Effects of body mass and water temperature on routine metabolism of American paddlefish Polyodon spathula

This study quantified the effects of temperature and fish mass on routine metabolism of the American paddlefish Polyodon spathula. Thermal sensitivity, as measured by Q₁₀ value, was low in P. spathula. Mean Q₁₀ was 1·78 while poikilotherms are generally expected to have Q₁₀ values in the 2·00–2·50 range. Mass‐specific metabolism did not decrease with increased fish size to the extent that this phenomenon is observed in teleosts, as evidenced by a mass exponent (β) value of 0·92 for P. spathula compared with 0·79 in a review of teleost species. Other Acipenseriformes have exhibited relatively high β values for mass‐specific respiration. Overall P. spathula metabolism appears to be more dependent on body mass and less dependent on temperature than for many other fishes. An equation utilizing temperature and fish mass to estimate gross respiration for P. spathula was derived and this equation was applied to respiratory data from other Acipenseriformes to assess inter‐species variation. Polyodon spathula respiration rates across water temperature and fish mass appear most similar to those of Atlantic sturgeon Acipenser naccarii and white sturgeon Acipenser transmontanus.     

Timing of paddlefish spawning in the Upper Missouri River,Montana, USA in relation to river conditions

Spawning activity of paddlefish Polyodon spathula in the Missouri River, Montana in 2008–2009 was examined to delineate spawning sites and times in relation to discharge, water temperature and turbidity. One hundred thirty‐six eggs were collected at water temperatures ranging from 12.0 to 20.7°C (mean, 16.3°C; SD, 2.5). Only 12 of 89 (13%) congregations of radio‐tagged adults observed during the spawning period coincided with egg captures. Six larvae were collected at water temperatures ranging from 19.1 to 21.7°C (mean, 20.5°C; SD, 0.86). Peak discharge in 2008 (903 m³ s^?1 on 14 June) was approximately 30% greater in magnitude and occurred 11 days later than peak discharge in 2009 (612 m³ s^?1 on 3 June). Despite these differences in the hydrograph, no significant differences in egg CPUE were found between years (anova , F = 0.69, P = 0.56). Logistic regression identified no significant river condition variables associated with the presence or absence of eggs (P > 0.14 for all variables). However, in both years maximum egg CPUE was recorded within 3 days of the hydrograph peak and at similar water temperatures (17.5°C in 2008, 16.8°C in 2009). These results suggest an overall association of peaking discharge and seasonally warming water temperatures with egg deposition. Higher catches of eggs and larvae than observed in this study may be necessary to clarify short‐term (day‐to‐day) effects of environmental changes on spawning activity. Continued investigation of the relationship between short‐term changes in river conditions and paddlefish spawning activity is needed to understand the mechanics underlying the reproductive success of this species.     

An approach for assessing paddlefish Polyodon spathula (Walbaum, 1792) populations using mark‐recapture information

Historically, management of fish populations has been achieved through the use of age‐derived estimates of growth and mortality. For long‐lived species such as the paddlefish, Polyodon spathula, the validation of calcified structures is necessary to correct for the presence of false annuli or the absence of growth rings. Regardless, numerous studies on paddlefish populations throughout their range have continued the use of un‐validated age estimates to evaluate dynamic rate functions. The use of mark‐recapture studies has been applied widely to evaluate growth of short‐lived fishes, but only recently to a few long‐lived freshwater fishes (i.e. white sturgeon, shovelnose sturgeon, and pallid sturgeon). This study provides the first simultaneous evaluation of both mark‐recapture and age‐estimate information in determining population characteristics for paddlefish. In doing so, this study has determined that the P. spathula population in the Black River below Clearwater Dam, Missouri is sustainable. Additionally, mark‐recapture information is sufficient to produce accurate and reliable assessments of paddlefish populations in lieu of validated aging structures; future management should be centered on accurate scientific methods, which is not the case when using un‐validated aging structures (e.g. scales, otoliths, fin rays, dentary bones) to determine population parameters. Mark‐recapture information can provide an accurate, alternative source of growth and mortality information for use in evaluating and managing paddlefish populations throughout their range.     

The paddlefish rostrum functions as an electrosensory antenna in plankton feeding

A novel electrosensory function is presented for the large, plankton-feeding, freshwater paddlefish, Polyodon spathula, along with a hypothesis which accounts for the distinctive, elongated rostrum of this unusual fish. Behavioural experiments conducted in the ''dark'' (under infrared illumination), to eliminate vision, show that paddlefish efficiently capture planktonic prey to distances up to 80–90 mm. They make feeding strikes at dipole electrodes in response to weak low-frequency electrical currents. Fish also avoid metal obstacles placed in the water, again in the dark. Electrophysiological experiments confirm that the Lorenzinian ampullae of paddlefish are sensitive to weak, low-frequency electrical signals, and demonstrate unequivocally that they respond to the very small electrical signals generated by their natural zooplankton prey (Daphnia sp.). We propose that the rostrum constitutes the biological equivalent of an electrical antenna, enabling the fish to accurately detect and capture its planktonic food in turbid river environments where vision is severely limited. The electrical sensitivity of paddlefish to metallic substrates may interfere with their migrations through locks and dams.     

Exploitation of paddlefish Polyodon spathula (Walbaum, 1792) in the Mississippi River

Concern over exploitation rates of the American paddlefish Polyodon spathula from sport and commercial fisheries has increased in recent decades and the Convention on International Trade of Endangered Species is now seeking information from state agencies regarding the sustainability of commercially harvested paddlefish populations. The Missouri Department of Conservation is addressing this through the implementation of a 5‐year tagging study on exploitation of paddlefish in the Mississippi River. The first 2 years of this project found that minimal exploitation of paddlefish along Missouri's eastern border was equal to 4.01% (SE = 0.02). After updating previously constructed spawning potential ratio modeling completed in 2016 with the more accurate estimates of exploitation determined in this study it becomes apparent that paddlefish populations of the Mississippi River are currently at sustainable levels. However, precautionary adjustment of regulations is advised to protect paddlefish through maturation and to counteract the possibility of increased harvest intensity resulting from increased demand of domestic caviar.     

DNA integrity of Polyodon spathula cryopreserved sperm

Comet assay was used to detect DNA integrity of paddlefish (Polyodon spathula) sperm following cryopreservation. At the same time, sperm velocities prior to freezing and post‐thawing were also assessed by the computer‐assisted sperm analysis (CASA) system. Significant differences (P < 0.05) were detected in the degree of DNA damage in cryopreserved sperm using different extenders. According to osmolality of the extenders, DNA damages of Sb (20 mm Tris, 75 mm sucrose, 0.5 mm KCl, pH 8.5) sperm was the least, which showed that the percentage of tail DNA of Sb (17.87–35.28%) was lower than those of Sa (20 mm Tris, 50 mm sucrose, 0.5 mm KCl, pH 8.5) and Sc (20 mm Tris, 100 mm sucrose, 0.5 mm KCl, pH 8.5). Moreover, A and B class sperm cells provided most of the Sb sperm (>50%). However, in light of the concentration of methanol, DNA damages of M8 (8% methanol concentration) sperm were the least, including a lower percentage of the tail DNA (21.56–30.86%), and C and D class sperm cells (<30%), regardless of the osmolality of the extenders. In conclusion, when the dilution was 20 mm Tris, 75 mm sucrose, 0.5 mm KCl, pH 8.5 and the concentration of methanol was 8%, the extenders were the best for cryopreservation of paddlefish sperm. In addition, the results indicated that the extent of damage to sperm motility caused by freeze‐thawing (VCL, VSL) was correlated with DNA breakage (|r| > 0.8). This implied that cryopreservation could damage sperm DNA of paddlefish and affect the sperm velocities when the osmolality and the concentrations of the cryoprotectants of the extender were inappropriate.     

Comparative precision of age estimates from two southern reservoir populations of paddlefish [Polyodon spathula (Walbaum, 1792)]

The aim of the study was to determine whether location and sex affected the age precision estimates between two southern, reservoir populations of paddlefish [Polyodon spathula (Walbaum, 1792)]. From 589 paddlefish collected in Grand Lake and Keystone Lake, Oklahoma in 2011, ages from dentaries were estimated using three independent readers and precision was compared with coefficient of variation between locations and sexes. Ages were more precisely estimated from Grand Lake and from females.     

Detection of Salmonella enterica in food using two-step enrichment and real-time polymerase chain reaction

Aims: A new real‐time polymerase chain reaction‐based method was developed for the detection of Salmonella enterica in food. Methods and Results: The method consisted of a novel two‐step enrichment involving overnight incubation in buffered peptone water and a 5‐h subculture in Rappaport–Vassiliadis medium, lysis of bacterial cells and a Salmonella‐specific 5′‐nuclease real‐time PCR with an exogenous internal amplification control. Because a two‐step enrichment was used, the detection limit for dead S. enterica cells in artificially contaminated ice cream and salami samples was high at 10⁷ CFU (25 g)^?1, eliminating potential false‐positive results. When the method was evaluated with a range of 100 naturally contaminated food samples, three positive samples were detected by both the real‐time PCR‐based method and by the standard microbiological method, according to EN ISO 6579. When the real‐time PCR‐based method was evaluated alongside the standard microbiological method according to EN ISO 6579 with 36 food samples artificially contaminated at a level of 10⁰ CFU (25 g)^?1, identical results were obtained from both methods. Conclusions: The real‐time PCR‐based method involving a two‐step enrichment produced equivalent results to EN ISO 6579 on the day after sample receipt. Significance and Impact of the Study: The developed method is suitable for rapid detection of S. enterica in food.     

Effect of cerebrocrast on body and organ weights,food and water intake,and urine output of normal rats

Type 2 diabetes is associated with obesity, insulin resistance, hyperglycemia, hyperphagia, polyuria, body weight gain, excessive secretion of glucocorticoids (GCs), thymus involution, adrenal gland hypertrophy, diabetic nephropathy, etc. We examined the effect of cerebrocrast, a new antidiabetic agent (synthesized in the Latvian Institute of Organic Synthesis), on body weight, food and water intake, urine output, and on changes of organ weight: that is, kidney, thymus, adrenal gland of normal rats. Cerebrocrast was administered at doses of 0.05 and 0.5 mg kg⁻¹ per os (p.o.) once a day for three consecutive days, and its effects were observed from 3 to 27 days after the last administration. Cerebrocrast, during the experimental period, decreased body weight by an average of approximately 32.3%, food intake by about 10–15% at the beginning of the experiments and by 22.6% at the end of the experiments, especially at a dose of 0.5 mg kg⁻¹. Water intake and urine output in comparison with controls were decreased. The daily food intake decreased about 1.0 and 2.1 g by administering single cerebrocrast doses of 0.05 and 0.5 mg kg⁻¹ body weight (b.w.), respectively, but by administering for three consecutive days, food intake decreased by about 2.2 and 3.4 g, respectively. The weekly body weight gain decreased by administering a single dose of cerebrocrast by 2.61 and 2.51 g, respectively, and by triple administration it decreased by 4.36 and 3.07 g, respectively. Cerebrocrast has long‐lasting effects on these parameters and on thymus and adrenal gland weight. As cerebrocrast decreased glucose levels in normal and streptozotocin (STZ)‐induced diabetic rats, it also promoted glucose uptake by the brain, intensified insulin action and formation de novo of insulin receptors. We can conclude that cerebrocrast may regulate food intake and body weight through glucose sensing by proopiomelanocortin (POMC) neurons, that are involved in control of glucose homeostasis, stimulation of α‐melanocyte‐stimulating hormone (α‐MSH) secretion, activation of MC4‐Rs and inhibition of neuropeptide Y (NPY) in the ARC of the hypothalamus, affecting the kidney, and causing decreased urine output and water intake. Moreover, it could stimulate secretion of vasopressin. By administration of cerebrocrast thymus mass was increased, thereby preventing the action of GCs. As cerebrocrast inhibited L‐ and T‐type calcium channels, it can prevent vasoconstriction of kidney arterioles and aldosterone secretion that have significant roles in the development of hypertension and diabetic nephropathy. These properties of cerebrocrast are important for treatment of Type 2 diabetes and its consequent development of hypertension and diabetic nephropathy. Copyright © 2008 John Wiley & Sons, Ltd.     

Body size and food thresholds for zero growth in Dreissena polymorpha: a mechanism underlying intraspecific competition

1. Dreissena polymorpha is an extraordinarily successful invasive species that shows high recruitment of small juvenile mussels on established mussel banks. Such juvenile settlement on, and overgrowth of, large adult mussels; however, leads to competition with adults, and often at high densities and low‐food concentrations. 2. The concept of food thresholds for zero growth has been a powerful approach to explaining size‐related exploitative competition in different zooplankton species. We applied it to investigate whether food threshold concentrations for zero growth (C₀) differ between juvenile and adult zebra mussels. 3. By determining body mass growth at various concentrations of a diet mixture (Nannochloropsis limnetica and Isochrysis aff. galbana) we demonstrate that the threshold food concentration for growth of juvenile mussels (C₀ = 0.08 mg C L⁻¹) is substantially lower than that for adults (C₀ = 0.36 mg C L⁻¹). 4. This indicates that, at low food availability, juvenile zebra mussels are competitively superior to their larger conspecifics. Within zebra mussel banks plankton food is substantially depleted and so the observed mechanism might ensure juvenile success and therefore the regeneration of mussel banks in nature.     

Balanced nitrogen economy as a flexible strategy on yield stabilizing and quality of aquatic food crops in wetland ecosystem

In wetland ecosystem, nitrogen along with other elements and its management is most imperative for the production of so many aquatic food, non-food and beneficial medicinal plants and for the improvement of soil and water characteristics. With great significant importance of INM (integrated nutrient management) as sources, emphasizing on management on nitrogen as a key element and its divergence, a case study was undertaken on such aquatic food crops (starch and protein-rich, most popular and remunerative) in the farmers’ field of low-lying ‘Tal’ situation of New Alluvial Zone of Indian subtropics. The study was designed in factorial randomized block design, where, three important aquatic food crops (water chestnut (Trapa bispinosa Roxb.), makhana (Euryale ferox Salisb.) and water lily (Nymphaea spp.) as major factor and eleven combinations of organic and inorganic sources of nutrients as sub-factor was considered in the experiment. It revealed from the results that the production of fresh kernels or nuts of water chestnut (8.57 t ha⁻¹), matured nut yield of makhana (3.06t ha⁻¹) and flower stalks of water-lily as vegetables (6.38 t ha⁻¹) including its nutritional quality (starch, protein, sugar and minerals) was remarkably influenced with the application of both organic (neem oilcake @ 0.2 t ha⁻¹) and inorganic sources (NPK @ 30:20:20 kg ha⁻¹ along with spraying of NPK @ 0.5% each over crop canopy at 20 days interval after transplanting) than the other INM combinations applied to the crops. Among the crops, highest WCYE (water chestnut yield equivalence) exhibited in makhana due to its high price of popped-form in the country, which is being exported to other countries at now. Sole application of both (organic and inorganic sources) with lower range did not produce any significant outcome from the study and exhibited lower value for all the crops. Besides production of food crops, INM also greatly influenced the soil and water characterization and it was favourably reflected in this study. The physico-chemical characteristics of soil (textural class, pH, organic carbon, organic matter, ammoniacal nitrogen, nitrate nitrogen, available nitrogen, phosphorus and potassium) are most important and contributed a significant improvement due to cultivation of these aquatic crops. Analysis of such wet bodies represented the water characteristics (pH, BOD, COD, CO ⁼₃ , HCO ⁻₃ , NO ⁻₃ N, SO ⁻₄ S and Cl⁻) were most responsive, adaptable and quite favourable for the cultivation of these crops in this vast waste unused wetlands for the mankind without any environmental degradation.

     

Behavioural responses of sablefish, Anoplopoma fimbria, to bait odour

A behavioural bioassay was used to determine the response threshold to squid extract of sablefish, Anoplopoma fimbria, held at three different feeding regimens. Sablefish responded to the odour of bait by changing swimming activity and turning behaviour. The response threshold to bait odour was influenced by both the amount of food eaten and the duration of food deprivation. The total concentration of amino acids in the bait extract was assumed to determine the response threshold as chemical fractionation studies have shown that this class of compounds is essential for the stimulatory capacities of food extracts. When fed to satiation (9.4% wet body weight) and tested after one day of food deprivation, the mean response threshold to total dissolved free amino acids was 4.4 × 10^?8m (range=7.6 × 10^?8 to 3.6 × 10^?8m ). When fed at 1.6-2.3% wet body weight, the threshold sensitivity had increased to a mean value of 1.8 × 10^?10m (range=8.4 × 10^?10 to 7.0 × 10^?11m ) after one day of food deprivation; after four days of deprivation, the sensitivity had increased even further to a mean value of 1.4 × 10^?11m (range=1.6 × 10^?10 to 1.4 × 10^?12m ). It was also apparent that the intensity of behavioural responses to the bait odour increased with both stimulus concentration and duration of food deprivation. These results suggest that sablefish intensify their search for prey under increased feeding motivation. The active space of a bait source was estimated from the threshold values obtained. Depending on state of food deprivation, rate of chemical release from the bait and the current velocity, maximum lengths of active space within which sablefish would exhibit food searching responses vary from 10 m to several km. Stock assessment based on catch data from baited gear will need techniques that take into account those factors influencing active space for food searching.     

Latitudinal and altitudinal growth patterns of brown trout Salmo trutta at different spatial scales

Spatial variation in growth of stream‐dwelling brown trout Salmo trutta was explored in 13 populations using a long‐term study (1993–2004) in the Bay of Biscay drainage, northern Spain. The high variability in fork length (L_F) of S. trutta in the study area was similar to the body‐size range found in the entire European distribution of the species. Mean L_F at age varied: 0+ years, 57·4–100·7 mm; 1+ years, 111·6–176·0 mm; 2+ years, 155·6–248·4 mm and 3+ years, 194·3–290·9 mm. Average L_F at age was higher in main courses and lower reaches compared with small tributaries and upper reaches. Annual specific growth rates (G_L) were: 0+ to 1+ years, 0·634–0·825 mm mm⁻¹ year⁻¹; 1+ to 2+ years, 0·243–0·342 mm mm⁻¹ year⁻¹; 2+ to 3+ years, 0·166–0·222 mm mm⁻¹ year⁻¹, showing a great homogeneity. Regression models showed that water temperature and altitude were the major determinants of L_F at age variability within the study area. A broader spatial analysis using available data from stream‐dwelling S. trutta populations throughout Europe indicated a negative relationship between latitude and L_F of individuals and a negative interaction between latitude and altitude. These findings support previous evidence of the pervasive role of water temperature on the L_F of this species. Altitude appeared as the overall factor that includes the local variation of other variables, such as water temperature or food availability. At a larger scale, latitude was the factor that encompassed these environmental gradients and explained the differences in L_F of S. trutta. In summary, L_F at age in stream‐dwelling S. trutta decreases with latitude in Europe, the converse of Bergmann's rule.     

Direct observation of swimming behaviour in a shallow-water scavenging amphipod Scopelocheirus onagawae in relation to chemoreceptive foraging

Direct observations on foraging behaviour of scavenging lysianassid amphipods have been limited, and no previous study has examined the effect of food odour quantitatively on the behaviour. The present study recorded the swimming behaviour of the amphipod Scopelocheirus onagawae using videographic techniques before and after the introduction of food odour (amino acid solution). S. onagawae showed consistent nocturnal activity swimming at a high speed (16.8 cm s^− 1) with an approximately straight trajectory in various directions before and after the introduction of odour in which the amino acid concentration was below the behavioural threshold concentration for this species (1.0 × 10^− 7 mol l^− 1). High speed multidirectional linear swimming is thought to be advantageous for these amphipods, enabling them to survey across a broad area. After the first encounter with the odour plume above the behavioural threshold concentration, the amphipods slowed down their swimming speed (ca. 9.7 cm s^− 1) with a short time-lag (ca. 0.42 s), and thereafter they frequently turned so that they remained within the odour plume. Once moved out of the odour plume, the amphipods quickly returned to the plume with a shorter response time (ca. 0.1 s) than that in the first detection of the odour plume, suggesting that the sensory adaptation is involved with the tracking of the odour. Our study demonstrated that chemoreception is a major factor causing behavioural change in scavenging amphipods at the edge of the odour plume.     

Habitat partitioning of native and exotic Daphnia in gradients of temperature and food: mesocosm experiments

1. Invasion of tropical zooplankton into temperate lakes provides an interesting opportunity to explore habitat segregation in a thermal gradient. 2. We explored differing vertical positioning of native and exotic Daphnia (Daphnia mendotae and Daphnia lumholtzi) in a large indoor mesocosm system (Plön plankton towers) during 2 month‐long experiments. The two towers were manipulated to provide gradients of both temperature (15–29 °C) and algal food (0.05–0.58 mg C L^?1) and a day–night cycle. 3. Both juvenile and adult D. lumholtzi showed a ‘typical’ vertical migration pattern, with higher densities in the epilimnion at night than during the day. They avoided the food‐poor middle layer. In contrast, D. mendotae adults showed little tendency to migrate into the epilimnion at night, remaining in the cooler hypolimnion while juveniles migrated. The vertical distribution of D. mendotae appeared unaffected by the presence of D. lumholtzi. 4. The strong migration behaviour of D. lumholtzi in the absence of fish cues suggests that this behaviour may be a constitutive trait. Habitat partitioning of the two species is probably the result of different thermal tolerances, with D. mendotae constrained to remaining in deeper water by high temperatures in the epilimnion and the tropical D. lumholtzi able to use the warm epilimnion at night.     

Viability and fertilizing capacity of cryopreserved sperm from three North American acipenseriform species: a retrospective study

Populations of sturgeon across the globe are threatened due to unregulated harvest and habitat loss, and the status varies among species across North America. Ready access to viable and functional sperm would contribute to recovery programmes for these species. In this study, we examined the motility, viability (cell membrane integrity) of cryopreserved sperm from three North American acipenseriform species and fertilizing capacity. Milt samples were collected from captive shortnose sturgeon (Acipenser brevirostrum), wild paddlefish (Polyodon spathula) and pallid sturgeon (Scaphirhynchus albus) and cryopreserved using combinations of Modified Tsvetkova’s (MT) extender, Original Tsvetkova’s extender, and modified Hanks’ balanced salt solution, along with the cryoprotectants methanol (MeOH) or dimethyl sulfoxide (DMSO). A dual‐staining technique using the fluorescent stains SYBR‐14 and propidium iodide was employed with flow cytometry to determine the percentages of spermatozoa that were viable by virtue of having intact membranes. The percentage of viable spermatozoa ranged from 5% to 12% in shortnose sturgeon, 30–59% in paddlefish, and 44–58% in pallid sturgeon. In the first experiment with shortnose sturgeon sperm, methanol allowed for higher values for dependent variables than did DMSO, and sperm viability generally correlated with post‐thaw motility. However, fertilization rate, neurulation, or hatching rates were independent from these factors. In the second experiment with shortnose sturgeon, 5% MeOH combined with MT yielded higher values for all parameters tested than the other combinations: viability was correlated with motility, fertilization rate, and hatching rate. Overall, viability and post‐thaw motility was not affected by the use of hyperosmotic extenders (OT) or cryoprotectants (DMSO), but their use decreased fertilization percentages. For paddlefish sperm (experiment 3), MT combined with 10% MeOH was clearly a good choice for cryopreservation; viability and motility results were correlated, but independent of fertilization. For pallid sturgeon sperm (experiment 4), MT with 5–10% MeOH showed significantly higher sperm quality and fertilization parameters. Membrane integrity can be used as a predictor of fertilization by cryopreserved sperm, however additional sperm quality parameters, supplementary to motility and membrane integrity, would be useful in the refining and optimizing cryopreservation protocols with acipenseriform sperm.     

Paddlefish (Polyodon spathula) in Europe: An aquaculture species and a potential invader

The paddlefish (Polyodon spathula) was first introduced to Europe in 1974, mainly due to its potential for rearing in natural polyculture ponds and large temperate reservoirs. The information on the history of paddlefish aquaculture efforts in Europe is scarce, as well as data on current paddlefish aquaculture status and trends. In addition, there is a lack of data on its presence and potential establishment in the wild, while its invasive potential and associated risks and impacts are largely unknown. In order to evaluate its current status in Europe, we conducted a survey among scientists, aquaculture producers and other stakeholders, and reviewed literature and data on the Internet. Based on the results obtained, we discuss the potential and the challenges in European paddlefish aquaculture development, and analyze paddlefish invasive potential and risks associated with its naturalization. Paddlefish aquaculture is well established only regionally in Europe, but offers relatively high potential for further development in pond farms. Nevertheless, future development will require careful planning, especially regarding market development and improved marketing strategies. While paddlefish likely represents a low‐risk invader, improved control and reporting on trade and intentional and unintentional releases will be required. Given the lack of knowledge on potential impacts following its introduction, due caution seems highly advisable.     

Modelling bioenergetic and population-level impacts of invasive bigheaded carps (Hypophthalmichthys spp.) on native paddlefish (Polyodon spathula) in backwaters of the lower Mississippi River

1. While invasions of large rivers by exotic fish species are well documented, assessing actual or potential impacts on native species is a challenge. Rapid assessments may be possible through the application of a combination of bioenergetic and population dynamic models.
2. Paddlefish (Polyodon spathula) is a native species in the central USA with a history of population decline due to waterway development and overharvesting for roe. It is not known whether paddlefish are impacted by resource competition from invasive bigheaded carp populations, including silver (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), which have expanded dramatically in the Mississippi River.
3. We used bioenergetic models to project the potential impact of invasive silver and bighead carp on zooplankton density and paddlefish somatic growth in backwater habitat. Bioenergetic outputs were translated to impacts on fecundity, becoming inputs for 50-year metapopulation simulations of backwater habitat connected to the main-stem Mississippi River by episodic flood events.
4. Competition with carp reduced growth and increased the risk of population decline for paddlefish. Impacts increased disproportionately with increased carp abundance and were further exacerbated in scenarios with increased diet overlap or decreased zooplankton abundance.
5. We also analysed paddlefish condition data collected at sites near the lower Mississippi River with varying histories of carp invasion. These data give credence to the bioenergetic model output; paddlefish had reduced body condition at sites with long-established, high-density carp populations.
6. We conclude that invasive bigheaded carps have great potential to reduce paddlefish growth, fecundity, and abundance. The pairing of bioenergetics and population models is likely to be broadly useful in assessing the risks posed by other invasive species.

     

Under-ice blooms and source-water odour in a nutrient-poor reservoir: biological, ecological and applied perspectives

1. Algal taste and odour is usually associated with open water blooms and eutrophic systems. However, some algal species can produce high biomass under ice‐cover, even at low nutrient concentrations, that can impact water quality. This paper describes a winter odour outbreak in oligotrophic Glenmore Reservoir (Calgary, Alberta, Canada), the major algal species, volatile organic compounds (VOCs) and some treatment implications. 2. Using sensory, chemical and microscope analyses, we monitored odour, algal biomass and taxa, bacteria and major nutrients. In a preliminary assessment of the effectiveness of standard water treatment with this type of algal biomass and odour, we used bench‐scale tests and sampled raw water from the Glenmore treatment plant at successive treatment stages. 3. In the winter of 1999–2000 Glenmore ice‐cover was delayed, nutrients were characteristically low (TP < ～5 μg L^–1), but organic carbon and bacteria were higher than in previous years. 4. During this period there was an increase in algal biomass dominated by the mixotrophic chrysoflagellate Dinobryon divergens. Temporal dynamics of this species were inversely correlated with bacteria, and biomass declined following the establishment of ice‐cover, while depth profiles showed the highest abundance at subsurface layers. This suggested that the population outbreak was triggered by high bacteria abundance but depended on a minimum amount of light, consistent with in vitro studies of other mixotrophic chrysophytes. 5. Other non‐bactiverous taxa were also numerous, notably Asterionella formosa, cryptomonads, dinoflagellates and the synurophyte Synura petersenii. 6. Raw water odour was characteristically fishy, mainly caused by the VOCs 2,4,7‐decatrienal, 2,4‐heptadienal and 2,4‐decadienal. Based on algal population and VOC dynamics, these compounds were attributed to Dinobryon. Trace amounts of 2,6‐nonadienal (S. petersenii) and 1,3,5 and 1,3,6‐octatriene (A. formosa) were also detected. It was concluded that 2,4,7‐decatrienal was the major source of the raw water odour. 7. Sensory and microscopic analyses of pre‐ and post‐treatment samples in the treatment plant indicated a complete removal of odour, but only a 30–60% removal of algal biomass and evident rupture of residual algal cells. Laboratory experiments showed that using standard treatment, chlorination rapidly oxidized 2,4,7‐decatrienal and 2,6‐nonadienal but had little effect on 2,4‐hepta‐ and decadienal.     

Feeding behavior and responsivity to food odors in Nile tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis> (Cichlidae) after chronic polisensory deprivation

The paper reports the study of the food searching behavior in the Nile tilapia Oreochromis niloticus before and after the experimental anosmia combined with visual deprivation. The threshold concentration of the water extract of the common food organisms (Chironomidae larvae) was found for the tilapia with intact olfaction to be 10^–4 g/L, which allows this fish to search for food under the restriction of visual reception. The food searching behavior in response to food odors is completely lost as a result of irreversible anosmia and do not be restored after a 4.5-month period even for the high concentrations of the extract (10^–1–10^–2 g/L). These findings point to the absence of external taste buds on the head, body, and fins, or to their extremely low numbers. It is assumed that tactile sense also plays a significant role in the food search and prey location in the Nile tilapia.