William F. Krise

Influence of tank design and hydraulic loading on the behavior, growth, and metabolism of rainbow trout (Oncorhynchus mykiss)

Subadult rainbow trout (Oncorhynchus mykiss) stocked at 48 kg/m3 (3 lb/ft3) were subjected to treatments of tank design (rectangular plug flow, circular, and cylindrical cross flow) and water exchange rate (1·5 and 2·5 exchanges/h) to determine their effects on fish behavior, growth, and metabolism. Ambient light levels and current velocities were also measured in each of three tank sectors (upstream, middle, and downstream) to determine their relative contributions to behavioral effects. Tank design significantly affected fish orientation to current, contact time with tank surfaces, and frequency of agonistic encounters, though aggression levels were relatively low overall. Gradients in fish distribution by sector were greatest in plug-flow tanks. Effects were either modified or eliminated by increasing the water exchange rate from 1·5 to 2·5/h. Multiple-regression analysis showed the following hieararchy of independent-variable effects on fish distribution: tank type > exchange rate > aggression level > current velocity > light level. Significant effects of tank design were also observed on fish growth in terms of biomass gain (cross flow > plug flow > circular). These results were matched in metabolic studies, where both oxygen consumption and ammonia excretion were highest in circular and lowest in cross-flow tanks. Reduction (cross-flow compared with circular tanks) in oxygen consumption averaged 13·6%, ammonia excretion 17·5%. These results were also modified by an increase in water exchange rate. Tank-design effects on fish metabolism and growth may be mediated, at least partly, through changes in fish behavior.

Review of the intensive culture of walleye fry

Abstract Efficient intensive culture of larval walleyes (Stizostedion vitreum) may soon be realized due to results of research on larval development, culture environment, preferred food organisms, and feeding techniques. Larval behavior and morphology (developmental state) can be used as indicators for appropriate handling and feeding techniques. Certain environmental conditions such as a rearing unit color that contrasts with food organisms, water temperatures of 18-22°C, uniform lighting, and a stocking density of no more than 35,000 fish/m3 reportedly contribute to increased growth and survival. Successful culture requires that suitable food such as cladocerans, copepods, and brine shrimp be continuously available at a high density (0.1 organism/mL). Cannibalism among walleye larvae has not been prevented but has been reduced through the use of suitable fish and food densities.

Technical Notes: Short-Term Cold Storage of Atlantic Sturgeon Sperm

Abstract Short-term cold storage of fish sperm with oxygen, an established fisheries technique, was successfully used to preserve milt from Atlantic sturgeon (Acipenser oxyrhynchus oxyrhynchus). All milt samples stored for 5 d on ice and replenished daily with oxygen retained at least 80% motility and at least 99% viability. One sample exhibited 40% motility after 17 d. For management personnel involved in restoration of this rare fish, this technique offers an alternative to dependence on the simultaneous capture of ripe males and females from severely depleted stocks. It may also be used during transport prior to fertilization or cryopreservation.

Effects of Rearing Density on Growth and Survival of Lake Trout

Abstract Lake trout (Salvelinus namaycush) were reared at density indices (allowable density in pounds/cubic foot divided by fish length in inches) of 0.25, 0.50, 1.0, and 2.0 in cages suspended in circular tanks. Water flow rates were such that dissolved oxygen remained above 8 ppm within all the cages. Thus treatment effects were attributed to density and not influenced by water quality. Growth and condition were not affected by density, but survival was lower at the higher density than at the three lower densities. We conclude that lake trout may be successfully reared at a density index of at least 1.0 if the water requirements for respiration and waste dilution are met.

Communications: Eye Abnormalities of Lake Trout Exposed to Gas Supersaturation

Abstract Lake trout (Salvelinus namaycush) reared for 1 year at six levels of differential (excess) gas pressure (▵P 4, 17, 33, 43, 58, and 75 mm Hg above equilibrium) were examined for incidences of eye abnormalities including nuclear cataracts, hemorrhages, corneal swelling, cloudiness, rupture, and loss of eyes. Frequencies of nuclear cataracts, eye hemorrhages, cloudy corneas, and bilateral anomalies were not directly related to increasing dissolved gas pressures. However, incidences of corneal swelling and of all abnormalities combined increased with gas supersaturation above ▵P 4.

Increased Walleye Egg Hatch and Larval Survival after Protease Treatment of Eggs

Abstract Various techniques for eliminating the clumping of newly spawned walleye eggs (Stizostedion vitreum) were evaluated by measuring hatch, growth, and survival. Percent hatch was highest (83%) in egg groups water hardened in 0.01% protease solution. Other water-hardening techniques tested were: (1) continuous stirring; (2) 250 mg/L tannic acid solution; and (3) bentonite clay suspension. Low hatching percentages for eggs continuously stirred or treated with bentonite were attributed to fungus. Fungus was minimal on eggs treated with protease or tannic acid. Fish hatched from each egg treatment group were intensively cultured for 21 d in one of four rearing environments: (1) well water; (2) well water receiving 1% sea salt for the initial 3 d; (3) well water receiving a 6-mL daily addition of antifoam emulsion for the initial 9 d; or (4) well water receiving both the 1% sea salt and antifoam treatments. There was slightly higher survival in larval fish hatched from eggs treated with protease or tanni...

Effect of Feeding Rate and Gas Supersaturation on Survival and Growth of Lake Trout

Abstract Fingerling lake trout (Salvelinus namaycush) were reared for 35 d in water with total dissolved gas pressures of 46, 78, 108, or 159 mm Hg above ambient conditions (▵P). Within each gas pressure treatment, daily feeding rations were (1) 1.7% of the total weight offish in the heaviest of three replicates, (2) 1.7% of the weight of fish in each individual tank, or (3) 0.9% of the weight in each tank (underfeeding). Signs of gas bubble trauma were first observed as hemorrhagic spots on the eyes of some fish reared at ▵P = 46, and external evidence of trauma increased as ▵P increased. All fish sampled at ▵P = 159 showed signs of gas bubble disease; the most common were eye hemorrhage and bubble formation inside the mouth. Mortality was 11% or less among fish reared at gas levels up to ▵P = 108. Mortality was as high as 55% at ▵P = 159, but did not differ among feeding treatments. Net weight gain by fish was low at ▵P = 159 because of both high mortality and slow growth. Growth was slowest for underfe...

Effects of One-Year Exposures to Gas Supersaturation on Lake Trout

Abstract Lake trout (Salvelinus namaycush) were reared for 1 year in water with one of six levels of incoming differential gas pressure (▵P): 4, 17, 33, 43, 58, or 75 mm Hg. Growth and survival of fish were evaluated as measures of response to the potential long-term stress of elevated dissolved gases in rearing water. Mortality rates were not different among fish held in supersaturated water up to ▵P 58 (108% of total gas saturation), but mortality at ▵P 75 (110% saturation) was significantly higher after day 28. From days 21 to 35, the number of nonfeeding, moribund fish increased with increasing gas level. By day 56, the length and weight of fish were significantly greater at ▵P 4 than at higher gas levels. Growth rate reductions were evident for lake trout in ▵P 17 and above for more than 252 d. Feed conversion efficiency was significantly better in fish held at ▵Ps 4 and 17 than at higher pressures. Lake trout grew fastest and most efficiently at ▵P 4 for 252 d, but ▵P 58 was also a safe rearing leve...

Effect of temperature on production of tiger muskellunge in intensive culture

Abstract Tiger muskellunge ( Esox masquinony × E. lucius ) juveniles were reared at constant temperatures in the temperature range 14–28°C. For fish 3–4 cm long, growth, production and feed conversion efficiency were greatest at 20–22°C. Survival was reduced and unaccountable mortality (cannibalism index) was greatest at 24°C. Growth per unit of temperature was about equal over the range 16–22°C. For fish 12–13 cm long, feed conversion efficiency and mean individual growth were greatest at 23°C; growth per unit of temperature was nearly equal over the range 20–24°C.

Tolerance of juvenile lake trout exposed to gas supersaturation

Abstract Lake trout (Salvelinus namaycush) 2.9–3.9 cm long that were exposed to five gas supersaturation levels ranging from ▵P 9 to ▵P 159 mm Hg above saturation for 30 d grew at the same rates. Survival was also virtually equal in all treatments, ranging from 93% at ▵P 42 to 99% at ▵P 126. After 30 d, signs of gas bubble disease were evident at ▵P 126; 3% of fish had exopthalmia and 12% had bubbles in the nares. At ▵P 159, 20% had bubbles inside the mouth or on the conjunctiva, or rim of the orbit, plus 3% had exopthalmia. There were no signs of gas bubbles on fish at ▵P 75 or less.