Weaning of alligator gar (Atractosteus spatula) larvae to artificial diets

Growth performance and survival of alligator gar (Atractosteus spatula) larvae fed Artemia nauplii, two artificial diets (with different protein content and buoyancy) and a control under starvation at first feeding [5 days after hatching (5 DAH)] were studied. All larvae under starvation (C) died at 10 DAH, while survival was near 60% for the rest of the treatments at the end of the experimental period. By the end of the experimental period morphological variables (total length, snout length, wet weight and dry weight) were better in larvae fed the artificial diets compared to live food. These results were confirmed by means of nucleic acid indexes and digestive enzymatic activity. The importance of the relationship between diet size and snout gape was evidenced from these results. Differences between artificial diets were attributed to different digestibility values. Alligator gar larvae are able to grow and survive satisfactorily when fed artificial diets from the start of exogenous feeding, provided that these have an adequate size, buoyancy and quality.     

Stimulatory effect of thyroid hormones improves larval development and reproductive performance in alligator gar (Atractosteus spatula) and spotted gar (Lepisosteus oculatus)

Development of alligator gar (Atractosteus spatula) and spotted gar (Lepisosteus oculatus) larvae was evaluated after exposure of embryos to thyroid hormones (TH) by two different methods of administration. For the first method, alligator gar embryos were placed in a water bath with triiodothyronine (T₃; 1 ppm for 2 h), and control treatment embryos were placed in a water bath without T₃. For the second method, spotted gar adult males and females were injected with different TH during induced spawning: a group was injected with T₃ [20 mg kg^?1 body weight (BW)], a second group with thyroxine (T₄; 20 mg kg^?1 BW), a third group with thyroid‐stimulating hormone (TSH; 4 IU kg^?1BW) and a control group with dimethyl sulfoxide. Both methods resulted in increases in the concentrations of T₃ and T₄ in embryos of both species. An increase in the alkaline enzymatic activity of TH‐treated larvae was observed as well as an increase in the RNA:DNA, RNA:Dry weight and DNA:Dry weight ratios at hatching. Some positive effects of TH application were: a significant increase in the hatching rate of spotted gar larvae from TH‐injected parents and a higher percentage of successful spawns. Evenness of larval sizes and a higher survival rate were observed in alligator gar larvae. Snout development was accelerated by TH treatment in both species.     

Alligator gar (Atractosteus spatula,Lacépède 1803) vitellogenin: purification,characterization and establishment of an enzyme‐linked immunosorbent assay

Alligator gar (Atractosteus spatula) is a non‐teleost bony fish distributed in North America. Gar populations have drastically declined as a consequence of habitat deterioration and the lack of regulation for their capture. Control of reproduction is critical for recovering their natural populations. The impossibility to distinguish genders and the determination of sexual maturity have hindered their successful reproduction. This research was aimed at developing an enzyme‐linked immunosorbent assay (ELISA) for the quantitative estimation of vitellogenin (VTG), a female‐specific protein. Plasmatic VTG from 17β‐estradiol (E2)‐induced juveniles and ovary vitellin from adult females were purified and characterized. Polyclonal antibodies against both proteins were produced to develop an ELISA. The immunoassay was validated by quality tests such as sensitivity, parallelism, recovery, reproducibility and specificity. Vitellogenin was determined in different tissues (plasma, mucus, liver and gills) of alligator gar. Vitellogenin and E2 concentrations in female breeders were found to be higher in November, before the spring spawning season. This approach represents a quick, reliable and non‐invasive practical alternative to distinguish genders and evaluate gonad maturation.     

The influence of ontogeny and prey abundance on feeding ecology of age-0 Lake Whitefish (Coregonus clupeaformis) in southeastern Lake Michigan

A shift towards oligotrophic conditions in Lake Michigan has led to concern that altered trophic pathways are leading to lower early life survival and recruitment for Lake Whitefish (Coregonus clupeaformis). This study evaluated ontogenetic shifts in age-0 Lake Whitefish diets and evaluated how feeding ecology and the amount of food eaten varied with prey abundance and composition at a site in southeastern Lake Michigan during 2014–2017. Although prey densities varied among years, cyclopoid copepods were overall the most abundant prey available. In turn, cyclopoids were the predominant prey item in diets each year, particularly for the smallest larval Lake Whitefish. However, there was a tendency for the importance of cyclopoids to decline somewhat in each diet index as fish grew and other prey such as calanoid copepods, Bosminidae, Daphniidae and/or chironomids increased in importance. High zooplankton abundance, especially high cyclopoid abundance, available to the small size groups of Lake Whitefish (<21 mm) in 2014 was associated with high food mass/fish, high number of zooplankton eaten/fish, and low incidence of empty stomachs compared with 2015–2017. As fish grew, the impact of food abundance on prey consumption diminished somewhat, indicating that the relationship between fish feeding ecology and the prey environment can change quickly with fish size during the early life period.     

Effect of light intensity,prey density,and ontogeny on foraging success and prey selection of larval yellow perch (Perca flavescens)

Light intensity has been shown to influence the foraging success of larval fish. However, the effect of light intensity on larval foraging is likely variable and influenced by both the density and characteristics of planktonic prey. In this study we examined the influence of light intensity of 0.1, 2.0, and 60 μmol·s^?1·m^?2 Photosynthetically Active Radiation (PAR) on foraging of yellow perch (Perca flavescens) larvae at two prey densities. We fed them with a mixture of zooplankton taxa common to lakes inhabited by yellow perch. In addition to light intensity and prey density, the effect of larval yellow perch size was examined by using fish ranging from 9 to 15 mm. The results of our study indicated that yellow perch larvae are well adapted to feed at a wide range of light intensities, as there was no difference in foraging success at investigated light intensities. Increasing prey density from 25 to 150 (zooplankton·l^?1) significantly improved the foraging success of larval yellow perch. However, the influence of prey density on foraging success was dependent on fish length. Improved foraging success at increased prey densities occurred only for individuals with a total length >10 mm. Overall, prey selection by fish larvae was influenced by light intensity, prey density, and fish length. However, the factors that influenced selection for specific prey types differed. Our study, combined with evidence from other field and laboratory work, highlight the need for a better understanding of the influence of prey density on foraging throughout ontogeny.     

胭脂鱼早期发育过程中集群行为的形成

为了探讨胭脂鱼个体发育过程中集群行为的发生机理,在20℃水温下,在胭脂鱼孵化后第5天开始至第39天,记录体长,采用视频分析的方法连续观察其游泳行为,计算胭脂鱼的游泳速度(V),相对全长最近邻距离(DNNL),分离游泳指数(ISS),根据胭脂鱼的游泳速度计算基于全长雷诺系数(RL).结果显示,随着日龄的增加,胭脂鱼仔鱼全长呈y=1.26033-0.015 58x+0.003 15x2-(4.849 78E-5)x3增加,游泳速度先增加后降低并趋于稳定,在19日龄后相对全长游泳速度稳定于(2.45 +0.15) TL/s.胭脂鱼仔鱼ISS随着时间显著降低,至第19天时显著低于随机分布预期值,至32天时稳定于最低值;DNNL的变化趋势与ISS相符;表明胭脂鱼仔鱼集群行为于19日龄(1.77 cm全长)开始,至32日龄(2.40 cm全长)时形成紧凑的集群行为.RL随日龄的增加呈y=-607.891 61+156.809 12x-4.212 9x2 +0.037 9x3方程增加,在仔鱼开口期(5-6日龄)即大于200,在19日龄时值为1 111.结果表明,仅从RL的角度不能解释胭脂鱼集群行为的发生,胭脂鱼的集群行为可能更多的与生物学因素如游泳行为有关,其游泳模式随着集群行为的发生由间歇高速游泳向持续巡游游泳转变.     

Maximum handling size,prey size and type selection by snakehead (Channa argus) feeding on juvenile Chinese mitten crab (Eriocheir sinensis)

Laboratory predation trials were conducted to investigate maximum handling size, prey size and type selection by small (35–37 cm in total length, L_T), medium (43–46 cm L_T) and larger (58–60 cm L_T) snakehead (Channa argus) when feeding on a wide size (9–34 mm in carapace width, C_W) range of juvenile Chinese mitten crab (Eriocheir sinensis). The maximum handling size of predator feeding on crabs monotonically increased with predator L_T and mouth gape width, G_W. Snakehead with at least 16.0 cm L_T or 27.7 mm G_W would be capability to consume the smallest size group of crabs, whereas the predator with 72.6 cm L_T or 63.4 mm G_W would be capability to consume all size groups of crabs in these trails. Prey‐size selection trials showed that snakehead has a high preference to the small‐sized crabs, and lower preference to the medium or large size crabs. The preference index was significantly affected by prey size and prey size × predator size interaction, however, was not affected by predator size. In prey type experiments, snakehead consumed lower proportions of juvenile crabs when fed on the crab and crucian carp than when fed on only the crab, which suggests alternative fish prey may reduce predation risk of the crab by snakehead in nature. These results could be useful for improving the fishery management and release strategies for the crab.     

The role of temperature in the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta)

Abstract – Cold water temperatures are widely supposed to reduce the food intake of stream salmonids. Although cold temperatures have been documented to reduce swimming ability, digestion and gastric evacuation rates, little is known about how temperature influences the ability of fish to capture prey. We examined the effects of water temperature on the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta) in a laboratory stream. Temperatures ranged between 5.7 °C and 14 °C. We found significant effects of water temperature on prey capture probability and capture manoeuvre time. The mean capture probability dropped from 96% at 14 °C to 53% at 5.7 °C. At 8 °C and higher temperatures, foraging performances did not differ much among treatments. We suggest that reduced swimming ability could be one of the most important mechanisms for the observed pattern of reduced prey capture probability at cold water temperatures, but prey detection limitations and predator avoidance may play a role. Our results will be of use for bioenergetics‐based drift‐foraging models, which to date have not incorporated a temperature‐dependent prey capture function.     

Diel distribution,behaviour and consumption of juvenile Chinook salmon (Oncorhynchus tshawytscha) in a Wilderness stream

Abstract – Understanding population regulation in juvenile salmonids requires distinguishing the effects of intrinsic (size, behaviour) and extrinsic (food, competition) factors. To examine the relative influence of these variables on juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Salmon River drainage (ID, USA), we examined diel differences in foraging microhabitats, behaviour and consumption in two areas with consistent differences in parr‐to‐smolt survival. In lower Big Creek (LBC, high‐survival area) and upper Big Creek (UBC, low‐survival area), we observed fish by snorkelling, recording length, behaviour (foraging rate and aggression) and physical (depth, velocity, cover, temperature) and biotic (density, size and species of neighbouring fish) microhabitat features. Stomach contents were extracted to estimate consumption. Depth and temperature were greater in LBC, where Chinook salmon were significantly larger and present at lower densities. Fish in LBC exhibited higher foraging activity during the day than night, but there were no size differences between day and night foragers. In UBC, a higher density area, foraging behaviour did not change between day and night, although the smallest size classes did not forage nocturnally. Regression models that integrated physical and biotic variables suggested that physical factors influenced foraging in both areas, but competition also affected foraging in UBC. Our results demonstrate that fish from low‐ and high‐survival populations in Big Creek are exposed to different physical and biological influences during their first growth season, which are reflected in different diel foraging behaviours.     

Evaluation of carbohydrate/lipid ratios on growth and metabolic response in tropical gar (Atractosteus tropicus) juvenile

Five experimental diets with different carbohydrates/lipid ratio (CHO:L, 0.75, 1.28, 2.10, 2.52, 4.63) were formulated. Fish were randomly assigned by triplicate (10 fish per tank, 0.50 ± 0.01 g). Growth was registered every 15 days until end of the experiment (45 days). Samples were taken for analysis of chemical carcass composition, blood chemistry, glycogen and lipid liver content, digestive and metabolic enzyme activities. Results showed that survival, growth performance parameters and plasma glucose were not affected by treatments (p > 0.05). Lipids of carcass and liver, as well as triglycerides and plasma cholesterol increase significantly as CHO:L ratio decreased. While an inversely proportional tendency was observed for carcass protein and liver glycogen (p < 0.05). Digestive enzymes did not show significant differences among treatments (p > 0.05). Finally, Hexokinase (HK), glucokinase (GK), phosphoenol pyruvate carboxykinase (PEPCK) and fructose‐1,6‐biphosphase (FBPase) showed high regulation by carbohydrates up to the CHO:L ratio of 2.10 (p < 0.05), while pyruvate kinase (PK) activity was not significantly affected by the CHO:L ratio. By the other side, glucose‐6‐phosphate dehydrogenase (G6PD) tends to significantly increase as the CHO:L ratio increases. We conclude that A. tropicus fry have a high capacity to utilize carbohydrates substituting lipids as energy source in balanced diets.     

Foraging behaviour of juvenile pink salmon (Oncorhynchus gorbuscha) and size‐dependent predation risk

Two hypotheses related to effects of juvenile pink salmon (Oncorhynchus gorbuscha) foraging behaviour and size on their predation risk were evaluated using field data collected in Prince William Sound, Alaska 1 995–97. My results supported the hypothesis that low macrozooplankton density leads to dispersion of juvenile salmon from shallow nearshore habitats and greater predation risk, but zooplankton type was an important factor. When the biomass of large copepods (primarily Neocalanus spp.) declined, salmon dispersed from shallow nearshore habitats, and mean daily individual predator consumption of salmon increased by a factor of 5. A concomitant five‐fold increase in the probability of occurrence of salmon in predator stomachs supported the notion that increased predation on salmon was caused by a greater overlap between predator and prey when salmon dispersed offshore, not an increase in the number of salmon consumed per feeding bout. The results also generally supported the hypothesis that the timing of predation events modifies the nature of size‐dependent predation losses of salmon to different predator groups (small and large planktivores and piscivores). Size‐dependent vulnerabilities of salmon to predators were a function of both predator and prey sizes. When simulated predation was shifted from May to June, the vulnerability of salmon became more dependent on their growth than initial size. But, the size‐ and growth‐dependent vulnerabilities of salmon differed more among predator groups than between May and June, suggesting that changes in the composition of predator fields could more strongly affect the nature of size‐dependent predation than changes in the timing of predation losses.     

Variation in prey selection and foraging success associated with early‐life ontogeny and habitat use of American paddlefish (Polyodon spathula)

Many fishes are planktivorous during early life and switch to piscivory or consume larger food items as ontogeny progresses. In contrast, paddlefish start as particulate feeders and later become filter feeders. Few studies have identified food items essential for paddlefish growth, survival and recruitment surrounding this ontogenetic diet shift. The objectives of this study were to investigate (i) prey types consumed by paddlefish, (ii) variability in prey selection surrounding an ontogenetic diet shift and (iii) whether habitat affected paddlefish prey selection or foraging success. We analysed gut contents of 189 wild age‐0 paddlefish from the middle Mississippi River (MMR) and also conducted a laboratory experiment to address these objectives. We found that paddlefish primarily foraged on benthic macroinvertebrates in the MMR, which differed from previous studies in lentic systems, suggesting young paddlefish prey selection may be labile depending on habitat (i.e., lotic versus lentic). Dominant prey of wild‐caught and experimental age‐0 paddlefish were caddisfly larvae (Trichoptera), followed by hemipterans and amphipods. We found little evidence that habitat attributes affected foraging success, but the most common prey items consumed were associated with wing dike habitat and the upstream and downstream tips of alluvial islands. Our experimental study revealed that if provided a mixture of organisms, age‐0 paddlefish will primarily consume macroinvertebrates while age‐1 paddlefish will mainly filter zooplankton. Overall results suggest young paddlefish prey selection can be highly variable, but also heavily reliant on a narrow group of prey resources.     

Ecology of larval blue sucker (Cycleptus elongatus) in the Mississippi River

Abstract –  Ecology of larval blue sucker, Cycleptus elongatus , a North American catostomid that has declined throughout its range, is poorly known because larvae have rarely been sampled. A total of 316 young blue suckers (16.0–39.0 mm total length) was captured over 3 years at 14 off-channel sites in Pool 25, Mississippi River. Blue suckers demonstrated distinct temporal and spatial abundance patterns. Blue suckers were only captured in late May/early June, and were more abundant during a year of little flooding. Abundance was correlated with the distance a site was from the main channel, being highest in island borders and island sloughs in proximity to the channel. Fish guts contained a relatively high biomass of chironomids and zooplankton, suggesting islands were providing suitable feeding opportunities. Because of their proximity to flows, slack waters provided by islands were accessible to blue sucker larvae dispersing from channel spawning areas and facilitated their development into rheophilic juveniles.     

Habitat use and foraging success of 0+ pike (Esox lucius L.) in experimental ponds related to prey fish, water transparency and light intensity

Abstract  – This study investigated the habitat use of 0+ pike (9–17 cm) in relation to two different water transparency regimes (clear water/chlorophyll water), two different light regimes (day/night) and the presence/absence of prey using 16 m² experimental ponds. Pike could freely choose between two structured habitats (a simple structured and a complex structured), an interface habitat (between the structured habitats and open water) and an open water habitat. Foraging success of the pike in relation to water transparency was investigated by comparing mean condition (Fultons K ) of the pike as well as the number of surviving prey fish. Habitat use was influenced by the presence/absence of prey and varied between waters with different transparency. The presence of prey intensified the use of structural habitats of 0+ pike in both clear and chlorophyll waters. A preference for complex habitats was found in clear water and was presumably related to foraging. The pike in chlorophyll water, in contrast, appeared more evenly distributed among all habitats, as illustrated by a more intensive use of open water in chlorophyll water compared to the clear water. No detectable impact of water transparency on the foraging success of 0+ pike was found.     

Ontogenetic development of digestive enzymes in larval and juvenile crimson snapper Lutjanus erythopterus (Bloch 1790)

Ontogenetic development of digestive system in crimson snapper (Lutjanus erythopterus Bloch 1790) larvae was histologically and enzymatically (alkaline phosphatase, amylase, lipase, pepsin, trypsin) examined from hatching to 36 days post hatching (DPH). The ontogenetic development of crimson snapper larval fish ontogeny was divided into three distinct phases: phase I starting from hatch to the onset of exogenous feeding, phase II starting from first feeding (2–3 DPH) until the formation of gastric glands (13–14 DPH) and phase III beginning from the appearance of gastric glands and continuing onwards. The specific activities of amylase, lipase, trypsin showed sharp increase and reached to the maximum from hatch to 4 DPH, 10 DPH, 20 DPH, respectively, followed by a declining trend with irregular fluctuation. In contrast to other enzymes, the specific activities of alkaline phosphatase showed a gradual increase from hatch to 29 DPH, followed by a sharp increase towards 36 DPH. The specific activity of pepsin was firstly detected on 17 DPH and gradually increased towards the end of this study. The total activities of these five enzymes showed a gradual increase till 29 DPH, followed by a sharp increase towards 36 DPH except for amylase and lipase reaching maximum at 32 DPH. The present study provides better understanding of the digestive ontogeny of crimson snapper during the larval stage and a guide to feeding and weaning of this economically important fish in hatcheries.     

Seasonal spawning and wind‐regulated retention‐dispersal of early life stage Atlantic cod (Gadus morhua) in a Newfoundland fjord

Sequential ichthyoplankton surveys were used to determine the spatial and temporal distribution of eggs and larvae over coastal spawning grounds of Atlantic cod (Gadus morhua) in Smith Sound, Trinity Bay, Newfoundland, during the spring and summer of 2006 and 2007. Egg densities showed similar patterns for both years with two peaks in abundance in spring (March–April) and late summer (late July). A clear progression of development stages (1–4) was observed in spring and summer in 2006 and summer in 2007, suggesting retention of eggs within the Sound during these periods. Modelled predictions of vertical egg distributions indicated eggs were broadly distributed near the surface during spring (March–April), but were concentrated below the pycnocline (>10 m) within the inner portions of the Sound during the summer months (July–August). Back‐calculated peaks in spawning based on water temperatures were estimated at 11 and 4 April for 2006 and 2007, respectfully, with late season peaks centred on 21–24 July for both years. Environmental data indicated cooler water temperatures and periods of high wind stress in spring, and warmer, calmer periods late summer, consistent with higher retention and faster development times on the spawning grounds later in the season. We conclude that spring and summer spawning events result in different distributions of early life stages and may lead to different distributions of juvenile and adult fish.     

A synthesis of large-scale patterns in the planktonic prey of larval and juvenile cod (Gadus morhua)

Data from 40 published studies of the diet composition of larval and juvenile cod (Gadus morhua) from around the northern North Atlantic were summarized to assess generic patterns in ontogenetic and regional variability in the key prey. The results showed that larvae at the northern edge of the latitudinal range of cod depend primarily on development stages of the copepod Calanus finmarchicus, whilst those at the southern edge depend on Para‐ and Pseudocalanus species. Juvenile cod preyed on a wider range of taxa than larvae, but euphausiids were the main target prey. Analysis of regional variations in the relative abundances of C. finmarchicus and Para/Pseudocalanus spp. in the plankton, as estimated by the continuous plankton recorder (CPR) surveys, showed a similar geographical pattern to the larval cod stomach contents. Comparison of CPR data from the 1960s and 70s with data from the 1990s showed that the boundary between C. finmarchicus and Para/Pseudocalanus spp. dominance has shifted northwards on both sides of the Atlantic, whilst the abundance of euphausiids in the southern cod stock regions has declined. The results are discussed in relation to regional differences in the response of cod stocks to climate variability.     

Growth potential and habitat requirements of endangered age‐0 pallid sturgeon (Scaphirhynchus albus) in the Missouri River,USA, determined using a individual‐based model framework

An individual‐based model framework was used to evaluate growth potential of the federally endangered pallid sturgeon (Scaphirhynchus albus) in the Missouri River. The model, developed for age‐0 sturgeon, combines information on functional feeding response, bioenergetics and swimming ability to regulate consumption and growth within a virtual foraging arena. Empirical data on water temperature, water velocity and prey density were obtained from three sites in the Missouri River and used as inputs in the model to evaluate hypotheses concerning factors affecting pallid sturgeon growth. The model was also used to evaluate the impacts of environmental heterogeneity and water velocity on individual growth variability, foraging success and dispersal ability. Growth was simulated for a period of 100 days using 100 individuals (first feeding; 19 mm and 0.035 g) per scenario. Higher growth was shown to occur at sites where high densities of Ephemeroptera and Chironomidae larvae occurred throughout the growing season. Highly heterogeneous habitats (i.e., wide range of environmental conditions) and moderate water velocities (0.3 m/s) were also found to positively affect growth rates. The model developed here provides an important management and conservation tool for evaluating growth hypotheses and(or) identifying habitats in the Missouri River that are favourable to age‐0 pallid sturgeon growth.     

Effects of live prey availability on growth and survival in the early stages of cuttlefish Sepia officinalis (Linnaeus, 1758) life cycle

This investigation examined the effects of live prey availability on growth and survival of Sepia officinalis. Two independent experiments, comprising two feed rations each, were performed, using adequate prey size. In the first experiment, cuttlefish hatchlings were fed live mysids, Paramysis nouvelli [(feed ratio I (fr I)], at 15% body weight per day (bw day^?1) (fr I₁₅) and 30% bw day^?1 (fr I₃₀). In the second experiment, juvenile cuttlefish were fed live Atlantic ditch shrimp, Paleomonetes varians (fr II), under the same experimental design. In both experiments, the final mean weight, feeding rate and instantaneous growth rate were higher when animals were fed feed ratio fr II₁₅ and fr II₃₀ (30% bw day^?1). The results indicate that prey availability influenced weight gain, irrespective of the prey used, during the first 2 months of cuttlefish life cycle. This effect seems to be more noticeable when a certain limit of prey is achieved. For cuttlefish fed fr II, the optimal prey density is thought to be under 2.5 g prey L^?1 (i.e. 14 shrimp L^?1). Results indicate that cuttlefish can withstand prey densities up to 120 mysids L^?1 for cuttlefish up to 3 weeks old and 19 shrimps L^?1 for cuttlefish up to 6 weeks old.     

Occurrence and distribution of larval and juvenile Japanese flounder Paralichthys olivaceus at sandy beaches in eastern Hiuchi-Nada, central Seto Inland Sea, Japan

ABSTRACT:   The occurrence and distribution of larval and juvenile Japanese flounder Paralichthys olivaceus and major demersal fish from May to September were examined at seven sandy beaches at the central Seto Inland Sea. The flounder appeared from late May to August and were mainly collected at a depth of 2–5 m. Settlement of larval flounder was seen from late May to late June. A total of 6412 individuals of 17 species representing 12 families were collected in the study area. The dominant fish species were Favonigobius gymnauchen (56.0%), Tarphops oligolepis (8.1%), Rudarius ercodes (7.8%), P. olivaceus (7.3%), Repomucenus spp. (7.0%) and Heteromycteris japonica (3.3%). The catches of flounder differed among beaches and months. The number of flounder in June at Ohama Beach, where the most flounder were collected, was 22.6 individuals per haul (400 m²). The density of the flounder correlated negatively to that of F. gymnauchen .