Fish Density Research Articles

Marine Noise Effects on Juvenile Sparid Fish Change among Species and Developmental Stages

Marine noise is an emerging pollutant inducing a variety of negative impacts on many animal taxa, including fish. Fish population persistence and dynamics rely on the supply of early life stages, which are often very sensitive to disturbance. Impacts of marine noise pollution (MNP) on juvenile fish have rarely been investigated in temperate regions. This is particularly true for the Mediterranean Sea, which is considered as an MNP hotspot due to intensive maritime traffic. In this study, we investigate the relationship between MNP related to boat traffic and (i) assemblage structure and (ii) the density of juvenile fishes (post-settlers at different stages) belonging to the Sparidae family. We quantified MNP produced by boating at four coastal locations in the French Riviera (NW Mediterranean Sea) by linearly combining five variables into a ‘noise index’ (NI): (i) boat visitation, (ii) number of boat passages/hour, (iii) the instantaneous underwater noise levels of passing boats, (iv) continuous boat underwater noise levels and (v) duration of exposure to boat noise. Then, using the NI, we identified an MNP gradient. By using juvenile fish visual censuses (running a total of 1488 counts), we found that (i) the assemblage structure and (ii) the density patterns of three fish species (i.e., Diplodus sargus, D. puntazzo, D. vulgaris) changed along the MNP gradient. Specifically, the density of early D. sargus post-settlers was negatively related to MNP, while late post-settler densities of D. puntazzo and, less evidently, D. vulgaris tended to decrease more rapidly with decreasing MNP. Our findings suggest the following potential impacts of MNP on juvenile sparids related to coastal boat traffic: (i) idiosyncratic effects on density depending on the species and the developmental stage (early vs. late post-settlers); (ii) negative effects on recruitment, due to possible alteration of late post-settlement movement patterns.

Urban-industrial seascapes can be abundant and dynamic fish habitat

Urban-industrial seascapes are prevalent around the world, yet we lack a basic understanding of how the mosaic of different habitats in these areas are used by mobile marine fauna, including features such as industrial ports and marinas. Urbanised areas have been alternately characterised in scientific literature as degraded, depauperate, or in some cases diverse and abundant. To advance our spatial and temporal understanding of the community of mobile marine fauna in these areas, we used repeated sonar image sampling over large swathes of two urban-industrial seascapes, combined with underwater video. 2,341 sonar segments were captured across Mackay Harbour and the Pioneer River estuary (North Queensland, Australia). We used this information to generate a preliminary understanding of the ecology of these locations. We found that overall, urban-industrial seascapes can contain counts of mobile marine fauna similar to natural areas, and that these seascapes are characterised by dynamic diel shifts in the spatial arrangement of mobile marine fauna in the water column. At night, large fish are prevalent in the water column, while during the day, assemblages are dominated by small fish. Within these urban-industrial seascapes, deeper areas containing heavy infrastructure such as ports can harbour large densities of fish, including heavily targeted fisheries species. These areas deserve recognition as marine habitat, are of consequence to fisheries, and have the potential to influence surrounding ecosystems. Important research questions remain regarding their impact on food webs and animal movement at larger scales.

Evaluation of fish density influence on the growth of the spotted rose snapper reared in floating net cages using growth models and non-parametric tests

In commercial fish farming, growth performance is the most influential factor in economic profitability; so, biomass optimization has become a growing concern. We analyzed the influence of 3 harvest densities (15, 20, and 22 kg·m–3) on the growth of spotted rose snappers reared in floating net cages during a production cycle. To assess the impact of stocking density on growth performance, we used 2 indicators: final total length-at-age (12 months) and the growth rate estimated from growth models (von Bertalanffy, logistic, and Gompertz). For the first indicator, we tested for normality. We did the Kruskal–Wallis and the post hoc Kruskal–Wallis tests to compare the mean total final length from each density. Accordingly, the means of densities D15 and D20 were the same (P value = 0.22). For the second indicator, we fitted the models with the subroutine optim of the R statistical package using the L-BFGS-B algorithm. Model selection was made with the Akaike and the Bayesian information criteria. Both criteria suggested that the logistic model fitted the data best. With the best model (logistic), we did 1,000 bootstrap simulations for each density scenario to determine the distribution of the maximum likelihood estimation for the instantaneous growth rate. Because the estimates were normally distributed, we used ANOVA to test the equality of the instantaneous growth. The Tukey HSD test suggested that all means were statistically different from each other. The fastest growth rate (K = 0.275) corresponded to the cage with a density of 20 kg·m–3. These findings demonstrate that the logistic model can predict the growth of spotted rose snappers under culture conditions using floating net cages. These results strengthen the productive potential and economic profitability of snapper aquaculture using floating cage and may help the start of commercial scale aquaculture.

Declines in lake whitefish larval densities after dreissenid mussel establishment in Lake Huron

Lake whitefish (Coregonus clupeaformis) is an ecologically and commercially significant species across the Laurentian Great Lakes. Over the past 20 years, lake whitefish population abundance has substantially declined across lakes Huron and Michigan, being driven by reduced recruitment of juvenile fish into the population. However, the life stage at which the recruitment bottleneck is occurring and what factors are contributing to the declines remain unknown. One hypothesis is that dreissenid mussels reduced zooplankton availability to larval lake whitefish, leading to poor growth and survival of this critical life stage. Here, we present results of a larval fish survey conducted at the Fishing Islands spawning region in Lake Huron and examine whether declines in juvenile recruitment are linked to reduced larval fish density. Larval fish were collected annually during two time periods: (1) a historical time period before dreissenid mussel establishment (1976–1986); and (2) a contemporary time period after dreissenid mussels became established (2017–2019, 2021). We found significant declines in larval densities and growth between historical and contemporary time periods. Following dreissenid establishment, larval densities and growth were on average only 23% and 55% of historical values, respectively. Moreover, year class strength at the juvenile stage (age 4) was positively related to larval density. Several explanatory variables contributed to annual variation in larval densities, with dreissenid mussels and water levels having the most consistent effect. Our results suggest that juvenile recruitment is being limited at the larval stage, owing to overall lower larval production and potentially exacerbated by slower growth.

Application of the machine learning method to estimate the biomass of pacific cod in the North Kuril zone

The biomass of pacific cod (Gadus macrocephalus) in the North Kuril fishing zone is estimated using a multifactorial approach, with evaluation of uncertainty. For this purpose, the density of fish over entire zone is restored using the data on density obtained in 2022 compared with the data of previous surveys and fishery data obtained in 2021 and earlier, converted to the same scale, with application of the machine learning method, as the random forest in the multiple imputation by chained equations procedure (MICE). The coefficient of the restored data determination with out-of-bag (test set) data was > 0.8 with the data of scientific survey in 2021 and > 0.5 with the data of Danish seine observations. The cod density variance in MICE data was in 82 % lower than in the data of the scientific survey; therefore the biomass estimation with MICE data has lower uncertainty than that one calculated just from the mean density in survey. The study showed insignificant difference of the cod biomass in 2021 and 2022. Spatial segregation is revealed for fishing gears used for the pacific cod fishery. There is proposed to extend the list of fishing gears and to expand the study area for reducing possible bias in the biomass estimation due to large area of extrapolation.

Infection of the European flounder (Platichthys flesus) with Glugea stephani, a possible new indicator of the weakening of the Baltic population

The strict limitations on the fishing quotas for Atlantic cod (Gadus morhua) have meant the European flounder (Platichthys flesus) has become the third most commercially fished species in the Baltic Sea. Recent reports from the International Council for the Exploration of the Sea and local fishermen, however, indicate a noticeable decline in the fitness of the species and catch volume in the Baltic Sea over the last decade. As the alimentary tract is one of the major entry routes for toxicants and parasites, and since any disturbances in its functioning are directly responsible for harmful changes in the health and welfare of the fish, a diachronic examination of the digestive tract of the European flounder sampled from the Slupsk Bank was carried out in order to determine possible factors behind the observed detrimental changes in its success in the Baltic Sea. The results obtained revealed a serious Glugea stephani infection and the presence of microsporidiosis in the fish studied (a prevalence of 41.9 % and a mean infection intensity of 9.15 xenomas per fish) considerably higher than those previously reported in less polluted regions studied across Atlantic and Pacific. This may suggest the influence of factors conducive to improving the success rate of the invading parasite, such as an increased level of environmental pollution and oxygen deficiency on the sea bottom, both of which contribute to a greater density of fish in a limited area. Our study indicates the need for comprehensive parasitological investigation of the European flounder in the Baltic Sea, in order to study microsporidiosis and the level of parasitic infection detected in histopathological and molecular analyses, including metacercariae of Zoogonoidae, nematodes of Cucullanidae, Anisakidaea and Parafilaroides normani. This study detected Parafilaroides normani, hitherto unknown in Europe, with a probability of 91.41 %.

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.

Reconstructing trophic position over the past century for five Puget Sound fish species

The comparison of historical and modern food web dynamics allows ecologists to test whether the trophic connectivity we observe today is ‘normal’ in its historical context. Fish densities and abundances have changed across time, making it likely that fish trophic interactions and their trophic positions have also changed. Historical trophic data of marine fishes can now be extracted from the tissues of fluid-preserved specimens held in natural history collections via compound-specific stable isotope analysis of amino acids (CSIA-AA) of nitrogen. We conducted CSIA-AA to quantify trophic position change over the past century in 5 ecologically important fishes of Puget Sound, Washington, USA: Pacific hake Merluccius productus, walleye pollock Gadus chalcogrammus, copper rockfish Sebastes caurinus, English sole Parophrys vetulus, and Pacific herring Clupea pallasii, and examined the canonical trophic (glutamic acid) and source (phenylalanine) amino acids. For all fishes except copper rockfish, trophic position, glutamic acid, and phenylalanine values remained similar across time. For copper rockfish, glutamic acid but not phenylalanine values increased over time, indicating an increase in this species’ trophic position. The observed increase in copper rockfish trophic position may be a function of diet switching and declining prey quality rather than a consequence of rockfish consuming higher trophic level prey. This study leverages more than 100 yr of trophic data of fishes representing various feeding guilds and demonstrates that some fish species may be more trophically resilient to major environmental change than expected. Efforts should be made to identify and conserve the trophic interactions of species experiencing change.

The condition of megabenthos and reef fish in coral reef ecosystems in Aru Islands National Conservation Area, Southeast Maluku, Indonesia

The waters of the Aru Islands are part of the National Marine Protected Areas (MNR), and have extensive coral reefs with high biodiversity. The study was conducted in October 2016 at twelve stations to determine the status of coral cover, composition, and density of megabenthos and reef fishes. Coral reef data collection refers to the Underwater Photo Transect (UPT), and data processing uses Coral Point Count for Excel (CPCe). The Benthos Belt Transect (BBT) method was used for megabenthos data, and the Underwater Visual Census (UVC) method was used for reef fish observations.The result of the benthic component analysis showed that the proportion of live corals at each station ranged from 10.60% to 54.27%, with an average cover value of 31.21%, which fell into the “fairly good” category. Megabenthos density analysis revealed that Drupella cornus had the highest density value (0.29 individuals/m2) and Holohuria edulis (0.01 individuals/m2) had the lowest density. Analysis of the reef fish community revealed that the indicator fish were 168 individuals from the family Chaetodontidae. The group of herbivore fish recorded 116 individuals from threee families: Acanthuridae, Scaridae, and Siganidae. Acanthurus auranticavus and Acanthurus pyroferus are common species found in the waters of the Aru Islands.

Distribution of fish in the subarctic lake

The paper studies fish population of an isolated lake in the subarctic zone. The study of the features of distribution of fish, the assessment of their abundance and size structure were carried out by the echometric method using hydroacoustic complexes and geoinformation systems. The research found out that the fish population is represented by 4 species of fish: roach, perch, pike and peled, with the absolute dominance of cyprinids. Their share of the total number of fish in the reservoir was >80%. Features of the horizontal distribution of fish are mainly due to trophic-defensive behavior (concentration of juveniles in the littoral), where it is possible to use macrophytes as shelters from visually oriented predators - perch and pike. In the horizons of the water column with depths <5 and >5 m, 72.4 and 27.6% of fish from their total abundance in the reservoir were recorded, the average density of fish at the considered horizons was 2149 and 398 ind. / ha. In the vertical aspect, the distribution of fish is determined by both trophic-defensive (concentration of juveniles in the littoral) and thermoregulatory behavior (concentration of peled on the drope of depth in the profundal zone).

Evaluation of local ingredient formulated diet for golden rabbitfish, Siganus guttatus grow-out

Golden rabbitfish, S. guttatus culture is feasible to be developed in ponds and floating net cages. To support rabbitfish culture, cheap and good quality feed using local ingredients is necessary. The study aimed to evaluate the local ingredients formulated feed for golden rabbitfish S. guttatus grow-out. Feed was formulated based on the least cost feed formulation. The feeding trial was carried out using 15 units of 1x1x2 m3 floating net cages, with a fish density of 23 fish/cage with an initial weight of 39.88±8.05 g. The study was completely randomized, with four treatments of feed formulation (A, B, C, D) and commercial feed as control (E) in triplicates for each treatment. Parameters observed included growth response, feed utilization, digestibility, carcass composition, and feed cost per kg of fish production. The data obtained were analyzed statistically using analysis of variance (ANOVA). The result showed feed B gave the highest growth rate (1.05±0.09%) and was not significantly different from commercial feed (P>0.05). Still, it had a cheaper cost of production (IDR 15,000/kg of fish production) compared to commercial feed (IDR 22,000/kg of fish production) (P<0.05) with a 31.82% efficiency of production cost.

Identification of Parasites on Fish Consumption at Several Fish Markets in Bogor City

This study aims to identify the types of parasites in fish consumed in several fish markets in Bogor City. This study used 100 consumption fish which included goldfish, tilapia, catfish, and mujahir fish. Sampling Fish were taken randomly at 5 fish markets in Bogor City, namely Gunung Batu Market, Pajajaran Market, Merdeka Market, Bogor Market, and Yasmin Market. Samples of fish organs examined were gills, fins and digestive organs (intestines). The examination results showed that the prevalence of consumption fish infected with parasites was 22% and included in the “Often” category. The highest prevalence of parasite infection was at Gunung Batu Market and Merdeka Market with a prevalence of 30% each. The types of parasites found were cestode worms namely Ligula intestinalis and Trematoda sub class Monogea namely Dactylogyrus sp and Gyrodactylus sp. Ligula intestinalis infects goldfish. Dactylogyrus sp and Gyrodactylus sp infected goldfish and mujair fish. Parasite infections in consuming fish at the Bogor City Fish Market are caused by dense fish density, poor water quality, optimal temperature for parasites and stress factors.

Keystone Porgy Species (Sparidae) Overcome the Alien Randall's Threadfin Bream (Nemipterus randalli) for Catch Balance in Space on An Oligotrophic Levant Shelf or Vice Versa?

Since 2008 spatiotemporal and ecological distributions of porgies (sparid, all indigenous fish) were examined in the presence or absence of Randall's threadfin bream, Nemipterus randalli in the present study area. Seasonal fish and environmental parameters samplings were conducted at three transects of the fishing (nMPA) or non-fishing (MPA) regions on an oligotrophic shelf (Levantine Sea) in 2014-2015 for understanding management and ecology of the porgies’ catches. Of 13 sparid fish determined during the present study, five species are rarely found. There were no seasonal significant differences in densities of the sparid fish with or without the alien nemipterid fish. However, there were differences in the densities by the bottom depths, the regions, and soft and hard bottoms vegetated by Caulerpa spp and meadow, respectively. Ecologically, fish assemblages and faunistic characters of the sparid fish were highly variable when excluding the N. randalli as highlighted and follows; i) seasonal variation occurred and ii) the depthwise community assemblages became irregular. N. randalli seemed to balance the sparid catch attributed to the biomass-abundance ratio in the ecosystem or vice versa in this trophically sensitive gulf (ultra-oligotrophic) of the eastern Mediterranean Sea.

Impact of Coral Bleaching on Coral Reef Fishes in Sekotong Bay, West Lombok Regency

Coral reef fish is one of the main components making up the ecosystem of coral reefs. There is a strong mutual dependence between reef-forming corals and fish that inhabit coral reefs. Various fish species use coral as a food source and habitat. This article describes the impact of coral bleaching on the diversity, density, and biomass of coral reef fish in the waters of Sekotong Bay, West Lombok. Underwater visual census (UVC) methods are used to obtain data on species, the number of individuals per species, and fish size at transect length 70 meters and width 5 meters. Simple linear regression analysis that is used to assess the impact of coral bleaching on the condition of coral reef fish shows that coral bleaching affects the diversity and density of reef fish. This analysis also showed that coral bleaching affected herbivorous fish biomass but not carnivorous fish. This study concludes that the degradation of coral fish in the Sekotong Bay of West Lombok occurs due to various factors, especially the declining health conditions of coral reefs

Effects of COVID-19 lockdown on the observed density of coral reef fish along coastal habitats of Moorea, French Polynesia.

The online version contains supplementary material available at 10.1007/s10113-022-02011-0.

Dietary Leucine Supplementation Improves Muscle Fiber Growth and Development by Activating AMPK/Sirt1 Pathway in Blunt Snout Bream (Megalobrama amblycephala).

This research is aimed at evaluating the effects of leucine supplementation on muscle fibers growth and development of blunt snout bream through a feeding trial and a primary muscle cells treatment. An 8-week trial with diets containing 1.61% leucine (LL) or 2.15% leucine (HL) was conducted in blunt snout bream (mean initial weight = 56.56 ± 0.83 g). Results demonstrated that the specific gain rate and the condition factor of fish in the HL group were the highest. The essential amino acids content of fish fed HL diets was significantly higher than that fed LL diets. The texture (hardness, springiness, resilience, and chewiness), the small-sized fiber ratio, fibers density, and sarcomere lengths in fish all obtained the highest in the HL group. Additionally, the proteins expression related with the activation of the AMPK pathway (p-Ampk, Ampk, p-Ampk/Ampk, and Sirt1) and the expression of genes (myogenin (myog), myogenic regulatory factor 4 (mrf4) and myoblast determination protein (myod), and protein (Pax7) related to muscle fiber formation were significantly upregulated with increasing level of dietary leucine. In vitro, the muscle cells were treated with 0, 40 and 160 mg/L leucine for 24 h. The results showed that treated with 40 mg/L leucine significantly raised the protein expressions of BCKDHA, Ampk, p-Ampk, p-Ampk/Ampk, Sirt1, and Pax7 and the gene expressions of myog, mrf4, and myogenic factor 5 (myf5) in muscle cells. In summary, leucine supplementation promoted muscle fibers growth and development, which may be related to the activation of BCKDH and AMPK.

Influence of In-stream Ecosystem Restoration Techniques on the Fish Ecology of the River Nabongo in Eastern Uganda

The study was the first in Uganda to assess the responses of fish community assemblages to introduced woody debris structures in a tropical river in Eastern Uganda. For comparison purposes, two different woody debris structures (simple and complex) were introduced in river Nabongo, and their effect on fish assemblage and feeding was established based on experiments conducted in two heterogeneous stream environments (a pool and a riffle). Results showed that sampling plots treated with restoration structures registered higher fish species richness, diversity, and abundance than sampling plots without restoration structures (control plots) at each site. The study (experiment) applied a stratified sampling design which used purposive identification of a pool and a riffle in River Nabongo Catchment. Fish were captured using a drift net, an electro-fishing gear, and a hand net. Data were analysed using a one-way ANOVA generated from STATA version 14. At the pool site, total fish density varied significantly from plot to plot (P<0.05) but was highest in the complex structures with 64±1.08 fishes/m2 and lowest with 24±0.82 fishes/m2 in untreated plots. K-factor did not vary significantly in untreated plots at the pool site but significantly differed from treated plots at P<0.05. The relative abundance of fish species at the pool site was highest in the complex structures with 40.7±0.66% and 21.5±0.42% before structures but was least in the control plot, varying significantly from plot to plot at P<0.05. It was concluded that woody debris restoration is an effective stream restoration technique. Fish individuals, trophic groups, and taxa more densely colonised sampling plots that had structures than those that did not have structures.

MATERIALS FOR THE RECOMMENDATIONS ON PRE-SPHERING MAINTENANCE, NATURAL SPRINGING OF THE BAIKAL OMUL IN THE SELENGA RIVER FOR THE PURPOSE OF ARTIFICIAL REPRODUCTION IN 2020

This paper presents data on the collection, analysis, processing of materials for keeping spawners of the Baikal omul, determining the optimal stocking density of fish in cages, determining the efficiency of using spawners in 2020.

Catchment-scale stream network spatio-temporal models, applied to the freshwater stages of a diadromous fish species, longfin eel (Anguilla dieffenbachii)

Spatio-temporal modelling frameworks are important tools for evaluating changes in the population structure of freshwater species, to inform population assessments. However, in the stream networks occupied by freshwater species, two data points in space are more related by physical connectivity than by straight-line, Euclidian distance. Therefore, there is a need for spatio-temporal modelling frameworks that represent the relatedness of points based on physical connectivity. We developed such a modelling framework, known as the “VAST stream network modelling framework", using the widely-employed vector autoregressive spatio-temporal modelling platform VAST and the Ornstein-Uhlenbeck process for spatial variance. Here, we demonstrate the VAST stream network spatio-temporal modelling platform with two applications to the freshwater stages of a diadromous fish species, the endemic New Zealand longfin eel (Anguilla dieffenbachii), and a simulation experiment. The first real-world application considers a single category (longfin eel) and models its probability of encounter in the Waitaki catchment, while the second distinguishes between two categories (smaller and larger longfin eels) and models their numerical densities in the greater Waikato region. These two applications demonstrate how stream network spatio-temporal models can usefully inform freshwater resource managers, providing insights into changes in fish encounter probability and density for different fish length classes and estimates of effective river length occupied. The simulation experiment uses the Waikato model as an operating model to evaluate alternative sampling scenarios for accuracy, precision and coverage, to advise on data requirements. A yearly sample size of 30 sites over a 20-year time series had the greatest precision and accuracy in trend estimates among all scenarios investigated. We also found that, for the scenario with declining female spawning biomass, increasing the yearly sample size from 15 sites to 30 sites in a 9-year time series increased the precision and resulted in unbiased estimates. There is a need to optimise sampling schemes for the freshwater stages of diadromous species, including longfin eel, and we, therefore, recommend further simulation experiments to explore scenarios of population trends, habitat features and sampling approaches.

The reef fish assemblage of a coral reef system in the southwestern Gulf of Mexico

Reef fish species richness of the Veracruz Reef System National Park (VRSNP) in the SW Gulf of Mexico is well known. However, the knowledge of the assemblage structure and its spatial variability in the reef ecosystem is quite limited. For that purpose, 5 field surveys (2012-2015) were performed, using the stationary visual census method, at 10 selected reefs. The most important findings were: 116 reef species were recorded. Average total reef fish density (2.31 Ind/m2) is similar to the records for the Caribbean reefs in the 20th century. The top 5 most abundant species were: Chromis multilineata, Ocyurus chrysurus, Abudefduf saxatilis, Stegastes leucostictus, and Elacatinus jarocho. We found evidence of a spatial distribution pattern with 3 well-defined groups of reefs: (1) those near the city of Veracruz, (2) those near the outlet of the Jamapa River, and (3) those farther from the city. Higher fish densities are associated to both high hermatypic coral and low crustose coralline algae bottom covers. The assemblage structure of reef fishes is different at distinct geomorphological reef zones. As expected, with some differences in the species abundance order, the assemblage structure of reef fishes is similar at all coral reefs in the Gulf of Mexico.