Fish Population Density Research Articles

A SIGNIFICANT STRUCTURE REVIEW: DEEP POOLS AND FISH SPAWNING HABITAT IN FISHERIES MANAGEMENT

The sustainability of fisheries is intricately linked to the conservation of critical habitats, particularly deep pools that serve as vital fish spawning grounds. This systematic literature review aims to explore the significance of deep pools in the reproductive success and management of fish populations. The study identifies critical challenges in fisheries management, including habitat loss, environmental changes, and the need for targeted conservation efforts. To address these challenges, a comprehensive search and analysis of peer-reviewed articles from databases such as Scopus and Web of Science was conducted, focusing on research published between 2022 and 2024. The methodology followed PRISMA guidelines to ensure a rigorous selection process, resulting in 40 high-quality studies being included in the final review. The findings were divided into three themes: (1) fisheries management and conservation, (2) environmental impact on fisheries, and (3) methodological approaches in fisheries research. The findings highlight the crucial role of deep pools in supporting fish spawning, with evidence showing that these habitats contribute significantly to the maintenance and enhancement of fish stocks. Results indicate that well-managed deep pools can lead to an increase in fish population densities, underscoring their importance in fisheries management. However, the review also needs to identify gaps in the current understanding of the complex interactions between fish species and their spawning habitats. The conclusion emphasizes the necessity for integrated management strategies that prioritize the protection of deep pools to ensure the long-term sustainability of global fisheries.

River degradation impacts fish assemblages in Kosovo’s Ibër basin

Fish sampling was conducted in 20 sites within the Ibër River and its tributaries in Kosovo (August 2023) collecting 23 taxa (1674 individuals) through a standardized electrofishing protocol. Relevant physico-chemical measurements and anthropogenic pressures were collected and analyzed with respect to the ichthyological data of the surveyed sites. The survey represents a rapid assessment procedure, limitations and prospects of the effort are described. Several attributes of the fish assemblages showed severe degradation, characterized by low population densities, low species diversity, minimal reproductive evidence and the absence of several sentinel species. Multiple anthropogenic pressures have severely modified the fish communities over a wide area; pollution, barriers to movement and hydroelectric dams stand out as important drivers of degradation. Only two fish species showed some level of tolerance to heavily polluted waters (Carassius gibellio, Rutilus rutilus). Low fish population densities were also correlated with various forms of hydromorphological degradation. Only Barbatula barbatula, Phoxinus sp. and Lepomis gibbosus had proportionately higher population densities in areas where impoundments and power-station dam hydropeaking were severe. In this regard, conservation actions are urgently needed.

Regional‐scale effects of deer‐induced forest degradation on river ecosystem dynamics

AbstractAlmost all ecosystems are open systems, meaning that significant changes in one ecosystem can lead to unexpected changes in others. Deer overabundance has become a problem worldwide, leading to forest degradation that has impacts on not only terrestrial, but also aquatic ecosystems. This study aims to investigate the regional‐scale importance of large herbivores in inter‐ecosystem interactions by examining the effects of deer‐induced forest degradation on fish populations. We selected similar‐scale catchments from river systems in Hyogo, Japan, that differed in the time since deer‐induced forest degradation. Conventional surveys for fish densities and microhabitat environments were conducted in 23 catchments, and surveys using quantitative eDNA metabarcoding were conducted in 95 catchments. We examined the relationships between fish population densities, microhabitats, and time since forest degradation, considering confounding effects. Data from 8 and 17 fish taxa detected by snorkeling and eDNA methods, respectively, were available for statistical analysis. Snorkeling‐counts (Individuals/1 m transect) and eDNA concentrations (Copies/L) in river water were strongly correlated. Fine sediments on riverbeds were increased in the 3–15 years following forest degradation and decreased after 16 years. Population densities of sand‐preferring fishes, as inferred from both eDNA and snorkeling, reasonably followed this pattern. These patterns may be caused by the depletion of fine sediments on mountain slopes. The results of this study suggest that deer‐induced worldwide alternation may also occur in aquatic ecosystems.

Population Study of Kedukang Fish (Hexanematichthys sagor) in The Waters of Percut River, Percut Sei Tuan District, Deli Serdang Regency, North Sumatera

Kedukang fish (Hexanematichthys sagor) is a consumable fish that is widely caught by fishermen and the community. Kedukang fishing is carried out every day in the Percut River, resulting in a decline in its population. This study aims to analyze the population by looking at density, sex ratio, growth pattern, gonad maturity level, gonad maturity index and fecundity of kedukang fish and analyze the relationship between physical-chemical factors of waters with population density of Kedukang fish. Samples were taken using purposive sampling method at 3 observation stations with 2 repetitions. Fish samples were taken using a net fishing gear installed at low tide and lifted at high tide. The results showed that the population density of kedukang fish in Percut River was low ranging from 0.048-0.123 ind/m2. The sex ratio kedukang fish at each observation station has an average of 1:0.5. The growth pattern of fish is allometric negative. The frequency distribution of fish length ranged from 21.5-47.9 cm. The greatest number of fish caught had a length range of 30.3-34.7 cm as many as 9 fish. The level of gonad maturity kedukang fish is dominated by TKG V. The average gonad maturity index of female kedukang fish is highest at the TPI location which is 20.729% and the highest fecundity at station II which is 4622.6. The relationship between the density of the kedukang fish population is very strong and positively correlated with DO, light intensity and nitrate. The population density of kedukang fish was strongly and negatively correlated with pH and phosphate.

Development of renewable energy based green hydrogen and oxygen production and electricity generation systems for sustainable aquaculture

Fish growth, health, and population density are profoundly affected by oxygen feeding in aquaculture. A novel solar-powered oxygen generator combined with water electrolysis and fuel cells is developed in an integrated fashion to achieve a more sustainable aquaculture and, hence, a more sustainable ecosystem. The proton exchange membrane (PEM) electrolysers are used in the proposed system to produce oxygen through water splitting process. The hydrogen produced, along with oxygen in the electrolyser, is utilized as the clean fuel in fuel cell stacks for generating electricity to store solar energy for later use. In this way, the sustainable development goals of the United Nations are achieved through cleaner aquaculture operations. The use of the proposed system in five different cities (Asansol, Calabar, Kinshasa, Meki, and Washuk) facing poverty from different countries is considered as case studies and evaluated based on the hydrogen and oxygen production capacities and hence energy and exergy efficiencies. With a solar power plant of 1 MWp, it is possible to produce oxygen 353.8 kg in Asansol, 304.4 kg in Calabar, 308.5 kg in Kinshasa, 382.1 kg in Meki and 431.8 kg in Washuk. The overall energy and exergy efficiencies of the solar-driven system are obtained to be 12.2% and 66%, respectively.

How do Different Types of River Maintenance Works Affect the Ichthyofauna of Small European Watercourses?

Abstract Watercourses serve the needs of agriculture in certain sections and are subject to strong anthropopressure. When agriculture prevails in the catchment, it often has abundant vegetation, macrophytes in particular, and the bottom is covered by a substantial layer of silt. In order to ensure patency of flow and access to water, small watercourses are very often subject to river maintenance works. The aim of the study was to assess the impact of 3 types of works on the diversity of fish species and density of fish in the 1 and 2 year after the works at 21 sites located on 8 rivers in the European Central Plains Ecoregion. As a result of the works, especially in the 1 year after the works, significant changes were found in hydrochemical and hydrological parameters, especially with the increase in velocity and mean depth in watercourses. Additionally, habitat change contributed to differences in the composition of the ichthyofaunal. After 1 year, the diversity of fish species and fish population density increased or remained unchanged after dredging and removal of plants from the river channel, but they decreased after the removal of macrophytes from river banks. After year 2, a decrease in the diversity of fish species and density was observed, associated with re-infestation and siltation of the watercourses. Particularly in the case of dredging and removal of macrophytes from the river bank, maintenance works should not be done too frequently, because some species of natural value disappear.

Artificial Spawning Techniques for Catfish (Clarias gariepinus) at the Cultivated Fisheries Production Business Service Center, Karawang, Indonesia

One of the primary challenges in the catfish cultivation industry is the uncertainty (mostly due to weather conditions, natural feed availability, pests and diseases), limited availability, and often poor quality of catfish frys. Fry quality is crucial in aquaculture, yet its reliability is hampered by the natural spawning process, which is influenced by seasonal variations. To address this issue, artificial spawning techniques offer a viable solution. This activity aims to comprehend and effectively execute the precise methods of artificial spawning for catfish, ultimately striving for the production of high-quality fingerlings. Data collection involved the acquirement of both primary and secondary data. The artificial spawning process encompasses container and medium preparation, meticulous broodstock selection and breeding, the artificial spawning procedure, larval rearing, and nursery management. Results from the artificial spawning efforts revealed a fecundity of 75,000 individuals, a remarkable 90% fertilization rate, an 89% hatching success, and an impressive 90% survival rate. Notably, catfish fingerlings were found to harbor parasites such as Gyrodactylus sp., Trichodina sp., and Dactylogyrus sp. This occurrence can be attributed to the high population density of fish, which contributes to a decline in water quality, emphasizing the importance of cautious management practices in aquaculture.

Model-based versus model-free feeding control and water-quality monitoring for fish-growth tracking in aquaculture systems

This paper proposes model-based and model-free control approaches to monitor the feeding rate and water quality for fish-growth tracking in aquaculture systems. The representative fish-growth model is revisited, which describes the total biomass change by incorporating the fish population density and mortality. Due to the challenging task of measuring the total fish biomass and population data, the new dynamic population model is validated with individual fish-growth data for tracking control. Ammonia exposure is a significant challenge in the fish-population growth tracking problem, affecting fish health and survival. To address this challenge, traditional and optimal controllers are first designed to track the weight reference within suboptimal temperature and dissolved oxygen (DO) profiles under various un-ionized ammonia (UIA) exposure levels by manipulating relative feeding. Then, a Q-learning approach is proposed to learn an optimal feeding-control policy from simulated data on fish-growth weight trajectories while managing ammonia effects. The proposed Q-learning feeding control prevents fish mortality and achieves good tracking errors for fish weight under UIA levels. However, it maintains a relative food consumption that potentially underfeeds fish. Finally, an optimal predictive algorithm that includes the temperature, DO, and UIA is proposed to optimize the feeding and water quality of the dynamic fish-population growth process, indicating that fish mortality is decreased and food consumption is reduced in all cases of UIA exposure.

Evaluating the cascade dam construction effects on endemic fish habitat and population status in spawning sites of Lancang River (in Tibet), China

Cascade dam constructions will alter the habitat of spawning sites and affect fish population in the Lancang River basin. This paper examines the impacts of cascade dam construction on four spawning sites, focusing on two co-distributed and endemic fish species: Schizothorax prenanti and Schizothorax davidi. An ecohydraulic modeling framework that combined hydro-morphodynamic, habitat, and population models was used to investigate changes in habitat quality and fish population under two scenarios: no-dam and with-dam. Fish habitat quality was evaluated using the habitat suitability index, and population fluctuations were assessed by the abundance and density of fish populations at all life stages. The simulation results indicated that cascade dam construction would fragment the spawning site habitat in the tailwater zone of the main stream and result in a decrease in fish population abundance and density. Conversely, spawning site habitats in backwater zone of tributaries would improve, and fish population abundance and density would increase. Additionally, the simulation results showed that the magnitude of fish population variations varied by species and life stages. These results highlight the different responses of spawning site location, fish species, and life stages to dam construction, which can help identify areas of the habitat with higher potential for finer-scale endemic fish conservation and recovery efforts. This study provides a comprehensive framework tool for fish ecological evaluation in dammed rivers, which has the potential to assist decision-makers involved in river ecosystem ecological conservation.

Assessment of habitat and reef fish population characteristics in Pari Island cluster waters Seribu Archipelago Indonesia

The Pari Island Cluster, located on the Southside of the Seribu Archipelago, is bordered by Jakarta and Tangerang Regency is covered Pari, Kudus, and Tikus Islands. The Pari Island cluster has potential ecosystems, such as coral reefs, seagrass, and mangrove. The presentation of this article is an overview of the results of research conducted by the Research Institute for Marine Fisheries and the Research Institute for Fisheries Enhancement, The Agency for Marine and Fisheries Research and Human Resources. This study aims to present and describe habitat and reef fish populations. The assessment result shows that the criteria for the coral reefs’ health were poor to good, mostly moderate, the best in the southeast and northeast waters, which had been designated MPAs. Reef fish population density on the criteria was very rare or low at all observation sites. The dominant group was Caesio cuning, Cephalopholis boenak, Scarus ghobban (target group), and Chaetodon octofasciatus (indicator group). The implementation hopes Pari Island Cluster waters would expand to be designated MPAs due to the large number of care areas used for fishing territories.

Quantifying the Effects of Global Warming on the Plankton Population: An Asymmetric Multifactor Mathematical Model-Based Approach

A nonlinear dynamical model for the plankton population in a fixed sea area under the influence of asymmetric multiple factors, including atmospheric CO2 concentration, atmospheric temperature, nutrient concentration, seawater temperature, light intensity, and predator density is proposed to address the survival of the plankton population due to global warming. The model’s accuracy is confirmed by comparison with actual data, and numerical simulations are carried out to justify the relevant findings. The results suggest that increasing plankton’s ability to absorb atmospheric CO2 or regulate atmospheric temperature can help to mitigate global warming. Furthermore, if the population density of fish, the primary predator of plankton, falls within a certain range, the increase in atmospheric temperature will be mitigated. Additionally, the stability conditions for the suggested model are obtained, along with the equilibrium point of the system. Overall, this paper considers the effects of asymmetric multifactor interaction on plankton population density and establishes a mathematical connection between environmental ecosystems and plankton that might aid in addressing the challenges posed by global warming and preserving the plankton population.

Secreted peptidases contribute to virulence of fish pathogen Flavobacterium columnare.

Flavobacterium columnare causes columnaris disease in freshwater fish in both natural and aquaculture settings. This disease is often lethal, especially when fish population density is high, and control options such as vaccines are limited. The type IX secretion system (T9SS) is required for F. columnare virulence, but secreted virulence factors have not been fully identified. Many T9SS-secreted proteins are predicted peptidases, and peptidases are common virulence factors of other pathogens. T9SS-deficient mutants, such as ΔgldN and ΔporV, exhibit strong defects in secreted proteolytic activity. The F. columnare genome has many peptidase-encoding genes that may be involved in nutrient acquisition and/or virulence. Mutants lacking individual peptidase-encoding genes, or lacking up to ten peptidase-encoding genes, were constructed and examined for extracellular proteolytic activity, for growth defects, and for virulence in zebrafish and rainbow trout. Most of the mutants retained virulence, but a mutant lacking 10 peptidases, and a mutant lacking the single peptidase TspA exhibited decreased virulence in rainbow trout fry, suggesting that peptidases contribute to F. columnare virulence.

Response of Lettuce (Lactuca sativa L.) To Aquaculture Wastewater Treatment

The fish feed waste and litters are organic matter that can be a source of nutrients for plants. This study is aimed to determine the growth and production of lettuce (Lactuca sativa L.) treated with wastewater from hard-lipped barb culture of several population densities. The research was carried out from April through June of 2020 at the greenhouse of the Agrotechnology Study Program, Faculty of Agriculture, Djuanda University, Bogor, Indonesia. The controlled study used a randomized block design with one factor, wastewater from fish population density of 10, 20 and 30 per 21 L of water, and AB Mix as a control. Plants treated with the AB Mix were significantly superior to those plants treated with the hard-lipped barb farming wastewater, demonstrated by taller plants, more and larger leaves, larger stem diameter and leaf area, longer roots, greater fresh and dry weight, as well as a higher leaf nitrate content. The aquaculture wastewater at the tested fish density in this study did not support optimal growth of lettuce, so lettuce production is still very low compared to those grown with the AB mix.

Optimal Automatic Wide-Area Discrimination of Fish Shoals from Seafloor Geology with Multi-Spectral Ocean Acoustic Waveguide Remote Sensing in the Gulf of Maine

Ocean Acoustic Waveguide Remote Sensing (OAWRS) enables fish population density distributions to be instantaneously quantified and continuously monitored over wide areas. Returns from seafloor geology can also be received as background or clutter by OAWRS when insufficient fish populations are present in any region. Given the large spatial regions that fish inhabit and roam over, it is important to develop automatic methods for determining whether fish are present at any pixel in an OAWRS image so that their population distributions, migrations and behaviour can be efficiently analyzed and monitored in large data sets. Here, a statistically optimal automated approach for distinguishing fish from seafloor geology in OAWRS imagery is demonstrated with Neyman–Pearson hypothesis testing which provides the highest true-positive classification rate for a given false-positive rate. Multispectral OAWRS images of large herring shoals during spawning migration to Georges Bank are analyzed. Automated Neyman-Pearson hypothesis testing is shown to accurately distinguish fish from seafloor geology through their differing spectral responses at any space and time pixel in OAWRS imagery. These spectral differences are most dramatic in the vicinity of swimbladder resonances of the fish probed by OAWRS. When such significantly different spectral dependencies exist between fish and geologic scattering, the approach presented provides an instantaneous, reliable and statistically optimal means of automatically distinguishing fish from seafloor geology at any spatial pixel in wide-area OAWRS images. Employing Kullback–Leibler divergence or the relative entropy in bits from Information Theory is shown to also enable automatic discrimination of fish from seafloor by their distinct statistical scattering properties across sensing frequency, but without the statistical optimal properties of the Neyman–Pearson approach.

Dynamic analysis of a phytoplankton-fish model with the impulsive feedback control depending on the fish density and its changing rate.

This paper proposes and studies a comprehensive control model that considers fish population density and its current growth rate, providing new ideas for fishing strategies. First, we established a phytoplankton-fish model with state-impulse feedback control based on fish density and rate of change. Secondly, the complex phase sets and impulse sets of the model are divided into three cases, then the Poincaré map of the model is defined and its complex dynamic properties are deeply studied. Furthermore, some necessary and sufficient conditions for the global stability of the fixed point (order-1 limit cycle) have been provided even for the Poincaré map. The existence conditions for periodic solutions of order-k(k≥2) are discussed, and the influence of dynamic thresholds on system dynamics is shown. Dynamic thresholds depend on fish density and rate of change, i.e., the form of control employed is more in line with the evolution of biological populations than in earlier studies. The analytical method presented in this paper also plays an important role in analyzing impulse models with complex phase sets or impulse sets.

A review of zoonotic pathogens in Tilapia

Oreochromis niloticus, or Nile tilapia, is widely consumed. This fish can cause several direct ecological imbalances in addition to transporting several pathogens. Pathogens in tilapia are responsible for several deaths in natural environments and commercial aquaculture, and hense, constitute an economic, social, and sanitary threat. This study gathered information from the literature and identified 18 species of pathogens with zoonotic potential found in tilapia, in addition to mapping the distribution of these fishes in Brazilian natural environments. We found that the most common pathogens involved were bacteria, protozoa, fungi and helminths (Trematoda and Nematoda). In Brazil, we also identified that the introduction of O. niloticus has grown in recent decades, and O. niloticus have been found mainly in the eastern region of the country, overlaying the region with the highest fish population density in Brazil. This work serves as an alert and a guide for planning public health policies to mitigate the possible consequences of the uncontrolled introduction of tilapia in the national territory.

Does drifting passage need to be linked to fish habitat assessment? Assessing environmental flow for multiple fish species with different spawning patterns with a framework integrating habitat connectivity

The use of environmental flow (e-flow) regimes has been widely implemented to improve fish habitat quality in river restoration efforts. However, e-flow designs focusing only on one key life stage (e.g., spawning) without considering potential bottlenecks in other stages (e.g., hatching) can result in little to no improvement, especially when targeting the restoration of fish with drifting eggs. Few e-flow assessments are available that closely link the spatial–temporal dependence of the hydrodynamic effect of drifting eggs on hatching habitats. Moreover, an understanding of how to allocate e-flows to achieve the best possible outcomes for biological diversity conservation is still lacking. In this study, a new framework was developed to assess e-flows, aiming to satisfy the requirements of multiple fish species with different spawning patterns concerning streamflow requirements during spawning and hatching periods. In this framework, the final weighted usable area (FWUA) was proposed by linking the spawning demand to the hydrodynamic effect of drifting eggs to assess habitat quality for fish that produce drifting eggs, and water temperature was used to guide when and how to shift from fixed to moving protection targets in allocating e-flows. Here, we used the Xiangjiaba Reservoir, located in the lower Jinsha River, as a case study to design e-flows for the conservation of multiple fish species with different spawning patterns, which was beneficial for increasing the probability of restoration success. By testing scenarios with an absence of drifting passage, the ecological base flow considering only spawning habitat appears to be lower than that considering both quality of spawning habitat and hatching passage. The ecological benefits (FWUA) generated from the ecological base flow identified by traditional models represent only 64.91% of our framework and are thus anticipated to have cascading deviant effects on ecological patterns and processes in riverine ecosystems. This underlying difference in FWUA generated due to different ecological base flows determined from traditional models and our framework, however, has been overshadowed in previous research. We highlight that the highest fish population density recovery potential will be reached at only certain ratios for both sets of habitat benefits. This work provides a tool that can help managers evaluate e-flows and compare different river restoration scenarios to protect degraded rivers or develop strategies to build resilience to climate change.

Predator kairomone triggers sexual reproduction of Daphnia population via increasing population density

Abstract Both predation risk and crowding can induce sexual reproduction in Daphnia, and predator kairomones can also cause population crowding. It is, however, unclear as to whether sexual reproduction is caused by kairomone per se or indirectly by kairomone‐induced crowding. In this study, we cultured Daphnia pulex in the presence of fish kairomone, with newborn offspring being retained (increasing population density) or removed (constant population density). The relationships among fish kairomone, population density, and indicators of sexual reproduction were assessed using structural equation models. The results showed that when offspring were retained in the population, the population density and sexual reproduction by Daphnia simultaneously increased in response to the presence of the fish kairomone, whereas sexual reproduction was not directly affected in the presence of fish kairomones alone. Conversely, when maintaining a constant population density, the number of ephippia and ratio of male to female of Daphnia increased with increasing population density, but the presence of fish kairomone did not promote sexual reproduction. Structural equation model analysis indicated that population density, rather than the fish kairomone, was the significant factor promoting sexual reproduction. The findings of this study indicate that population density directly triggers sexual reproduction in Daphnia populations. Our observations provide new insights into environmentally induced sexual reproduction, and on this basis, we suggest that a more thorough consideration of the interactions among environmental factors in determining sexual reproduction is necessary.

Estimating Deep-Sea Fish Population Density From the Odour Extension Area: A Theoretical Basis and Comparison With the Conventional Methods

Accurately estimating the population density of deep-sea fish with a baited camera system has long been a significant challenge. Although several theoretical models have been developed using the first arrival time of an individual fish or time-varying fish abundance at the bait, none of the models allows for the spatio-temporal variability of the odour plume area extending from the bait. This study shows theoretically that the population density can be formulated as the inverse of the sample mean of the odour plume area extended until it reaches a first fish under the condition that fish at rest have a random dispersion. Each area estimate is governed by the homogeneous Poisson process and, hence, its probability density follows an exponential distribution. A large uncertainty can occur for each area estimate (sample), but the uncertainty decreases as the number of samples used to derive the sample mean increases by the law of large numbers. Numerical experiments conducted in the study indicate that the proposed method for inferring population density is also potentially applicable to cases in which the fish have a uniform or large-scale clumped dispersion. The experiments also show that the conventional method based on first arrival time fails to estimate the population density for any of the dispersion cases. This study also indicates that the reliability of the most popular inference method for estimating population density from the time-profile of fish abundance at the bait site was found to depend on the extension of the odour plume area and the dispersion pattern.

Effect of Fish Stock Density on Hormone Genes Expression from Brain and Gastrointestinal Tract of Salmo salar.

Simple SummaryVarious long-term stress conditions may exist in fish cultivation, damaging the physiological responses that regulate the fish growth and feed. Different signalers connect the brain with the gastrointestinal tract, including the perception of stress factors for the regulation of physiological responses. Here, we evaluated the effect of varying culture densities of Salmo salar post-smolt on the gene expression of some brain and gastrointestinal hormone signalers. We found that high stock densities could promote the levels of molecules associated with feed inhibition, which could be related to the stress pathway regulated by corticoids. Thus, the expression of these peptide hormones could be used as biological markers to improve production practices in fish aquaculture.A variety of long-term stress conditions may exist in fish cultivation, some of which are so severe that fish can no longer reestablish homeostasis. In teleost fish, the brain and gastrointestinal tract integrate signals that include the perception of stress factors regulating physiological responses, such as social stress by fish population density, where peripheral and central signals, such as peptide hormones, are the main regulators. Therefore, we proposed in this study to analyze the effect of different stock densities (SD) in the gene expression of brain neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP), together with the gastrointestinal peptide hormones leptin (Lep), vasointestinal peptide (VIP), and protachykinin-1 (Prk-1) in Salmo salar post-smolt. The coding sequence of S. salar VIP and Prk-1 precursors were firstly cloned and characterized. Then, the mRNA expression of these genes, together with the NPY, Lep, and CGRP genes, were evaluated in post-smolts kept at 11 Kg/m3, 20 Kg/m3, and 40 Kg/m3. At 14 days of culture, the brain CGRP and liver leptin mRNA levels increased three and tenfold in the post-smolt salmons kept at the highest SD, respectively. The high levels of leptin were kept during all the fish culture experiments. In addition, the highest expression of intestine VIP mRNA was obtained on Day 21 in the group of 40 Kg/m3 returning to baseline on Day 40. In terms of stress biochemical parameters, cortisol levels were increased in the 20 Kg/m3 and 40 Kg/m3 groups on Day 40 and were the highest in the 20 Kg/m3 group on Day 14. This study provides new insight into the gastrointestinal signals that could be affected by chronic stress induced by high stock density in fish farming. Thus, the expression of these peptide hormones could be used as molecular markers to improve production practices in fish aquaculture.