Size Classes Of Fish Research Articles

The impact of multi-type artificial reef habitats on the feeding ecology and trophic niche of dominant rocky reef fish species (Hexagrammos otakii and Sebastes schlegelii)

Large-scale artificial reef constructions have been carried out in the coast of northern Yellow Sea, which has effectively enhanced populations of rocky reef fish species. However, there is a lack of evidence regarding the differences in community composition among different types of artificial reef habitats. This study scrutinizes the foraging dynamics and ecological niche partitioning of Hexagrammos otakii and Sebastes schlegelii, which are two representative rocky reef fish species in the northern Yellow Sea. Stomach content analysis indicates that H. otakii exhibits a more diverse diet compared to S. schlegelii, with both species achieving the highest dietary diversity within concrete reef habitats. When factoring in body size, the dietary diversity for fish in the 0–15 cm size class was found to be the greatest within rock reef habitat, while larger individuals exhibited higher diversity within ship artificial reef habitats. The prey composition results demonstrate spatial differentiation patterns consistent across all size classes, with these discrepancies predominantly situated between ship and concrete or rock artificial reef habitats. The taxa driving these differences varied with fish species and body size, encompassing various prey categories such as Decapoda, Teleost, Polychaeta and Amphipod. Findings from the Stable Isotope Mixing Model (SIMMR) revealed significant dietary variations linked to species, habitat type and size class, which were fundamentally in agreement with the stomach content analysis. Niche analysis disclosed that overall niche breadth for both fish populations was largest in concrete artificial reef habitat. This suggests that each reef type caters to specific fish size classes, showcasing distinct spatial and interspecific variations in foraging tactics.

Body length determines flow refuging for rainbow trout (Oncorhynchus mykiss) behind wing dams.

Complex hydrodynamics abound in natural streams, yet the selective pressures these impose upon different size classes of fish are not well understood. Attached vortices are produced by relatively large objects that block freestream flow, which fish routinely utilize for flow refuging. To test how flow refuging and the potential harvesting of energy (as seen in Kármán gaiting) vary across size classes in rainbow trout (Oncorhynchus mykiss; fingerling, 8 cm; parr, 14 cm; adult, 22 cm; n=4 per size class), we used a water flume (4100 l; freestream flow at 65 cm s-1) and created vortices using 45deg wing dams of varying size (small, 15 cm; medium, 31 cm; large, 48 cm). We monitored microhabitat selection and swimming kinematics of individual trout and measured the flow field in the wake of wing dams using time-resolved particle image velocimetry (PIV). Trout of each size class preferentially swam in vortices rather than the freestream, but the capacity to flow refuge varied according to the ratio of vortex width to fish length (WV:LF). Consistent refuging behavior was exhibited when WV:LF≥1.5. All size classes exhibited increased wavelength and Strouhal number and decreased tailbeat frequency within vortices compared with freestream, suggesting that swimming in vortices requires less power output. In 17% of the trials, fish preferentially swam in a manner that suggests energy harvesting from the shear layer. Our results can inform efforts toward riparian restoration and fishway design to improve salmonid conservation.

Tolerance of juvenile lumpfish (Cyclopterus Lumpus) to high rearing densities

AbstractLumpfish (Cyclopterus lumpus) are raised as cleaner fish for controlling sea lice. Intensive rearing is complicated by fin nipping that occurs between juvenile conspecifics. Lumpfish density‐dependent interactions are not well understood; therefore, the effects of rearing density for different fish size classes warranted evaluation. Two size classes (2‐ and 13‐g) of juvenile lumpfish were stocked at four different rearing densities (40, 60, 70, and 90 g/L) with growth, survival, and fish aggression assessed over 8 weeks. Mean weight gain and specific growth rates ranged from 170% to 307% and 1.77% to 2.50%, respectively, depending on density treatments, for the 2‐g fish, and from 286% to 471% and 2.42% to 3.10% for the 13‐g fish. Growth was negatively correlated with density, with faster growth linked to lower densities. No mortality occurred in any treatment and significant fish aggression only occurred among the larger lumpfish in the higher rearing densities. Based on these findings, growth of 2‐g lumpfish can be increased if reared at 40 g/L or slowed at 70 g/L without impacting aggression. For grow out of 13‐g fish to ~70 g with minimal aggression, a 40 g/L rearing density is recommended for faster growth and 60 g/L for slower growth.

Nocturnal substrate association of four coral reef fish groups (parrotfishes, surgeonfishes, groupers and butterflyfishes) in relation to substrate architectural characteristics.

Although numerous coral reef fish species utilize substrates with high structural complexities as habitats and refuge spaces, quantitative analysis of nocturnal fish substrate associations has not been sufficiently examined yet. The aims of the present study were to clarify the nocturnal substrate associations of 17 coral reef fish species (nine parrotfish, two surgeonfish, two grouper and four butterflyfish) in relation to substrate architectural characteristics. Substrate architectural characteristics were categorized into seven types: (1) eave-like space, (2) large inter-branch space, (3) overhang by protrusion of fine branching structure, (4) overhang by coarse structure, (5) uneven structure without large space or overhang, (6) flat and (7) macroalgae. Overall, fishes were primarily associated with three architectural characteristics (eave-like space, large inter-branch space and overhang by coarse structure). The main providers of these three architectural characteristics were tabular and corymbose Acropora, staghorn Acropora, and rock. Species-specific significant positive associations with particular architectural characteristics were found as follows. For the nine parrotfish species, Chlorurus microrhinos with large inter-branch space and overhang by coarse structure; Ch. spilurus with eave-like space and large inter-branch space; Hipposcarus longiceps with large inter-branch space; Scarus ghobban with overhang by coarse structure; five species (Scarus forsteni, S. niger, S. oviceps, S. rivulatus and S.schlegeli) with eave-like space. For the two surgeonfish species, Naso unicornis with overhang by coarse structure; N. lituratus with eave-like space. For the two grouper species, Plectropomus leopardus with eave-like space; Epinephelus ongus with overhang by coarse structure. For the four butterflyfish species, Chaetodon trifascialis with eave-like space and large inter-branch space; C. lunulatus and C. ephippium with large inter-branch space; C. auriga showed no significant associations with any architectural characteristics. Four species (Ch. microrhinos, H. longiceps, S. niger and N. unicornis) also showed clear variations in substrate associations among the different fish size classes. Since parrotfishes, surgeonfishes and groupers are main fisheries targets in coral reefs, conservation and restoration of coral species that provide eave-like space (tabular and corymbose Acropora) and large inter-branch space (staghorn Acropora) as well as hard substrates with coarse structure that provide overhang (rock) should be considered for effective fisheries management in coral reefs. For butterflyfishes, coral species that provide eave-like space (tabular Acropora) and large inter-branch space (staghorn Acropora) should also be conserved and restored for provision of sleeping sites.

Phenotypic variation of protandrous hermaphrodite fish Eleutheronema tetradactylum (Shaw, 1804) from Thailand coastal waters

This study was conducted to investigate the intraspecific variation of Eleutheronema tetradactylum (Shaw, 1804) using traditional morphometric measurements. In total, 136 samples were collected from four fishing areas across Thailand coastal waters. Raw data were standardized and then evaluated with univariate analysis of variance, canonical discriminant function analysis, and dendrogram of cluster analysis regarding to site, size, and sex. Result from ANOVA test exhibited that all morphological characters were significantly different among sites (P < 0.05). Nevertheless, forty-one morphometric characters were significantly different among size of male and female fish (P < 0.05) except for pre-orbital length, pupil diameter, eye diameter, and depth of maxilla for male fish. Forty-four morphometric characters were significantly different (P < 0.05) except of fork length among sex. From CDFA, E. tetradactylum showed phenotypic heterogeneity and two distinct stocks in the four selected fishing areas. Phenotypic variation on sites was determined by six morphological characters (MnFL, DFAF, DOM, HW, PeBFL and ED) for males, while eight characters for females (PrOL, AFSL, PeBFL, DOM, UJL, PD, AFRL and ED) in decreasing order. Differentiations between fish size classes, relied on PrDFL2, BD and UCFL in males and PrOL, PrePeFL and DFAF in females. Among sexes, PeFAF, PrDFL2, MxFL, MnFL, PrePeFL, HSDF and PrePFL were highly influential. Discriminate functions (DF1) clarified that 83.60% and 94.10% of the total variance were found among the sites of males and females, and 99.20% and 93.20% of the total variance were found among the sizes of males and females, respectively. and 73% of the total variance were found among the sexes. In the confusion matrix of CDFA, the overall assignments of individuals into their correctly classified original population were 98.68% and 100% for males and females based on site and size, and 75.74% of sex groups, respectively. Our study highlighted that the hermaphroditism of E. tetradactylum showed that three distinct stocks of males and two stocks of females inhabited Thai coastal waters.

Influence of angling methods and terminal tackle on survival of salmon and steelhead caught and released in the Cowlitz River, Washington

Efforts to recover depressed stocks of salmon and steelhead trout in North America include implementation of mark-selective recreational fisheries, whereby anglers are allowed to harvest hatchery-origin fish but must release natural-origin fish. Catch and release angling (C&R) is generally thought to be an effective tool for conservation relative to traditional retention fisheries due to high survival of released adult salmon and steelhead in freshwater. Studies designed to estimate C&R mortality have produced highly variable results among species and size classes of fish, gear types, and environmental conditions. Therefore, crude approximations of C&R mortality are commonly used to quantify impacts to natural-origin salmon and steelhead. In addition, managers often restrict use of certain angling methods and terminal tackle that are assumed to result in higher mortality, leading to a multiplicity of different regulatory requirements with limited empirical support. We conducted a novel three-year mark-recapture study in the Cowlitz River, Washington to estimate effects of a variety of factors hypothesized to influence salmon and steelhead C&R survival using a control-treatment design. Three species of anadromous salmonids were captured and released as treatments using various angling techniques and terminal tackle. Fight time, handling time, and water temperature were recorded during each capture event. Non-angled fish were captured in a trap and released back into the fishery to serve as controls. Recovery rates of Coho Salmon differed less than a percent between angled and non-angled fish across multiple gear types, indicating negligible effects of C&R. Angled Spring Chinook Salmon experienced 3.6–10.2 % C&R mortality relative to non-angled control fish, depending on terminal tackle. Barbless hooks were associated with higher survival than barbed hooks for both Chinook and Coho Salmon, although differences were small for Chinook and negligible for Coho. In contrast, steelhead trout angled on barbed hooks were recovered at slightly higher rates than those caught on barbless hooks. We also found evidence for a reduction in landing rates when angling using barbless hooks. Finally, use of bait increased the probability that salmon would be hooked in a critical location such as the esophagus or stomach. Our findings are useful for assessing trade-offs between conservation measures and harvest opportunity when defining fishing regulations in mark-selective salmon and steelhead fisheries.

Do temperature and population size structure influence the quantity of fish eDNA in water?

Various factors can influence the concentration of eDNA found in the environment and blur the link between eDNA results and in situ fish abundances, biomasses or even occurrences. We studied the influence of one abiotic factor, the temperature, and one biotic factor, the fish size class, on the amount of fish eDNA detectable in water. To do so, we conducted two controlled experiments using tench (Tinca tinca, L) placed into outdoor mesocosms during 1 week. The quantification of fish eDNA abundances was performed using quantitative PCR after filtrating a large volume of water (30 L). The Bayesian hierarchical ANOVAs performed on qPCR results did not detect the effect of size class on eDNA amount, but fish eDNA concentration was shown to increase significantly when temperature rose by 6°C (no effect detected at 3°C). This suggests that fish assemblage quantification of two thermally contrasting sites through eDNA is not directly comparable.

Gill net catchability of walleye (Sander vitreus): Are provincial standards suitable for estimating adult density outside the region?

Standard gill netting protocols are increasingly used to assess freshwater fish populations. Understanding the catchability (q) of fish following these protocols enables direct estimation of density, which has advantages over relative abundance from analytical and applied research perspectives. However, catchability is complex. The application of q estimated in one region may be inappropriate for another if physical and biological processes driving catchability differ. Cross-region assessments of q are needed to assess the applicability of estimates over a broader geographic and environmental range. In this study, we evaluated whether the global estimate of q (1.044 ha/gang; variance = 0.2268) derived by Giacomini et al. (2020) for walleye Sander vitreus ≥ 350 mm total length (TL) was suitable for application in two Colorado, USA reservoirs supporting recreational fisheries and wild spawn operations. We followed provincial standards in Ontario and Quebec, Canada (i.e., Fall Walleye Index Netting) combined with other corrections for size-dependent catchability to estimate the density of mature, adult walleye ≥ 470 mm TL for comparison to independent estimates from mark-recapture analyses. Following similar methodologies, we found that the global estimate of q combined with size-dependent gill net retention coefficients underestimated the density of adults by nearly 80%, but uncertainty in point estimates can be high. Results highlighted the need to better understand sources of uncertainty, including factors influencing size-dependence in gill net encounter when extending estimates of q to other size classes of fish, systems, and regions. Estimates of catchability for large-bodied adult walleye in our systems were consistent, but relatively low, ranging from 0.203 ha/gang (95% confidence limits = 0.133–0.298) to 0.227 ha/gang (0.091–0.556). We expand the geographic and environmental range of paired mark-recapture and gill net Catch Per Unit Effort information and discuss potential factors contributing variability to estimates of catchability for adult walleye.

Polycyclic Aromatic Hydrocarbons (PAHs) Contamination in Chrysichthys nigrodigitatus Lacépède, 1803 from Lake Togo-Lagoon of Aného, Togo: Possible Human Health Risk Suitable to Their Consumption.

The Lake Togo-Lagoon of Aného is located in the coastal zone where phosphorite mining is carried out. This mining discharges all kinds of waste such as fuel oil into the surrounding environment without prior treatment. Moreover, the hydrosystem receives runoff and river inputs after having crossed and leached from mining and urban soils. This study aims to determine the polycyclic aromatic hydrocarbons (PAHs) contamination in commercially consumed fish species (Chrysichthys nigrodigitatus) from that hydrosystem and the associated health risks for consumers. For that, fish sample collection was performed during the dry season. Afterwards, their muscles, gills, and livers were cut and 12 PAHs were analyzed using gas chromatography coupled with a mass spectrometer (GC-MS). The total PAHs (tPAHs) concentrations in fish tissues ranged from 5.24 to 48.40 µg/kg with average concentration of 14.51 ± 8.95 µg/kg in muscles, from 5.90 to 28.20 µg/kg averaging 14.90 ± 5.19 µg/kg in gills, and from 43.20 to 149.00 µg/kg with an average of 80.74 ± 27.08 µg/kg in livers. The average concentrations of low molecular weight PAHs (LMW PAHs) were 10.82 ± 9.61 µg/kg in muscles, 8.25 ± 5.43 µg/kg in gills, and 47.97 ± 22.56 µg/kg in livers whereas those of high molecular weight of PAHs (HMW PAHs) were 4.10 ± 2.14 µg/kg in muscles, 7.98 ± 3.96 µg/kg in gills, and 32.77 ± 8.66 µg/kg in livers. An overall trend of decreasing concentrations with increasing fish size classes was observed for some PAHs (Naphtalene, Pyrene in muscles, for Pyrene, Benzo(a)Anthracene, Chrysene in gills and for Naphtalene, Phenanthrene in livers). The PAHs in these fish might have pyrogenic and petrogenic sources, with the dominance of pyrogenic, and all of the total hazard quotients (THQ) are less than 1. This situation must not be neglected for better planning sustainable management of the target ecosystem.

Scales surface topography: Comparative ultrastructural and decorative characteristics of a modern elasmoid fish scales in a cyprinid fish, Garra shamal (Teleostei: Cyprinidae) using digital optical light and scanning electron microscope imaging.

The complex architecture of fish scale has been investigated for several decades to show an existing link between scale morphology/microstructure and systematic/evolutionary relationships of fishes. In the present study, the surface architecture structure associated with the scales of a hill stream cyprinid fish Garra shamal restricted to the Hajar Mountains of the Arabian Peninsula was examined by optical light and scanning electron microscopy; (i) to describe the whole morphology, architectural design and hidden microstructures of scales in an endemic fish of the Arabian Peninsula, G. shamal, (ii) to investigate the phenotypic plasticity of scales in six selected regions of the fish body, (iii) to show an ontogenetic pattern of scale morphology in different size classes, and (iv) to study morphometric parameters for scales, and determine the most valuable indices for differentiating the scales of different body regions and the different size groups of studied species. For this purpose, scales were removed from six body regions of three size classes. The scale of G. shamal, as an ossified platelet and hard structure covering the outer part of fish in different body parts and size groups, demonstrated numerous hidden morphological and structural characteristics, and sculptural design, for example, type, shape, and size in general term, and circuli (thickness, arrangement, and relative spacing of circuli around the focus), radii (number, shape, its origin from focus), lepidonts (the texture, shape, size, orientation, and type of its attachment), and granules (shape, size, number, and configurations) in a specific term, that can contribute efficiently in fish identification and classification at the genus and species levels. Position of focus, presence of radii in all four fields of scales (anterior, posterior, and laterals) and thus tetra-sectioned type, presence of specific tubercle arrangement on the posterior region, and some scale indices can be used as a taxonomic tool in Garra identification. Moreover, scales in G. shamal demonstrated plasticity in different fish size classes, and the origin of scales on the fish body, revealing a kind of ontogenetic variation, and the importance of key scales (scales below the dorsal fin) in the lepidological studies. The quantitative and qualitative traits described here based on the optical light microscopy and electron scanning microscopy can be implemented along with other morphological and molecular characteristics to have a better taxonomic resolution of the genus Garra. RESEARCH HIGHLIGHTS: The optical light microscopy (LM) and scanning electron microscopy (SEM) techniques enhanced our knowledge of scale morphology in a cyprinid fish restricted to the Arabian Peninsula. The scale of G. shamal, in different body parts and size groups, demonstrated numerous hidden morphological and structural characteristics, and sculptural design that can contribute efficiently in fish identification and classification at the genus and species levels. Tetra-sectioned cycloid type, position of focus, presence of specific tubercle arrangement on the posterior region, and some scale indices can be used as a taxonomic tool for identification of the genus Garra. The scales showed plasticity in different fish size classes, and the origin of scales on the fish body, revealing a kind of ontogenetic variation.

POST MORTEM VARIATION OF TOTAL VOLATILE BASE NITROGEN (TVB-N) AND TRIMETHYLAMINE NITROGEN (TMA-N) IN VETKI (Lates calcarifer)

Total Volatile Base Nitrogen (TVB-N) and Trimethylamine Nitrogen (TMA-N) contents of Vetki (Lates calcarifer) were investigated following Conway’s Microdiffusion technique at 4 hour interval in Fish Quality Control Laboratory, Fisheries and Marine Resource Technology Discipline, Khulna University. Observed TVB-N and TMA-N value did not vary significantly among different size classes. At fresh condition, TVB-N content was observed as 11.106±0.8 mg, 11.162±0.8 mg, and 11.162±0.8 mg in small, medium and large size classes of fish respectively and it increased to 59.087±0.8 mg, 68.417±1.5 mg and 75.967±2.7 mg for 100 g-1 respectively at complete spoilage stage (after 28 hrs). At fresh condition, TMA–N content was 6.7±0.016 mg, 11.069±1.79 mg and 11.172±1.01 mg for 100 g-1 in small, medium and large size classes of fish respectively and it increased to 48.893±3.01 mg, 52.492±.089 mg and 57.717±1.95 mg for 100 g-1 respectively at complete spoilage stage. TVB-N and TMA-N values started to increase gradually in all size groups with the passage of time but the rate of increase became faster after 20th hour and continued till the final stage was reached.

Biological Aspects of Three Species Family Gobiidae in the Bilah River, Labuhanbatu Regency, Sumatera Utara Province

The Bilah river is known to have a fairly high fish biodiversity. Some species of Gobiidae are usually caught by fishermen in the estuary area. But until now there is no data and information related to the biological aspects of the Gobiidae family. The purpose of this study was to determine aspects of the size class and long relationship of the weight of Gobiidae fish caught by fishermen in the Bilah river. This study is exploratory, where fish sampling stations are determined based on fish habitat from fishermen's information (purposive sampling). Fish are caught using traditional fishing gear in the form of splint. The fish caught is then measured in total length and weight. Then the fish obtained based on the catch are grouped in small, medium, and large sizes. Data analysis using Microsoft Excel 2010 applications. In this study, three species of fish that are included in the family Gobiidae namely Butis butis, Butis aureus, and Eleotris fusca. The small category B. butis (9-11.9 cm) fish size class is obtained as many as 2 individuals, medium size (12-14.9 cm) 9 individuals, and large size (15-17.9 cm) 2 individuals. The small size class (6-8.9 cm) of B. aureus fish obtained 2 individuals, medium (9-11.9 cm) 8 individuals, and large 12-14.9 cm) 4 individuals. Small size class (9-11.9 cm) E. fusca as many as 6 individuals, medium (12-14.9 cm) 7 individuals, and large (15-17.9 cm) 3 individuals. The growth pattern of the crazy fish (B. butis) (value b = 0.10), B. aureus (value b = 0.27), and E. fusca (value b = 0.20).

Relative Bias in Catch Among Long-Term Fish Monitoring Surveys Within the San Francisco Estuary

Fish monitoring gears rarely capture all available fish, an inherent bias in monitoring programs referred to as catchability. Catchability is a source of bias that can be affected by numerous aspects of gear deployment (e.g., deployment speed, mesh size, and avoidance behavior). Thus, care must be taken when multiple surveys—especially those using different sampling methods—are combined to answer spatio-temporal questions about population and community dynamics. We assessed relative catchability differences among four long-term fish monitoring surveys from the San Francisco Estuary: the Bay Study Otter Trawl (BSOT), the Bay Study Midwater Trawl (BSMT), the Fall Midwater Trawl (FMWT), and the Suisun Marsh Otter Trawl (SMOT). We used generalized additive models with a spatio-temporal smoother and survey as a fixed effect to predict gear-specific estimates of catch for 45 different fish species within large and small size classes. We used estimates of the fixed effect coefficients for each survey (e.g., BSOT) relative to the reference gear (FMWT) to develop relative measures of catchability among taxa, surveys, and fish-size classes, termed the catch-ratio. We found higher relative catchability of 27%, 22%, and 57% of fish species in large size classes from the FMWT than in the BSMT, BSOT, or SMOT, respectively. In the small size class, relative catchability was higher in the FMWT than the BSMT, BSOT, or SMOT for 50%, 18%, and 25% of fish species, respectively. As expected, relative catchability of demersal species was higher in the otter trawls (BSOT, SMOT) while relative catchability of pelagic species was higher in the midwater trawls (FMWT, BSMT). Our results demonstrate that catchability is a source of bias among monitoring efforts within the San Francisco Estuary, and assuming equal catchability among surveys, species, and size classes could result in significant bias when describing spatio-temporal patterns in catch if ignored.

Relative Bias in Catch Among Long-Term Fish Monitoring Surveys Within the San Francisco Estuary

Fish monitoring gears rarely capture all available fish, an inherent bias in monitoring programs referred to as catchability. Catchability is a source of bias that can be affected by numerous aspects of gear deployment (e.g., deployment speed, mesh size, and avoidance behavior). Thus, care must be taken when multiple surveys—especially those using different sampling methods—are combined to answer spatio-temporal questions about population and community dynamics. We assessed relative catchability differences among four long-term fish monitoring surveys from the San Francisco Estuary: the Bay Study Otter Trawl (BSOT), the Bay Study Midwater Trawl (BSMT), the Fall Midwater Trawl (FMWT), and the Suisun Marsh Otter Trawl (SMOT). We used generalized additive models with a spatio-temporal smoother and survey as a fixed effect to predict gear-specific estimates of catch for 45 different fish species within large and small size classes. We used estimates of the fixed effect coefficients for each survey (e.g., BSOT) relative to the reference gear (FMWT) to develop relative measures of catchability among taxa, surveys, and fish-size classes, termed the catch-ratio. We found higher relative catchability of 27%, 22%, and 57% of fish species in large size classes from the FMWT than in the BSMT, BSOT, or SMOT, respectively. In the small size class, relative catchability was higher in the FMWT than the BSMT, BSOT, or SMOT for 50%, 18%, and 25% of fish species, respectively. As expected, relative catchability of demersal species was higher in the otter trawls (BSOT, SMOT) while relative catchability of pelagic species was higher in the midwater trawls (FMWT, BSMT). Our results demonstrate that catchability is a source of bias among monitoring efforts within the San Francisco Estuary, and assuming equal catchability among surveys, species, and size classes could result in significant bias when describing spatio-temporal patterns in catch if ignored.

Fatty acid profile of pebbly fish, Alestes baremoze (Joannis, 1835) from Lake Albert, Uganda: Implications for its feed requirements

The objective of this study was to establish the fatty acid profile of Alestes baremoze, with a view of establishing its dietary fatty acid requirements. Fish samples from Lake Albert were categorized into four classes according to fork lengths (1–10 cm, 11–20 cm, 21–30 cm, and 31–40 cm), with each class comprising of six fish. In addition, eggs were collected from six sexually mature females. A total of 35 fatty acids were identified and categorized into saturated fatty acids (SFAs), monounsaturated acids (MUFAs), and polyunsaturated fatty acids (PUFAs). SFAs accounted for 5.07% to 37.05%, MUFAs and PUFAs constituted 20.65% to 53.78%, and 10.34% to 66.10% respectively, of total fatty acids in all studied fish size classes. The results from this study indicated that fatty acid composition in A. baremoze varied significantly with size classes. The findings may provide guidance on the fatty acid inclusions for diets formulated for this fish under culture conditions.

On Baltic herring morphometry and its impact on the backscattering properties.

Previous studies, dedicated to backscattering properties of Baltic herring, have shown the different target strength (TS – which is a measure of fish capacity to scatter sound) values, for the same species in different regions and seasons. The intraspecies differentiation in fish physiology and morphology as well as fish swimbladder morphometry between herring aggregations, occupying various parts of the Baltic Sea, has been supposed as one of the reasons for the variability.The paper addresses analysis of herring swimbladder morphometry and its impact on TS of individuals from ICES subdivision 26, one of the areas where Poland is responsible for herring biomass estimation. The collection of the X-rays images for 74 herring individuals, sampled in this subdivision, was created. The two-dimensional digitized dorsal images of herring swimbladder and body, as well as the angles between the swimbladder and the body longitudinal axis, were used to compute the target strength. The differentiation of herring morphometry within particular fish size classes was analysed and its consequences for the averaged target strength within the class was discussed. The difference from the previous numerical studies, in which the simplified herring morphometry was used, was also demonstrated. The computational results were considered in regard to the available in situ measured data on Baltic herring TS. The study of the Baltic herring target strength is important for increasing accuracy of acoustic biomass estimation of this ecologically and economically important species.

Does the size structure of the littoral community reflect water level fluctuations in shallow waterbodies?

The littoral zone of shallow water bodies (SWB) is highly susceptible to water level fluctuations (WLF) caused by ongoing climate-related hydrologic regime changes. The present study assessed the macrozoobenthos structure in the littoral of three temperate SWB after pronounced WLF and accompanying reduction of macrophyte coverage caused by excessive precipitation. The three SWB differed in environmental conditions – S1 (transparent lake covered with submerged macrophytes dominated by Ceratophyllum demersum); S2 (turbid lake without macrophyte coverage) represented the two interconnected backwater basins of the Sutla River watershed; and SK (Škrčev kut oxbow; highly turbid lake sparsely covered by floating-leaved Nuphar lutea) located in the Krapina River watershed (Croatia). With the aim to disentangle the littoral food web structure, and interactions among environmental conditions as well as structural and functional traits of the littoral community within the three SWB, the macrozoobenthos functional traits, trophic guilds and body size were correlated with the littoral environmental conditions, and with the traits of the potential macrozoobenthos prey (zooplankton) and predators (fish). Our results suggest that the littoral macrozoobenthos assemblage responded to the water level increase mainly by the decline of macroinvertebrate diversity and abundance. Due to loss of habitat heterogeneity, in general, larger-sized macroinvertebrates dominated the littoral zone of turbid SWB, particularly with high WLF, while smaller-sized detritivores and grazers prevailed in the littoral zone of the transparent SWB covered by submerged macrophytes. The correlations between different macrozoobenthos, zooplankton and fish size classes indicated that the larger-sized predatory macroinvertebrates prey on smaller-sized zooplankters and avoid predation of mid-sized fish. On the other hand, the abundance of smaller-sized macroinvertebrate detritivores and grazers, which were significantly correlated with concentrations of suspended detritus and algae, prevailed in the SWB covered by submerged macrophytes. Within the macrophyte-covered littoral habitats, macroinvertebrates coexisted with small-sized fish and zooplankters as well as with large-sized pelagic zooplankters, likely seeking shelter from fish. We assume that the increased abundance of larger-sized specimens affected macroinvertebrates and fish within the littoral community upon water level increase. Such a pattern could be recognized as an indicative trait in the evaluation of ecosystem functioning. Furthermore, we conclude that the structural and functional traits of the SWBs’ littoral communities could help us predict the ecological consequences of the climate-induced WLF.

Spatial and Size Variation in Dietary Niche of a Non-native Freshwater Fish

Invasive fishes continue to adversely impact the structure and function of aquatic ecosystems globally. The effects of introduced populations may, however, differ according to key characteristics such as size, abundance, invaded habitat type, and community composition. Here, we conduct diet analyses to describe the feeding characteristics of the nonnative North American Pumpkinseed, Lepomis gibbosus, across multiple habitat types (three lentic and three lotic systems) and fish size classes. Pumpkinseeds exhibited a broad diet, inclusive of numerous threatened species groups (e.g., amphibians) and commonly included dipterans and detritus overall. Observed diets were more diverse in ponds compared to stream habitats, as well as for larger individuals, with individuals in streams tending to consume terrestrial insects in higher numbers. Our results show that the impact of Lepomis gibbosus differs not only according to size and ontogeny, but also depending on the habitat type, probably due to different prey availabilities and biotic interactions. This has implications for ecological impacts of this invasive species in lentic and lotic systems, with a generalist diet potentially facilitating impacts on a broad range of prey taxa, with concomitant adverse competitive effects on native predator species.

Isotopic niche plasticity in a marine top predator as indicator of a large marine ecosystem food web status

As marine ecosystems are harvested or modified by anthropogenic or natural factors, there is an increasing demand for indicators of trophic web health or status. The Magellanic Penguin (Spheniscus magellanicus) is a widely distributed species that forages in the Patagonian Shelf. During breeding, this species is a central-place forager that feeds mainly on schooling fish, with Argentine anchovy (Engraulis anchoita) being the dominant prey in the north and Fuegian sprat (Sprattus fuegensis) in the south of the Argentine Patagonian distribution (40–55°S). Like most forage fish, both prey species display large natural interannual recruitment fluctuations. We used stable isotope analysis of adult Magellanic penguin blood obtained at twelve colonies along its Patagonian latitudinal range to assess changes in isotopic niche and in trophic level as a response to interannual changes in abundance and spatial segregation of forage fish size classes, respectively. Magellanic penguins showed large isotopic niche fluctuations among breeding seasons, explained by the contribution of forage fish in their diet. Furthermore, the size of the isotopic niche negatively correlated with forage fish biomass estimated from acoustic surveys and with their contribution in penguin diet. We defined an isotopic niche size threshold that indicates low abundance of forage fish in nearby feeding grounds. In addition, the trophic level of Magellanic penguins increased with latitude, which corresponds to the size-distribution of both main forage fish species, showing that penguins from different colonies target different size classes of their main prey. We present here a simple and easy to implement indicator to monitor the status of the base of the food web in one of the most productive marine areas in the world, which constitutes the feeding ground of a diverse group of high trophic level predators and sustains large-scale fisheries.

Systematic variation in food web body-size structure linked to external subsidies.

The relationship between body mass (M) and size class abundance (N) depicts patterns of community structure and energy flow through food webs. While the general assumption is that M and N scale linearly (on log-log axes), nonlinearity is regularly observed in natural systems, and is theorized to be driven by nonlinear scaling of trophic level (TL) with M resulting in the rapid transfer of energy to consumers in certain size classes. We tested this hypothesis with data from 31 stream food webs. We predicted that allochthonous subsidies higher in the web results in nonlinear M-TL relationships and systematic abundance peaks in macroinvertebrate and fish size classes (latter containing salmonids), that exploit terrestrial plant material and terrestrial invertebrates, respectively. Indeed, both M-N and M-TL significantly deviated from linear relationships and the observed curvature in M-TL scaling was inversely related to that observed in M-N relationships. Systemic peaks in M-N, and troughs in M-TL occurred in size classes dominated by generalist invertebrates, and brown trout. Our study reveals how allochthonous resources entering high in the web systematically shape community size structure and demonstrates the relevance of a generalized metabolic scaling model for understanding patterns of energy transfer in energetically 'open' food webs.