirmed asynchronous development of secondary growth oocytes, pointing to a batch spawning strategy. Digital image analysis of the nuptial coloration showed that the presence of a black spot above the pectoral fin in males was significantly correlated with the spawning capable phase, while blueish coloration was influenced by sex, size and maturity phase, with larger spawning males having the largest areas of blueish coloration. The results of this study represent a significant improvement of our understanding of the reproductive biology of T. draco.

Long-term dynamics of fish populations in lakes of the “Russian North” National Park

Long-term dynamics of fish populations in lakes of the “Russian North” National Park

Effect of wind variability on the recruitment of anchovy Engraulis ringens in the southern Humboldt upwelling ecosystem

AbstractRecruitment is a critical process in the dynamics of fish populations since it represents the abundance of new fish that enter a population each year. In Ekman‐type upwelling ecosystems, wind is a critical factor for small pelagic fish recruitment, as it controls food availability and physical constraints such as turbulence and offshore advection. In this study, we evaluate the effect of wind, chlorophyll‐a, and spawning biomass as independent variables on anchovy recruitment. Using generalized additive models (GAMs), we tested (i) the significance of each factor, (ii) the shape of the relationship between recruitment and predictors variables, (iii) recruitment regimes in the series, and (iv) whether extended windy events are associated with low recruitment levels potentially related to offshore transport of early life stages. The study period spanned from 1990 to 2021, focusing on the austral spring in south‐central Chile (35–40°S) when both upwelling and anchovy spawning are maximized. GAMs revealed a parabolic relationship between the velocity of upwelling‐favorable winds and anchovy recruitment. Maximized recruitment occurred at wind speeds around 6 m s−1 but decreased with winds above 7 m s−1 and below 5 m s−1, and during periods of extended windy events (i.e., those lasting more than 15 days). Chlorophyll‐a showed no significance on anchovy recruitment, suggesting that phytoplankton were not a limiting factor for anchovy early survival. We also found that anchovy recruitment regimes were associated with specific wind intensities. We discussed the pertinence of incorporating a recruitment index based on wind in the fishery management of the anchovy in south‐central Chile.

Comparisons of energy metabolism and personality traits before and after angling in crucian carp (Carassius auratus)

Catch and release has become a very popular fish conservation strategy and fisheries management tool. The physiological and behavioral changes in individuals who experience catch and release may be adaptive. These individuals may exhibit more cautious bait use or hook avoidance behavior when faced with lures again. Here, our study was conducted on crucian carp (Carassius auratus) to compare energy metabolism and personality (e.g. activity) before and after angling for three bouts of repeated angling. Our study showed that the standard metabolic rate, maximum metabolic rate, aerobic scope and factorial aerobic scope were all lower after three bouts of repeated angling, and the metabolic rates were greater before angling than after angling in the first two bouts of angling. In addition, the total magnitude of excess postexercise oxygen consumption after repeated angling also showed a decreasing trend as the number of angled bouts increased. The percentage of time spent moving increased after three bouts of repeated angling, but there were no changes in either individual swimming speed or total distance traveled. Our results suggest that repeated angling causes a high death rate and decreases the aerobic/anaerobic metabolic capacity of crucian carp, which may reduce their metabolic potential for other physiological functions, such as locomotion, growth and digestion. Future studies should continue to focus on the effects of fishing on the physiology, behavior, and population dynamics of fish.

Understanding How Parasites from Farmed Fish May Influence Wild Fish Declines Using Epidemiological Modelling

Beside various fields of its applications, in this study epidemiological modelling was used to understand how parasites from farmed fish may cause wild fish declines. Two separate strategic models were constructed addressing the transmission of micro-parasites and macro-parasites between farmed and wild fish: A SIR (Susceptible-Infective-Removed) model for micro-parasite infections and a compartmental density-dependent model for macro-parasite infestations. The results indicated that parasites originated in wild fish populations, after infecting farmed fish can cause epizootics. Subsequently, these parasites can be transmitted from farmed to wild fish and might have negative impact on the dynamics of wild fish populations. Sensitivity analysis of the basic model parameters in both models showed that model parameters, which are influenced by abiotic factors and allow passive manipulation, such as pathogen specific transmission rate (β), pathogen specific transmission rate between infected farmed and susceptible wild fish (δ), the rate of production of infective stages by an adult parasite (λ) and transmission rate between host and parasite infective stages (β) are more sensitive compared to model parameters which encompass chemical control and fallowing. This emphasizes the importance of the preventive medicine rather than intervention procedures in aquaculture aiming at eradicating epizootics caused by parasites and protecting wild fish stocks.