Adult Carp Research Articles

Infectivity of an emerging fish parasite Gyrodactylus sprostonae in juvenile carp (Cyprinus carpio)

AbstractThe gill monogenean ectoparasite Gyrodactylus sprostonae is an emerging pathogen within recreational UK carp fisheries, and a major cause of mortality in adult carp. This gill infection has only been noted in adult carp and not in juveniles, and no reports of its fundamental infection dynamics exist. The current study compared the infective potential of G. sprostonae between adult and juvenile common carp (Cyprinus carpio) and quantified parasite numbers on the body surface and gills of infected juveniles at two temperatures (14 and 24°C). G. sprostonae was able to infect the body surface and the gills of juvenile carp, and temperature significantly impacted the duration of infection and number of parasites. Interestingly, however, all juveniles under both temperature treatments lost their infections after a maximum of 40 days, with no observed clinical signs of parasitaemia or mortalities. This study therefore indicates that G. sprostonae does not appear to be harmful to juvenile common carp, and we discuss why this infection only seems to impact prised adult carp in the UK.

Effect of water temperature on the anesthetic effects of alfaxalone in carp (Cyprinus carpio).

To evaluate the effect of water temperature on intramuscular injected alfaxalone anesthesia in carp (Cyprinus carpio). Six healthy adult carp (C. carpio) were intramuscularly injected with alfaxalone (2.5, 5.0, or 7.5 mg/kg) at normal water temperature (25°C) and at low water temperature (2.5 mg/kg, 15°C). The respiratory rate, heart rate (HR), and anesthesia depth (AD) were evaluated every 5 min for 30 min after administration and every 1 h after 60 min after injection. The respiratory and HRs did not change significantly upon alfaxalone injection, regardless of dose. However, a dose-dependent increase in AD scores was observed. Furthermore, 2.5 mg/kg alfaxalone injected in 15°C water showed an almost equal anesthetic effect to that of 5.0 mg/kg alfaxalone in 25°C water. Alfaxalone is readily available, and its anesthetic effect in carp was enhanced by lowering water temperature, illustrating the possibility of intramuscular injection of alfaxalone in fish.

Consumption of Non-Native Bigheaded Carps by Native Blue Catfish in an Impounded Bay of the Upper Mississippi River

Adult bigheaded carps Hypophthalmichthys spp. have never been observed in the diets of native fishes in the Mississippi River Basin. In addition, blue catfish Ictalurus furcatus diet preference and foraging behavior have never been studied in the presence of non-native bigheaded carps in the Mississippi River system. We examined the gut contents of adult blue catfish (567–1020 mm, n = 65), captured from a Mississippi River backwater using trammel nets. All items in diets were separated and enumerated, and all fish-like diet items were genetically identified to confirm species-level ID. Bigheaded carp ages were determined by sectioning hard structures (pectoral spines, post-cleithra, and vertebrae). Adult silver carp Hypophthalmichthys molitrix (age 3–5, mean = 3.9 years, SE = 0.2; n = 21) had the highest frequency of occurrence (70%) and constituted the greatest percentage by number (58%) and weight (60%) in/of blue catfish diets. Gizzard shad Dorosoma cepedianum ranked second by all three measures (34%, 25%, and 26%). Finally, 50% to 100% of probable age-based sizes of silver carp exceeded gape measurements of blue catfish, suggesting scavenging was the dominant means of predation. More intensive sampling efforts are required to determine the system-wide importance of bigheaded carp in blue catfish diets.

Comparison of gut microbial communities, free amino acids or fatty acids contents in the muscle of wild Aristichthys nobilis from Xinlicheng reservoir and Chagan lake

BackgroundFish is favored by consumers, while amino acids and fatty acids are the main nutrients of muscle. At present, it has been found that the gut microbial community may be involved in the regulation of host material anabolism. Juvenile and adult bighead carp (A. nobilis) from Chagan lake and Xinlicheng reservoir were selected, and divided into four groups to compare the differences of gut microbial communities, free amino acid and fatty acids in muscle.ResultsThe results showed that fish in different lakes or ages contained specific microbiota, the gut microbial structure was similar, but the microbial content was significantly different. Gut microbial abundance of juvenile fish in Chagan lake was significantly higher than that of other groups. Phylum level analysis Proteobacteria was the dominant gut bacteria of fish in both adult and juvenile fish from two separate lakes. Actinobacteria was another dominant bacterial phylum in juvenile fish in both lakes. Contents of free amino acids and fatty acids in muscle were detected, and the relationships between them and gut microbial communities were analyzed. Bighead carp grew from juvenile to adult, Actinobacteria abundance decreased (P < 0.05) and Proteobacteria increased (P < 0.05). Proteobacteria was positively correlated with the contents of Thr, Lys, Pro, Asp, Gly and Glu, Actinobacteria was negatively correlated with Met and His. Meanwhile, EPA and DHA were positively correlated with Proteobacteria, EPA and DHA were not significantly associated with Actinobacteria.ConclusionIt was speculated that the contents of free amino acids and fatty acids in muscle might be affected by the difference of gut microbiota, thus affecting the taste and nutritional quality.

Migration, homing and spatial ecology of common carp in interconnected lakes

AbstractThe common carp,Cyprinus carpio, is a large, long‐lived, fecund and mobile cyprinid, which evolved in complex inter‐braided Ponto‐Caspian rivers that experience both springtime flooding and freezing winters. Studies suggest adults often move to productive, shallow lakes and floodplains to spawn because they often lack egg predators and then return to deeper normoxic waters to overwinter. Whether these movements involve individuals consistently selecting, or homing to, the same spawning and refuge lakes as part of a strategy benefiting their reproductive success is unknown. To address this question, we examined the movements of 67 radio‐tagged adult carp for 3 years in a watershed with 11 interconnected lakes. Carp were tagged and released into a centrally located, normoxic deep lake in spring and fall. Each spring over 95% of its adults left via a single stream and swam into one of 5 shallow lakes, with most individuals (84%) selecting the same lake(s) in which to spawn each year (median Bhattacharyya affinity coefficient of similarity of 0.82). Young were later found in those lakes without egg predators, which cannot survive winter anoxia. After spawning, carp spent summers moving between productive lakes in an individualistic fashion, presumably foraging, with most (89%) eventually returning to the same deep lake to overwinter (median Bhattacharyya affinity of 1.0). These movements appear to reveal a life‐history tactic involving seasonal homing migration, first to a spawning location and later to winter refuges, that is well adapted to productive but highly heterogeneous and interconnected freshwater environments.

Primary signs of internal organ diseases in carp in case of standard condition violations in fish farming ponds

Hematological and histopathological study results of adult carp from a private fish farm are presented. Abnormalities in the main hematological parameters (blood elements ratio, leukocyte formula, erythropoiesis level, possible pathologies of erythrocytes) were not revealed. One third of the examined fish were found to have abnormalities in the tissues of gills, liver, and heart muscle in the form of minor focal formations (detachment of the gill epithelium, dissection of myofibrils, disorders of glycogen metabolism, foci of necrosis and infiltration) which indicates the initial stage of the pathological process. Kidneys, gonads, and somatic muscle fibers showed no signs of pathology. The main factors determining the primary signs of internal organ diseases are water quality (water saturated with magnesium, calcium, and iron salts, increased hardness) and an unbalanced diet (primarily, an insufficient amount of raw protein) that does not meet the standards adopted in fish farming. The registered initial signs of the pathological process in the gills, liver and heart muscle can be leveled by improving the carp keeping conditions.

A Method for Estimating the Velocity at Which Anaerobic Metabolism Begins in Swimming Fish

Anaerobic metabolism begins before fish reach their critical swimming speed. Anaerobic metabolism affects the swimming ability of fish, which is not conducive to their upward tracking. The initiation of anaerobic metabolism therefore provides a better predictor of flow barriers than critical swimming speed. To estimate the anaerobic element of metabolism for swimming fish, the respiratory metabolism and swimming performance of adult crucian carp (Carassius auratus, mass = 260.10 ± 7.93, body length = 19.32 ± 0.24) were tested in a closed tank at 20 ± 1 °C. The swimming behavior and rate of oxygen consumption of these carp were recorded at various swimming speeds. Results indicate (1) The critical swimming speed of the crucian carp was 0.85 ± 0.032 m/s (4.40 ± 0.16 BL/s). (2) When a power function was fitted to the data, oxygen consumption, as a function of swimming speed, was determined to be AMR = 131.24 + 461.26Us1.27 (R2 = 0.948, p &lt; 0.001) and the power value (1.27) of Us indicated high swimming efficiency. (3) Increased swimming speed led to increases in the tail beat frequency. (4) Swimming costs were calculated via rate of oxygen consumption and hydrodynamic modeling. Then, the drag coefficient of the crucian carp during swimming was calibrated (0.126–0.140), and the velocity at which anaerobic metabolism was initiated was estimated (0.52 m/s), via the new method described herein. This study adds to our understanding of the metabolic patterns of fish at different swimming speeds.

Toxicity and bioaccumulation of manganese and chromium in different organs of common carp (Cyprinus carpio) fish.

The present research work was carried out to determine the bioaccumulation of manganese and chromium in the gills, intestine, muscles, skin and bones, as well as its acute toxicity and effects on hematological and biochemical parameters in Common carp (Cyprinus carpio). Adult carps were exposed for 96 h to manganese sulphate and chromium chloride solution, a sub lethal concentration was used in the experiment. Bioaccumulation was highest in the gills followed by intestine > muscles > skin > bones. The concentration of hematocrit (HCT) (37.3 ± 0.36), hemoglobin (HGB) (9.0 ± 0.04), Red Blood Cells (RBCs) (3.7 ± 0.025), mean corpuscular volume (MCV) (121.2 ± 0.36), mean corpuscular hemoglobin (MCH) (41.3 ± 0.3) and mean corpuscular hemoglobin concentration (MCHC) (41.06 ± 0.072) was significantly higher at 96 h (P < 0.01) after exposure to manganese and chromium, while the concentration of platelets (PLT) (16.8 ± 0.12) and white blood cells (WBCs) (62.7 ± 0.11) was lower at 96 h of exposure. Serum glutamic pyruvic transaminase (SGPT) (40.6 ± 0.4), Blood Urea (13 ± 0.1), serum triglycerides (231.21 ± 0.04), high-density lipoprotein (HDL) (39 ± 0.07), serum Alkaline PO4 (242 ± 0.2), lactate dehydrogenase (LDH) (1239 ± 13.21), and serum Uric Acid (4.81 ± 0.33) were significantly higher (P < 0.01) at 96 h of exposure. The highest concentration of serum cholesterol (339 ± 0.09), serum reatinine (0.9 ± 0.01), low density lipid (240 ± 0.2) was observed at 24 h. Serum glutamic-oxaloacetic transaminase (SGOT) (19 ± 0.13), and serum albumin were at the highest level at 72 h (3.19 ± 0.07) (P < 0.01) post exposure.

Phytochemical and Safety Evaluations of Volatile Terpenoids from Zingiber Cassumunar Roxb. On Mature Carp Peripheral Blood Mononuclear Cells and Embryonic Zebrafish.

Pharmaceutical products of essential oil from Zingiber cassumunar Roxb. are extensively being developed, while the research on their safety is seldom documented. The aim of the present study was to evaluate the phytochemical profile and the effect of cassumunar ginger oil on cell-based assay and the zebrafish model. The essential oil was isolated from fresh rhizomes of Z. cassumunar using simultaneous steam-distillation. Chemical composition was analyzed using gas chromatograph coupled to a mass spectrometer (GC-MS). Effect of cassumunar ginger oil on adult carp fish peripheral blood mononuclear cells (PBMCs) was investigated using MTT assay. The embryotoxic and teratogenic effects of cassumunar ginger oil were studied in zebrafish embryos. GC-MS results showed that the essential oil was composed of sabinene (43.54%) and terpinen-4-ol (29.52%) as the major phytoconstituents. No fish PBMC cytotoxic effect was observed with the concentration less than 50 µg/mL of cassumunar ginger oil. Our results showed for the first time the embryotoxic and teratogenic effects of cassumunar ginger oil in zebrafish embryos. The result indicated that the cassumunar ginger oil induced zebrafish embryotoxicity in a concentration-dependent manner. At 500 µg/mL of cassumunar ginger oil demonstrated significantly moderated embryotoxicity within 24 h (p < 0.05). The survival rate of 100 µg/mL of cassumunar ginger group was markedly declined to zero at 96-h post-fertilization (log-rank test, p = 0.001). However, survival rates of zebrafish embryo in the 1 and 10 µg/mL cassumunar ginger groups were more than 90% throughout the trial period. Moreover, very low teratogenicity to the zebrafish embryo was also observed in 1 and 10 µg/mL of cassumunar ginger groups. Our findings suggest that there is hardly any cytotoxicity, embryotoxicity and teratogenicity at concentrations less than 10 µg/mL of cassumunar ginger oil. However, the toxicity assessment of its pharmaceutical product should prove for further consumer protection.

Habitat preferences and habitat restoration options for small‐bodied and juvenile fish species in the northern Murray–Darling Basin

SummaryDegradation of instream habitats in the northern Murray–Darling Basin has occurred through numerous stressors, including siltation, clearing of bankside vegetation, intrusion of livestock and impacts of pest species. A better understanding of habitat preferences of native fish species could help guide future instream habitat restoration actions. The habitat choices of seven native fish species, juvenile Murray Cod (Maccullochella peelii), juvenile Golden Perch (Macquaria ambigua ambigua), juvenile Silver Perch (Bidyanus bidyanus), adult Murray–Darling Rainbowfish (Melanotaenia fluviatilis), adult Olive Perchlet (Ambassis agassizii), adult Un‐specked Hardyhead (Craterocephalus stercusmuscarum fulvus) and adult carp gudgeons (Hypseleotris spp.) were tested in preference troughs to help inform potential habitat restoration actions in the Condamine catchment. Each species was given a choice between pair combinations of open sandy habitat, submerged macrophytes, emergent plants and rocky rubble. Habitat preferences varied between species. Murray Cod, Golden Perch, carp gudgeons and Olive Perchlets preferred structure over open sandy habitat, whilst juvenile Silver Perch, Un‐specked Hardyhead and Murray–Darling Rainbowfish did not avoid open sandy habitats. Juvenile Murray Cod preferred rocky rubble habitat over all other habitat choices. Use of complex rock piles to provide nursery habitat for Murray Cod populations is a potential restoration option. Introduction of rock could also benefit Golden Perch and carp gudgeons. Use of emergent plants, submerged macrophytes and rocky rubble for habitat restoration all appear to have merit for one or more species of small‐bodied fishes or juvenile stages of larger sized fishes. Rocky rubble or floating attached macrophytes could be viable restoration options in areas too turbid to establish submerged macrophytes. These habitat interventions would complement existing actions such as re‐snagging and provision of fish passage to assist with sustainable management of native fish populations.

Light microscopic study on the absorptive cells and goblet cells in the intestine of adult common carp Cyprinus carpio

The purpose of this study was to describe of some histological structures and histochemical features of the absorptive cells and goblet cells in intestine of common carp. In this study, Fifteen adult male common carp were catching alive from the AL-Forat river, with age about (7 - 12) months and mean of their weight was (2100 ± 81 g) and mean standard length was (50.4 ± 3.1 cm), immediately after death.Incision was made through the midventral line of the fish just from cranial to the anus to expose the intestine, specimens of intestine were taken and washed with (0.9 %) normal saline solution. Ten samples were obtained from different regions of each portion of the intestine (anterior, middle and posterior), fixed by either 10% neutral buffered formalin or Bouin’s solution approximately 24 hours at room temperature and then treated by routine histological processing. The stains were used, Hematoxylin and Eosin, periodic acid Schiff, Alcian blue pH 2.5, and Combinated Alcian blue PH 2.5 plus periodic acid Schiff. The Mean number, height and width of mucosal folds were measured and counts of goblet cells in the mucosal folds of each portion of the intestine. The results showed that the intestinal epithelium is simple columnar, the enterocytes were tall columnar cells with brush border; goblet cells were ovoid, located between the enterocytes. The folds composed of the entire thickness of the mucosa, mean number, height and width of the mucosal folds were few in posterior portion of intestine compare with that in other portions. The anterior portion of the intestine has largest number of mucosal folds, while has less number of goblet cells compare to middle and posterior portions of the intestine. The epithelial cells stained red-purple by periodic acid Schiff stain with Alcian blue, the goblet cells were take positive reaction with periodic acid Schiff stain, and with Alcian blue plus periodic acid Schiff, while negative with only Alcian blue stain. Glycoprotein staining intensity varied from very weak to moderate, whereby the presence of neutral, acidic and sulphatedglycoconjugates. In conclusion, numbers of goblet cells were observed to be increased towards posterior portion of intestine required as lubricant for fecal expulsion, and reversed relation between number of the folds and goblet cells.

Selection of suitable candidate genes for miRNA expression normalization in Yellow River Carp (Cyprinus carpio. var)

Yellow River carp is widely cultivated in the world due to its economic value in aquaculture, and the faster growth of females compared to males. It is believed that microRNAs (miRNA) are involved in gonadal differentiation and development. qPCR is the most preferred method for miRNA functional analysis. Reliable reference genes for normalization in qRT-PCR are the key to ensuring the accuracy of this method. The aim of present research was to evaluate as well as identify the efficacy of reference genes for miRNA expression using qRT-PCR in Yellow River carp. Nine ncRNAs (miR-101, miR-23a, let7a, miR-26a, miR-146a, miR-451, U6, 5S, and 18S) were chosen and tested in four sample sets: (1) different tissues in adult carp, (2) different tissues in juvenile carp, (3) different early developmental stages of carp, and (4) different developmental stages of carp gonads. The stability and suitability values were calculated using NormFinder, geNorm, and BestKeeper software. The results showed that 5S was a suitable reference gene in different tissues of adult and juvenile carp. The genes 5S, 18S, and U6 were the most stable reference genes in the early developmental stages of carp. Let-7a and miR-23a were considered as the suitable reference genes in the development of gonads. All these reference genes were subsequently validated using miR-430. The results showed that genes 5S and 18S were the most suitable reference genes to normalize miRNA expression under normal growth conditions in early different developmental stages. The genes Let-7a, and miR-23a were the most suitable in different developmental stages. The present study is the first comprehensive study of the stability of miRNA reference genes in Yellow River carp, providing valuable as well as basic data for investigating more accurate miRNA expression during gonadal differentiation and development of carp.

Selenium deficiency inhibits micRNA-146a to promote ROS-induced inflammation via regulation of the MAPK pathway in the head kidney of carp

Selenium (Se) is a necessity in multiple species of fish. Se plays an important role in immunoregulation, inflammation, and antioxidant systems in fish and other animals. The head kidney is the major immune organ in adult carp, and it produces white blood cells and destroys old red blood cells. The present study aimed to explore the effects and regulatory molecular mechanisms of Se on ROS and micRNA-146a as part of the inflammatory response in fancy carp. Adult fancy carp were fed different concentrations of Se in their diets. The Se content of the head kidney changed in a pattern consistent with the dietary content of Se. Se deficiency induced a significant increase in ROS, restrained the activities of GPx, SOD and CAT and increased MDA content. qPCR analysis showed a reduction in micRNA-146a with Se deficiency. The Se content, miRNA-146a expression and ROS levels were correlated. H2O2 cell stimulation assays found that ROS could activate the MAPK pathway, and ELISA results showed p38, JNK and ERK phosphorylation significantly increased with H2O2 stimulation. TNF-α, IL-1β, and IL-6 were appreciably increased. At same time, miRNA-146a, which should have increased to regulate the inflammatory response, was reduced with Se deficiency. Therefore, with Se deficiency, the head kidney was inflamed. All these results indicated that Se deficiency inhibits micRNA-146a to promote ROS-induced inflammation via regulating the MAPK pathway in the head kidney of carp. The present study revealed that supplementing the diet of carp with selenium is beneficial for growth and disease prevention.

A small native predator reduces reproductive success of a large invasive fish as revealed by whole-lake experiments.

The extent to which native fish communities might control the success of invasive fish has been of interest to ecologists, but it has been rarely addressed using experiments. We conducted an experiment in six small lakes in the Upper Mississippi Region to test the effects of a small native predator, bluegill sunfish (Lepomis macrochirus) on the recruitment of a large, invasive fish, the common carp (Cyprinus carpio). Bluegills are predominant throughout the region and were previously shown to consume carp eggs and larvae. We stocked both lakes at each of our 3 sites with adult carp (spawners) and one lake at each site with bluegills. We repeated the experiment at two of the three sites for two consecutive years. In each lake we assessed the abundance of post-larval carp one month after spawning (backpack electrofishing surveys) and at the end of the season (mark-recapture). For each site/year combination, catch rate of post-larval carp was typically an order of magnitude higher in control than bluegill lakes, but it often declined quickly over time. The abundance of end-of-seasonal juveniles was significantly higher (no 95% CI overlap) in control lakes than in bluegill lakes, except for one pair of lakes during one year when both the control and bluegill lake had similar, low abundance of end-of-season carp. Overall, our results support the hypothesis that common carp recruitment is substantially reduced in habitats dominated by bluegills. We also suggest our results may be applicable to other species, and that managers should explore how predation on early life stages may control other invasive species.

Application of a robust design occupancy model for assessing fish recruitment

Fish recruitment is complex, regulated by environmental factors that induce high mortality early in life. Additionally, age-0 fish can be difficult to sample, making recruitment difficult to detect. We used a robust design occupancy model to evaluate the effects of biotic (age-0 and adult common carp (Cyprinus carpio), bluegill (Lepomis macrochirus), walleye (Sander vitreus), and northern pike (Esox lucius) relative abundance, prey availability, age-0 carp length) and abiotic (water level, temperature) factors on age-0 carp occupancy, detection, and extinction in 13 lakes in South Dakota, USA, for July–April 2008–2010. Age-0 carp occupancy decreased with increasing adult carp abundance and increased with increasing water levels. Age-0 carp detection probability was high during summer (&gt;0.75) but decreased in fall and spring (0.34). Most lakes were occupied in July but overwinter extinction probability was high (59%), resulting in 51% occupancy probability by April. Other environmental factors were not supported, suggesting they had little effect on reproduction and survival. Our results indicate reproduction was universally successful but difficult to detect and that overwinter mortality often resulted in recruitment failure.

Morphometric and Meristic Characterization of Common Carp, Cyprinus Carpio Strains Sourced from Jos, Bauchi and Ibadan, Nigeria

The study investigated the morphometric and meristic characterization of Common carp (Cyprinus carpio) sourced from Jos Bauchi and Ibadan (Nigeria). In comparing the morphometric and meristic characters one hundred and eighty (180) adult Common carp, Cyprinus carpio were used. Twenty four (24) morphometric and six (6) meristic characters were studied. Measurements of the morphometric features were taken to the nearest centimeter by means of a measuring board, measuring rule, pair of dividers for the length, while the weight was taken by means of a weighing scale (salter scale) to the nearest gram. ANOVA, multivariate technique principal component analysis (PCA) and discriminant function analysis were also applied to the transformed morphometric data to; classify the fish into one or several mutually exclusive groups. The Morphometric study indicated that seven parameters did not differ significantly (p&gt;0.05) between Jos (male and female), and Bauchi (male and Female) strains. The parameters are the body depth, caudal fin length, pectoral fin height, standard weight, pre dorsal distance, eye diameter and body weight. In the meristic count, only the dorsal fin spine did not differ significantly (p &gt;0.05) among the Jos, Bauchi, and Ibadan strains in all sexes. The study revealed that there was a genetic distance between male and female Carp sourced from Ibadan and that of Jos and Bauchi, where as male and female Carp from Jos and Bauchi showed genetic closeness.

Fish community responses to invasive fish removal and installation of an exclusion barrier at Lake Ohinewai, Waikato

ABSTRACTIntroduced common carp (Cyprinus carpio) are a recognised threat to New Zealand’s freshwater ecosystems. In 2011, an invasive fish removal programme was undertaken in 16.8 ha Lake Ohinewai, a Waikato riverine lake. Active fish removal using netting and boat electrofishing was supported by installation of a one-way exclusion barrier on the outflow to Lake Ohinewai. The barrier was designed to allow fish passage downstream out of the lake, while preventing adult carp from moving upstream. The estimated carp population was reduced from 8,548 fish (5,863–12,937, 95% confidence limits) in 2011–454 fish (251–889, 95% CL) in 2014. However, by 2016 the carp population had recovered to 2,063 fish (1,070–4,328, 95% CL) with increased abundance in invasive brown bullhead catfish (Ameiurus nebulosus) also observed. This research demonstrates that carp populations can be reduced to low abundances in the short to medium term, but continued removal will be required for on-going control.

Pichia pastoris yeast as a vehicle for oral vaccination of larval and adult teleosts

Oral vaccination is of major interest because it can be used for mass vaccination of fish of various size and age. Given that their administration is relatively easy and stress-free, oral vaccines have both economic and animal welfare benefits. Yet, mostly due to their limited efficacy, only very few oral vaccines are available to aquaculture industry. Here we present a method for oral vaccine delivery based on the yeast Pichia pastoris. We could express a model antigen, green fluorescent protein (GFP), in this yeast and subsequently show delivery of the GFP protein to the intestine of juvenile flounder or adult carp and trout. We tested this approach in several commercially-relevant fish species, from juvenile to adult stage. To test the oral delivery of antigen to larval fish, the GFP-expressing Pichia pastoris was first fed to planktonic crustacean Daphnia or rotifers that served as ‘bioencapsulation vehicles’ and afterwards, fed to flounder larvae. Again, we could show delivery of intact GFP protein to the intestine. In rainbow trout, the orally-administered GFP-expressing yeast elicited a rapid local innate immune response in the intestine and a subsequent systemic response in the spleen. Our results show that Pichia pastoris is a good vehicle for oral antigen delivery and that it can be used in non-encapsulated form for older fish or in bioencapsulated form for larval fish. We discuss the immunomodulatory properties of the yeast itself, and its potential to enhance local immune responses and act as an adjuvant.

Synthesis and Evaluation of Two Novel All -trans-Retinoic Acid Conjugates: Biocompatible and Functional Tools for Retina Research.

The vitamin A derivative all- trans-retinoic acid (ATRA) is an important biologically active metabolite that regulates a variety of essential biological processes in particular via gene-regulatory mechanisms. In the retina, ATRA is a light-dependent byproduct of the phototransduction cascade. Here, ATRA is not only needed for proper retinal development, but it also acts as a neuromodulator on horizontal cells, second-order inhibitory neurons in the outer retina, which reveal morphological and physiological changes when the retina is treated with ATRA. There is evidence that gene-regulatory mechanisms may only be partially involved in these neuromodulatory processes and the underlying nontranscriptional mechanisms are still elusive. This is, among other things, due to the lack of appropriately labeled ATRA, which would allow the tracking of ATRA in cells or a given tissue. To overcome this obstacle, we designed, synthesized, and evaluated two conjugates of ATRA, one conjugated with biotin (biotin-ATRA) and one conjugated with diaminoterephthalate fluorophore (DAT-ATRA), as molecular tools for different fields of application. The biocompatibility of both compounds was demonstrated via cell viability assays in cultured N2a-cells. N2a-cells exposed to the compounds showed no significant changes in the viability rate. The functionality of synthesized ATRA-conjugates was verified using retinal tissue derived from adult carp. The binding of ATRA-conjugates to distinct retinal cells was assessed in primary cultures of carp retina. Hereby, horizontal and Müller cells have been identified as specific target cells of the new ATRA compounds. Electron microscopy further confirmed that the new substances are still able to induce synaptic plasticity at horizontal cell dendrites resulting in formation of spine synapses, as it is shown for native ATRA. Taken together, the novel ATRA-conjugates represent biocompatible and functional molecular tools, which may further provide the possibility to track ATRA in neuronal cells and study its modulatory effects in different cell systems.

Source–sink dynamics explain the distribution and persistence of an invasive population of common carp across a model Midwestern watershed

Source–sink theory is an ecological framework that describes how site and habitat-specific demographic rates and patch connectivity can explain population structure and persistence across heterogeneous landscapes. Although commonly used in conservation planning, source–sink theory has rarely been applied to the management of invasive species. This study tested whether the common carp, one of the world’s most invasive species, exhibits source–sink dynamics in a representative watershed in the Upper Mississippi River Basin comprised of a dozen interconnected ponds and lakes. To test for source–sink population structure, we used standard fish sampling techniques, tagging, and genetic assignment methods to describe habitat-specific recruitment rates and dispersal. Five years of sampling revealed that while adult carp were found across the entire watershed, reproductive success (the presence of young carp) was restricted to shallow ponds. Additionally, nearly a third of the carp tagged in a representative pond dispersed into the connected deeper lakes, suggesting that ponds in this system serve as sources and lakes as sinks. This possibility was confirmed by microsatellite analysis of carp tissue samples (n = 1041) which revealed the presence of two distinct strains of carp cohabitating in the lakes, whose natal origins could be traced back to one of two pond systems, with many adult carp attempting to migrate back into these natal ponds to spawn. We conclude that the distribution and persistence of invasive carp in complex interconnected systems may often be driven by source–sink dynamics and that their populations could be controlled by suppressing reproduction in source habitats or by disrupting dispersal pathways, instead of culling individuals from sink habitats.