An initial investigation replacing fish meal with a commercial fermented soybean meal product in the diets of juvenile rainbow trout

The inclusion of PepSoyGen (PSG), a commercially-available fermented soybean meal product, was evaluated with juvenile rainbow trout, Oncorhynchus mykiss in an initial 70-day feeding trial, with a supplemental trial involving a subset of the experimental diets continuing for an additional 40 d. Six diets containing 0%, 10%, 20%, 30%, 40%, or 50% PSG, with the PSG directly replacing fish meal, were used in the first trial. There were no significant differences in weight gain or feed conversion ratio between the fish meal-based control diet and diets containing up to 30% PSG. However, weight gain was significantly reduced and feed conversion ratio significantly increased with the 40% and 50% PSG diets. No health assessment differences were observed in fish receiving any of the diets, and no evidence of gross gut inflammation was evident. There were no significant differences in weight gain or feed conversion ratio among the four dietary treatments ranging from 0% to 30% PSG which were fed for an additional 40 d after the initial 70-d trial (110 days total). Based on these results, juvenile rainbow trout diets can contain up to 30% PSG without any loss of rearing performance, thereby replacing at least 60% of the fish meal.

Vertically-Suspended Environmental Enrichment Alters the Velocity Profiles of Circular Fish Rearing Tanks

The inclusion of vertically-suspended environmental enrichment in circular tanks has produced substantial benefits during fish rearing. This study examined the tank water velocity profiles of four different vertically-suspended structures?(rod array, extended rod array, single angle array, double angle array) and a control (no environmental enrichment) at two incoming water velocities (18.3 cm/s and 54.9 cm/s) in 1.8-m diameter circular tanks. At both of the incoming water velocities, overall water velocities throughout the tank were significantly reduced with the addition of any environmental enrichment in comparison to the control. In addition, the overall water velocities in the double angle array were significantly lower than the other three enrichment treatments. The pattern of significant reductions in velocity with the use of any environmental enrichment, with further significant velocity reductions in the double angle treatment, was repeated when the data were?combined for each sampling depth, radius from the center, and degree (circular arc). Although considerable variation in water velocity was observed at each specific sampling location with both incoming velocities, significantly lower velocities?were observed at nearly every sampling location with the addition of any environmental enrichment to the circular tank. In addition, the double angle array consistently produced the lowest velocities among the environmental enrichment treatments. The changes in velocity profiles from vertically-suspended?environmental enrichment may be at least partially-responsible for the frequently-observed improvements in fish growth.

Impact of Vertically-Suspended Environmental Enrichment and Two Densities of Fish on Circular Tank Velocity Profiles

Vertically-suspended environmental enrichment has been shown to produce improvements in fish growth during hatchery rearing in circular tanks. This study documented the effects of a novel suspended structure on the velocity profile of a 3.63-m diameter circular tank containing juvenile landlocked fall Chinook salmon (Oncorhynchus tshawytscha) at two different densities (9.0 and 34.3 kg/m3). The addition of vertically-suspended structure to the tank significantly decreased velocities at nearly every sampling point, with velocities typically dropping from 15 cm/s without structure to less than 6 cm/s when structure was present. Fish density also significantly impacted in-tank velocities, with an inverse relationship observed between the density of fish and water velocity. Significant interactions were present among the presence or absence of structure and fish density. When structure and fish were absent, the velocity at the edge of the tank was 15.63 cm/s, which was significantly higher than the 4.75 cm/s velocity when both structure and the lower fish density were added, which was in turn significantly higher than the 2.29 cm/s velocity observed with structure and higher fish density. Despite the potentially unique features of this study, vertically-suspended environmental enrichment and the presence of fish clearly alter circular tank water velocities, which may at least partially explain the improvements in fish rearing performance observed with the use of suspended structure.

Occupational Noise Levels in Two Fish Rearing Buildings at an Aquaculture Facility

Occupational noise is commonly encountered during aquaculture. This study documented noise levels in two buildings at a production fish hatchery, a tank room with 32, 1.8-m diameter tanks, and a rearing pavilion with 32, 6.1-m diameter tanks. With water flowing to all of the tanks in the tank room, mean noise levels were 68.4 dB, and significantly increased to 73.0 dB during tank cleaning and 73.2 dB when intermittent automatic feeders were running. The highest tank room values of 77.1 dB were recorded directly next to individual tanks during cleaning. With water flowing to all of the tanks in the rearing pavilion, mean noise levels were 70.2 dB. A significant increase to 76.1 dB was observed when the pavilion tanks were being power washed, with the highest value of 83.2 dB recorded immediately adjacent to the power washer. Although none of the noise levels exceeded regulatory limits, the use of techniques to reduce occupational noise in aquaculture environments is recommended.

Vertically-Suspended Environmental Enrichment Improves Growth of Landlocked Fall Chinook Salmon during Initial Hatchery Rearing

Environmental enrichment has been shown to improve juvenile salmonid growth during hatchery rearing. This study examined the effects of vertically-suspended environmental enrichment starting seven days after feed training and continuing for the next 32 days of landlocked fall Chinook salmon (Oncorhynchus tshawytscha) rearing. At the end of this experiment, final tank weights, gain, percent gain, and feed conversion ratio were all significantly improved in the tanks of salmon with environmental enrichment compared to barren tanks, with a nearly 25% improvement in feed conversion ratio. Individual salmon in tanks with environmental enrichment were significantly longer and weighed significantly more than salmon from tanks without enrichment. Specific growth rate was also significantly improved with the use of enrichment. The use of vertically-suspended environmental enrichment to improve growth and rearing efficiency is recommended during the initial rearing of landlocked fall Chinook salmon.

Fish Ladder Weir Modifications to Minimize Escapement

A fish ladder, weir, and raceway at Whitlock Spawning Station are used to capture and retain feral fall Chinook salmon (Oncorhynchus tshawytscha) for spawning from Lake Oahe, South Dakota. Nearly 40% of the salmon ascending the fish ladder have been documented to escape from the holding raceway by descending the ladder. This manuscript describes modifications to the weir that eliminated nearly all escapements, except for an inconsequential number of small non-spawning fish. The modified design using the existing structure incorporated free-swinging, spaced steel bars with a back-stop to create a one-way gate. The modified gate does not require springs, hydraulics, or electrical power. It is relatively simple to construct and requires minimal maintenance.

Brown Trout Redd Locations in the Northernmost Section of Spearfish Creek in Spearfish, South Dakota, USA

Salmonid fish are known to reproduce throughout the Black Hills in South Dakota, however, it is not known when or where they are spawning or how successful their spawning is. This study documented for the first-time brown trout (Salmo trutta) redd locations and redd construction timing in a 1.6 km reach of Spearfish Creek, within the northern most part of the city of Spearfish, South Dakota, USA in 2020. Redds were first observed on October 13, 2020, with observations continuing until November 17 when no new redds were spotted. Redd construction peaked during the first week of November, with 52 observed. A total of 146 redds was recorded over the course of the study, resulting in a density of 91 redds/km. This is the first study to document redds in this section of Spearfish Creek. These observations will allow for comparisons to future spawning activity which may be impacted by the increased urbanization likely along this section of the creek. Hopefully, This study can also guide future research and habitat projects throughout this section of Spearfish Creek, and potentially throughout this region.

Nitrogen Gas Saturation in Karst Springs Varies Throughout the Day

This experiment examined the fluctuations in nitrogen gas supersaturation throughout the day in three karst springs (upper, side, and lower) at McNenny State Fish Hatchery, rural Spearfish, Lawrence County, South Dakota, USA. Total gas pressures, oxygen percent saturation, and nitrogen percent saturation were recorded six times/day on eight days over a 26-day period in each of the three springs. Total gas pressure did not vary significantly throughout the day in any of the springs. However, percent oxygen and nitrogen saturation were significantly different throughout the day in all three springs. The highest mean (SE) nitrogen supersaturation value of 118.5 (1.1)% was observed in the lower spring at 07:00. The lowest mean nitrogen supersaturation values were 114.5 (1.1)% at 13:00 in the upper spring, and 114.2 (0.2)% and 113.1 (0.7)% at 15:00 in the side and lower spring, respectively. At 118% nitrogen supersaturation, gas bubble disease is likely to occur in fish, resulting in potentially high levels of mortality if untreated spring water was used for fish production. The results of this study indicate the importance of recording nitrogen gas levels at sunrise or early in the morning, when nitrogen is highest and oxygen is lowest, to obtain accurate and reproducible data.

Short-Term Stress Response of Juvenile Rainbow Trout Subjected to Two Different Rearing Densities

Juvenile rainbow trout Oncorhynchus mykiss were subjected to one of four treatments in a two-by-two experimental design: 1) fed at a density of 1.8 g/m3, 2) Fasted at 1.8 g/m3, 3) fed at 30.1 g/m3, and 4) fasted at 30.1 g/m3. Blood glucose and hematocrit were measured at 4, 6, 48, 168, and 336 hours after placement in one of the two rearing densities, with relative fin lengths and organosomatic indices recorded at 336 hours. Glucose levels over time were not significantly different among the density and feeding treatments. Hematocrit levels over time were also not significantly different. Total lengths, weight, hepatosomatic index, viscerosomatic index, and any of the relative fin lengths were not significantly different between the high and low densities. However, the hepatosomatic index was significantly greater in the fed fish compared to those fasted. The splenosomatic index was significantly greater in the higher density treatment. These results likely indicate no short-term stress response to the higher rearing density used in this short-term experiment and no interaction between starvation and density-related stressors.

Rearing Velocity Impacts on Landlocked Fall Chinook Salmon (<i>Oncorhynchus tshawytscha</i>) Growth, Condition, and Survival

Juvenile landlocked Chinook salmon (Oncorhynchus tshawytscha) (mean ± SD initial weight 2.6 ± 0.7 g, fork length 6.3 ± 0.5) were reared in three different water velocities [0.5, 1.5 and 3.0 body length/s (BL/s)] for four weeks to determine possible effects of water velocity on growth, condition, and survival. Fish were sampled for weight, fork length, condition factor, hepatosomatic index (HSI), viscerosomatic index (VSI), and fin erosion after four weeks of feeding to satiation. At the end of the feeding trial, the fish were handled and transported to simulate stocking, with survival observed over the following 10 d. Following four weeks of feeding, fish reared in 0.5 and 1.5 BL/s had the same growth and food conversion ratio, but fish reared at 3.0 BL/s had a significant reduction in both metrics. Furthermore, fish reared at 1.5 BL/s had a significantly higher condition factor than fish reared in other treatments. No significant differences were found for HSI, VSI, fin erosion, or survival. The results from this study indicate that a moderate velocity (1.5 BL/s), which is necessary for circular tanks to be self-cleaning, is not detrimental to fish growth or condition, but a faster water velocity (3.0 BL/s) negatively affects fish growth and food utilization.

Rearing Performance of Atlantic Salmon Grown in Circular Tanks with Vertically-Suspended Environmental Enrichment

Environmental enrichment is the incorporation of materials into hatchery tanks to simulate a more natural rearing environment. This study investigated the use of a vertically-suspended plastic conduit array as enrichment in 3.63 m circular tanks during Atlantic salmon (Salmo salar) rearing. After 168 days, feed conversion ratio was significantly improved for salmon reared in tanks with enrichment compared to the barren control tanks. Final tank weights and weight gain were not significantly different, although the difference in mean gain of 182.0 kg in the enriched tanks compared to 162.9 kg in the control tanks approached significance. There were no significant differences in individual fish length, weight, or condition factor between the treatments, likely because of large variances in body size due to sexual dimorphism and small sample sizes. The suspended array did not interfere with the hydraulic self-cleaning of the circular tanks. The results of this study support the use of vertically-suspended structures to improve the hatchery rearing performance of Atlantic salmon in circular tanks.

Influence of Water Velocity and Vertically-Suspended Structures on Rainbow Trout Rearing Performance

This study evaluated the effects of two water velocities and three types of vertically-suspended environmental enrichment during the rearing of juvenile rainbow trout (Oncorhynchus mykiss;mean ± SE, initial weight 4 ± 1 g and total length 71 ± 2 mm) in 1.8m diameter circular tanks. The 2 × 3 experimental design used two velocities (12.2 cm·s-1 and 30.5 cm·s-1) and three structural treatments (aluminum rod array, plastic spheres, or no structure). After 116 days, the fish reared without any structure (control) at 30.5 cm·s-1 had significantly lower total tank weight, gain, percent gain, feed conversion ratio, and specific growth rate compared to the other treatments. Similarly, the fish reared with a velocity of 30.5 cm·s-1 without structure were significantly shorter and lighter than those in the other treatments. There was no significant difference in condition factor and relative fin lengths among the treatments. These results indicate that vertically-suspended environmental enrichment may be impacting fish rearing performance by altering tank water velocities.

Rearing Performance of Juvenile Brown Trout (<i>Salmo trutta</i>) Subjected to Exercise and Dietary Bioprocessed Soybean Meal

This 121-day experiment evaluated the rearing performance of brown trout Salmo trutta fed one of two isonitrogenous and isocaloric diets and reared at velocities of either 2.8 or 16.1 cm/s. Fishmeal was the primary protein source for the reference diet, and bioprocessed soybean meal replaced approximately 67% of the fishmeal in the experimental diet. At the end of the experiment, there were no significant differences in gain, percent gain, feed conversion rates, or specific growth rates between the dietary treatments. There were also no significant differences in intestinal morphology, splenosomatic, hepatosomatic, and viscerosomatic indices related to diet composition. However, gain, percent gain, feed fed, and specific growth rate were all significantly greater in brown trout reared at the higher velocity. No significant differences in any of the other variables measured were observed between the velocity treatments. There were no significant interactions between diet and velocity in any of the variables. Based on the results of this study, bioprocessed soybean meal can replace at least 67% of the fishmeal in brown trout diets, regardless of the rearing velocities used in this study. However, higher rearing velocities are recommended to maximize juvenile brown trout growth rates.

Trout Redd Locations in Two Streams in the Black Hills, South Dakota, USA

This study examined the spatial and temporal characteristics of brook trout Salvelinus fontinalis and brown trout Salmo trutta redds in two sites from two creeks in the Black Hills of South Dakota, USA. Spawning began in both streams in early October and continued through mid-November. Significant spatial clustering was only observed on both Rapid Creek sites, where-as random redd development was observed in both of the sites on Box Elder Creek. Based on visual observations, brown trout redds were more abundant in Rapid Creek, where-as brook trout redds were more abundant in Box Elder Creek. Differences in redd clustering could be due to species-specific, geological, or hydrological differences between the

Assessment of a Novel Surgical Technique for Acoustic Transmitter Insertion

This study compared three surgical techniques to implant acoustic transmitters in rainbow trout (Oncorhynchus mykiss): 1) acoustic transmitter insertion via a ventral incision closed with two sutures, 2) insertion via a ventral incision with no sutures, 3) insertion via a lateral incision with no sutures. A control group consisting of fish that were only anesthetized and handled was also included. Tag retention, wound healing, inflammation, growth, and survival were recorded over a 12-week period. Tag retention was significantly different among the treatments, at 100% in the unsutured ventral incision group, 89% in the lateral incision group, and 63% in the sutured ventral incision group. Surgical wounds in the unsutured treatment groups showed significantly less inflammation than the sutured treatment. Wound closure occurred significantly faster in the ventral incision groups compared to the lateral incision group. The results of this study show the utility of using unsutured surgical methods for implanting acoustic transmitters in rainbow trout.

Novel Surgical Technique for Acoustic Transmitter Insertion in Rainbow Trout Reduces the Need for Surgical Training

The implantation of acoustic transmitters into the peritoneal cavity of fish is typically performed by experienced surgeons. This study compared the effectiveness of an experienced and inexperienced surgeon performing two different types of transmitter insertion techniques on rainbow trout (Oncorhynchus mykiss). The methods used were either a traditional sutured ventral incision or a novel unsutured lateral incision. There was no significant difference in surgical duration, tag retention, or fish survival between the experienced and naïve surgeon. The time to complete surgical wound closure was not significantly different between the fish operated on by an experienced or naïve surgeon, and surgeon experience had no significant effect on the duration of inflammation. However, there were significant differences between the two surgical techniques, regardless of surgeon experience. The ventral incision with sutures method took approximately three times longer to complete than the lateral incision-only method. However, complete wound closure was significantly faster in the sutured ventral incision treatment compared to the unsutured lateral treatment. Post-surgery inflammation was over seven times longer in the fish with sutures compared to those only receiving a lateral incision. Tag retention was not significantly different between the two surgical methods. The results of this study indicate that the unsutured lateral surgical technique used in this experiment can be completed with minimal training and surgical experience in contrast to the standard technique requiring sutures. These results also provide additional support to the use of sutureless surgical techniques for acoustic transmitter implantation.

Juvenile rainbow trout responses to diets containing distillers dried grain with solubles, phytase, and amino acid supplements

Distillers dried grain with solubles (DDGS) was evaluated in juvenile Shasta-strain rainbow trout Oncorhynchus mykiss diets during a 36-day feeding trial. Two experimental diets containing either 10% or 20% DDGS with supplemented amino acids (lysine, methionine, isoleucine, and his-tidine) and phytase were compared to a fish meal-only control diet. Tanks of trout receiving diets containing either concentration of DDGS weighed significantly less at the end of the trial and had significantly poorer feed conversion ratios than tanks of fish being fed the fish meal- only control. There was no significant difference in individual fish length, weight, condition factor, or any fish health measurements among diet treatments. Both the hepatosomatic index and viscerosomatic index were significantly less in the fish fed 10% DDGS than those fed the control diet. Body fat was significantly greater in the fish receiving 20% DDGS compared to fish fed either of the other two diets. Fillet composition, as determined by crude protein, crude lipid, ash, and water, was not significantly different among fish reared on any of the diets. There was also no significant difference in estimated protein digestibility coefficients among fish receiving any of the diets. The results suggest that DDGS, even if supplemented with essential amino acids and phytase, will lead to decreased juvenile rainbow trout growth at dietary concentrations of at 10% or greater.

Long-Term Passive Integrated Transponders (PIT) Tag Retention in Juvenile Rainbow Trout and Brown Trout

Two hundred and forty-three juvenile rainbow trout Oncorhynchus mykiss ranging from 73 to 119 mm were implanted with 8, 9, or 10 mm Passive Integrated Transponder (PIT) tags, with tag retention and fish survival observed for 343 days. Similarly, 173 brown trout Salmo trutta ranging from 71 to 86 mm were implanted with 8 or 10 mm PIT tags and observed for 293 days. Over the entire duration of the study, rainbow trout ejected only six tags, while no tags were ejected from the brown trout. All of the rainbow trout tag ejections occurred before 50 days post-tagging. There was no significant difference in the length or weight of fish that ejected tags compared to those that retained tags. No fish died during the trials. These results indicate that rainbow trout and brown trout at the sizes used in this study can be safely implanted with, and subsequently retain, up to 10 mm PIT tags for durations of nearly one year.

Color of Vertically-Suspended Structure Does Not Impact the Growth of Rainbow Trout Reared in Circular Tanks

This study examined the effects of five different colors of vertically-suspended environmental enrichment on the growth of juvenile Shasta strain rainbow trout (Oncorhynchus mykiss) during hatchery rearing in circular tanks. The colors used were silver (unpainted aluminum—control), safety red, semi-gloss black, hunter green, and safety blue. After 86 days, total tank weight, weight gain, and feed conversion ration were not significantly different among any of the color treatments. Individual fish weights, lengths, and condition factors were also not significantly different among the treatments. The results of this study indicate that the relatively small amount of color present on the suspended structure did not affect rainbow trout growth. Thus, the inherent silver color of the aluminum angles does not need to be changed.

Exercise and Structure Improve Juvenile Chinook Salmon Rearing Performance

This experiment evaluated the use of an exercise routine and vertically-sus-pended structure during juvenile landlocked fall Chinook salmon (Oncorhynchus tshawytscha; mean ± SE, initial weight 1.47 ± 0.03 g, total length 56.4 ± 0.4 mm) rearing. Four treatments were used: 1) no exercise routine nor vertically-suspended structure, 2) exercise and structure, 3) exercise and no structure, and 4) no exercise and structure. Water velocities in tanks without exercise were 12 cm/s, where-as the exercise routine consisted of seven days at 12 cm/s followed by seven days at 18 cm/s. The structure was an array consisting of four vertically-suspended aluminum angles. Total tank gain and percent gain were significantly greater after 50 days in the tanks of salmon subjected to the exercise routine and structure compared to the three other treatments. Gain and percent gain were also significantly greater in the tanks receiving structure without exercise compared to tanks with exercise and no structure or tanks with neither exercise nor structure. Feed conversion ratio was significantly improved in the salmon tanks with structure and without exercise compared to all other treatments. There were no significant differences for individual fish weight, total length, specific growth rate, or condition factor among any of the treatments at the end of the experiment. These results indicate that the use of both an exercise routine and vertically-suspended structure may be beneficial during the rearing of juvenile landlocked fall Chinook salmon.