Notemigonus Research Articles

Evaluation of 36%‐Protein Diets with or without Animal Protein for Rearing Tank‐Hatched Golden Shiner Fry in Ponds

AbstractThe objective of this study was to determine whether fry of golden shiners Notemigonus crysoleucas reared in ponds differed with respect to growth, survival, feed conversion, total yield, condition, and response to low dissolved oxygen when fed a practical diet of 36% protein from animal and plant sources (five ponds) versus a diet of only plant sources (six ponds). Newly hatched fry (1 mg) were stocked at 2.5 × 106/ha in 12 fertilized ponds (0.04 ha each). Fish were fed twice daily at a rate of 8.0–15.9 kg/ha for 12 weeks. Chlorophyll a was not different between diets, indicating that natural food production in ponds was similar between treatments. Between‐treatment differences in average individual weight (0.56–0.59 g), relative weight (114.4– 115.6), Fulton's condition index (K = 0.88), total yield (40.8–45.6 kg), feed conversion (0.85– 0.95), and survival (75.9–79.2%) were not significant. Postharvest survival of fish exposed to low dissolved oxygen at 20°C in a laboratory test was not affected by diet. These results indicate that diets with all plant protein sources are suitable for raising golden shiners in fertilized ponds from first‐feeding fry to small juveniles.

Variation in Condition Factor and Growth in Young-of-Year Fishes in Floodplain and Riverine Habitats of the Cosumnes River, California

Condition factors and growth rates of postlarval (young-of-year) fishes in a Central California river were compared in order to determine the relative importance of floodplain and riverine habitats for rearing. Sampling took place between April and June of 2001 and 2002 in the lower Cosumnes River and its floodplain. Sacramento splittail showed higher condition and length increment in floodplain habitats than in riverine habitats. Sacramento suckers showed differences in condition between sites, but suckers from the floodplain had lower weight increments than those from the river. The weight increment in Sacramento splittail was not significantly different between habitats. In addition, two alien species, common carp and golden shiner, had similar condition factors and growth rates. This study shows the usefulness of condition factor and growth rate in evaluating the importance of different habitats for early life history stages of fishes.

Biomanipulation: A Classic Example in a Shallow Eutrophic Pond

ABSTRACT Moe Pond, Otsego County, New York, is an artificial impoundment created by the damming of a natural wetland in 1939. It was dominated by blue-green algal blooms between at least 1970–1998. During that time a few scattered clones of sedges (Cyperaceae) along the shoreline were the only vascular plants present. The zooplankton community was dominated by small individuals, primarily rotifers, which were unable to effectively graze the algal community. During this interval, golden shiner (Notemigonus crysoleucas) and brown bullhead (Ictalurus nebulosus) made up the entire fish community. Largemouth and smallmouth bass (Micropterus dolomieu and M. salmoides) were added between 1998 and spring 1999. Golden shiner recruitment functionally ended at that time, and by 2002 they had been virtually eliminated. Secchi transparencies increased and mean chlorophyll a decreased significantly (p<0.05), with algal blooms becoming practically nonexistent. Water weed (Elodea canadensis) now covers the bottom of most of the pond, reaching the surface in many areas up to 2 m in depth. Increased transparency, as well as potential changes in nutrient dynamics, both indirectly brought about by the addition of piscivorous fish, apparently has enabled Elodea to out-compete plank tonic algae for available nutrients. This documents a situation where top-down management of the fish community has affected the biota and water quality through trophic cascades. The introduction of piscivorous fish (top-down management) may be used to manage water quality through increased algal grazing by zooplankton. However, a substantial increase in macrophytes, as documented here, may be an outcome.

Effects of Temperature and Size on Ammonia Excretion by Fasted Golden Shiners

AbstractThe golden shiner Notemigonus crysoleucas is the major species of baitfish raised and sold in the United States. They are shipped in trucks from large farms to distributors up to 2,500 km distant. The costs associated with shipping could be greatly reduced if truck loading were increased, but higher densities of fish elevate ammonia concentrations to detrimental levels. In our work, we have simulated live hauling conditions to measure the ammonia excretion rates of golden shiners at 15, 20, and 25°C. The experiments were conducted for 24 h in three recirculating systems after fingerling golden shiners were fasted and acclimated for 2 d. The experiment was repeated four times using different lots and sizes of golden shiners. The results indicated that there were no significant differences in the hourly ammonia excretion rates (HER) between two lots of same‐size golden shiners. The hourly ammonia excretion rates were inversely proportional to fish weight and increased with temperature. The average HER for all sizes of fish ranged from 2.9 to 7.4 g NH3‐N/kg fish/h at 15°C, 5.2–11.2 g NH3‐N/kg fish/h at 20°C, and 6.2–15.0 g NH3‐N/kg fish/h at 25°C. The results of this study will be used to design ammonia control systems to safely increase fish density on commercial fish hauling trucks.

Morphological and genetic characteristics of Flavobacterium columnare isolates: correlations with virulence in fish

Variability in pathogenicity of Flavobacterium columnare makes disease treatment difficult because there is currently no way to easily recognize those strains that warrant aggressive treatments. In order to identify suitable virulence markers, 17 isolates of F. columnare were cultured from six different fish species. The DNA from all isolates was analysed using random amplified polymorphic DNA (RAPD). Bootstrap analysis of the RAPD data produced a tree with three major groups supported by bootstrap scores of 80-100%. Virulence of the isolates was determined by bath exposure of channel catfish, Ictaluruspunctatus (Rafinesque), and golden shiners, Notemigonus crysoleucas (Mitchill), to broth cultures of F. columnare. In channel catfish, 13 of 17 isolates produced 100% mortality within 48 h post-exposure. All isolates of cyprinid fish origin clustered in a single RAPD group. At least two of the four isolates that were not virulent in channel catfish were of cyprinid fish origin. There was a wide variation in cell morphology between isolates with lengths of cells or cell chains ranging from 3 to 11 microm, even under identical culture conditions. Most of the shorter or single cell isolates fell into a single RAPD group. No clear association was identified between virulence and any other characteristic, including RAPD group.

Molecular, Physical, and Clinical Evidence that Golden Shiner Virus and Grass Carp Reovirus are Variants of the Same Virus

AbstractMoribund golden shiners Notemigonus crysoleucas sampled during winter and spring and moribund grass carp Ctenopharyngodon idella sampled during summer were necropsied and cultured on cyprinid cell lines. In all cases, a syncytial cytopathic effect occurred and viruses were successfully passaged. Characterization by electron microscopy, diethyl ether resistance, iododeoxyuridine resistance, and acid resistance confirmed that the isolates were aquareoviruses. We used polymerase chain reaction to test all isolates; primer sets were based on a published sequence for segments 1, 2, 3, and 10 of the grass carp reovirus (GCRV). Products of the expected sizes were amplified, then cloned and sequenced. The isolates were about 97–100% identical to each other and to a published sequence for golden shiner virus (GSV) and were 90–93% identical to GCRV. At the amino acid level, our isolates were 96–100% identical to each other and to GCRV. The similarity among our isolates and the published GCRV sequence was equivalent to the similarity among published GCRV sequences; we therefore conclude that GSV and GCRV are the same virus. This conclusion is confirmed by our isolation of this virus from both moribund golden shiners and moribund grass carp. Based on our work, we conclude that GSV is synonymous with GCRV, and that GSV was probably imported into the USA concurrently with the introduction of grass carp by federal agencies in 1963.

Alternative Complement Activity and Resistance to Heat Stress in Golden Shiners (Notemigonus crysoleucas) Are Increased by Dietary Vitamin C Levels in Excess of Requirements for Prevention of Deficiency Signs

Golden shiners (Notemigonus crysoleucas) require a dietary source of ascorbic acid (AA) for growth or survival, depending on diet composition. However, no quantitative requirements of golden shiners for AA for growth, health or survival have been determined, and specific deficiency signs have not been observed. The purpose of this study was to determine the effects of different dietary levels of AA on the growth and health of golden shiners fed diets containing 0-218.5 mg AA/kg diet for 10-16 wk. Weight gain, survival and gross deformities were assessed at 10 wk. The remaining fish were fed the same diets from wk 11-16; hematology and alternative complement activity were then assessed and a subset of live fish from each tank was exposed to elevated temperature. Gross deformities appeared in fish fed 0 mg AA/kg diet at 9 wk. The 19.5 mg AA/kg diet was sufficient to prevent the deformities and optimize survival, whereas growth did not differ among treatments. Fish fed 40.3 mg of AA/kg diet had a higher survival rate than fish fed 0 or 19.5 mg AA/kg diet after exposure to elevated temperatures (34-35.5 degrees C). Alternative complement activity and visceral AA concentrations were greater in fish fed diets with 218.5 mg AA/kg than in all other groups. The results indicate that the dietary requirement of AA for golden shiners increases in response to heat stress, and that the alternative complement activity (one index of immune competence) was strongly enhanced in fish fed a diet with approximately 10 times the amount of AA required to prevent deficiency signs.

Mercury effects on predator avoidance behavior of a forage fish, golden shiner (Notemigonus crysoleucas)

Mercury contamination of fish is widespread in North America and has resulted in the establishment of fish consumption advisories to protect human health. However, the effects of mercury exposure to fish have seldom been investigated. We examined the effects of dietary mercury exposure at environmental levels in a common forage species, golden shiner (Notemigonus crysoleucas). Fish were fed either an unaltered diet (12 ng/g wet wt methylmercury [MeHg] as Hg), a low-Hg diet (455 ng/g Hg), or a high-Hg diet (959 ng/g Hg). After 90 d mean fish whole-body total Hg concentrations were 41, 230, and 518 ng/g wet wt, respectively, which were within the range of concentrations found in this species in northern U.S. lakes. There were no mortalities or differences in growth rate among groups. Groups of fish from each treatment were exposed to a model avian predator and their behavioral response videotaped for analysis. Brain acetylcholinesterase (AChE) activity was determined in fish after behavioral testing. Fish fed the high-Hg diet had significantly greater shoal vertical dispersal following predator exposure, took longer to return to pre-exposure activity level, and had greater shoal area after return to pre-exposure activity than did the other treatments, all of which would increase vulnerability of the fish to predation. There were no differences in brain AChE among treatments. We conclude that mercury exposure at levels currently occurring in northern United States lakes alters fish predator-avoidance behavior in a manner that may increase vulnerability to predation. This finding has significant implications for food chain transfer of Hg and Hg exposure of fish predators.

Long-Term Changes in the Fish Assemblages of the Big Blue River Basin 40 Years after the Construction of Tuttle Creek Reservoir

Long-term changes in the fish assemblage of the Big Blue River basin, Kansas, were examined by comparison of a stream survey conducted prior to the construction of Tuttle Creek Reservoir (1957 to 1958) with two surveys conducted approximately 40 years later. The most recent survey, in 2001, included 14 of the original sites sampled in the late 1950s. The most notable changes to the fish assemblages were the introduction and presumed establishment of four species (Notropis atherinoides, Pimephales vigilax, Gambusia affinis, and Notemigonus crysoleucas) and the apparent extirpation of Macrhybopsis aestivalis. Other than the loss of M. aestivalis, incidence and relative abundance of other species remained similar to that which occurred before the construction of the reservoir. Percent similarity of the fish assemblage between the 1950s and the recent samples ranged between 34.7% and 84.4%, dependent on stream type (mud, gravel, or sand substrate). In addition, species incidence patterns were significantly concordant between the 1950s and the two recent surveys, with the exception of mud-bottomed streams sampled during 2001. Finally, Jaccard's index was used to compare assemblage similarity between 14 sites sampled in both the late 1950s and 2001. Although assemblage similarity between time periods was on average low (x̄ = 0.411), a Mantel test suggested a significant concordance between sampling periods, indicating the spatial structure of the assemblage was stable. We conclude that Tuttle Creek Reservoir has served as a source for the establishment and subsequent dispersal of introduced species in the Big Blue River system and that it is important to monitor routinely these assemblages because species may continue to invade the Big Blue River system with unpredictable consequences for the native fish fauna.

Nitrogen Fertilization of Golden Shiner Ponds

Abstract Ammonium sulfate and sodium nitrate were used as nitrogen fertilizers in 0.1-ha ponds stocked with golden shiners Notemigonus crysoleucas at Auburn, Alabama. Biweekly from 30 March to 15 October 1999, 9 kg P2O5/ha from triple superphosphate and 9 kg N/ha were applied to treatment ponds. Control ponds were treated only with biweekly applications of triple superphosphate at 9 kg P2O5/ha. Fish production did not differ between the two nitrogen sources or between the nitrogen sources and the control. Ammonium sulfate treatment caused the total alkalinity and pH of ponds to decline as a result of acidity produced by nitrifying bacteria in the oxidation of ammonia to nitrate. Alkalinity and pH did not decline in the sodium nitrate treatment or control. No other benefits of sodium nitrate versus ammonium sulfate application were observed.

THE EFFECTS OF PREY AVAILABILITY ON THE NUMERICAL RESPONSE OF WADING BIRDS

Reduced prey availability has emerged as a primary hypothesis to explain population constraints on wading birds in numerous wetlands around the world. However, there is almost no understanding of which component of prey availability (i.e., prey density or vulnerability of prey to capture) is affecting populations and whether the relative effects of each component differ among species. In this study, I manipulated prey density and water depth (i.e., prey availability) in 12 0.2-ha ponds to determine their relative effects on the numeric response of eight species of free-ranging wading birds (White Ibis, Eudocimus albus; Wood Stork, Mycteria americana; Snowy Egret, Egretta thula; Glossy Ibis, Plegadis falcinellus; Great Egret, Ardea alba; Tricolored Heron, Egretta tricolor; Great Blue Heron, Ardea herodias; and Little Blue Heron, Egretta caerulea). The experiment was conducted in a constructed wetland adjacent to, and west of, the northern tip of the remnant Everglades, in Palm Beach County, Florida, USA. Each pond was set to a water depth of 10 cm, 19 cm, or 28 cm, and was stocked with golden shiners (Notemigonus crysoleucas) at a density of either 3 fish/m2 or 10 fish/m2. Total bird use (all treatments pooled) increased from day 1 (day after stocking) to day 6, stabilized for several days at ∼280 birds, and then decreased until day 16, when bird use nearly ceased. Fish were depleted most rapidly in the shallow treatment and least rapidly in the deep treatment. The giving-up-density (GUD) of prey increased with increasing water depth. There was no significant difference among species in the slope of that relationship; however, a visual inspection of the data showed that differences in GUDs were becoming more apparent in the deepest treatment. At that depth, the White Ibis, Wood Stork, and Snowy Egret had higher GUDs than did the Glossy Ibis, Great Egret, Tricolored Heron, Great Blue Heron, and Little Blue Heron. Also, the first three species were affected significantly by both prey density and water depth, whereas the latter five species showed a decidedly weaker response to one or the other component of prey availability. The first three species were more abundant in the shallow treatments and the high prey density treatments, and they abandoned the study site before other species reached their maximum density. The feeding strategy of the first group appeared to be one of searching for new high-quality food patches rather than staying and exploiting food patches that were declining in quality. Species that employed a searching strategy also have shown the most severe population declines, suggesting that factors affecting bird density at feeding sites may also have affected population size.

The Effects of Prey Availability on the Numerical Response of Wading Birds

Reduced prey availability has emerged as a primary hypothesis to explain population constraints on wading birds in numerous wetlands around the world. However, there is almost no understanding of which component of prey availability (i.e., prey density or vulnerability of prey to capture) is affecting populations and whether the relative effects of each component differ among species. In this study, I manipulated prey density and water depth (i.e., prey availability) in 12 0.2-ha ponds to determine their relative effects on the numeric response of eight species of free-ranging wading birds (White Ibis, Eudocimus albus; Wood Stork, Mycteria americana; Snowy Egret, Egretta thula; Glossy Ibis, Plegadis falcinellus; Great Egret, Ardea alba; Tricolored Heron, Egretta tricolor; Great Blue Heron, Ardea herodias; and Little Blue Heron, Egretta caerulea). The experiment was conducted in a constructed wetland adjacent to, and west of, the northern tip of the remnant Everglades, in Palm Beach County, Florida, USA. Each pond was set to a water depth of 10 cm, 19 cm, or 28 cm, and was stocked with golden shiners (Notemigonus crysoleucas) at a density of either 3 fish/m2 or 10 fish/m2. Total bird use (all treatments pooled) increased from day 1 (day after stocking) to day 6, stabilized for several days at ∼280 birds, and then decreased until day 16, when bird use nearly ceased. Fish were depleted most rapidly in the shallow treatment and least rapidly in the deep treatment. The giving-up-density (GUD) of prey increased with increasing water depth. There was no significant difference among species in the slope of that relationship; however, a visual inspection of the data showed that differences in GUDs were becoming more apparent in the deepest treatment. At that depth, the White Ibis, Wood Stork, and Snowy Egret had higher GUDs than did the Glossy Ibis, Great Egret, Tricolored Heron, Great Blue Heron, and Little Blue Heron. Also, the first three species were affected significantly by both prey density and water depth, whereas the latter five species showed a decidedly weaker response to one or the other component of prey availability. The first three species were more abundant in the shallow treatments and the high prey density treatments, and they abandoned the study site before other species reached their maximum density. The feeding strategy of the first group appeared to be one of searching for new high-quality food patches rather than staying and exploiting food patches that were declining in quality. Species that employed a searching strategy also have shown the most severe population declines, suggesting that factors affecting bird density at feeding sites may also have affected population size.

Common evolutionary origin of aquareoviruses and orthoreoviruses revealed by genome characterization of Golden shiner reovirus, Grass carp reovirus, Striped bass reovirus and golden ide reovirus (genus Aquareovirus, family Reoviridae).

Full-length and partial genome sequences of four members of the genus Aquareovirus, family Reoviridae (Golden shiner reovirus, Grass carp reovirus, Striped bass reovirus and golden ide reovirus) were characterized. Based on sequence comparison, the unclassified Grass carp reovirus was shown to be a member of the species Aquareovirus C. The status of golden ide reovirus, another unclassified aquareovirus, was also examined. Sequence analysis showed that it did not belong to the species Aquareovirus A or C, but assessment of its relationship to the species Aquareovirus B, D, E and F was hampered by the absence of genetic data from these species. In agreement with previous reports of ultrastructural resemblance between aquareoviruses and orthoreoviruses, genetic analysis revealed homology in the genes of the two groups. This homology concerned eight of the 11 segments of the aquareovirus genome (amino acid identity 17-42%), and similar genetic organization was observed in two other segments. The conserved terminal sequences in the genomes of members of the two groups were also similar. These data are undoubtedly an indication of the common evolutionary origin of these viruses. This clear genetic relatedness between members of distinct genera is unique within the family Reoviridae. Such a genetic relationship is usually observed between members of a single genus. However, the current taxonomic classification of aquareoviruses and orthoreoviruses in two different genera is supported by a number of characteristics, including their distinct G+C contents, unequal numbers of genome segments, absence of an antigenic relationship, different cytopathic effects and specific econiches.

Captive Double‐crested Cormorant Phalacrocorax auritus Predation on Channel Catfish Ictalurus punctatus Fingerlings and Its Influence on Single‐batch Cropping Production

Abstract.— We studied the effects of captive doublecrested cormorant Phalacrocorax auritus predation on channel catfish Ictalurus puncratus inventories from research ponds with and without alternative prey during the years 1998–2000. In 1998, predation by two groups of captive cormorants on ponds without alternative prey produced inventory reductions relative to a control pond that were equivalent to 10.2 (516 g) and 10.5 (608 g) catfishhird per d. In 1999 and 2000 individual cormorants foraging on 0.02‐ha pond halves for 10 d (500 cormoranta) stocked with both catfish and golden shiners Noremigonus crysoleucas produced inventory reductions at harvest (7.5 mo after predation occurred) averaging approximately 7 and 9 catfishhird per d, respectively. In 1999, two ponds averaged a 30% reduction in fish inventoried and a 23% loss in biomass from ponds stocked at 12,355 fishha using a single batch cropping system. Production losses from predation were not apparent at a third pond where disease reduced the catfish population by more than 50%. In contrast, two ponds with more modest disease problems in 2000 had additive predation losses that exceeded those observed in 1999. Observations of cormorants foraging during 1999 and 2000 suggested that differences in catfish predation between these years may have been related to less shiner utilization by cormorants in 2000. However, based on availability, there was no preference for shiners over catfish (Chesson's alpha c0.41) in either year, although shiners were a more readily manipulated prey. Despite the possible moderating effects of alternative prey utilization, we conclude that cormorants can cause significant economic losses to catfish at harvest.

Cortisol response of golden shiners (Notemigonus crysoleucas) fed diets differing in lipid content

The purpose of this study was to characterize the plasma cortisol response in golden shiners (Notemigonus crysoleucas) under crowding stress, and to determine whether dietary lipid affects the cortisol response. The main differences between the diets were the relative amounts and types of fatty acids of the n-3 and n-6 families. In experiment 1, triplicate groups of golden shiners were fed diets with 4 or 13% menhaden fish oil, or 4 or 13% poultry fat at 3% body weight for 4 weeks before the crowding stress. In experiment 2, fish were fed diets with 8% lipid from soybean oil (SBO), cod liver oil (CLO), (SBO+CLO), or cottonseed oil (CSO) for 6 weeks before the stress test. Plasma cortisol was measured initially, two hours after the stressor was applied, and two hours after the stressor was removed. The overall pattern of the cortisol response was similar to that seen in other warmwater fishes, but the rate and magnitude of the response were not affected by diet in either experiment. Golden shiners have an intermediate cortisol response compared to other fish that have been exposed to similarly stressful conditions.

Plasticity of diel and circadian activity rhythms in fishes

In many fish species, some individuals arediurnal while others are nocturnal. Sometimes,the same individual can be diurnal at first andthen switch to nocturnalism, or vice-versa.This review examines the factors that areassociated with such plasticity. It covers thebreakdown of activity rhythms during migration,spawning, and the parental phase; reversals ofactivity patterns during ontogeny or from oneseason to the next; effects of light intensity,temperature, predation risk, shoal size, foodavailability, and intraspecific competition.Case studies featuring goldfish (Carassiusauratus), golden shiner (Notemigonuscrysoleucas), lake chub (Couesiusplumbeus), salmonids, sea bass (Dicentrarchus labrax), and parentalsticklebacks and cichlids illustrate some ofthese influences. It is argued that mostspecies have a circadian system but that havingsuch a system does not necessarily imply strictdiurnalism or nocturnalism. Rigidity ofactivity phase seems more common in species,mostly marine, that display behavioral sleep,and for these animals the circadian clock canhelp maintain the integrity of the sleepperiod and ensure that its occurrence takes place atthat time of day to which the animal's sensoryequipment is not as well adapted. However, inother fishes, mostly from freshwater habitats,the circadian clock seems to be used mainly foranticipation of daily events such as thearrival of day, night, or food, and possiblyfor other abilities such as time-place learningand sun compass orientation, rather than forstrict control of activity phase. In thesespecies, various considerations relating toforaging success and predation risk maydetermine whether the animal is diurnal ornocturnal at any particular time and place.

Experimental Infection of an Exotic Heterophyid Trematode,Centrocestus formosanus, in Four Aquaculture Fishes

Centrocestus formosanus, an exotic digenetic trematode that was recently found infecting wild fish in Texas, was evaluated to determine whether it could infect four propagated warmwater fish species. Channel catfish Ictalurus punctatus, sunshine bass (the hybrid of female white bass Morone chrysops and male striped bass Morone saxatilis), golden shiners Notemigonus crysoleucas, and fathead minnows Pimephales promelas were experimentally infected with cercariae of C. formosanus. The trematodes were embedded along the gill filament cartilage. Cyst production, cartilage displacement, and hyperplasia of the lamellar epithelium were observed in wet mounts of sunshine bass and fathead minnow gills. These pathological changes also occurred in golden shiners and channel catfish but appeared to be delayed and less pronounced. Histological examination showed that the parasites were encased in cartilage, and distorted areas were evident in the filament cartilage. Because this trematode has the ability to infect and produce lesions in these fish, it could pose problems for the producers of commercially raised baitfish and food fish.

Stable Car bon Iso tope Ratios and Stan dard Pro duction Data as Indices of Golden Shiner, Notemigonus crysoleucas, Per for mance in Pond Feed ing Trials

This study shows the ef fect of production variables on assimilation of foods by golden shin ers, Notemigonus crysoleucas, in ponds was ex am ined in con cur rent 8-week feed ing tri als at the Uni versity of Ar kan sas at Pine Bluff (UAPB) and Texas A&M Uni ver sity (TAMU). Ten 0.04-ha ponds per site were fer til ized with defatted rice bran and stocked with golden shin ers (ini tial weight = 1.3 g) at a rate of 750,000/ha (UAPB) or 375,000/ha (TAMU). Fish in five ponds per site were fed a nu tri tion ally com plete pre pared diet at 4% of body weight, while fish in the re main ing ponds were not fed. As sim i la tion of nat u ral foods by “unfed” fish was com pared to that of fish fed the pre pared diet at each site. Stan dard pro duc tion data (weight gain, Secchi depth, dissolved ox y gen [DO]) were com pared to sta ble car bon iso tope ra tio (d1 3 C) data as an in dex of fish per for mance (weight change or fish d13 C, re sult ing from as sim i la tion of var i ous food sources). Fish weight change and fish iso tope ra tio were re gressed sep a rately against in de pend ent vari ables (feed amount, Secchi depth, DO, fed/unfed dummy vari able, and study site dummy vari able) to de ter mine their re la tion ships. Nat u ral pro duc tiv ity was con sis tently lower at TAMU than at UAPB, while temper a ture and min i mum DO were sim i lar be tween sites. Weight gains of fed and unfed fish at TAMU were higher than those of fed and unfed fish at UAPB. The d13 C of fed and unfed fish at UAPB changed lit tle dur ing the study and did not al low dis crim i na tion among their food sources. The d13 C of fed fish at TAMU ap proached that of the pre pared diet, while that of unfed fish re sem bled that of the plank ton and rice bran. Pre pared diet quan tity and the study site sig nif i cantly (P > 0.1) af fected fish weight change, but Secchi depth and min i mum DO did not. Weight gain increased with in creas ing diet in put up to a max i mum value, then de clined with ad di tional in puts. Min i mum DO, plank ton iso tope ra tio, and the fed/unfed and site vari ables sig nif i cantly af fected fish iso tope ra tio.

Population biology of eyeflukes in fish from a large fluvial ecosystem: the importance of gulls and habitat characteristics

Spottail shiners (Notropis hudsonius) were monitored for eyeflukes monthly at four sites in the St. Lawrence River, Quebec, from spring through autumn in 1997 and 1998. In general, mean abundance of Diplostomum spp. in the lens of spottail shiners was highest at sites near large ring-billed gull (Larus delawarensis) colonies and was higher in 1998 than in 1997. Population studies demonstrated a major period of recruitment in the late summer – early autumn. Mean abundance increased between November and May, when sampling was logistically not possible, reflecting late-fall or early-spring recruitment. Golden shiners (Notemigonus crysoleucas) and small yellow perch (Perca flavescens) were monitored at a single site (Île aux Ours) in 1997 and 1998. Mean abundance of Diplostomum spp. in the lens of golden shiners at Île aux Ours was higher in 1998 than in 1997. Recruitment occurred in the early summer and between November and May, suggesting late-fall or early-spring transmission. Mean abundance decreased between August and October in both years. Yellow perch at Île aux Ours were infected with four different parasite species in their eyes. Mean abundance of Diplostomum spp. in the vitreous humour or retina increased during the summer and fall and then decreased between the fall and following spring. Diplostomum spp. in the lens increased in abundance in the early summer, and then decreased during the fall. Both Tylodelphys scheuringi and Neascus spp. in the vitreous humour were more abundant in 0+ than in 1+ perch. Mean abundance of T. scheuringi increased over the summer in 1997 and then dropped to zero in the same cohort over winter, suggesting that the parasite lives for only 1 year. Neascus spp. only were found in 1998. Distributional data, together with seasonal information, suggest that habitat characteristics contribute significantly to the abundance of Diplostomum spp. along the St. Lawrence River. Proximity to gull colonies enhances abundance, but higher rates of predation at wetland sites depress abundance and restrict the accumulation of parasites.

Responses of Juvenile Golden Shiner Notemigonus crysoleucas Fed Semipurified or Practical Diets With or Without Supplemental Ascorbic Acid

A 12-wk feeding trial was conducted in a flow-through system to determine whether juvenile golden shiner Notemigonus crysoleucas have a dietary requirement for ascorbic acid. Triplicate groups of 30 fish each weighing 0.44 g initially were fed semi-purified (casein) diets supplemented with 0 or 250 mg ascorbic acid/kg, or practical (fish meal) diets supplemented with 0 or 250 mg ascorbic acid/kg. The form of ascorbic acid used was L-ascorbyl-2-polyphosphate. Survival was higher in fish fed the semi-purified diet with 250 mg ascorbic acid/kg than in those fed the unsupplemented semi-purified diet, while weight gain did not differ between treatments. Weight gain was higher in fish fed the practical (fish meal) diet supplemented with 250 mg ascorbic acid/kg than in those fed the unsupplemented practical diet, while survival did not differ between treatments. No other signs of ascorbic acid deficiency were observed, but fish fed the casein diets had skin and fin erosion indicative of a possible bacterial infection. Whole-body concentrations of ascorbic acid (total, reduced, and percent of reduced ascorbic acid) were higher in fish fed semi-purified or practical diets supplemented with 250 mg ascorbic acid/kg than in fish fed unsupplemented diets. Golden shiners appear to require a dietary source of ascorbic acid for growth or survival, depending on experimental conditions. The two main differences in the study were in diet composition (semi-purified versus practical diets) and apparent health status of fish fed the different diet types. Additional studies are needed to define requirements further.