Fin Erosion Research Articles

Dorsal fin height is not an effective tool to distinguish hatchery and wild steelhead in the field

AbstractObjectiveTo maximize harvest of hatchery steelhead Oncorhynchus mykiss and Pacific salmon Oncorhynchus spp. while reducing impacts to wild conspecifics, fishery managers rely on the ability of anglers to distinguish between the two. Fin erosion, including dorsal fin erosion, is a common result of hatchery rearing of juvenile salmonids. Since the 1980s, managers in the Pacific Northwest have utilized adult steelhead dorsal fin height as a regulatory control rule, requiring anglers to release steelhead with dorsal fins over a height threshold. This approach assumes that all or most hatchery fish have shorter dorsal fins than their wild counterparts. This study was designed to test this assumption.MethodsWe compared steelhead origin (hatchery or wild) determined using scale analysis and adipose fin clipping (hatchery n = 127, wild n = 71) with origin estimated using dorsal fin height.ResultOverall, a static dorsal fin height threshold (2.25 in, 5.72 cm) correctly identified 90% of hatchery‐origin steelhead but misidentified nearly half (44%) of wild fish as hatchery. Dorsal fin height of known hatchery fish correlated with fish length, indicating a weakness of using a static dorsal height threshold as a management tool. The accuracy of distinguishing wild fish improved, but only marginally (56–76%), using a classification model where dorsal fin height of known origin fish from this study was a continuous predictor of origin. In comparison, adipose fin status correctly identified 97% of unmarked fish as wild.ConclusionThe low accuracy of the classification model and static dorsal fin height thresholds at distinguishing hatchery and wild steelhead due to a strong correlation between dorsal fin height and fork length and the high fork length variability of hatchery origin fish. Given the low cost and accuracy of adipose fin clipping and the potentially high conservation risk associated with misidentification, we recommend discontinuing the use of dorsal fin height as a harvest control rule for steelhead.

Kekerabatan Zeylanicobdella arugamensis pada Ikan Kerapu Cantang dengan Pendekatan Molekuler di Jawa Timur dan Lombok

Giant grouper is a highly sought-after cultivated fish in Indonesia due to its high market value. One of the challenges in grouper aquaculture is the infestation of the sea leech ektoparasite Zeylanicobdella arugamensis. The prevalence rate of ektoparasite infestation reaches up to 100%. An effective method to manage ektoparasite infestation is through molecular profiling, serving as preliminary literature in the development of molecular biology efforts to overcome cultivation challenges in giant grouper. This research aims to study the homology and relationship of Zeylanicobdella arugamensis on giant grouper in East Java, specifically in Lamongan, Mandangin, Situbondo, and Lombok. The method used is RT-PCR with mtDNA COI gene primers. Molecular sequence data were collected from samples and compared with data from NCBI GenBank, and analyzed using Neighbor-joining phylogenetic tree method and homology data analysis on BLAST. The research results indicate clinical symptoms in giant grouper including swelling, lesions/wounds, pale skin, decreased appetite, and fin erosion. Electrophoresis results from PCR products show a single band at 750bp for samples from Lamongan, Situbondo, Mandangin, and Lombok. DNA sequencing results on NCBI BLAST and homology analysis against the reference gene were conducted. Homology analysis results between samples from Situbondo and Lamongan show the highest similarity at 98.28%, whereas the lowest similarity is between samples from Mandangin and Situbondo at 88.51%. Based on phylogenetic tree analysis, samples from Lamongan and Situbondo waters show a close relationship with a genetic distance of 0.009272.

Molecular characterization of Aeromonas hydrophila detected in Channa marulius and Sperata sarwari sampled from rivers of Punjab in Pakistan.

Aeromonas hydrophila is one of the major pathogenic bacteria responsible for causing severe outbreaks at fish farms and is also a major global public health concern. This bacterium harbors many virulence genes. The current study was designed to evaluate the antidrug and virulence potential of A. hydrophila by amplifying its antimicrobial resistance and virulence genes using PCR and examining their effects on fish tissues and organs. A total of 960 fish samples of Channa marulius and Sperata sarwari were collected from four sites of the rivers of the Punjab, Pakistan. A. hydrophila isolates were subjected to biochemical identification and detection of virulence and antimicrobial resistance (AMR) genes by PCR. We retrieved 181 (6.46%) A. hydrophila isolates from C. marulius and 177 (6.25%) isolates from S. sarwari. Amplification through PCR revealed the incidence of virulence genes in 95.7% of isolates in C. marulius and 94.4% in S. sarwari. Similarly, amplification through PCR also revealed occurrence of AMR genes in 87.1% of isolates in C. marulius and 83.9% in S. sarwari. Histopathological examination revealed congestion (5.2%) and hepatocyte necrosis (4.6%) in liver, lamellar fusion (3.3%) and the presence of bacterial colonies (3.7%) in gills, fin erosion (6%), and the presence of biofilms (3.5%) in tail fins of infected fish. Phylogenetic tree analysis of 16S rRNA and gyrB gene of A. hydrophila revealed 100% and 97% similarity, respectively, with 16S rRNA gene and gyrB of A. hydrophila isolated in previous studies. The results of antimicrobial susceptibility testing showed that all isolates demonstrated resistance to sulfamethoxazole, ampicillin, neomycin, and norfloxacin, while susceptibility to gentamicin, chloramphenicol, and tetracycline, and intermediate resistance was observed against cefotaxime. The results concluded that examined fish samples were markedly contaminated with virulent and multidrug strains of A. hydrophila which may be of a potential health risk. The study emphasizes the responsible antimicrobial use in aquaculture and the urgent need for effective strategies to control the spread of virulence and antimicrobial resistance genes in A. hydrophila.

Air bubble curtain improves the welfare of captive rainbow trout fry and fingerlings

Fish welfare is becoming a priority for the fish farming industry. The search for practical, easy-to-implement methods to promote farmed fish welfare is therefore essential. Environmental enrichment aims to improve the psychological and physiological needs of a captive animal by increasing the complexity of its environment. During previous studies, we observed that fish seemed to be positively affected by short diffusions of air bubbles. In this study, we evaluated the effects of an innovative enrichment strategy consisting of introducing into the tank at the earliest stages of life, a pipe generating a curtain of air bubbles. Using rainbow trout (Oncorhynchus mykiss) as a captive fish model, we compared the short- (∼7 weeks) and long-term (∼21 weeks) effects of this bubble curtain diffused for one hour four times a day (Bubble condition) to a standard condition without bubbles (Control) on fish growth, aggressive and abnormal behaviors, as well as on fish motivation to access a bubble curtain, their emotional responses and their learning abilities. We found that bubble diffusion decreased aggressive and abnormal behaviors during diffusions in both the short-term and the long-term experiments. In the long-term experiment, this decrease was also observed during feedings and neutral periods when no bubble was diffused. Bubbles were found to be attractive for young Control fish (bubble-naive fish) subjected to a motivation test in the short-term experiment. When subjected to the emotional reactivity test, Bubble fish seemed less fearful, exhibiting a lower maximum velocity than Control fish in the long-term experiment only. However, the other behavioral parameters measured during this test, appetite and plasma cortisol levels were similar between treatments, irrespective of the experimental period. The latency to consume the reward observed in the spatial learning test in the long-term experiment was decreased in Bubble fish compared with Control fish, showing enhanced learning abilities in fish that experienced bubbles for 21 weeks. Growth parameters and fin erosion index did not differ between treatments. We conclude that repeated bubble diffusions act as an environmental enrichment for fish, combining physical, occupational, and sensory enrichment via the tactile stimulations provided by the air bubbles. This type of enrichment had a positive impact on the behavior of farmed rainbow trout in the long term, and would make it possible to integrate the notion of “positive welfare” into fish farms, while guaranteeing easy technical maintenance.

Efficiency of Persicaria salicifolia as a natural alternative antifungal against Aspergillus flavus infection in Oreochromis niloticus from Aswan Governorate, Egypt

Fungal diseases in fish cause economic losses all over the world, and knowledge about them is scarce and outdated in Aswan Governorate, Egypt, making interpretation, prevention, and treatment difficult. The necessity to find a fungicide that is natural, environmentally friendly, and does not emerge drug resistance is a must. Therefore, the current study aimed to isolate and diagnose fungal infection in farmed Oreochromis niloticus, causing mortalities, in Aswan Governorate. During 2021, 200 fresh O. niloticus samples were collected from the Sahary Fish Hatchery and Aswan General Authority for Fish Resources Development fish farm. Some fish showed hemorrhagic lesions all over the body, detachment of scales, and fin erosion. Collected tissue samples were cultured on potato dextrose agar and Sabouraud dextrose agar for phenotypic characterization. Macroscopic and microscopic analyses were used to identify the isolated fungi. A total of 18 fungal species and two varieties appertaining to ten fungal genera were recovered from 48 samples out of 200 examined O. niloticus (24%), with Aspergillus flavus being the most prevalent at a rate of 25.6%. The isolated A. flavus was proven to be pathogenic to farmed O. niloticus, as by experimental infection. The natural herb Persicaria salicifolia had an LC50 value of 41.68 mg/l in exposed O. niloticus and was used to treat A. flavus-infected O. niloticus. It can be concluded that A. flavus poses a major hazard to O. niloticus aquaculture and can be treated with 40 mg/kg in feed or 20 mg/l in water of P. salicifolia for 6 days.

Doxycycline treatment modulates the immune response of tilapia and controls Aeromonas hydrophila infection

The objective of this study was to evaluate the immunopharmacological activity of doxycycline, administered orally in Nile tilapia (Oreochromis niloticus), during experimental infection by Aeromonas hydrophila, through the correlation between therapeutic efficacy and fish immune response. 160 Nile tilapia (±100 g) from the same spawning were distributed in 16 tanks (100 L, n = 10), constituting four treatments: control (infected and untreated); Infected and Treated with 20, 40 and 80 mg of doxycycline/Kg of b.w. Control fish and treated with the lowest dose of doxycycline (20 mg) exhibited typical signs of aeromonosis, including exophthalmos, fin erosion, hemorrhagic septicemia, corneal opacity and ascites. No clinical signs were observed in animals treated with 40 and 80 mg of doxycycline. There was a dose-response effect to the treatment with this tetracycline with relative percentage of survival (RPS) of 60, 73.3 and 93.3% for the treatments with 20, 40 and 80 mg/kg of b.w. when compared to control animals, as well as increased in the production of antibodies anti-A. hydrophila. Doxycycline treatment decreased monocytosis and reactive oxygen species (ROS) production observed in tilapia during A. hydrophila infection. Therefore, doxycycline administered orally to O. niloticus revealed the potential of this antimicrobial for use in tilapia farming, providing convincing results of the therapeutic efficacy against A. hydrophila. These results confirm the hypothesis that the antimicrobial action of doxycycline favored the defense mechanisms of tilapia treated mainly at a dose of 80 mg/kg. Although the exact mechanism of increased antibody response remains to be elucidated, the present observations demonstrate important practical significance for the sanitary management of tilapia farming.

Pathological analysis and antimicrobial susceptibility of Chryseobacterium balustinum RTFCP 298 isolated from diseased rainbow trout, Oncorhynchus mykiss

In this study, six isolates of Chryseobacterium balustinum were characterized from diseased rainbow trout fingerlings. The virulence characteristics, pathogenicity, and antimicrobial susceptibility pattern of these isolates were investigated. The bacterium showed positive results for catalase, cytochrome oxidase, and aesculin hydrolysis, while negative results were obtained for DNase, gelatinase, methyl red, Voges-Proskauer's reaction, Simon citrate, Hydrogen sulphide, and starch hydrolysis. Amino acid metabolism analysis revealed the inability to metabolize arginine, lysine, and ornithine decarboxylase. Molecular characterization (16S rRNA) and phylogenetic analysis revealed the test isolates as C. balustinum, closely related to strain WLT (99.85% similarity) and C. balustinum P-27 (99.77%). Virulence assay indicated haemolytic activity and biofilm formation by the test bacterium. The challenge test confirmed moderate pathogenicity in rainbow trout and established Koch's postulates. The clinical manifestations of infection included fin erosion, eye and body surface haemorrhage, exophthalmia, and organ liquefaction. The minimum inhibitory concentrations of various antimicrobials ranged from 1 to > 256 µg mL−1. The novel synthetic antimicrobial peptides exhibited MICs of 8 to > 256 µg mL−1, suggesting a potential control method. These findings suggest that C. balustinum is an opportunistic pathogen with moderate pathogenicity in rainbow trout. Further research on the host–pathogen relationship is necessary to understand virulence characteristics and pathogenicity in aquaculture.

Chronic stress negatively impacts wound healing, welfare, and stress regulation in internally tagged Atlantic salmon (Salmo salar).

The desire to understand fish welfare better has led to the development of live monitoring sensor tags embedded within individuals for long periods. Improving and understanding welfare must not come at the cost of impaired welfare due to a tag's presence and implantation process. When welfare is compromised, the individual will experience negative emotions such as fear, pain, and distress, impacting the stress response. In this study, Atlantic salmon (Salmo salar) underwent surgical implantation of a dummy tag. Additionally, half of this group was introduced to daily crowding stress. Both groups and an untagged group were followed for 8weeks using triplicate tanks per group. Sampling took place once a week, and where stress was given, it was conducted 24h before sampling. Stress-related measurements were taken to understand if tagging caused chronic stress and explore the chronic stress response and its impact on wound healing. Primary stress response hormones measured included CRH, dopamine, adrenocorticotropic hormone, and cortisol. Secondary stress response parameters measured included glucose, lactate, magnesium, calcium, chloride, and osmolality. Tertiary stress response parameters measured included weight, length, and five fins for fin erosion. Wound healing was calculated by taking the incision length and width, the inflammation length and width, and the inside wound length and width. The wound healing process showed that stressed fish have a larger and longer-lasting inflammation period and a slower wound healing process, as seen from the inside wound. The tagging of Atlantic salmon did not cause chronic stress. In contrast, daily stress led to an allostatic overload type two response. ACTH was elevated in the plasma after 4weeks, and cortisol followed elevation after 6weeks, highlighting a breakdown of the stress regulation. Fin erosion was elevated alongside cortisol increase in the stressed group. This data suggests that tagging previously unstressed fish in a controlled environment does not negatively affect welfare regarding stress responses. It also indicates that stress delays wound healing and increases the inflammatory response, highlighting how continued stress causes a breakdown in some stress responses. Ultimately, the tagging of Atlantic salmon can be successful under certain conditions where proper healing is observed, tag retention is high, and chronic stress is not present, which could allow for the possible measurement of welfare indicators via smart-tags.

Evaluation of different feeding frequencies in RAS-based juvenile pikeperch (Sander lucioperca) aquaculture

Feeding regime, which involve selection of appropriate diet and application of feed itself is a decisive factor in intensive, RAS-based production system – more so, for carnivorous fish culture. It is critical for the economics, resource (feed/nutrients) use efficiency and final profit yield. The present study examined different feeding strategies in juvenile pikeperch reared in RAS for growth performance, survivability, feed utilization, and fish welfare. Juvenile pikeperch (106.59 ± 24.84 g) were cultured in RAS for 112 days and fed at five different feeding intervals (2-h, 4-h, 6-h, 8-h and 12-h) using automatic feeder Imetronic® (Pessac, France). Fishes were fed a commercially standardized pikeperch diet. A higher degree of growth heterogeneity was observed in groups fed in shorter feeding intervals (2-h, 4-h and 6-h). At the end of the experiment, slightly higher fin damage was observed in all tested groups compared to fin conditions of stocked fish especially for dorsal and caudal fins. No significant differences were observed in selected biochemical parameters indicating liver, pancreas, and intestinal function. All tested fish were adequately fed providing sufficient nutrients for proper pikeperch growth and welfare. Nevertheless, the feeding interval 8-hour was evaluated as optimal. This frequency supports higher fish conditions (Fulton's coefficient) and the specific growth rate (SGR), survival rate (SR), weight heterogeneity (CV2), lower fin erosion compared to the other tested frequency and optimal level of biochemical parameters in blood plasma.

Toxic Effects of Arsenic in Commercially Important Fish Rohu Carp, Labeo rohita of Bangladesh

This study was designed to elucidate the effects of arsenic (As) on the morpho-behavior, growth development and molecular mechanisms of a commercially important fish, rohu carp, Labeo rohita, in Bangladesh. Fish fry with an average weight of 387.5 ± 169.25 mg and an average length of 3.35 ± 0.37 cm were collected from a local hatchery in Mymensingh, Bangladesh and acclimatized for a week in the Department of Fisheries, University of Dhaka before starting the exposure with arsenic. Fishes were exposed for a period of 14 days with three treatments of NaAsO2, namely treatment 1(T1)—2.5 mg/L; treatment 2 (T2)—15 mg/L; and treatment 3 (T3)—30 mg/L, along with a control (C)—0.0 mg/L, with three replicates. These concentrations were determined based on the LC50 value for 96 h measured for this experiment. This study revealed remarkable morphological abnormalities and deformities in arsenic-exposed rohu carp. In fish exposed to 30 mg/L, caudal fin erosion was a frequent deformity. There was no significant difference in RNA:DNA ratio among the treatments. The overall weight of fish was decreased as the concentration of arsenic was increased. The T3 fish had a statistically significant negative weight gain (−0.05 ± 0.07 g), but the other treatments (T1 and T2) and control fish had no significant weight gain. Different types of histopathological changes were observed in the gills and intestines of arsenic-treated fish. Necrosis and severe damages were found in the secondary lamellae of gills at the highest arsenic concentration (30 mg/L). Epithelial lifting, irregular shape and damages in the gill raker were also observed in the primary lamellae of the gills for the same treatment. In this study, the expression of heat shock protein (HSP 60) and metallothionein (MT) genes was assessed by qPCR, and these genes were upregulated in different treatments compared to controls. The findings of the present study suggest that arsenic pollution significantly changes the morphology, behavior, growth, development, histopathology and molecular mechanisms of this economically important fish, rohu carp, in Bangladesh.

Feed Digestion, Growth and Disease Prevalence in Nile Tilapia (Oreochromis niloticus) Cultured at Different Water Exchange Rates in a Recirculating Aquaculture System

The quality of culture water and the rate of water flow within a culture system can affect fish growth and health. In this study, the effects of different water flow rates on digestion efficiency, growth and welfare of juvenile Nile tilapia (Oreochromis niloticus) (Initial weight: 25.75±0.47 g) were investigated. Fish (15 per tank) were randomly stocked into twelve 150 L thermoplastic tanks of a recirculating aquaculture system and subjected in quadruplicate groups to water flow rates of 50 Lh-1 (Low exchange; LE), 100 Lh-1 (Medium exchange; ME) and 150 Lh-1 (High exchange; HE) for 72 days. Water quality parameters including total ammonia nitrogen, nitrate and alkalinity, dry matter, protein and lipid digestibilities, somatic growth and some welfare indicators including haematology and disease prevelance were monitored. There were no significant differences in growth among the treatments. Higher prevalence of cataract, fin erosion, oral and dermal lesions were observed in the LE and ME treatments indicating compromised welfare. There were no statistical differences among the treatments in terms of nutrient digestibility. This study has shown that culturing Nile tilapia under moderately high water flow rates of at least 100% tank water replacement per hour in RAS ensures good growth and feed utilization.

Isolation, Identification and Characterization of a Novel Megalocytivirus from Cultured Tilapia (Oreochromis spp.) from Southern California, USA.

Simple SummaryAquaculture is the world’s fastest-growing food production sector, with tilapia (Oreochromis spp.) among the most important cultured species. First reported in red seabream, Pagrus major, in 1990, an increasing number of megalocytiviruses are responsible for losses that threaten the production and economic sustainability of important cultured fish species, including tilapia. In the current study, we describe an epizootic in tilapia fingerlings from Southern California, USA and report the discovery of a novel megalocytivirus associated with the mortalities. In spring 2019, diseased four-month-old tilapia (Oreochromis spp.) from an aquaculture farm in Southern California, USA were received for diagnostic evaluation with signs of lethargy, anorexia, abnormal swimming, and low-level mortalities. At necropsy, non-specific external lesions were noted including fin erosion, cutaneous melanosis, gill pallor, and coelomic distension. Internal changes included ascites, hepatomegaly, renomegaly, splenomegaly, and multifocal yellow-white nodules in the spleen and kidney. Cultures of spleen and kidney produced bacterial colonies identified as Francisella orientalis. Homogenized samples of gill, brain, liver, spleen, and kidney inoculated onto Mozambique tilapia brain cells (OmB) developed cytopathic effects, characterized by rounding of cells and detaching from the monolayer 6–10 days post-inoculation at 25 °C. Transmission electron microscopy revealed 115.4 ± 5.8 nm icosahedral virions with dense central cores in the cytoplasm of OmB cells. A consensus PCR, targeting the DNA polymerase gene of large double-stranded DNA viruses, performed on cell culture supernatant yielded a sequence consistent with an iridovirus. Phylogenetic analyses based on the concatenated full length major capsid protein and DNA polymerase gene sequences supported the tilapia virus as a novel species within the genus Megalocytivirus, most closely related to scale drop disease virus and European chub iridovirus. An intracoelomic injection challenge in Nile tilapia (O. niloticus) fingerlings resulted in 39% mortality after 16 days. Histopathology revealed necrosis of head kidney and splenic hematopoietic tissues.

Effects of Baffles on Raceway Cleaning, Fin Erosion, In‐Hatchery Survival, and Postrelease Angler Catch of Catchable‐Sized Hatchery Rainbow Trout

AbstractHatchery fish exposed to exercise training often exhibit physiological and behavioral benefits compared with unexercised fish, but results from previous studies have been equivocal and have rarely examined postrelease performance of stocked fish. We evaluated various in‐hatchery and postrelease consequences of rearing catchable‐sized (~254‐mm) Rainbow Trout Oncorhynchus mykiss in a raceway installed with baffles, the intent being to self‐clean the raceway and exercise fish. Installing baffles increased water velocities experienced by fish, with some velocities exceeding 0.26 m/s (1.0 body length per second). In contrast, the maximum velocity experienced by fish in the control raceway was 0.07 m/s (0.27 body lengths per second). Prior to stocking, fin erosion (as measured by relative dorsal and pectoral fin lengths) did not differ between the baffled and unbaffled raceways, but surprisingly, survival was reduced for baffled fish. Catch by anglers and mean time to capture did not differ between raceways but did differ by water type (i.e., lentic, lotic, and community pond waters). While the augmented velocities along the bottom of the baffled raceway assisted with clearing some fish waste, they were not entirely effective and raceways still required some sweeping. Taken collectively, our results suggest that installing baffles in production‐scale raceways rearing catchable‐sized Rainbow Trout is not advantageous.

Nutrition and Metabolism of Minerals in Fish.

Simple SummaryOur aim is to introduce the mineral nutrition of fish and explain the complexity of determining requirements for these elements, which are absorbed and excreted by the fish into the surrounding water. To date, only the requirements for nine minerals have been investigated. The review is focused on the absorption and the dietary factors that reduce their absorption from feed ingredients of plant and animal origin. Some diseases, such as cataracts, anemia and bone deformity, have been linked to dietary deficiency of minerals.Aquatic animals have unique physiological mechanisms to absorb and retain minerals from their diets and water. Research and development in the area of mineral nutrition of farmed fish and crustaceans have been relatively slow and major gaps exist in the knowledge of trace element requirements, physiological functions and bioavailability from feed ingredients. Quantitative dietary requirements have been reported for three macroelements (calcium, phosphorus and magnesium) and six trace minerals (zinc, iron, copper, manganese, iodine and selenium) for selected fish species. Mineral deficiency signs in fish include reduced bone mineralization, anorexia, lens cataracts (zinc), skeletal deformities (phosphorus, magnesium, zinc), fin erosion (copper, zinc), nephrocalcinosis (magnesium deficiency, selenium toxicity), thyroid hyperplasia (iodine), muscular dystrophy (selenium) and hypochromic microcytic anemia (iron). An excessive intake of minerals from either diet or gill uptake causes toxicity and therefore a fine balance between mineral deficiency and toxicity is vital for aquatic organisms to maintain their homeostasis, either through increased absorption or excretion. Release of minerals from uneaten or undigested feed and from urinary excretion can cause eutrophication of natural waters, which requires additional consideration in feed formulation. The current knowledge in mineral nutrition of fish is briefly reviewed.

Health status of cultured catla (Gibelion catla) in Hill tracts region of Bangladesh

A study was carried out for a period 8 months from March 2020 to October 2020 to observe the health status of cultured catla (Gibelion catla) in three Upazilas viz., Khagrachari Sadar, Ramgarh and Mahalchari upazila of Khagrachari district through clinical procedures. Data were collected through personal contact, sampling, questionnaire interview and discussions with key informants. Clinically, Fish from Vhaibonchara and Perachara at Khagrachari Sadar Upazila, Patachara at Ramgarh Upazila were found to be healthy during summer. During rainy season, catla of Mahalchari Upazila were affected with dropsy like clinical signs where major signs were swollen of abdomen, removal of scales and superficial injury. Tail and fin rot affected catla were collected from Ramgarh Upazila having erosion of fins and tail and the presence of white spots in fin and tail region. Cultured catla in rainy season were more affected than those of summer season. However, catla of summer season had reduced clinical changes than those of rainy season. From clinical and pathological point of view healthy catla were noticed in summer and moderately infected in rainy season. It could be mentioned that production and health status of catla were increased in summer season of Khagrachari Sadar area compared with other areas and season. During the study period water temperature were ranged between 23°C to 35°C in summer and 23°C in rainy season. The highest pH was 8.2 ± 0.20 recorded from Mobachari of Mahalchari in summer and the lowest was 6.5 ± 0.25 from the Perachara of Khagrachari Sadar Upazila. Thus necessary measures need to be taken especially during rainy season.

Addressing the welfare needs of farmed lumpfish: Knowledge gaps, challenges and solutions

AbstractLumpfish (Cyclopterus lumpus L.) are increasingly being used as cleaner fish to control parasitic sea lice, one of the most important threats to salmon farming. However, lumpfish cannot survive feeding solely on sea lice, and their mortality in salmon net‐pens can be high, which has welfare, ethical and economic implications. The industry is under increasing pressure to improve the welfare of lumpfish, but little guidance exists on how this can be achieved. We undertook a knowledge gap and prioritisation exercise using a Delphi approach with participants from the fish farming sector, animal welfare, academia and regulators to assess consensus on the main challenges and potential solutions for improving lumpfish welfare. Consensus among participants on the utility of 5 behavioural and 12 physical welfare indicators was high (87–89%), reliable (Cronbach's alpha = 0.79, 95CI = 0.69–0.92) and independent of participant background. Participants highlighted fin erosion and body damage as the most useful and practical operational welfare indicators, and blood parameters and behavioural indicators as the least practical. Species profiling revealed profound differences between Atlantic salmon and lumpfish in relation to behaviour, habitat preferences, nutritional needs and response to stress, suggesting that applying a common set of welfare standards to both species cohabiting in salmon net‐pens may not work well for lumpfish. Our study offers 16 practical solutions for improving the welfare of lumpfish and illustrates the merits of the Delphi approach for achieving consensus among stakeholders on welfare needs, targeting research where is most needed and generating workable solutions.

Resistome characterization of Flavobacterium columnare isolated from freshwater cultured Asian sea bass (Lates calcarifer) revealed diversity of quinolone resistance associated genes

Flavobacterium columnare is a Gram-negative bacterium which causes columnaris disease in freshwater fish species worldwide. Antibiotics, especially quinolone, is a primary therapeutic option to mitigate the economic loss caused by this disease. Phenotypic characterization and susceptibility testing were performed to identify quinolone resistance (QR)-associated genes in F. columnare isolated from freshwater cultured Asian sea bass. A total of 15 F. columnare isolates were collected from moribund fish that exhibited columnaris-like clinical signs and lesions including gill necrosis, saddleback lesion, and fin erosion. Phylogenetic analysis based on 16S rRNA and dnaK revealed that these isolates belonged to genetic group (GG) 2 and 4. Disk diffusion test results indicated that the 15 isolates were susceptible to all tested antibiotics except quinolones. Five and six isolates were resistant to oxolinic (OA) (33.33%) and nalidixic acid (NA) (40%) respectively. Broth microdilution indicated that highest OA, NA and enrofloxacin (ENR) minimum inhibitory concentration (MIC) values were 16, 64 and 1 μg/mL respectively. The MIC level to quinolone of GG 2 was higher for the GG 4 counterparts. Sequence analysis revealed a serine:phenylalanine amino acid substitution at position 83 (S83F) and a glutamine:histidine amino acid substitution at position 458 (Q458H) of quinolone resistance-determining regions (QRDRs) of gyrA and gyrB respectively. The Q458H in gyrB was identified as a novel non-synonymous mutation of the Flavobacteriaceae family. A genome-scale resistome analysis revealed that connections between GG and QR level potentially correlated with the presence or absence of chromosomal antimicrobial resistance genes and accumulated mutations in QRDRs. This study provide a guidance for choosing antibiotics for treatment columnaris disease and point out the important quinolone resistance mechanisms in F. columnare.

Phenotypic, Phylogenetic Characterization and Antimicrobial Susceptibility Determination of Chryseobacterium piscicola Isolates Recovered from Diseased Rainbow Trout

Twelve isolates recovered from rainbow trout weighing 1-4 grams showing signs of anorexia, exophthalmos, darkening, and dorsal fin erosion were used in our study. In addition to conventional microbiological tests, comprehensive phenotypic characterization has been performed using the Biolog GEN III microplate. Molecular identification and characterization were performed using the 16S rRNA region. Antimicrobial susceptibilities of the isolates were determined using the disk diffusion method. Our isolates were identified as Chryseobacterium piscicola in molecular identification performed by sequence analysis based on the 16S rRNA region. In a phylogenetic analysis of our isolates, obtained from three different hosts in America, Chile, and Finland, five genogroups were determined with high similarity rate. Isolates from Finland, Chile, the United States, and Turkey (only C-316) were found in the same genogroup. It was determined that the phylogenetic analysis created with the 16S rRNA region could not distinguish the host from which the bacteria was isolated. The phenotypic characterization of six representative isolates selected according to phylogenetic analysis, was determined with the Biolog GENIII microplate. Based on the Biolog GENIII results of the representative isolates, the results of 40 out of 94 tests were found to be variable. With this result, it was found that C. piscicola isolates were not phenotypically homogeneous. Besides, it was found that the zone diameters of our isolates against florfenicol, enrofloxacin, and sulfamethoxazole/trimethoprim were higher than the other isolates, in addition to that C-41 was the most resistant isolate.

Identification and characterization of Sinuolinea niloticus from Nile tilapia (Oreochromis niloticus) farmed in Botucatu, Brazil

Myxozoans can induce losses in production of marine and freshwater fish. Recently, a new parasitic myxozoan species, Sinuolinea niloticus, was identified and its importance highlighted. This study aimed to investigate Sinuolinea niloticus and its macroscopic and microscopic alterations in Nile tilapia (Oreochromis niloticus) specimens from fish farms in Botucatu, Sao Paulo, Brazil, as well as its molecular detection. Thirty tilapias from three different fish farms were collected and submitted to necropsy examination, where organs were sampled for histopathological and molecular analysis. The main necroscopic findings at all three fish farms were hemorrhaging, fin erosion, hepatomegaly, and splenomegaly. Microscopically, the main findings were degeneration of hepatocytes and hepatitis, epithelial and goblet cell hyperplasia in the gills, nephritis, gastritis, and presence of myxozoan-like structures in different organs. S. niloticus, detected by qPCR, showed a 90% prevalence among surveyed fish at farm 1 and 100% at farms 2 and 3. The high prevalence found in this study shows the importance of this myxozoan as a potential pathogenic agent of farmed O. niloticus that negatively affects fish health and, consequently, production.

Prevalence and Intensity of Salmincola edwardsii in Brook Trout in Northwest New Brunswick, Canada.

Parasites can compromise the health and fitness of individual fish, and it is important to generate baseline information that can then be used to document changes in the abundance and distribution of potentially pathogenic parasites. The ectoparasitic copepod Salmincola edwardsii was assessed with respect to prevalence (percentage of infected fish per site), infection intensity (number of parasites per infected fish), and attachment location on Brook Trout Salvelinus fontinalis in northwest New Brunswick, Canada. Ten sample sites were assessed, with six sites on two streams in the Quisibis River basin and four sites on three streams in the Restigouche River basin. Parasite species identity was supported by 100% sequence identity with S.edwardsii in a variable region within 28S rDNA. The prevalence of fish infected per site ranged from 19.0% to 79.6%, with an overall prevalence of 48.5±19.1% (mean±SD) per site. Mean infection intensity was 1.5±0.9 copepods/fish (range=1-7), with parasites almost exclusively surrounding the dorsal fin and/or adipose fin (97.6%). There was no influence of trout age-class on parasite prevalence. Some fish presented with fin erosion at the site of parasite attachment (12.5%), and 6.2% also presented with hyperplastic skin lesions where no parasites were observed, that could be misinterpreted as secondary bacterial or fungal infections. Skin and fin damage were significantly more common when fish were infected with three or more individual parasites. The pathogenic potential of this parasite makes its presence noteworthy as a risk to salmonids that are both recreationally and ecologically important.