Dan J. Durben

Partial Overhead Tank Cover Use during Feral Brown Trout Rearing

Abstract Overhead cover is an essential component of the habitat of wild brown trout Salmo trutta but is typically lacking during hatchery rearing. To evaluate the effect of cover during hatchery rearing, we grew feral brown trout in circular tanks that were either completely open on top or partially (29%) covered. After 51 d of rearing in 2001, the total biomass of fish per tank was significantly greater in the partially covered tanks than in the completely open tanks. Feed conversion was also significantly reduced by the use of partial tank covers (1.13 versus 1.29 in the open tanks). After 45 d of rearing in 2003, the mean total weight gain of fish per tank was 13.8 kg in tanks with partial covers and 12.9 kg in uncovered tanks, and feed conversion was 0.79 for partially covered tanks and 0.85 for uncovered tanks. In addition, fish reared in tanks with partial covers were significantly longer and heavier (56.3 mm, 1.62 g) than fish reared in open tanks (54.1 mm, 1.42 g), although there was no significa...

A Survey of Bacteria in the Ovarian Fluid of Landlocked Fall Chinook Salmon and their Relationship with Egg Survival

Abstract A survey of the bacteria in the ovarian fluid of landlocked fall Chinook salmon Oncorhynchus tshawytscha from Lake Oahe, South Dakota, was conducted to investigate possible effects on egg mortality. Bacteria were isolated from the ovarian fluid of 15 out of 19 spawning females. A number of bacteria, including known and potentially pathogenic species, were identified: Acinetobacter spp., Aeromonas hydrophila, Aeromonas veronii, Arthrobacter spp., Pseudomonas spp. (including P. putida), Moraxella spp., and Microbacterium spp. With the exception of Aeromonas hydrophila, none of these bacteria had previously been isolated from Chinook salmon ovarian fluid. There was no observable association between the aeromonads or pseudomonads and egg survival. However, there was a weak but significant positive correlation between bacterial density (colony-forming units/mL of ovarian fluid) and egg survival; the significance of this correlation is uncertain.

Poststocking Harvest of Catchable-Sized Rainbow Trout Enhanced by Dietary Supplementation with a Fully Fermented Commercial Yeast Culture during Hatchery Rearing

Abstract Catchable-sized salmonids are often stocked without regard to their hatchery rearing history, including the diets used. To evaluate the possible effects of a proprietary, fully fermented yeast Saccharomyces cerevisiae dietary supplement (DVAqua; Diamond V Mills, Cedar Rapids, Iowa) on poststocking harvest, Shasta-strain rainbow trout Oncorhynchus mykiss (280 mm) were fed either a hatchery diet containing 0.125% yeast product or a control diet prior to four stockings over the course of 3 months in two small put-and-take fishing lakes (Upper Mirror and Lower Mirror lakes, South Dakota). An angler census indicated that for each lake on each of four stocking dates, rainbow trout receiving yeast supplementation were harvested at higher rates than fish fed the control diet; each lake had one stocking for which the percent harvest of fish fed the yeast-supplemented diet was more than 30% higher than that of control fish. Overall, returns to the creel in Upper Mirror and Lower Mirror lakes were 17% and 1...

Changes in Water Hardness Influence Colonization of Saprolegnia diclina

Abstract Experiments were conducted to determine the effects of different water hardness concentrations on colonization of Saprolegnia diclina in an attempt to explain some of the differences in fungal growth and antifungal chemical effectiveness observed at various fish hatcheries. Fungal growth on nonviable seeds of hemp Cannabis sativa was observed significantly sooner in water where hardness was elevated due to the addition of calcium sulfate dihydrate in each of the experiments. Seeds in test tubes containing water with a hardness of 300 mg/L exhibited fungal colonization in approximately one-half the amount of time observed with seeds in water with hardness less than 150 mg/L. In petri dishes containing inoculated corn meal plugs, the growth of S. diclina was observed at only 24 h on seeds in water with a hardness of 450 mg/L, which was significantly quicker than the 31 h from seeds in water hardness of 150 and 300 mg/L. This, in turn, was significantly quicker than the 35 h required for growth in t...

Effects of Partial Tank Covers on the Growth of Juvenile Feral Rainbow Trout during Hatchery Rearing

Abstract Partial tank covers were evaluated for their effects on the growth of juvenile feral McConaughy strain rainbow trout Oncorhynchus mykiss during hatchery rearing. Trout were reared in 1999 and 2000 in circular tanks that were either completely open on top or partially (29%) covered. Trout reared in tanks with partial covers were 93 mm long at the end of 55 d of rearing in 1999, which was significantly longer than the 88-mm mean length of trout reared in uncovered tanks. Total lengths were also significantly different after 34 d of rearing in 2000: 81 mm for fish from partially covered tanks and 78 mm for fish from open tanks. The total weight gains of fish per tank were significantly greater (23.9 versus 22.7 kg) and feed conversions were significantly better (0.83 versus 0.87) in partially covered tanks in 1999. In 2000, the total weight gain of fish per tank was 15.4 kg in tanks with partial covers and 13.5 kg in uncovered tanks, and the respective feed conversions were 0.90 and 1.05. However, n...

Petri Dish Incubation of Eyed Eggs from Rainbow Trout and Splake

Abstract Four experiments were conducted from 2004 to 2006 to evaluate different protocols for incubating eyed eggs of salmonids in petri dishes. In the first two experiments, which used eyed eggs from Erwin strain rainbow trout Oncorhynchus mykiss or splake (lake trout Salvelinus namaycush ×brook trout S. fontinalis), dishes were loaded at either 10 or 20 eggs/dish and incubated at 10°C. Water changes occurred every 3 or 7 d until complete hatch; for each species, one group of dishes received no water change. Survival to hatch was not affected by the number of eggs per dish or the frequency of water changes in either species. However, in experiments 1 and 2, hatch was significantly earlier in the dishes containing 20 eggs than in dishes containing 10 eggs. In the last two experiments, 15 eyed eggs from Shasta or McConaughy strain rainbow trout were incubated at either 10°C or 12°C; the water was changed every 3 d or not at all. Shasta strain eggs exhibited no significant difference in survival or time to...

Lack of Correlation between Chinook Salmon Spawn Survival and the Number of Overripe Eggs as Determined by Digital Imagery

Abstract The number of overripe eggs in spawn of landlocked fall Chinook salmon Oncorhynchus tshawytscha was determined quantitatively from digital images recorded prior to fertilization. The percentage of overripe eggs recorded from the digital images was not significantly correlated with survival at egg eye-up, fry hatch, or swim-up but was significantly correlated with the visually estimated number of overripe eggs (r 2 = 0.914, P < 0.001). There was also no significant difference between the percentages of overripe eggs determined by the two methods. Neither the digital image nor visual-estimation techniques for assessing overripe eggs are reliable predictors of egg survival, but the digital imagery validated the use of visual estimates.

Critical factors for success in an introductory astronomy class

A number of researchers suggest that a students learning preference curve can be an effective predictor of student success in a particular course. Others suggest that cognitive development, as measured by a students development of learning and study strategies, may be more relevant. Still others suggest that preconceived notions of science and astronomy may be more useful yet. In this paper we explore the critical factors in each of these areas as they relate to student success in an introductory astronomy class. In this study, 65 students were given the visual, aural, read/write, and kinesthetic learning style inventory (VARK), the learning and studies strategies inventory (LASSI), and the astronomy diagnostic test (ADT). Results of these inventories along with gender, age, and previous academic performance were correlated with overall classroom performance. A step-wise regression analysis was then performed to determine the most critical factors that affect student performance in this area.

An Evaluation of Two Egg Collection and Two Fertilization Techniques during Landlocked Fall Chinook Salmon Spawning

Abstract In an attempt to improve embryo survival of landlocked fall Chinook salmon Oncorhynchus tshawytscha, we compared two egg collection techniques and two different egg fertilization (sperm activation) protocols on egg survival to the eyed stage of development. A total of four treatments were used with 13 females: egg collection into a suspended net and fertilization either with or without ovarian fluid and egg collection into a hard plastic pan and subsequent fertilization either with or without ovarian fluid. There was no significant difference in survival to the eyed stage with respect to collection technique. However, the presence of ovarian fluid during sperm activation and fertilization had a small but significantly negative effect on egg survival, decreasing mean eyed egg survival by approximately 4.0%. Overall, eyed egg survival was improved in 10 of the 13 spawns fertilized without ovarian fluid. To maximize embryo survival, removal of ovarian fluid prior to fertilization is recommended for ...

Concentration of Stocked Rainbow Trout Catch and Harvest by a Small Number of Recreational Anglers

While studies on recreational angler usage have provided valuable information to fisheries managers, questions still remain regarding the timing and partitioning of angler catch and harvest. This study used vehicle license plate data to define the patterns of post-stocking catch and harvest by unique angling parties on two small lakes managed by put-and-take rainbow trout Oncorhynchus mykiss stockings during three summer months as part of a creel census when every angling party was interviewed and every fish harvested recorded. A total of 1,077 trout were harvested, with 2.4% of the angling parties (25 vehicles) accounting for over 45% of the total harvest. The same 25 vehicles accounted for 32.1% of the overall catch. Over 85% of harvest in both lakes occurred within the first three weeks following stocking, with appreciable drops in harvest by the fourth week. The potentially-high impact of relatively few anglers on overall harvest numbers and the relatively short timeframe in which harvest occurs following stockings have implications for fisheries managers attempting to maximize angler satisfaction in small put-and-take fisheries.