Nathan R. Jensen

Persistence of DNA in carcasses, slime and avian feces may affect interpretation of environmental DNA data

The prevention of non-indigenous aquatic invasive species spreading into new areas is a goal of many resource managers. New techniques have been developed to survey for species that are difficult to capture with conventional gears that involve the detection of their DNA in water samples (eDNA). This technique is currently used to track the invasion of bigheaded carps (silver carp and bighead carp; Hypophthalmichthys molitrix and H. nobilis) in the Chicago Area Waterway System and Upper Mississippi River. In both systems DNA has been detected from silver carp without the capture of a live fish, which has led to some uncertainty about the source of the DNA. The potential contribution to eDNA by vectors and fomites has not been explored. Because barges move from areas with a high abundance of bigheaded carps to areas monitored for the potential presence of silver carp, we used juvenile silver carp to simulate the barge transport of dead bigheaded carp carcasses, slime residue, and predator feces to determine the potential of these sources to supply DNA to uninhabited waters where it could be detected and misinterpreted as indicative of the presence of live bigheaded carp. Our results indicate that all three vectors are feasible sources of detectable eDNA for at least one month after their deposition. This suggests that current monitoring programs must consider alternative vectors of DNA in the environment and consider alternative strategies to minimize the detection of DNA not directly released from live bigheaded carps.

Evaluation of Egg Incubation Methods and Larval Feeding Regimes for North American Burbot

Abstract Incubation methods and larval feeding regimes were investigated for North American burbot Lota lota maculosa over 2 years. Three upwelling incubators were tested: 6.0-L McDonald-type jars, 2.0-L pelagic egg jars, and 1.2-L Imhoff cones. Larvae were allocated to five feeding regimes in year 1 (trial 1) and three feeding regimes in year 2 (trial 2). In trial 1, a live diet (marine rotifers Brachionus plicatilis and brine shrimp Artemia spp.) was administered from 11 d posthatch (dph) until introduction of a commercial diet at 21, 31, or 41 dph; the fourth treatment applied the commercial diet exclusively starting at 11 dph, and the fifth treatment used only the live diet. Trial 2 examined (1) exclusive use of live feed beginning at 16 dph; (2) use of live feed at 16–50 dph, which was combined with commercial feed at 31–50 dph, and use of only the commercial diet at 51–76 dph; and (3) use of the live diet at 16–50 dph, the addition of frozen brine shrimp at 31–50 dph, and use of the commercial diet ...

Carbon Dioxide as a Tool to Deter the Movement of Invasive Bigheaded Carps

AbstractNonnative bigheaded carps are established in the Mississippi River and there is substantial concern about their potential entry into the interconnected Laurentian Great Lakes. While electrical barriers currently exist as a preventative measure, there is need for additional control mechanisms to promote barrier security through redundancy. We tested the effectiveness of infused carbon dioxide gas (CO2) as a tool to influence the movement and behavior invasive bigheaded carps, namely Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix, as well as native Bigmouth Buffalo Ictiobus cyprinellus, Channel Catfish Ictalurus punctatus, Paddlefish Polyodon spathula, and Yellow Perch Perca flavescens in an experimental pond. Individuals were monitored with acoustic telemetry before, during, and after CO2 addition to the pond. We noted distinct changes in fish behavior following CO2 addition. Each species except Paddlefish maintained farther distances from the CO2 infusion manifold relative to ...

Movement of Lake-Origin Burbot Reared in a Hatchery Environment and Released into a Large River Drainage

Abstract Burbot Lota lota in Kootenay Lake and the Kootenay River of British Columbia, Idaho, and Montana (U.S. spelling: “Kootenai River”) are at risk of demographic extinction. We conducted a pilot study to evaluate poststocking dispersal and movement of hatchery-reared, lake-strain burbot (Moyie Lake, British Columbia) in a riverine environment to determine the potential utility of this hatchery strain for future burbot rehabilitation efforts in this system. We implanted ultrasonic tags into 30 hatchery-reared burbot (ages 2 and 3) and released them into the Goat River, a tributary to the Kootenay River, in October 2009. Dispersal over a distance of 2 km from the Goat River release site to the Kootenay River occurred within 1–9 d after release (mean = 3.1 d; n = 28 active tags). Thereafter, 14 burbot remained in the Kootenay River for the rest of the 144-d study period; nine of these fish were observed moving upstream from the Goat River confluence, and five were observed both upstream and downstream f...

Performance and Macronutrient Composition of Age-0 Burbot Fed Four Diet Treatments

Abstract As there are few larval-diet rearing methods for burbot Lota lota, it is important to develop these methods for ongoing conservation and future commercial aquaculture efforts. The performance and macronutrient composition of age-0 burbot were compared after fish were fed four different diets for 8 weeks. Diets included three commercial larval-rearing diets and Daphnia magna. Performance metrics involved mean length and weight, survival, and cannibalism. The macronutrient composition (dry matter) of fish and diets was measured as the percentages of moisture, lipid, protein, and ash, along with energy content. Significant differences in mean length and weight occurred, although survival and cannibalism were not different among treatments at the end of the experiment. Mean weight and length were significantly higher with diets 1 and 2. Fish fed diet 2 had the greatest mean survival (32%), followed by those fed the D. magna diet (30%), diet 3 (27%), and diet 1 (25%). Fish fed diet 1 experienced the g...

Assessment of Formalin and Hydrogen Peroxide Use during Egg Incubation of North American Burbot

Abstract Control of aquatic fungi in the family Saprolegniacea during egg incubation was investigated as part of a program aimed at developing aquaculture methods for Kootenai River burbot Lota lota maculosa, a species relatively unknown to North American aquaculture. The concentration effectiveness of two antifungal control methods, formalin and hydrogen peroxide, was compared over two consecutive breeding seasons in a newly developed micro-incubation system. The results indicated that daily 15-min treatments of 1,667 mg of formalin/L and 500 mg of hydrogen peroxide/L inhibited fungal growth on eggs and increased egg survival by up to 200% during the incubation period relative to the untreated controls. Lower concentrations of 1,000 mg/L formalin and 250 mg/L hydrogen peroxide also yielded increased survival but were not sufficient to completely inhibit fungal growth on eggs. Concentrations up to 5,000 mg/L formalin and 500 mg/L hydrogen peroxide did not appear to negatively influence egg survival during...

Time Required for Yolk Coagulation in Pink Salmon and Steelhead Eggs Exposed to Mechanical Shock

Abstract Incubation success in management studies and environmental assessments is often applied as a measure of natural spawning productivity as based on the live: dead ratios of excavated eggs. If sampling occurs too early in the development of the embryo, eggs will die from the sampling procedure and could be mistaken for incubation mortality if the yolk coagulates rapidly after experiencing lethal shock. In this study we examined how long it takes for the yolk of fertilized eggs of pink salmon Oncorhynchus gorbuscha and steelhead O. mykiss to coagulate after experiencing lethal mechanical shock, as it applies to that question. Tests were conducted at 12°C from 24 and 48 h (12–24 degree-days) postfertilization to the eyed stage of developing embryos (156 degree-days for steelhead and 223 degree-days for pink salmon). Results demonstrated that yolk coagulation was visible within seconds after shocking, involving as much as 50% of the yolk material within 5 min of shocking. We conclude, therefore, that m...

Characterization of Oocyte Development in Hatchery-Reared Burbot

Abstract Burbot Lota lota are an emerging aquaculture species. To aid in predicting the natural and hormonal-manipulated timing of ovulation and for ensuring maximum viability of eggs at spawning, this study describes oocyte maturation of hatchery-reared burbot from vitellogenesis through ovulation. At a temperature of 4°C, visual polarization of the oil globule occurred 7–13 d preovulation. The lack of uniformity in individual oocyte development was observed and persisted until approximately 2 d before ovulation, at which point complete polarization was observed in all oocytes and a condensed blastomere was observed along the inner chorion. These preliminary observations imply that implantation of gonatotropin-releasing hormone (GnRH) decreased the final maturation stage of oocyte development by 2–4 d and may aid in initiating the maturation process, the induction of which appeared to be a threshold for either a females progression to ovulation or nonovulation and atresia. Although additional investigat...

Assessing consumption of bioactive micro-particles by filter-feeding Asian carp

Silver carp Hypophthalmichthys molitrix (SVC) and bighead carp H. nobilis (BHC) have impacted waters in the US since their escape. Current chemical controls for aquatic nuisance species are non-selective. Development of a bioactive micro-particle that exploits filter-feeding habits of SVC or BHC could result in a new control tool. It is not fully understood if SVC or BHC will consume bioactive micro-particles. Two discrete trials were performed to: 1) evaluate if SVC and BHC consume the candidate micro-particle formulation; 2) determine what size they consume; 3) establish methods to evaluate consumption of filter-feeders for future experiments. Both SVC and BHC were exposed to small (50-100 μm) and large (150-200 μm) micro-particles in two 24-h trials. Particles in water were counted electronically and manually (microscopy). Particles on gill rakers were counted manually and intestinal tracts inspected for the presence of micro-particles. In Trial 1, both manual and electronic count data confirmed reductions of both size particles; SVC appeared to remove more small particles than large; more BHC consumed particles; SVC had fewer overall particles in their gill rakers than BHC. In Trial 2, electronic counts confirmed reductions of both size particles; both SVC and BHC consumed particles, yet more SVC consumed micro-particles compared to BHC. Of the fish that ate micro-particles, SVC consumed more than BHC. It is recommended to use multiple metrics to assess consumption of candidate micro-particles by filter-feeders when attempting to distinguish differential particle consumption. This study has implications for developing micro-particles for species-specific delivery of bioactive controls to help fisheries, provides some methods for further experiments with bioactive micro-particles, and may also have applications in aquaculture.

Profiles of digestive enzymes of two competing planktivores, silver carp and gizzard shad, differ

Typically, studies in digestive physiology in fish focus on a few enzymes and provide insight into the specific processes of the enzyme in a targeted species. Comparative studies assessing a wide number of digestive enzymes on fishes that compete for food resources are lacking, especially in the context of an introduced species. It is generally thought that the invasive silver carp (SVC; Hypophthalmichthys molitrix) directly compete for food resources with the native gizzard shad (GZS; Dorosoma cepedianum) in waters where they coexist. We compared 19 digestive enzymes between SVC and GZS throughout a year and in two rivers in the Midwestern United States: Illinois River and Wabash River. All digestive enzymes analyzed were detected in both SVC and GZS in both rivers. However, the profiles of the digestive enzymes varied by species. Alkaline phosphatase, valine arylamidase, acid phosphatase, naphthol-AS-BI-phosphohydrolase and N-acetyl-β-glucosaminidase were all much higher in SVC than in GZS. Differences between digestive enzyme profiles were also observed between rivers and months. This study demonstrates the utility of using an ecological approach to compare physiological features in fishes.