A naturally-reproducing brown trout (Salmo trutta) population exists in the reach of Spearfish Creek in the city of Spearfish, South Dakota, USA. This study recorded redd spawning locations and environmental factors in three different sections within this reach in 2025. The first redd was observed on 3 October, and the last redds were observed on 7 November. A total of 46 redds were observed in all three sections over the seven-week study period. Peak spawning activity occurred on 24 and 31 October, with 14 and 16 redds observed, respectively. The northernmost (downstream) section had over twice the number of redds as the two upstream sections. In addition, redds in this section were primarily located in two hot spots.

Recirculating aquaculture system (RAS) technology is increasingly used to produce fish in recreational and conservation fish hatcheries. However, little is known about the post-stocking survival of RAS-reared walleye (Sander vitreus). This study evaluated the survival and growth of RAS-reared walleye stocked in Owen Dam, South Dakota, USA. RAS-reared juvenile walleye were stocked annually from 2023 to 2025. Walleye were collected by both trap nets and electrofishing during every sampling year, except for 2023, when no walleye were caught in trap nets. The total number of walleye captured from both netting and electrofishing was 16 in 2023, 219 in 2024, and 57 in 2025. Catch-per-unit-effort from electrofishing was 48 fish/h in 2023, 3.9 fish/h in 2024, and 44.4 fish/h in 2025. Trap net catch-per-unit effort was 0 in 2023, 35.8 fish/net night in 2024, and 4.0 fish/net night in 2025. Stock-length walleye over 254 mm were obtained from both trap nets and electrofishing during 2024 and 2025. Length-frequency distributions differed among survey years. These results indicate RAS-reared walleye survived and grew following stocking across multiple years in a small reservoir system. These results support the use of RAS as a viable tool for hatchery production of walleye for stocking recreational fishing waters.

Disinfection of fish eggs with iodophor is a common biosecurity procedure. This study evaluated the effects of three concentrations of iodine on walleye (Sander vitreus) egg survival and bacterial loadings. Approximately five hours post fertilization, eggs from ten female walleyes were disinfected in active iodine concentrations of 0, 100, 200, and 400 mg/L for 10 min. There was a significant decrease in survival in the 200 mg/L treatment group compared to the 0 mg/L (control) and 100 mg/L groups. Near-total mortality occurred in the eggs receiving the 400 mg/L disinfection regime. Bacterial Colony Forming Units (CFU) were significantly reduced with any iodine disinfection compared to the control, but there was no significant difference in CFU among any of the iodine treatment concentrations. There was no relationship between egg survival and either pre- or post-disinfection CFU levels. These results indicate that 10 min treatments of active iodine at a concentration of 100 mg/L can be safely used to reduce bacterial loadings on newly spawned walleye eggs, but complete disinfection will not occur. Higher iodine concentrations, which lead to walleye egg mortality, do not further decrease bacterial numbers.

Metal tags secured to the jaw of fish have long been used in fisheries management to collect data on fish behavior and growth. This study was undertaken to evaluate the possible effects of these jaw tags on relatively large rainbow trout Oncorhynchus mykiss growth and physiology. A total of 160 rainbow trout, initial weight 1134 ± 19 g (mean ± SE) and total length 444 ± 2 mm, were used in this study. Half of the fish (n = 80) were tagged, with 20 tagged and 20 untagged fish subsequently co-reared in four compartments for 42 days post-tagging. Length, weight, condition factor, hematocrit, hepatosomatic index (HSI), viscerosomatic index (VSI), and splenosomatic index (SSI) were recorded every seven days. Survival rate was the same in both treatments at 96.3%. Tag retention was 98.8%, with one jaw tag lost in the fourth week during weekly sampling. There were no significant differences in length, weight, hematocrit, HSI, VSI, and SSI between the tagged and untagged groups. Condition factor was significantly different between the groups at the one- and four-week sampling periods. Overall, these results indicate that the effects of jaw tags on adult rainbow trout are relatively benign, at least for the variables measured in this study.

Fish hatchery workers may be exposed to potentially health-threatening radon gas liberated from ground water used during fish rearing. This study surveyed the radon levels in three fish rearing buildings (small tankroom, tankroom, and rearing pavilion) at Cleghorn Springs State Fish Hatchery, Rapid City, South Dakota, USA. Overall radon values ranged from below the detection limit in all three buildings to a high of 2,317.68 Bq/m3 (62.64 pCi/L) in the tankroom. The pavilion had the lowest mean ± SE value of 56.57 ± 40.71 Bq/m3 (1.23 ± 0.11 pCi/L), while the highest mean value of 796.21 ± 54.61 Bq/m3 (23.67 ± 1.34 pCi/L) was in the small tankroom. Maximum radon levels were 1,231.36, 2,317.68, and 365.93 Bq/m3 (33.28, 62.64, and 9.89 pCi/L) in the small tankroom, tankroom, and pavilion, respectively. Radon levels were significantly correlated with the number of tanks receiving water in both the small tankroom and tankroom, but no such correlation was observed in the relatively open-air pavilion. Even though the water at the hatchery was aerated outside, additional aeration from rearing tank spray bars inside the enclosed small tankroom and tankroom resulted in relatively high radon levels.

ObjectiveDensity-related information for landlocked fall Chinook Salmon Oncorhynchus tshawytscha shortly after first feeding is poorly understood. This study was undertaken to determine the effects of a range of rearing densities (low, intermediate, and high) on rearing performance and survival of newly feed-trained juvenile landlocked fall Chinook Salmon.MethodsThe fish were reared for 66 days in 1.8-m (diameter) tanks with approximate volume of 2036 L at one of three loadings of approximately 2500, 5000, or 10,000 fish/tank.ResultThe initial and final densities for each of the three loadings were 0.73 and 8.93, 1.45 and 16.41, and 2.90 and 26.86 kg/m3, respectively. At the end of the study, the specific growth rates were significantly lower, total lengths were significantly shorter, and feed conversion ratios were significantly greater in the fish from the highest-density treatment relative to the fish in the other treatments. Percentage of weight gain, final weights, and condition factor were significantly reduced in fish from the highest-density treatment relative those at the lowest density. There were no significant differences in any growth metrics between fish that were reared at the lowest and intermediate densities. The intermediate density (5000 fish/tank) produced intermediate results that did not significantly differ from either the highest or lowest densities. Mortality was not significantly different among the density treatments.ConclusionAn initial loading of 5000 fish in 1.8-m (diameter) circular tanks, corresponding to initial and final densities of 1.45 and 16.41 kg/m3, respectively, is recommended to minimize the detrimental effects of density on newly feeding Chinook Salmon while maximizing their production in often limited hatchery space. The use of intermediate tank loadings of fall Chinook Salmon in 1.8-m (diameter) circular tanks (corresponding to initial and final densities of 1.45 and 16.41 kg/m3, respectively) minimized the detrimental effects of rearing density on newly feeding salmon while maximizing Chinook Salmon production in limited hatchery space.Impact statement

Many fisheries professionals involved in walleye (Sander vitreus) culture exclude large females from spawning

ObjectiveEggs of Walleye Sander vitreus are typically incubated in upwelling jars. The relatively large number of eggs required for efficient and effective incubation in each jar, along with the difficulties in accurately quantifying egg survival to fry hatch, inhibits the replication needed for the controlled experimentation of Walleye spawning procedures and egg development. In addition, the use of production-sized incubators for experiments can be problematic because of the risks associated with potentially hazardous treatments on large numbers of eggs. This study evaluated the technique of incubating small numbers of Walleye eggs in Petri dishes.MethodsEight treatments were used: (1) 20 eggs/dish with daily water exchanges, (2) 40 eggs/dish with daily water exchanges, (3) 20 eggs/dish with every-other-day water exchanges, (4) 40 eggs/dish with every-other-day water exchanges, (5) 20 eggs/dish with every-third-day water exchanges, (6) 40 eggs/dish with every-third-day water exchanges, (7) 10 eggs/dish with no water exchanges, and (8) 20 eggs/dish with no water exchanges. At the eyed stage of egg development, water in all dishes was exchanged daily; at hatch, water was changed and hatched fry were removed twice daily.ResultMean (SE) survival to hatch was 74% (2) and was not significantly different among any of the treatments.ConclusionThese results indicate that small numbers of Walleye eggs can be successfully incubated in Petri dishes without any water changes before the eyed stage of development, making this a viable technique for use in controlled experiments. Successful incubation of Walleye eggs in Petri dishes is the groundwork for small-scale replication for use in future controlled experimentation on spawning and incubation techniques.Impact statement

This study investigated the effect of a single aqua-acupuncture (aqua-AP) treatment on wound healing after surgical ventral incision in rainbow trout, Oncorhynchus mykiss. Three experiments were conducted using 20 fish per experiment (10 aqua-AP, 10 non-acupuncture): 1) ventral incision closed with two sutures and insertion of an acoustic transmitter, 2) ventral incision closed with two sutures (no transmitter), and 3) unclosed ventral incision. Aqua-acupuncture was performed by injecting a 0.25 mL bleb of vitamin B12 - saline mixture intramuscularly at 4 points around the surgical site. Statistical differences between aqua-AP and non-acupuncture for survival, transmitter retention, wound closure and redness (inflammation) were conducted (p<0.05). Experiment 1 had significantly lower (p=0.007) redness scores with aqua-AP treatment when compared to non-acupuncture. In the second and third experiments, there were no significant differences in wound closure times or redness, and acoustic transmitter retention was not significantly different between treatments. Experiment 3 had granuloma formation (50% both groups) in place of skin edge closure at 6 weeks. By study termination (12 weeks), only 1 aqua-AP fish still had a granuloma compared to 4 fish in non-acupuncture (p<0.04). There were no significant differences in wound closure times (aqua-AP versus non-acupuncture). While the overall results of this study were inconclusive for wound healing time, the decreased redness (Experiment 1) and improved granuloma resolution (Experiment 3) suggest that there may be potential benefit from aqua-AP use in rainbow trout wound healing. Aqua-AP appears safe to use on fish with future research directed at technique refinement.

This study surveyed freshwater mussels (family Unionidae) in 116 lakes and reservoirs east of the Missouri River in South Dakota, USA, during 2017. Using two-person–hour/site timed searches, evidence of a total of 1789 mussels, including 1053 live mussels, was obtained from 50 waters. Nine species, from two different orders, were found in lakes and reservoirs throughout five of the six major river drainages east of the Missouri River. The native species observed included Giant Floater Pyganodon grandis, Fatmucket Lampsilis siliquoidea, Threeridge Amblema plicata, White Heelsplitter Lasmigona complanata, Wabash Pigtoe Fusconaia flava, Deertoe Truncilla truncata, and Pink Heelsplitter Potamilus alatus. Giant Floater was the most widespread and abundant species observed, representing 63.3% of the live mussels sampled. Two non-native species, Zebra Mussel Dreissena polymorpha and Chinese Basket Clam Corbicula fluminea, were also documented from three water bodies in the lower Missouri River drainage. Overall, mussel abundance was negatively correlated with lake water conductivity and positively correlated with turbidity. No significant correlations were observed between species abundance and water temperature, pH, dissolved oxygen, or substrate particle size.

ObjectiveAutomatic feeders are commonly used in aquaculture, but the feed delivery pattern cannot be adjusted to accommodate a variety of rearing unit sizes. For those few feeders that can be adjusted, their use has been limited because of initial costs, availability, and other issues. This paper describes modification to a commercially available fish feeder (Texas Hunter Products 31.75-kg [70-lb] Lake and Pond Directional Fish Feeder) to effectively provide feed to different-sized ponds.MethodsThis feeder has a 14-m fish feed distribution pattern, making it unusable for smaller ponds. To reduce the distance of fish feed projected from the feeder, a resistor (rheostat) was installed in series with the fan motor.ResultThe rheostat reduced the power to the fan motor, thereby decreasing the feed projection distance. In addition, because the rheostat was adjustable, the resistance-and the resulting power to the fan motor-could be easily changed, making it possible for the same feeder to be used in different-sized ponds while using approximately the same amount of power from the battery and solar panels.ConclusionThis modification was inexpensive and relatively easy to perform. The feeders reliably dispensed feed in a number of small ponds during an 8-month evaluation period. Impact statement This paper describes an inexpensive and relatively easy to perform modification to a commercial fish feeder so that it can effectively dispense feed in small rearing ponds.