Size Groups Of Fish Research Articles

Influence of the host sex, size, and season on Ergasilus lizae infestation of Thicklip Grey Mullet (Chelon labrosus, L., 1758) in Beymelek Lagoon Lake (Antalya, Türkiye)

The aim of the study was investigation of the changes in infestation levels of Ergasilus lizae on economically important fish species, thicklip grey mullet (Chelon labrossus) from Beymelek Lagoon Lake located on the western Mediterranean coast (Antalya, Türkiye). In this context, the infestation levels of E. lizae with respect to fish sexes, fish sizes and season were evaluated statistically. The research was conducted seasonally between May 2008 to April 2009, and the gills which belong to 103 fish samples were examined. The overall infection prevalence and mean intensity values were 60.2% and 15.95, respectively. The prevalence and mean intensity of E. lizae for thicklip grey mullet male and sexually unidentified fish samples were higher than that for females. Prevalence and mean intensity were determined the highest in size class I with 69.6% and 26.3, and almost the same values in size groups II and III. E. lizae on host fish were observed in every season. The highest prevalence and mean intensity of E. lizae was recorded in spring with 100%, 24.88. The lowest prevalence of E. lizae was recorded in summer at 12% and the lowest mean intensity of E. lizae was in the summer and the winter with 9, 8.67 respectively. The infestation level of E. lizae was statistically significant with host sex and season, but there was no effect on the fish size groups.

Culture suitability of stinging catfish Heteropneustes fossilis in homestead tank: Selection of suitable stocking size

The present experiment was conducted for a period of 150 days to assess the effects of different stocking size on growth and production of stinging catfish (Heteropneustes fossilis) in three homestead cemented tanks (12×10×4 ft). Three different size groups of fish viz., 3.79±0.11, 3.09±0.13 and 2.53±0.18 cm was stocked at treatment T1, T2 and T3, respectively at a stocking density of 5000 individuals/tank each with three replications. Fish were feed twice daily with floating feed containing 35-40% protein at the rate of 15-10% for 1st 60 days, 8-6% for 2nd 60 days and 5-2.50% for rest of the culture period. The water quality parameters were within the suitable ranges for the fish culture. Mean weight gain (g) of stinging catfish was 49.03 ± 1.04, 36.72 ± 1.59 and 28.09 ± 0.41g, specific growth rate was 1.76 ± 0.02, 1.70 ± 0.04 and 1.66 ± 0.05 %/day in T1, T2 and T3, respectively. Food conversion ratio was 3.45 ± 0.82, 3.31 ± 0.10 and 3.30 ± 0.06 and survival rate were 90.67 ± 1.51, 88.20 ± 2.62 and 87.56 ± 1.26% in T1, T2 and T3, respectively. Higher stocking size also resulted in a significantly higher economic output in the form of benefit cost ratio (BCR) at T1 (2.13 ± 0.05) and the lowest at T3 (1.21 ± 0.03). The findings of the present study revealed that the highest weight gain and BCR was found in T1 which dictates that larger stocking size has a significant impact on better production.

Life‐history traits of a tropical bagrid catfish, Mystus mysticetus Roberts, 1992, caught from the Mekong Delta, Vietnam

AbstractPopulation's biological parameters, including length at first capture, mortalities, exploitation rates, growth coefficient, longevity, and recruitment times, are essential in assessing fishing status, but there is no data on Mystus mysticetus. Therefore, the study was conducted to provide these parameters to assess the fishing status of this species at Cai Rang, Can Tho (CRCT) and Long Phu, Soc Trang (LPST). A collection of 741 individual fish was used for analysis and showed that most fish size groups ranged from 9.0 cm to 12.0 cm, and the asymptotic length was 16.8 cm for both CRCT and LPST populations. The fish population von Bertalanffy curve was Lt = 16.80(1 − e−0.51(t + 0.38)) at CRCT and Lt = 16.80(1 − e−0.48(t + 0.40)) at LPST. The fish growth coefficient at CRCT (2.16) was higher than at LPST (2.13), whereas the reverse case was true for longevity ranging from 5.88 years (at CRCT) to 6.25 years (at LPST). At CRCT, fishing mortality, natural mortality, total mortality, and exploitation rate were 0.69/year, 1.40/year, 2.09/year, and 0.33, respectively; at LPST, these values were 0.75/year, 1.33/year, 2.08/year, and 0.36, respectively. Although the population parameter of this fish species exhibited a spatial variation, both CRCT and LPST fish resources have not been subjected to overexploit because E (0.33 at CRCT and 0.36 at LPST) is lower than E0.1 (0.707 at CRCT and 0.616 at LPST).

Сезонная динамика размерно-возрастной структуры бурого морского петушка Alectrias alectrolophus (Stichaeidae) в приливно-отливной зоне Авачинской губы (Юго-Восточная Камчатка)

Basing on materials collected in April-September 2014-2022 in the intertidal zone of the northeastern part of Avacha Bay, the seasonal dynamics of the size-age structure of stone cockscomb Alectrias alectrolophus living here was analyzed. It has been established that in April through late June this species is represented in the littoral by individuals in the second year of life (1+) (body length 35-67 mm, body weight 0.19-1.37 g) as well as by individuals aged 2+ to 7 years (64-143 mm, 1.09-15.9 g, respectively), which form two rather well-separated size groups of fish. In August, as the size of individuals in the second year of life (1+) increases, these groups merge, forming a single bimodal curve of size composition. In the second half of June, underyearlings of the stone cockscomb, 16-20 mm long with a body weight of 20-30 mg, begin to appear in the intertidal zone, forming the third size group from 20 to 35 mm with a body weight of 40-230 mg in July. Therefore, starting from July, in the intertidal zone of Avacha Bay, the stone cockscomb of all age groups, from underyearlings to individuals 7+ years old, lives. Data on seasonal changes in the ratio of juveniles and adult fish in the intertidal zone are presented.

Food Preference of Bullet Tuna (<i>Auxis rochei</i> Risso, 1810) in Prigi Coast of Trenggalek Regency, East Java

As a commercial fish, bullet tuna is constantly caught in purse seine fisheries to provide economic benefits for coastal communities. Biological information such as food preference has to be known due to their sustainability in the future. This research aims to figure out the food composition and preference of bullet tuna (Auxis rochei Risso, 1810) in Prigi Coast, Trenggalek Regency East Java. A total of 294 fish landed by purse seine fishermen have been collected from March up to May 2018. Each individual was measured in its total length and weight, then was dissected for sex determination, measured the length of intestine, and analyse the stomach content. The data analysis encompasses frequency distribution of total length, relative gut length, frequency of occurrence, index of preponderance, trophic level, niche breadth, and food overlapping. The research result indicates that the main foods of Auxis rochei are fish and crustacean, while the complementary and additional foods were copepod, mollusc, annelid, and debris. Bullet tuna was a carnivorous fish with the trophic level of 3.7 and shows the existence of competition for food resources. Overlapping of feeding occurred in the 19-20 cm long group against the 23-24 cm long group in male fish and the 19-20 cm size group against the 21-22 cm length group in female fish. Bullet tuna use the same feed resources among the size groups of fish, where females use feed over a wider area than males.

Imaging scale surface topography of an endemic cyprinid fish, Garra sharq from the Arabian Peninsula: An integrated optical light and scanning electron microscopy approach

AbstractThe optical light microscopy and scanning electron microscopy techniques have proven to play a key and noteworthy role in the advancement of morphological studies in general, and in investigating fish scale morphology in particular. These techniques have illustrated several hidden architectural structures in scales that contribute effectively to fish identification and classification. The scale morphological and topological characters such as type, size, shape, lateral surface, focus position, circuli appearance, radii type, lepidonts, and posterior and anterior margin shapes were obtained using macro‐ and microscopic analysis in six body regions for three size classes of Garra sharq, a cyprinid endemic fish of the Arabian Peninsula. The general scale type in the studied G. sharq species was a basal elasmoid cycloid and a sectioned type. As a protective structure, the scales display several specific characteristics including firm attachment to the fish body, overlapping, and thin structure with a high surface area and high strength. These characteristics improve scale resistance to penetration, increase protection against mechanical injury and microbial infection, enhance scale flexibility, reduce fish weight (reduce friction drag), and increase scale transparency. The scales demonstrate plasticity in focus shape, size, and position in the six fish body parts and fish size groups. The examined scales displayed narrow or wide grooves (radii) in three types including primary, secondary, and tertiary present in all four scale fields (anterior, posterior, and laterals), thus a tetra‐sectioned type that is almost specific to the genus Garra. This characteristic also increases scale flexibility. The rostral margin of scales was characterized by the presence of waved and striate types. The lepidont shape and size varied being blunt, flat, pointed, tiny, sharp, short, and long. Some of these scale characters and their morphologies could be used as an alternative tool for identification, classification, and phylogenetic interpretation among the different freshwater fish species and genera.

FEEDING HABITS OF SOLDIER CROAKER Dendrophysa russelii (Cuvier, 1829) DISTRIBUTED IN COASTAL AREAS OF THE MEKONG DELTA, VIETNAM

This study researched the feeding habits of soldier croaker Dendrophysa russelii (Cuvier,1829) distributed in coastal areas of the Mekong Delta from May to December, 2021. Fish samples were randomly collected in different sizes by trawl-net. Fish stomachs were fixed in a 4% formalin solution to prevent contents in the stomach from being digested. The results showed that soldier croaker had a small mouth, the teeth on the jaw were short and pointed with no canine tooth, the gill rakers were sparse, the stomach was pouch-shaped, the caeca have 4-8 tubes, and the intestine was short. Relative between gut length and body length (RLG) < 1 indicated that soldier croaker is a carnivorous fish. The food spectrum of immature fish was narrower thanthat of mature fish. However, the feed ingredient was shrimp which always accounts for the highestpercentage in the two fish size groups, followed by fish and other foods that accounted for a low proportion.

Factors influencing food composition, feeding habits and intensity of Glossogobius giuris caught from the vietnamese mekong delta

ObjectiveKnowledge of diet composition and feeding habits are essential to our understanding of fish ecological adaptation and aquaculture studies. This study aims to gain knowledge on diet composition, feeding intensity and habits for Glossogobius giuris – a commercial goby residing in brackish to freshwater regions of the Vietnamese Mekong Delta. MethodsA collection of 1,291 samples (632 males and 659 females) were caught monthly from January 2020 to December 2020 at four sites using trawl nets. A combined analysis of prey occurrence and weight was used to calculate the diet composition of this fish. ResultsThis fish displayed high feeding intensity, and its diet composition was seen to be comprised of small fish, Acetes spp., Uca spp., molluscs, and others (e.g., detritus and fish scales). Although males and females of two fish size groups, two seasons and at the four sites displayed the same feeding trends as Costello graphical analysis showed, the diet composition was seen to vary with season and site. It suggested that the difference in salinity between seasons and the four sites regulated food composition within this fish. ConclusionThese findings advance the understanding of fish adaptation capacities and food flexibility.

Ligula Intestinalis Infection in a Native Leuciscid Hybrid (Alburnus Derjugini x Squalius Orientalis) in The Kürtün Dam Lake, Northeast Anatolia.

SummaryTaxonomic evaluations are needed to accurately determine the host selection of fish parasites. The present study is a multidisciplinary research in the field of basic and fish diseases sciences. The description of the hybrid species of Squalius orientalis and Alburnus derjugini and infection of Ligula intestinalis in these hybrid fish were reported for the first time from the Kürtün Dam Lake in northeast Turkey. A total of 450 fish were sampled in March, August, and October in 2020 using gillnets. Detailed morphological characteristics (n = 24) were compared to determine the difference among ancestors and hybrid species. The prevalence of L. intestinalis between the sampling periods and the size groups of fish (0 – 10, 11 – 15, and ≥16 cm in length) were examined. Moreover, the highest prevalence of the parasite was observed in October (78.94 %), with a size range of 0 – 10 cm in length (77.8 %). In addition, the total prevalence of the parasite was 48.44 %. The results revealed that most of the diagnostic metric and meristic features of hybrid fish were ranging between the data of S. orientalis and A. derjugini. According to previous reports, when hybrid individuals were compared with their ancestors in terms of prevalence, hybrid individuals were more susceptible to L. intestinalis infections. This study was unique as it provided the first record of L. intestinalis in a hybrid fish population.

Seasonal analysis of food items and feeding habits of endangered riverine catfish Rita rita (Hamilton, 1822).

This investigation presents the food and feeding activity of and endangered riverine catfish Rita rita, during February 2017-January 2018. A total of 225 fish individuals was analyzed for stomach contents by characterizing the dominant food items and morphometric features. The results divulged ten major food items consumed, preferably fish scales and eggs, teleost fishes, copepods, cladocerans, rotifers, and mollusks. Total length and body weight of fish varied between 9-34 cm (20.53 ± 6.90 cm) and 10-400 g (9125.94 ± 102.07 g), respectively. The index of relative importance (IRI%) showed the importance of rotifers over the other food items. Morisita's index of diet overlap indicated seasonal variations in catfish diets with summer and monsoon displaying the least overlap, while maximum overlap during monsoon and winter seasons. The non-metric multidimensional scaling (nMDS) indicated the close association between the food items available during summer and winter seasons with a significant difference among the seasons (ANOSIM, R = 0.638, P = 0.013). Levin's niche breadth index arranged in the order of 0.88>0.81>0.78>0.63>0.43 for the size classes of V, IV, III, II and I, respectively. The PCA explained 95.39% of the total variance among the food items and fish size groups. Small-sized fish individuals displayed a greater correlation with food items suitable for their mouth size. In conclusion, the variety and frequency of food items recorded indicated considerable feeding plasticity and opportunistic feeding behavior with a shift from carnivorous to omnivorous feeding nature. This study could render useful information on the food and feeding habits of R. rita and provide background for preparing its diet for future aquaculture practices.

Развитие осевой локомоторной мускулатуры у половозрелого окуня-клювача Sebastes mentella (Sebastidae)

The results of the study of the histological structure of the locomotor axial (skeletal) muscle tissue of the beaked redfish Sebastes mentella are presented and its ontogenetic changes are considered. Its skeletal muscles compose of glycolytic (white) and oxidative (red) fibers. Data show the quantitative distribution of these fibers along the body of sexually mature fish in the cranio-caudal direction, their ratio in the trunk and tail parts. The diameter of these two types of fibers reaches significant sizes, as in a number of deep-sea slow-growing species (> 300 μm - white fibers, > 150 μm - red fibers). The density of glycolytic fibers is higher than that of red ones (80,7±2,0 versus 54,7±1,5 %), which is due to the different content of adipose and connective tissue (endomysium). The variability of white fibers in most fish size groups is significantly lower than that of red ones. A feature that is not noted in other deep-sea fish species with a low growth rate is the relatively frequent occurrence of red fibers with stratification of sarcoplasm into two zones (layers) - external and internal (double structures), the nature of which is not yet clear.

The Digestive Tract Morphology and Clark index of Mud Sleeper Butis koilomatodon Living in some Coastal and Estuarine areas belonging to Tra Vinh, Soc Trang, Bac Lieu and Ca Mau

This study provides new data on the characteristics of the gastrointestinal morphology and the variation of Clark index according to sexes, fish size groups, seasons and sampling sites of mud sleeper Butis koilomatodon, one of the commercially valuable gobiid species in the Mekong Delta. Analytical results of 1,227 fish samples collected monthly from April 2019 to March 2020 in Duyen Hai (Tra Vinh), Cu Lao Dung (Soc Trang), Tran De (Soc Trang), Hoa Binh (Bac Lieu), Dong Hai (Bac Lieu) and Dam Doi (Ca Mau) showed that this species had a slightly sloping mouth, the length between two jaws was relatively equal, teeth were small and grew in long lines on both jaws with the outer row having larger teeth. The length of the gut was shorter than the total length of the fish and so this species belonged to predator group. The Clark index depended on length of fish, sampling time and site but excluding season and gender. It was also effected by interactions of fish length x season; fish length x site and season x site. Conversly, the interactions of gender x season and gender x site did not impact on the Clark index. The outcomes of research will provide useful data in artificial aquaculture Butis koilomatodon.

Measuring the long-term success of small-scale marine protected areas in a Philippine reef fishery

Tropical coral reefs are subject to multiple pressures from both natural and anthropogenic sources. These pressures have caused widespread declines in reef health, resulting in the increased use of spatial management tools such as marine protected areas (MPAs). MPAs have proven generally effective if well designed and enforced, but there are limited long-term studies investigating how the presence of small-scale MPAs affects fish populations and reef communities. Using a 12-year time series, we found that small-scale (10–50 ha) community-managed MPAs along the Danajon Bank of the Philippines preserved average fish biomass within their boundaries over time relative to surrounding fished reefs. Unprotected areas are, however, showing significant long-term biomass decline. MPAs were also found to preserve more key trophic groups and larger-bodied commercially targeted reef fish families. Fish biomass of piscivore, scavenger and invertivore trophic groups inside individual MPAs is, however, still declining at a similar rate as outside. Surprisingly, long-term benthic cover and growth form composition were not significantly affected overall by MPA presence, despite the sporadic use of highly destructive dynamite fishing in this region. Coral cover has remained historically low (21–28%) throughout the study, following widespread bleaching mortality. While management tempered overall abundance declines, we found that irrespective of MPA presence, there was a generalised decline of both large- and small-bodied fish size groups across the study region, most steeply within the 20–30 cm length fish, and a shift towards proportionally higher abundances of small (5–10 cm) fish. This indicates a combination of over-exploitation, inadequate MPA size and coverage for larger fish, and the lingering effects of the 1998 bleaching event. Generalised shifts in body size and trophic structure reported here could lead to future reductions in fishery productivity and stability and will be further exacerbated unless broader fishery regulations and enforcement is instated.

Optimal dietary protein concentrations for largemouth bass (Micropterus salmoides) of different sizes (10–500 g)

Three feeding trials were conducted to determine the optimal dietary protein levels for largemouth bass (Micropterus salmoides) of different sizes. Six isolipidic (12%) diets with different protein levels (46%, 48%, 50%, 52%, 54% and 56%) were tested to feed three size groups of fish for 56 days (Trial 1 and Trial 2) or 84 days (Trial 3). The initial body weights were approximately 10 g in Trial 1, 100 g in Trial 2, and 200 g in Trial 3, respectively. The fish in each size class were randomly distributed into 18 cages (1 m × 1 m × 1 m) in six groups (three replicates) and fed by hand to apparent satiation two times per day. At the end of the feeding trials, the fish grew to an average size of 26–36 g, 276–320 g, and 434–526 g, respectively. The weight gain (WG) showed an increasing trend with increasing dietary protein level up to 52%, 50%, and 48%, respectively, and then plateaued in all the three trials, which indicated that the minimum dietary protein requirements for largemouth bass decrease with increasing fish size. The feed efficiency (FE) in the three trials showed a similar trend to growth performance. Protein efficiency ratio (PER) tended to decline when dietary protein levels exceeded 48%, 50%, and 48% in the three trails, respectively. Broken-line regression analysis showed that the optimal dietary protein levels based on SGR for largemouth bass of different sizes (initial size 10, 100, and 200 g) were 51.6%, 50.5%, and 47.8%, respectively.

The Relative Gut Length and Gastro-somaticindexes of the Mudskipper Periophthalmodon septemradiatus (Hamilton, 1822) from the HauRiver

This study provided an understanding of feeding habit and intensity of the mudskipper Periophthalmodon septemradiatus, which was a potential aquarium pet, by analyzing the relative gut length (RGL) andgastro-somatic (GaSI) indexes. Fish specimens were caught by fishing rods from the estuary in Soc Trang province to the upstream in An Giang province of Hau River during a period of one year from August 2017 to July 2018. Data analysis of a collection of 1,504 fishes showed that RGL did not change with fish size, resulting in the feeding habit of P. septemradiatus did not change with fish size. By contrast, the feeding habit of this mudskipper varied with place, month and season as the RGL significantly different between place, month and season, but both males and females fall into carnivorous fish as RGL was <1. Similarly, the feeding intensity of this specice did not change with fish size, as the GaSI was not significantly different among four fish size groups. Meanwhile, the mudskipper displayed spatial, temporal and seasonal variations in feeding intensity since GaSI significantly changed with place, month and season. The changes of feeding habit and intensity of P. Septemradiatus were not regulated by the interaction of fish size and place, fish size and season, and place and season. These results provided new knowledge on feeding habit and intensity of this fish specice, being used for the understanding of fish adaption and conservation in the study region.
 Keywords
 Gastro-somatic index, mudskipper, Periophthalmodon septemradiatus, relative gut length
 References
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Human exposure to trace elements via farmed and cage aggregated wild Axillary seabream (Pagellus acarne) in a copper alloy cage site in the Northern Aegean Sea

Axillary seabream (Pagellus acarne) farmed in a copper alloy mesh pen and wild individuals of P. acarne aggregated near the copper-alloy cages presented higher concentrations of trace metals in the liver, skin and gills than in fish muscle tissues in two batches of small and large fish sizes. Elevated mean levels of metals (mg kg−1) in muscle tissues in both small and large fish size groups were observed in the rank order of Zn(3.43) > Fe(3.01) > Cu(0.59) > Mn(0.13) and Fe(3.82) > Zn(3.32) > Cu(0.62) > Mn(0.17) for copper cage-farmed fish, relative to ranked mean levels for Zn(2.64) > Fe(1.95) > Cu(0.25) > Mn(0.09) and Fe(5.79) > Zn(3.58) > Cu(0.58) > Mn(0.28) for the copper cage-aggregated wild fish. Nevertheless, trace metal concentrations in fish harvested from the copper cage or those of the cage-aggregated wild individuals in both size groups were far below maximum levels of seafood safety recommended by USEPA and FAO/WHO. Target hazard quotients, calculated to estimate the non-carcinogenic health risks of metals by consuming these fish, were below “1″ (THQ < 1), indicating that there were no potential health risks for humans when consuming copper-caged fish or wild-caught individuals aggregated around the copper mesh pen, with respect to the limits suggested by US Food and Drug Administration and EU Regulations for Seafood Consumption.

Supplying rapeseed meal to the diets with or without potassium iodide for yellow catfish (Tachysurus fulvidraco)

The aims of the study were (1) to determine the effect of rapeseed meal on growth, body composition, thyroid hormones, and expressions of three genes involved in thyroid function and (2) to determine if potassium iodide in the diet counteracts the adverse effect caused by rapeseed meal on growth. One fish meal-based diet was serviced as the control. The other six diets were designed on the basis of 3 × 2 factorial design. The rapeseed meal inclusion (10, 20, and 30%) and potassium iodide inclusion (0 and 72 mg (kg)−1) were set to be two factors. The fish experiment was designed according to a randomized block model with three size groups of fish (27.7, 19.9, and 8.1 g). The feeding period lasted for 71 days. The results showed that final weight, weight gain, specific growth rate (SGR), and feed conversion ratio (FCR) of fish fed with 10% rapeseed meal-based diets were significantly better than those fed with 20 and 30% rapeseed meal. The highest nitrogen retention and protein efficiency ratio (PER) were in the 10% rapeseed group. Inclusion of 30% rapeseed meal in the diets significantly reduced whole-fish dry matter, Ile, and Phe contents. The gene expressions of the thyrotropin receptor (TSHR), sodium/iodide symporter (NIS), and thyroid peroxidase (TPO), as well as the thyroid hormone (T3 and T4) levels in the plasma, were not affected by the different diets. However, TSHR and TPO gene expressions negatively correlated with T4 and lipid retention. NIS gene expression positively correlated with cumulative feed intake, final weight, weight gain, SGR, nitrogen retention, and PER. It also negatively correlated with FCR. In conclusion, the rapeseed meal inclusion level in the diet was suggested to be 10%. Potassium iodide in the diet (72 mg (kg)−1) did not counteract the adverse effects caused by rapeseed meal on fish growth. Correlations provided evidence to support the link between NIS gene and fish growth.

Trophic behaviour of juvenile reef fishes inhabiting interlinked mangrove-seagrass habitats in offshore mangrove islets.

Stable isotope (δ(13)C and δ(15)N) and gut content analyses were used to investigate size-related feeding habits of four reef fishes (the beaugregory Stegastes leucostictus, the french grunt Haemulon flavolineatum, the schoolmaster snapper Lutjanus apodus and the yellowtail snapper Ocyurus chrysurus) inhabiting an offshore (non-estuarine) mangrove islet off Belize, Central America. Comparisons of isotopic niche space and Schoener diet similarity index suggested a low to moderate degree of niche overlap between fish size groups. The δ(13)C gradient between mangrove and seagrass prey as well as results of Bayesian mixing models revealed that sampled fishes relied mostly on seagrass prey items. Only small and large juveniles of the carnivorous species L. apodus derived a part of their diet from mangroves by targeting mangrove-associated Grapsidae crabs and fish prey, respectively. Isotopic niche shifts were particularly obvious for carnivorous fishes that ingested larger prey items (Xanthidae crabs and fishes) during their ontogeny. The utilization of mangrove food resources is less than expected and depends on the ecology and life history of the fish species considered. This research highlights that mangrove-derived carbon contributed relatively little to the diets of four fish taxa from an offshore mangrove islet.

Longer is not always better: The influence of beach seine net haul distance on fish catchability

The aim of this study was to compare the influence of different haul distances of a codend beach seine on the catchability of fish in a surf zone. Two different surf zone sites (A and B) at the Cassino Beach (Rio Grande do Sul, Brazil) were sampled at three different distances, parallel to the beach (30, 60, and 90 m). Starting 40 m from the beach line, diagonal distances of approximately 50, 70, and 100 m were swept. The total CPUE and CPUA haul distances are compatible with a declining trend in catch rates with increased haul distance at both sites. However, statistically significant differences were observed only for the short distance CPUA (50 m) in relation to the other haul distances at one of the sites sampled. Two fish size groups were observed (TL 40 mm), but only small individuals (< 40 mm) captured in the shorter haul distance at site B showed significant differences in CPUA. This result indicates that size structure for hauls at different distances was equal and that smaller individuals determined the pattern of fish abundance. The net performance indicates that a short haul (< 50 m) is the best strategy to reduce net avoidance and fish escape when using this type of sampling gear.

Особливості плодючості бичка кругляка (Neogobius melanostomus) за різних екологічних умов

Наводиться порівняльний аналіз абсолютної та відносної плодючості бичка кругляка (Neogobius melanostomus (Pallas, 1814)) з Каховського водосховища та Азовського моря. Абсолютна плодючість у морі склала 3 395, у водосховищі – 2 053 ооцити. Різниця за стадіями зрілості статевих продуктів між рибами з досліджуваних водойм – від 200 до 1 000 шт. Визначено залежність плодючості бичка кругляка від маси тіла, довжини та віку самиць. Кореляційний аналіз залежності плодючості від довжини особин у Каховському водосховищі склав 0,81, а в Азовському морі – 0,62. Такий розподіл відмічений залежно від маси риб: для Азовського моря – 0,63, для Каховського водосховища – 0,74. Наведений порівняльний аналіз показників плодючості в історичному розрізі показав відмінності між нашими та 40-річним даними: як для Азовського моря (в усі періоди), так і для Каховського водосховища. Різниця складає від 800 до 1 000 ооцитів у всіх розмірно-масових групах. Зменшення кількості ооцитів відмічене у риб із Кахов­ського водосховища як за показниками абсолютної та відносної плодючості, так і за віковими групами.