Characterization of Herpes virus vitreum isolated from hyperplastic epidermal tissue of walleye,Stizostedion vitreum vitreum (Mitchill)*

Abstract. A new virus, provisionally named Herpesvirus vitreum, was isolated from hyperplastic epidermal tissue from a walleye, Stizostedion vitreum vitreum (Mitchill), taken in Saskatchewan, Canada. The virus, which was isolated in the walleye ovarian (WO) cell line, was identified as a herpesvirus on the basis of size (190–230 nm), morphology and apparent pattern of replication. The virus, which passes polycarbonate membranes of 200 nm mean pore diameter, was ether-labile. Virus replicated in WC-1 cells at 4 and 15°C, but not at 20°C. Although walleye cell lines (WO, WC-1, We-2) were susceptible to infection at 15°C, non-period cell lines were refractory. Syncytial formation and lysis occurred in susceptible cell lines. Virus was quantified by plaque assay at 13 to 15°C for two weeks. Replication was inhibited by 10^-3.0m phosphonoacetate and by 10^-5.0m 5-bromodeoxyuridine (BUDR), but addition of excess thymidine reversed the inhibition by BUDR. Viral replication in WO cells, but not in WC-1 cells, was inhibited by the antiherpetic drug acyclovir (10^-5.0m ). The relationship of the herpesvirus isolate and epithelial neoplasms was not determined.     

Pond Production of Fingerling Walleye,Stizostedion vitreum,in the Northern Great Plains

The cultural practices used to produce fingerling walleye, Stizostedion vitreum, in drainable earthen ponds are described for a state fish hatchery in Nebraska and two federal hatcheries in North Dakota. The ponds were filled 1 to 7 days before D2-D4 (Dl=the day of hatch) walleye fry were stocked. At one hatchery, ponds were sometimes double-cropped, first for production of northern pike, Esoxlucius. The two federal hatcheries fertilized ponds with ground alfalfa hay or pellets, while the standard practice at the Nebraska hatchery was not to fertilize walleye ponds, because of concern that fertilization would result in weed problems and oxygen depletion. One hatchery seeded the ponds with rye grass in the fall. Two of the hatcheries regularly used herbicides to prevent the stranding of fingerlings during harvest and their mortality caused by entangment with net algae, Hydrodicton. When used, herbicide treatment was applied before ponds were filled (Aquazine^TM) or as needed during the culture interval (Aquazine^TM) or copper sulfate). Harvesting was done after 24 to 58 days; the extreme range represented variation among hatcheries; the variation among ponds at a given hatchery ranged from 4 to 10 days. Harvest occurred when fingerlings were 25 to 50 mm total length and weighed 1,500-5,440 fish/kg. Harvests ranged from 11,933 to 308,537 fingerlings/ha. Survival ranged from 3 to 104% of the estimated number of fry stocked.     

Evaluation of Experimental and Practical Diets for Walleye Stizostedion vitreum

Culture of walleye Sfizostedion vitreum is one of the largest components of public sector aquaculture in the eastern U.S. and there is increasing interest in private sector culture. However, the nutritional requirements of walleye are unknown and experimental diets for use in quantifying nutritional requirements have not been identified. We formulated four experimental and four practical diets and fed those to triplicate groups of walleye with an initial weight of 13 g per fish. The experimental diets contained either casein (CAS), casein + gelatin (CG), casein + arginine (CA), or casein + gelatin + crystalline amino acids (CGAA) as sources of amino acids. The practical diets were formulated to mimic salmon grower (SG) and trout grower (TG) diets, a fish meal‐free diet for trout (TFMF), and a walleye grower (WG) diet. Fish were fed twice daily to satiation for 9 wk. Feed consumption, percent weight gain, specific growth rates, feed efficiency, protein efficiency ratio, and protein retention efficiency were not significantly different among fish fed CGAA, SG, and TG, but those values were significantly higher than in fish fed other diets. Weight gain of fish fed CGAA was approximately 80% of that in fish fed SG and 91% of that in fish fed TG. Protein retention efficiency of fish fed CGAA was approximately 69% and 81% of that observed for fish fed SG, and TG, respectively. In general, the carcasses of fish fed diets CGAA, SG and TG had significantly lower moisture and ash concentrations, and higher lipid levels than fish fed other diets. There were no significant differences in carcass protein concentration, muscle proximate composition, or liver lipid concentration among treatments. Livers from fish fed all diets were characterized by microvesicular degeneration and glycogen accumulation in hepatocytes. Results from the study indicate that CGAA can be used as a basal experimental diet in future nutritional research with juvenile walleye and confirms the benefits of trout and salmon grower diets. Fish meal‐free diets formulated around the requirements for rainbow trout were consumed at approximately 80% of the values in fish fed TG and SG, but weight gain was approximately 20% of that in fish fed TG and SG. It appears the nutritional requirements for walleye are different than those of rainbow trout.     

Host response to the chondracanthid copepod Chondracanthus goldsmidi,a gill parasite of the striped trumpeter,Latris lineata (Forster), in Tasmania

The chondracanthid copepod, Chondracanthus goldsmidi is an ectoparasite of gills, inner opercula and nasal cavities of cultured striped trumpeter, Latris lineata (Forster). Whilst often present in high numbers (up to 60 parasites per host), little is known about its effect on striped trumpeter. In this study C. goldsmidi was associated with extensive epithelial hyperplasia and necrosis. Pathological changes were most pronounced near the parasite’s attachment site, with papilloma‐like growths surrounding the entire parasite resulting in deformation of the filament. The number of mucous cells increased near the parasite attachment sites on both the opercula and gills. Mast cells were absent in healthy gills; in contrast numerous mast cells were identified in the papilloma‐like growths. Immunostaining identified piscidin‐positive mast cells in the papilloma‐like growths, presenting the first evidence of piscidin in the family Latridae.     

Water Management to Control Clam Shrimp,Cyzicus morsie in Walleye,Stizostedion vitreum,Production Ponds

Clam shrimp, Cyzicus morsie , can occur in hatchery ponds in such dense numbers that they interfere with production of fish. Hatchery ponds are frequently left dry during the fall and winter and are filed in spring or early summer, simulating the vernal pools where clam shrimp naturally occur. Ponds left dry over winter and ponds that were full over winter, but were drained and dried for a period of time immediately prior to stocking, had the highest numbers of clam shrimp (P = 0.001). Few or no clam shrimp were collected in ponds that were full over winter and were not dried in the spring. High turbidities were observed in ponds with high numbers of clam shrimp; however, clam shrimp were not the only cause of turbidity. The largest number of walleye were produced in ponds which contained few or no clam shrimp. Clam shrimp were controlled by preventing hatchery pond substrate from drying during winter and early spring; however, the absence of drying may cause other problems that interfere with fish production.     

Preservation-induced changes in morphometrics of fishes: influence on prey size-choice in juvenile walleye, Stizostedion vitreum (Mitchill)

Abstract– Juveniles of the Gulf coast population of walleye, Stizostedion vitreum , 22.4–89.9 mm SL ( n =111) shrank significantly in SL and throat diameter over 12 months after being fixed in 10% formalin for 1 week and preserved in 50% isopropyl alcohol thereafter. Significant changes in body depth and total length (TL) were also determined for select larval fish prey that juvenile walleye might encounter in nature. The relationship between fresh SL and throat diameter in juveniles of the Gulf coast population of walleye (22.4–172.4 mm SL) is: throat diameter (mm) =−0.8783 + 0.0786 SL (mm) ( r ²= 0.988, P < 0.0001, n = 135). In laboratory experiments on prey size choice, walleye selected available prey near or less than their mean throat diameter, although several larger prey (7.4% of total) were also consumed. To determine the actual spectrum of prey sizes available to juvenile piscivores, we must adjust the realized size of the predator and prey for changes caused by preservation. Preservation-induced alterations in morphology translated into errors in the perceived pattern of prey size choice in walleye. The preservation-induced changes documented in this study, which are also supported by a number of other empirical data sets, must be included when modeling the relationships between feeding ecology, morphology, growth, and ecologically relevant indices (condition factors, relative weights, etc.).     

Production of Walleye,Stizostedion vitreum,in Earthen Ponds Fertilized with Organic and Inorganic Fertilizers and Stocked at Three Rates

Walleye, Stizostedion vitreum, fry were raised at densities of 20,30 and 40/m³ in ponds initially fertilized with alfalfa and yeast and supplementally fertilized with liquid inorganic fertilizers. Liquid fertilizers were added weekly to maintain N and P concentrations of 600 and 30 ug/L, respectively. Fish growth was not affected by stocking rate, but survival was significantly (P < 0.05) reduced in ponds stocked at the two higher rates. The fertilization procedure we used did not provide a sufficient forage base to support more that 20 walleye/m³.     

Length reduction and dry weight loss in frozen and formalin-preserved larval walleye, Stizostedion vitreum (Mitchill)

Abstract We examined the relationships between fresh and preserved measurements of length and dry weight for larval walleye, Stizostedion vitreum (Mitchill), subjected to freezing and preservation in formalin. Length reductions for both preservation techniques were <5% and decreased with larval size. Dry weight losses ranged from 32·1 to 54·0% for frozen larvae and from 18·2 to 30·1% for larvae preserved in formalin with larger larvae losing proportionately less weight. Freezing caused significantly greater length shrinkage and dry weight loss than preservation in formalin.     

Effects of Fertilization and of Fry Stocking Density on Pond Production of Fingerling Walleye,Stizostedion vitreum

The influence of fertilization and of fry stocking density on production of fingering walleye, Stizostedion vitreum, was evaluated in earthen ponds at North Platte State Fish Hatchery, North Platte, Nebraska. In 1990, five 0.4-ha ponds were fertilized with alfalfa pellets, and five were fertilized with soybean meal; four unfertilized ponds served as controls. All ponds were stocked with D2 (Dl = the day at hatch) walleye fry at 250.000ha. Differences in yield, number of fingerlings harvested, mean length, and mean weight amone treatments were not statistically significant (P> 0.05). In 691, two fertilization schedules (no fertilizer and fertilization with alfalfa pellets) and two fry stocking rates (250.000 and 375,000 fry/ha) were evaluated. Four ponds were used for each treatment. Statistically significant treatment differences were found in yield, number of fingerlings harvested/ha, average length, and average weight. Yield was higher in fertilized ponds compared with yield from unfertilized ponds at both stocking densities, but yield did not differ significantly between stocking density treatments given the same fertilizer treatment. Survival did not differ between density treatments, but total number of fish harvested was significantly greater from ponds stocked at the higher density. Fingerlings with the largest average weight were raised in fertilized ponds that were stocked at 250,00O/ha, while the smallest fingerlings were from unfertilized ponds that were stocked at 375,000ka. Days in culture interval, which varied among ponds by 9 days in 1990 and 10 days in 1991, was significantly correlated with most production variables in 1990 and with all production variables in 1991. Means of water quality variables were not significantly different between fertilized and unfertilized ponds in either year, but significant differences were found in means of three water quality variables between 1990 and 1991. Yield in both fertilized and unfertilized ponds in 1991 was less than in 1990.     

Acceptability of various microparticulate diets to first-feeding walleye Stizostedion vitreum larvae

The acceptability of eight diets made by a wide variety of microparticulate manufacturing processes was studied using first-feeding walleye Stizostedion vitreum larvae. Diets were formulated using a common dietary mix but differed in manufacture technique. The microparticulate diets fed were (1) carrageenan bound, (2) alginate bound, (3) starch/konjack bound, (4) microextruded/maurmurized (MEM), (5) zein bound, (6) carboxymethyl cellulose bound (CMC), (7) particle-assisted rotationally agglomerated (PARA) and (8) a commercial microparticulate diet (Fry Feed Kyowa B-700, FFK). Controls were groups fed live Artemia nauplii and unfed. Gut fullness was measured as the cross-sectional optical area of the bolus visible through the transparent body of the larvae using computer-aided image analysis. Feeding incidence on MEM particles (71 ± 8%, mean ± standard error), zein-bound particles (69 ± 7%), alginate-bound particles (68 ± 2%) and PARA particles (65 ± 6%) were not significantly different ( P   0.05) from the feeding incidence for Artemia (71 ± 6%). FFK (49 ± 14%) and particles bound with carboxymethyl cellulose (27 ± 0.07%), starch (21 ± 10%) or carrageenan (20 ± 0.8%) had significantly ( P  < 0.05) lower feeding incidence. Larvae that did initiate feeding did not differ significantly ( P  > 0.05) in the amount of each microparticulate diet or Artemia consumed. This data indicates that once first-feeding walleye start on a diet, they will consume that diet to a similar fixed level of satiation. Given the differences in the amounts of water and nutrients in the various diets, more nutrients were delivered to the gut of walleye larvae feeding on microparticulate diets than on the Artemia control.     

Changes in yellow perch (Perca flavescens) growth associated with the establishment of a walleye (Stizostedion vitreum) population in Canadarago Lake, New York (USA)

Abstract – Piscivorous fish can affect prey growth in two ways: directly by reducing prey density and indirectly by inducing predator-avoidance behaviors. We investigated these two pathways in yellow perch ( Perca flavescens ) growth responses to walleye ( Stizostedion vitreum ) stocking in Canadarago Lake, New York (USA) using a 25-year time series. Before walleye stocking, yellow perch growth rate was low and independent of body size. As walleye abundance increased, yellow perch growth increased and became size-dependent. The switch to size-dependent growth occurred in 1 year, indicating a rapid behavioral response to predators. Mean growth rate increased more gradually and was linearly related to walleye density, indicating a slower numerical effect of walleye on yellow perch densities. Although the net effect was an increase in perch growth, small perch growth initially decreased as walleye became established. Therefore, the combination of numerical and behavioral effects produced a complex pattern of size-dependent changes in growth of yellow perch.     

Comparison of Organic and Inorganic Fertilizers for the Pond Production of Walleye,Stizostedion vitreum

ABSTRACT

Walleye were stocked at 20 fry/m³ and raised for 45-47 days in earthen ponds that were fertilized with organic or inorganic fertilizers. Organically fertilized ponds received periodic doses of alfalfa meal and torrula yeast. Nitrogen and phosphorus levels of 600 ug/L and 30 ug/L, respectively, were maintained by twice-weekly additions of liquid fertilizers in ponds of the inorganic treatment. Growth, survival, and production offish were not affected by the fertilizer treatment. The use of inorganic fertilizers is recommended for the pond production of walleye because it is easier and less costly than traditional methods involving the use of organic fertilizers.     

Modification of Walleyes Stizostedion vitreum Tolerance to Hydrogen Peroxide Bath Treatment

Abstract— Hydrogen peroxide is being evaluated for its potential as a therapeutic compound for a variety of external disease organisms of fish. The value of hydrogen peroxide as a therapeutic compound for use in walleye Stizustedion vitreum culture has been questioned due to the high sensitivity (i.e., high mortality) of walleyes to this compound. We conducted bioassays and histopathological studies to determine if exposure of walleye to hydrogen peroxide bath treatments would result in increased tolerance to subsequent exposure. Test fish exhibited increased tolerance to hydrogen peroxide after initial exposures. This phenomenon of increased tolerance of walleyes to hydrogen peroxide may be of value in the development of management strategies for the successful treatment of fish diseases.     

Tumours and microbial diseases of marine fishes in Alaskan waters

Abstract. In an effort further to define the current health status of demersal fish in the Bering Sea, 36 618 fish captured by otter trawl during 1976 were examined for pathological conditions. Of the 26 species examined, 22 were found to have no detectable abnormalities. The four species with abnormalities were Pacific cod Gadus macrocephalus Tilesius with pseudobranchial tumours and skin lesions, walleye pollock Theragra chalcogramma (Pallas) with pseudobranchial tumours, yellowfin sole Limanda aspera (Pallas) with lymphocystis, and rock sole Lepidopsetta bilineata (Ayres) with epidermal papillomas. The prevalence, geographical distribution and biological and pathological characteristics of affected individuals were determined.
Pseudobranchial tumours of both Pacific cod and walleye pollock were occasionally found to be invasive. Fish bearing these tumours were distributed throughout the sampling area. The epidermal papillomas on rock sole resembled similar tumours found on several flatfish species along the West Coast of North America. The distribution of this disease appeared to be depth related. The virus-caused lymphocystis growths were located on the 'blind' side of yellowfin sole. The highest frequencies of fish with lymphocystis were in the south-eastern Bering Sea. Two main types of skin lesions were seen on Pacific cod: ulcers and ring-shaped lesions. Isolates of bacteria ( Pseudomonas sp.) were routinely obtained from the cod ulcers and may be the cause of this disease. The ring-shaped skin lesions, when examined microscopically, contained unidentified epidermal basophilic bodies.     

Endocrine and gonadal changes during the annual reproductive cycle of the freshwater teleost,Stizostedion vitreum

The annual reproductive cycle of walleye (Stizostedion vitreum) was characterized by documenting changes in gonadal development and serum levels of estradiol-17β (E₂), testosterone (T), 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P), and 11-ketotestosterone (11-KT) in wild fish captured from upper midwestern lakes and rivers throughout the year. Fish from the populations used in this study spawn annually in early- to mid-April. Walleye showed group synchronous ovarian development with exogenous vitellogenesis beginning in autumn. Oocyte diameters increased rapidly from ∼ 200 μm in October to ∼ 1,000 μm in November, and reached a maximum of 1,500 μm just prior to spawning. Changes in gonadosomatic indices (GSIs) paralleled changes in oocyte diameters. Serum E₂ levels in females increased rapidly from low values in October (< 0.1 ng ml⁻¹) to peak levels of 3.7 ng ml⁻¹ in November, coinciding with the period of the most rapid ovarian growth. Subsequently, E₂ levels decreased from December through spawning. Serum T levels exhibited a bimodal pattern, increasing to 1.6 ng ml⁻¹ in November, and peaking again at 3.3 ng ml⁻¹ just prior to spawning. We detected 11-KT in the serum of some females at concentrations up to 5.6 ng ml⁻¹, but no seasonal pattern was apparent. In this study (unlike our results in a related study) 17,20-P was not detected. In males, differentiation of spermatogonia began in late August, and by January the testes were filled (> 95% of germ cells) with spermatozoa. Mature spermatozoa could be expressed from males from January through April. GSIs ranged from 0.2% (post-spawn) to 3.2% (pre-spawn). Serum T levels rose from undetectable levels in post-spawn males to 1.6 ng ml⁻¹ by November, remained elevated throughout the winter, and peaked at 2.8 ng ml⁻¹ I prior to spawning. Levels of 11-KT in males remained low (< 10 ng ml⁻¹, from post-spawning through January, then increased significantly by March and peaked just prior to spawning at 39.7 ng ml⁻¹. Our results indicate that vitellogenesis and spermatogenesis are complete or nearly so, in walleye by early winter, and suggest that it may be possible to induce spawning in this species several months prior to the normal spawning season by subjecting fish to relatively simple environmental and hormonal treatments.     

The effect of vitamins C and E in (n-3) highly unsaturated fatty acids-enriched Artemia nauplii on growth, survival, and stress resistance of fresh water walleye Stizostedion vitreum larvae

This study aimed to evaluate the effect of enriching Artemia nauplii with vitamin C (ascorbyl-6 palmitate) or vitamin E (α-tocopherol acetate), 20% w/w, together with a mixture of concentrated eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3) on the growth, survival, and stress resistance of fresh water walleye Stizostedion vitreum larvae. Either cod liver oil (CLO) or EPA/DHA ethyl esters concentrate was used as lipid sources in the Artemia enrichment. Walleye larvae were fed ad libitum for 40 days. At day 40, submersion in salt water (25 g L⁻¹) was performed to evaluate larvae resistance to stress. EPA and DHA levels in walleye juveniles fed EPA/DHA-enriched Artemia increased significantly, by an average of 650% compared with fish fed non-enriched Artemia . A significant increase was found for vitamins C (71.8 ± 1.0 and 42.7 ± 1.2 μg g⁻¹ wet weight (WW)) and E (17.0 ± 3.7 and 6.5 ± 0.9 μg g⁻¹WW) concentrations in fish fed enriched and unenriched Artemia , respectively. Growth was comparable throughout treatments, whereas survival was significantly higher in fish fed CLO-enriched Artemia nauplii compared with fish fed Artemia nauplii enriched with EPA/DHA concentrate. The addition of vitamin C increased fish survival by 1.4-fold compared with fish fed Artemia enriched with only EPA/DHA concentrate. The survival of the latter was similar to control fish ( Artemia without enrichment). The supplementation of vitamin E did not affect fish survival significantly. Stress tests revealed that the resistance of walleye larvae to salinity changes increased when Artemia enrichment was supplemented with vitamin C. However, walleye larvae fed CLO-enriched Artemia had the best performances in the stress test.     

Evaluating the relationship between yearling walleye,Sander vitreus,electrofishing catch‐per‐unit‐effort and density in northern Wisconsin lakes

Recruitment declines of walleye, Sander vitreus (Mitchill), observed in some northern Wisconsin lakes have resulted in management actions to evaluate and rehabilitate populations. An effective index for estimating relative abundance of yearling walleye is required. The objectives herein were : (a) to evaluate the relationship between yearling walleye electrofishing CPUE and density in northern Wisconsin lakes; (b) to test for the influence of lake‐specific factors on electrofishing catchability of yearling walleye; and (c) to develop an index whereby electrofishing CPUE can be used to quantify yearling walleye relative abundance. Yearling density was significantly positively related to electrofishing CPUE on a long‐term dataset from Escanaba Lake as well as a dataset including several lakes combined. Electrofishing catchability of yearling walleye was negatively related to lake‐surface area but was not related to other lake‐specific variables. This index can provide an efficient method to continue monitoring natural recruitment and also to evaluate survival of stocked walleye.     

Increasing growth and feed efficiency of Juvenile Walleye,Sander vitreus (Mitchill, 1818), through novel,subsatiation, restrict/feed cycles from late summer into fall

The role of restricted feeding on the growth and feed efficiency (FE) of juvenile walleye, Sander vitreus, was investigated through two experiments. In the summer/fall experiment, 7.44‐g walleye were fed on one of the three schedules for 84 days: control (daily satiation feeding at 6% BW day^?1), D2 (2 days of feed deprivation, then fed at 12% BW day^?1 for 7 days, repeated throughout the study) and SS80 (subsatiation feeding involving 2 weeks of maintenance ration, then fed at 80% of the control group's feeding level). Juvenile walleye growth rates were significantly higher in the SS80 than in the control group, however, their growth rates in the D2 group were no different than in the control. Mean FE of the SS80 group (0.49), significantly exceeded those of the control (0.36) and D2 (0.28) groups. In contrast with the summer/fall experiment, no differences in growth rate were detected among the control, SS80 and D2 groups in the subsequent 84‐d spring experiment, where the juvenile walleye (97.45 g) were substantially larger, and their mean FE values were generally lower, with less distinction observed among the groups. Our findings indicate potential to increase growth and FE of juvenile walleye in advance of fall, by applying restrict‐feed schedules.     

Survival and Growth of Walleye Stizostedion vitreum Fry as Affected by Water Recirculation, Feed Transition Age, and Stocking Density

Abstract.— The effects of recirculation aquaculture on walleye Stizostedion vitreuin fry culture was evaluated from hatch (day 0) to day 65 and compared to traditional flow-through aquaculture used at New York State's Fish Culture Station, Oneida, New York, USA. A comparison of survival rates of walleye fry through a feed transition period was also conducted with the variable being the age (d) at which dry feed was first introduced to fingerlings; this trial was conducted using recirculation aquaculture systems only. Comparisons were made of growth rates and survival rates broken down into two life stages: stage one was from day 0 to day 45 and stage two from day 45 to day 65. All systems were taken off live feed completely on day 45 resulting in a feed transition period between days 45 and 65. Fish in the flow-through system had the highest cumulative growth rates through day 70 (P < 0.05) while fish in the recirculating system grew faster through day 53 (P < 0.10). The recirculating system showed significantly higher survival rates during the feed transition period (day 45–65) than fish in the conventional flow-through system (P < 0.05). This is important because the transition period is the most stressful period in training fingerlings onto dry feed from a live diet. It was found that fish started on a dry diet on day I or day 14 in addition to the live diet had a significantly higher survival rate through the feed transition period than fish started on dry feed on day 30 (P < 0.1). The age at which dry feed was introduced had no significant impact on growth rates. There was a significant positive correlation (P < 0.05) between survival rates and the initial stocking density over a range of densities from 3,500 to 7,000 fish/m³.