Evaluating the potential effectiveness of harvest restrictions on riverine sunfish populations in Georgia, USA

Abstract  The effects of minimum length limits (MLLs) on bluegill, Lepomis macrochirus Rafinesque, redbreast sunfish, Lepomis auritus (Linnaeus), and redear sunfish, L. microlophus (Günther), fisheries in 13 river sections located across Georgia were evaluated. A Beverton–Holt equilibrium yield model was used to predict and compare the response of these fisheries to three MLL scenarios: 100 (i.e. no size limit), 125 and 150 mm. Model results indicated that natural mortality rates of all sunfish species examined in this study were low enough to allow harvest restrictions to be effective if growth was fast. If sunfish reached 203 mm in <4.0 years, then MLLs were generally effective in increasing size structure without decreasing yield or causing unacceptable declines in the number of fish available for anglers to harvest. Harvest restrictions resulted in minimal increases in size structure, declines in yield and a large decrease in the number of fish harvested by anglers if time to reach 203 mm was ≥ 8.0 years. Response to MLLs was more variable when fish grew to 203 mm in 4.0–6.5 years. Examination of mortality caps largely supported the results from the model, but there was indication that empirical rates of total annual mortality may have been biased high in some instances.     

Prey selection and diets of bluegill Lepomis macrochirus with differing population characteristics in two Nebraska natural lakes

Abstract  Environmental prey samples and stomach contents of bluegill Lepomis macrochirus (Rafinesque) were collected in spring and summer 2000 from two Nebraska Sandhill lakes. Watts Lake contained a low-density bluegill population, whereas Cozad Lake contained a high-density bluegill population. Bluegill diets from both lakes were compared to determine if bluegill prey preference differed between the two populations. The highest median per cent (by calories) of zooplankton in the diet was 1.3%; the remainder was macroinvertebrates. Watts Lake bluegills preferred (based on Manly's alpha) amphipods in spring and chironomids in summer. Cozad Lake bluegills did not show a strong preference (compared with Watts Lake) for any macroinvertebrates, but still utilized amphipods and chironomids during both seasons. Larger bluegills in Watts Lake preferred chironomids in summer, but Cozad Lake bluegills did not exhibit this relationship. The higher density Cozad Lake bluegill population appeared to be more opportunistic than the lower density Watts Lake population, but both preferred macroinvertebrates.     

Effects of littoral habitat complexity and sunfish composition on fish production

Carey MP, Maloney KO, Chipps SR, Wahl DH. Effects of littoral habitat complexity and sunfish composition on fish production. Ecology of Freshwater Fish 2010: 19: 466–476. © 2010 John Wiley & Sons A/S Abstract – Habitat complexity is a key driver of food web dynamics because physical structure dictates resource availability to a community. Changes in fish diversity can also alter trophic interactions and energy pathways in food webs. Few studies have examined the direct, indirect, and interactive effects of biodiversity and habitat complexity on fish production. We explored the effects of habitat complexity (simulated vegetation), sunfish diversity (intra‐ vs. inter‐specific sunfish), and their interaction using a mesocosm experiment. Total fish production was examined across two levels of habitat complexity (low: 161 strands m^?2 and high: 714 strands m^?2) and two sunfish diversity treatments: bluegill only (Lepomis macrochirus) and bluegill, redear sunfish (Lepomis microlophus), and green sunfish (Lepomis cyanellus) combination. We also measured changes in total phosphorus, phytoplankton, periphyton, and invertebrates to explain patterns in fish production. Bluegill and total fish production were unaffected by the sunfish treatments. Habitat complexity had a large influence on food web structure by shifting primary productivity from pelagic to a more littoral pathway in the high habitat treatments. Periphyton was higher with dense vegetation, leading to reductions in total phosphorus, phytoplankton, cladoceran abundance and fish biomass. In tanks with low vegetation, bluegill exhibited increased growth. Habitat complexity can alter energy flow through food webs ultimately influencing higher trophic levels. The lack of an effect of sunfish diversity on fish production does not imply that conserving biodiversity is unimportant; rather, we suggest that understanding the context in which biodiversity is important to food web dynamics is critical to conservation planning.     

Habitat characteristics at bluegill spawning colonies in a South Dakota glacial lake

Abstract –  Bluegill ( Lepomis macrochirus ) primarily reproduce in spawning colonies. We assessed habitat characteristics at 15 bluegill spawning colonies in a South Dakota glacial lake. Nesting sites were visually identified and angling was used to verify the species of nesting fish. Habitat characteristics were measured at each nesting site and compared with those measured at 75 randomly selected sites. In Lake Cochrane, mean water depth of spawning colonies was 1.0 m. Of the 13 habitat characteristics measured, four (substrate type, substrate firmness, vegetation density and dissolved oxygen levels) were significantly different ( P  ≤ 0.05) between nesting and random sites. Every bluegill nest site contained gravel substrate, despite the availability of muck, sand and rock. Substrate firmness was indexed at 0-cm penetration and vegetation density was low at all nesting sites. Additionally, bluegills selected nesting locations with relatively moderate dissolved oxygen levels. Lake Cochrane bluegill nest sites consisted of shallow, gravel areas with short, low-density, live submergent Chara vegetation.     

Bioenergetic relations in submerged aquatic vegetation: an experimental test of prey use by juvenile bluegills

Abstract— We experimentally tested the hypotheses that bluegills in vegetated habitats grow more rapidly than in nonvegetated habitats because (1) vegetated habitats contain a greater caloric density and (2) are less susceptible to energetic depletion. The 10-week experiment was conducted in enclosures containing factorial combinations of the presence or absence of Vallisneria americana and juvenile bluegills Lepomis macrochirus . After 6 weeks, Vallisneria -only treatments contained a mean of 1048 cal/m² in the benthos, whereas treatments with both Vallisneria and bluegills contained 610 cal/m². Hyalella azteca , a preferred prey of bluegill, were nearly depleted in nonvegetated enclosures, whereas Hyalella densities in enclosures with Vallisneria were much less effected by fish. Bluegill growth was significantly greater with Vallisneria than without but declining water temperatures after week 6 resulted in slower growth despite abundant prey. Ultimately, growth of bluegill resulted from an interaction between availability and ingestion of prey, and water temperature.     

Patterns of movement of centrarchids in two warmwater streams in eastern Tennessee

We studied the movements of redbreast sunfish (Lepomis auritus), bluegill (Lepomis macrochirus), rock bass (Ambloplites rupestris), largemouth brass (Micropterus salmoides), and warmouth (Lepomis gulosus) by tagging fishes with individually numbered tags. We sampled quarterly over a 3-year period (1985–1988) at six 800- to 2300-m-long sites in 2 streams near Oak Ridge, Tennessee. Overall, distances between successive captures were < 100 m for approximately two-thirds of all fishes. Only rarely did we document movements over long distances; distances of 17.0-17.6 km between successive captures were obtained for 5 fishes (1 redbreast sunfish, 1 largemouth bass and 3 bluegill), and only one other fish moved > 10 km. In general, all species were highly sedentary in both streams, with rock bass and redbreast sunfish being the most sedentary and bluegill and largemouth bass being the least. In most instances, redbreast sunfish showed the same distribution of distances between captures regardless of the interval between captures (1 week, 3 months, 6 months or more). This species also tended to be more mobile in the spring and less mobile in the winter, with large fish exibiting the greatest distances between captures. Some redbreast sunfish showed a very restricted home range, being captured 3 or more times over ≥ 6 months in the same 50-m section of stream. A few individuals moved 4-9 km only to return to their original location, but most fish exhibited behaviors intermediate between these extremes. For all species, upstream and downstream movements were equally common, although movements in one direction predominated at some sites for limited periods of time. Knowledge of movement patterns and differences in behavior among species is important not only in understanding the basic ecology of the species but also in designing, conducting and interpreting environmental monitoring studies.     

Prey fish selection by Far Eastern catfish <Emphasis Type="Italic">Silurus asotus</Emphasis> and largemouth bass <Emphasis Type="Italic">Micropterus salmoides</Emphasis>

ABSTRACT:   Prey fish selection by Far Eastern catfish and largemouth bass were examined using bluegill, Japanese dace and crucian carp as food fish. In both aquaria (1.2 m × 0.45 m) and ponds (2.8 m × 1.2 m), bluegill was not preyed on by catfish and bass more than dace and crucian carp. In aquaria, there was no significant difference in the consumption of dace and crucian carp between catfish and bass, but in ponds, catfish preyed on dace and crucian carp more and less than bass, respectively. In the case that only bluegill and catfish were introduced in ponds, catfish consumed 4–15 g of bluegill per day. The introduction of catfish into ponds and lakes for the purpose of eradicating bluegill is considered appropriate for areas with few native fish species.     

Growth and mortality of juvenile sunfishes (Lepomis sp.) under heavy predation

The relationship among growth, energy storage and mortality of juvenile bluegills (Lepomis macrochirus, Rafinesque) experiencing heavy predation was experimentally investigated in a large reservoir where piscivorous largemouth bass (Micropterus salmoides, Lacépède) were abundant. I conducted experiments evaluating interspecific competition, density-dependent growth and lipid content and habitat-specific growth and mortality rates of juvenile bluegills in this reservoir. Enclosure experiments showed that the growth rates of bluegills were unaffected by presence of other Lepomis species but decreased with increasing bluegill density. However, at densities corresponding to those found in the reservoir, the growth rates of bluegills were high, and competition appeared to be relatively unimportant. The percentage lipid content of bluegills was unaffected by the presence of other species, density of bluegills or habitat. The growth rates of bluegills in vegetated refuge areas were significantly higher and mortality rates were significantly lower compared with open water habitats. The low densities and high growth rates of juvenile bluegills in refuge environments suggests that there is a strong lethal effect of predators on this population of bluegills.     

Pressure Induced Triploidy in Hybrid Lepomis

Worldwide expansion of aquaculture will require identification of species more adapted to localized conditions and less likely to affect genetic diversity of natural populations in the event of escape. Hybrids of Lepomis sunfish have the potential as an alternative for aquaculture in regions of North America where the growing season is unsuitable for production of traditional coldwater and warm-water species. Triploidy was induced in hybrids of green sunfish Lepomis cyanellus males and bluegill L. macrochirus females using hydrostatic pressure shocks. A total of 27 combinations of pressure (41,369, 48,264, and 55,158 kPa), duration (2, 3, 4 min), and post-fertilization time of shock initiation (2, 3, 4 min) were tested to identify those which were most efficient for inducing triploidy. Several of the shock regimes produced 100% triploid hybrid sunfish with at least 90% survival relative to unshocked controls. The two shock treatments deemed best overall were: 1) 48,264 kPa for 4 min begun 2 min after fertilization; and 2) 41,369 kPa for 2 min begun 3 min after fertilization.     

Patterns of foraging and distribution of bluegill sunfish in a Mississippi River backwater: influence of macrophytes and predation

Abstract— We studied the trophic interactions and spatial distributions of bluegills Lepomis macrochirus and largemouth bass Micropterus salmoides in a macrophyte bed in Lake Onalaska, a backwater lake in the upper Mississippi River. The diets of adult and age-0 bluegills were similar and changed seasonally probably in response to changes in life stages of macroinvertebrates (i. e. emergence of winged adults). Diets and diel patterns of abundance of bluegill suggest that age-O and adults were feeding in the vegetated, littoral zone. Predation by age-O largemouth bass appears to influence use of vegetated habitat by age-0 bluegills. In summer, when most age-O bluegills were vulnerable to predation by age-O largemouth bass, bluegill abundance was strongly correlated with vegetation biomass. In October and November, piscivory by age-O largemouth bass was limited by gape. Consequently, the relationship between the abundance of age-O bluegills and vegetation biomass was weakened because predation risk by age-O largemouth bass was reduced.     

Effects of a nonsteroidal aromatase inhibitor on gonadal differentiation of bluegill sunfish Lepomis macrochirus

In the present study, the efficacy of Letrozole, a potent nonsteroidal aromatase inhibitor (AI), on gonadal sex differentiation and sex reversal was examined in bluegill sunfish (Lepomis macrochirus). In Experiment 1, using AI diet treatments (50, 150, 250 and 500 mg kg⁻¹) from 30 to 90 days posthatch (dph), AI interrupted ovarian cavity formation at a dose of 500 mg kg¹ diet and one intersex fish was identified in this group. The proportions of males in all the treated groups were significantly higher than those in the control group. In Experiment 2, using AI immersion treatments (250, 500 and 1000 μg L⁻¹) during 30–50 dph, the treated groups of 500 and 1000 μg L⁻¹ produced significantly more males than the control and 250 μg L⁻¹ groups. Histological examination revealed no differences in ovary or testis tissue between control and AI‐treated fish. There were no significant differences detected in body weight and length among the AI treated and control groups (P>0.05) for both experiments. The results from these two experiments suggest that inhibition of aromatase activity by AI could influence sex differentiation in bluegill sunfish.     

Comparison of dietary essential amino acid requirements determined from group‐housed versus individually‐housed juvenile bluegill,Lepomis macrochirus

Two 60‐day experiments were conducted sequentially to determine (i) lysine requirement of juvenile bluegill, Lepomis macrochirus based on the dose–response method, (ii) requirements for other essential amino acids (EAAs) using whole‐body amino acid profile and (iii) whether differences in growth rates of group‐housed versus individually‐housed bluegills lead to different lysine requirement levels because of the presence and absence, respectively, of social hierarchies. Seven, semi‐purified, experimental diets (isonitrogenous, isocaloric) were prepared to contain graded levels of digestible lysine (10–31 g kg⁻¹). Experiment‐1 involved group‐housed bluegills (approximately 27 g, n = 10 fish/chamber, 4 chambers/diet) whereas experiment‐2 involved individually‐housed bluegills (approximately 30 g, n = 1 fish/chamber, 14 chambers/diet). Fish were fed twice daily to apparent satiation. Bluegill growth responses in both experiments generally improved (P < 0.05, anova ) with increasing dietary lysine levels from 10 to 16 g kg⁻¹, and then levelled off with further increase in lysine level (P > 0.05). Optimal dietary lysine level (digestible basis) was estimated to be 15 g kg⁻¹ based on broken‐line regression analyses of relative growth rate and feed conversion ratio with no differences being observed between the two rearing methods. Determined dietary requirement levels for other EAAs ranged from 2.4 g kg⁻¹ (tryptophan) to 15.3 g kg⁻¹ (leucine).     

Replacing fish meal with increasing levels of meat and bone meal,soybean meal and corn gluten meal,in diets of juvenile bluegill,Lepomis macrochirus

A 60‐day study was conducted to determine the response of juvenile bluegill Lepomis macrochirus to seven experimental diets, formulated using a blend of alternative protein sources as a replacement for fish meal. Adequate levels (digestible basis) of energy, protein and amino acids were maintained in diets 1–6, whereas slightly lower protein and energy levels were provided in diet 7. Feed cost per tonne ranged from $ 798.9 (diet 1, 550 g Kg^?1 fish meal) to $ 515.8 (diet 6, 0 g kg^?1 fish meal), or to $ 507.2 (diet 7, 0 g Kg^?1 fish meal). Three commercial diets were included in the study as reference diets: a high‐energy and a low‐energy trout diet, as well as a catfish diet. Quintuplicate bluegill groups (~22 g, n = 10 fish group^?1) were fed the experimental diets twice daily to apparent satiation. No major differences in feed consumption, feed efficiency and growth rates were detected among the bluegill groups fed the experimental diets. Trout diets generally produced higher fish fat deposition, whereas the catfish diet produced a poorer fish growth rate relative to the experimental diets. Under the reported conditions, results indicate diet 6, comprising predominantly soybean meal and porcine meat and bone meal, to be the most economical diet for juvenile bluegill.     

Seasonal intestinal coccidiosis in wild bluegill Lepomis macrochirus is associated with a spring bacterial epizootic

Wild bluegill, Lepomis macrochirus Rafinesque, succumb to seasonal mortality in the early spring during cool water temperatures, shown previously to be related to bacteraemia caused by a psychrotrophic bacterium, Pseudomonas mandelii. In the study herein, intestinal coccidiosis in wild bluegill had seasonal prevalence causing heavy intestinal infections and sloughing of intestinal epithelium occurring in late winter/early spring. Infections were predominantly related to two different species, Goussia washuti n. sp., an epicellular coccidium, and a coccidium closely resembling Goussia desseri Molnár 1996, previously only described in percid fish in Europe. In 2019, co‐infections of bacteraemia and intestinal coccidiosis occurred in bluegills. Evaluating coccidium infection intensity by fresh parasite examination and histology, an association was observed in which fish with moderate‐to‐heavy intestinal coccidiosis were 8–12 times more likely to have bacteraemia compared to fish with no or light coccidiosis. The association of these co‐infections suggests that intestinal coccidiosis could contribute to seasonal bacterial epizootics of wild bluegill.     

Growth and Body Composition of Juvenile Hybrid Bluegill Lepomis cyanellus × L. macrochirus Fed Practical Diets Containing Various Percentages of Protein

Growth, survival, and body composition were evaluated in two feeding trials using juvenile hybrid bluegill Lepomis cyanellus × L. macrochirus . In Experiment 1, hybrid bluegill (20 g) were stocked into 1.25-m³ cages at a rate of 300 fish/cage and fed diets containing 35, 40, 44, or 48% protein for 12 wk. Fish meal comprised 32% of the dietary protein in all diets. Fish were fed all they could consume in 40 min. No significant differences ( P > 0.05) in individual length, individual weight, specific growth rate (SGR), condition factor (K), and feed conversion ratio (FCR) were found among treatments and averaged 13.4 cm, 47.4 g, 1.02%/d, 1.96, and 4.06, respectively. Whole-body composition of hybrid bluegill indicated that fish fed a diet containing 35% protein had a significantly lower ( P < 0.05) percentage protein (56.3%) and a higher ( P < 0.05) percentage lipid (29.3%) compared to fish fed diets containing 40, 44, and 48% protein. In Experiment 2, 15 hybrid bluegill (15 g) were stocked into 110-L aquaria and fed one of four diets containing 28, 32, 36, or 38% protein for 10 wk. Fish were fed twice daily all they would consume in 20 min. Fish fed a diet containing 38% protein had higher ( P < 0.05) percentage weight gain (265%) than fish fed diets containing 28% (203%) and 32% (219%) protein, but were not significantly different ( P > 0.05) compared to fish fed a diet containing 36% protein (251%). Feed conversion ratio (FCR) of hybrid bluegill fed diets containing 36% and 38% protein (average 1.39) were significantly lower ( P < 0.05) than fish fed a diet with 28% protein (1.73). Results from these studies indicate that hybrid bluegill can be fed a practical diet containing 35–36% protein (with fish meal comprising 32% of the protein). Further refinement of the diet formulation may allow producers to reduce diet and production costs.     

Bluegill Picornavirus isolated from a mortality event involving Bluegill (Lepomis macrochirus) in the upper Mississippi River

A mortality event involving an estimated 1,000 adult bluegills (Lepomis macrochirus) was observed in an ice‐covered backwater lake of the upper Mississippi River near Alma, Wisconsin, in December of 2017. Macroscopic signs of disease included abdominal distension due to fluid accumulation within the internal organs as well as external and internal haemorrhaging. Histological evaluation revealed chronic peritonitis with peritoneal adhesions in all fish examined. Kidney, spleen and ascites fluid samples were collected from diseased bluegills and examined for the presence of pathogens. Bluegill picornavirus (BGPV) was isolated using tissue cell culture methods utilizing a recently developed, uncharacterized bluegill fry cell line (BF‐4), and the presence of this virus was confirmed through molecular identification. The current geographic range, known susceptible hosts as well as historical epizootics associated with BPGV is discussed. The ability of BGPV to cause significant mortality in wild fish further emphasizes the importance of monitoring both wild and hatchery populations for this pathogen.     

蓝鳃太阳鱼诺卡氏菌的分离鉴定及药敏分析

为探明患结节病蓝鳃太阳鱼的病因,从蓝鳃太阳鱼(Lepomis macrochirus)脾脏结节处分离获得一病原菌SD1810。通过菌落形态、细菌生理生化鉴定和16S rRNA基因序列分析,确定所得菌株为鰤鱼诺卡氏菌(Nocardia seriolae)。人工回归感染试验结果显示,注射浓度为2.8×107 CFU/mL的菌液能使蓝鳃太阳鱼患病致死,发病症状与原感染鱼相似。从死亡太阳鱼体内可重新分离到与SD1810形态特征、生理生化指标相一致的病菌。对分离获得的鰤鱼诺卡氏菌进行药敏试验分析,结果表明,鰤鱼诺卡氏菌SD1810对红霉素、利福平、庆大霉素、氯霉素、阿米卡星、氟苯尼考等10种抗生素极其敏感,对头孢唑啉,诺氟沙星,青霉素、氨苄青霉素和阿莫西林等6种抗生素具有耐药性。     

Evaluating potential competitive bottlenecks between invasive common carp and native bluegill and yellow perch

Processes influencing fish recruitment are often highly complex and inherently difficult to understand. Invasive species may complicate recruitment through habitat and food web modifications resulting in competitive bottlenecks. Common carp Cyprinus carpio have been distributed worldwide, and their introductions have resulted in destructive effects on aquatic ecosystems and food web dynamics. Common carp are highly fecund, and high densities of age‐0 carp may occur in some years that may reduce invertebrate prey resources and adversely affect native age‐0 fishes. We used enclosures and field observations to examine potential effects of age‐0 common carp on growth and survival of age‐0 yellow perch Perca flavescens and bluegill Lepomis macrochirus. Yellow perch and bluegill were stocked into enclosures with and without common carp (31 fish/m³) using a substitution experimental design, and fish growth and survival and invertebrate prey resources were assessed. Common carp reduced growth of yellow perch but not bluegill and did not affect survival of either species in mesocosms. Next, we used patterns of common carp, bluegill, and yellow perch abundance and total length across 38 lake‐years to evaluate potential interspecific interactions in natural systems. Age‐0 common carp abundance was not negatively related to size or abundance of bluegill or yellow perch. However, adult common carp and age‐0 yellow perch abundance were inversely related, suggesting a potential competitive bottleneck. Thus, age‐0 common carp may suppress growth of yellow perch when prey is limited, but adult common carp may have larger effects than early life stages on native juvenile fishes.     

Experimental pathogenicity of reovirus 13p2 for juvenile American oysters Crassostrea virginica (Gmelin) and bluegill fingerlings Lepomis macrochirus (Rafinesque)

Abstract. A viral agent (13p₂), isolated from clinically normal juvenile American oysters ( Crassostrea virginica ) and characterized as a new serotype of reovirus, was tested to determine if it could replicate and produce disease in experimental juvenile oysters. Because the virus replicated well in the bluegill fry (BF-2) fish cell line, fingerling bluegills Lepomis macrochirus were included in the pathogenicity experiments. Exposure of oysters to the 13p₂ virus in ambient seawater resulted in no significant mortality and no increased virus titres or histological lesions. Virus particles were not observed in tissues of exposed oysters when examined with transmission electron microscopy (TEM). Intraperitoneal inoculation of the 13p₂ virus into bluegills resulted in 44% mortality associated with a focal necrotic hepatitis. Evidence of virus replication, when evaluated histological or by virus titration, was observed in 94% of 32 inoculated fish. Samples of infected livers examined with TEM revealed typical cytoplasmic arrays of 13p₂ virus particles in affected hepatocytes. Rising virus titres and hepatic lesions also occurred in bluegills exposed to water containing the 13p₂ virus. These results indicated the natural host of the 13p₂ virus was not the American oyster, but that it was a significant pathogen for at least one fish species.     

Apparent digestibilities of common feedstuffs for bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides using individual test ingredients

Apparent digestibility of dry matter and energy, and availability of amino acids from blood meal (BM), fish meal (FM), meat and bone meal (MBM), poultry by-product meal (PBM), soybean meal (SBM), corn, wheat and yellow grease (YG) were determined for bluegill Lepomis macrochirus (mean weight, 57 g), and likewise, but not for BM or wheat, for largemouth bass Micropterus salmoides (mean weight, 30 g). To avoid nutrient interaction from a reference diet, diets containing 98.5% (985 g kg⁻¹) of test ingredients were used, except for semi-solid, YG which was mixed with corn to permit pelletization. Faeces were collected by a siphoning method. Apparent dry matter digestibility values ranged from 50% (corn) to 87% (BM) for bluegill and from 53% (MBM) to 76% (PBM) for largemouth bass. Apparent energy digestibility values ranged from 53% (corn) to 92% (BM) for bluegill and from 63% (MBM) to 93% (YG) for largemouth bass. Apparent digestibility of most amino acids exceeded 90% for evaluated protein sources, except for MBM which showed slightly lower values (80–90%) for both fishes. Isoleucine digestibility from BM was relatively low (82%) for bluegill. High digestibility values for SBM, PBM and BM, indicate good potential for replacing FM in diets for both fishes.