Seasonal patterns in the community of gill monogeneans on wild versus cultured orange‐spotted grouper,Epinephelus coioides Hamilton, 1822 in Daya Bay,South China Sea

Epinephelus is among the most important fish genera in the Southeast Asian Pacific coastal systems. In Chinese coast, the orange‐spotted grouper Epinephelus coioides is one of the most significant species based on culture volume, and it is consumed all over the world. Very little information exists on this species’ parasitofauna. Composition and temporal variation in the community structure of the gill monogeneans on wild versus cultured E. coioides from Daya Bay (23°25′N, 117°2′E), South China Sea were determined using seasonal samples taken between April 2008 and January 2009. Eight species of monogeneans of three families and four genera on the gills of E. coioides were found: Neobenedenia melleni, Haliotrema cromileptis, Diplectanum grouperi, Pseudorhabdosynochus justinei, P. lantauensis, P. coioidesis, P. serrani and P. shenzhenensis. Eight of the monogenean species exhibited seasonal variation in their infection dynamics associated with environmental changes during seasons. The variations in the infection dynamics generated changes in the community structure during the sampling periods. Moreover, in the three different host living environments (wild, monocultured and polycultured), the monogenean communities exhibited the different seasonal patterns.     

Can barber goby Elacatinus figaro control Neobedenia melleni infections on dusky grouper Epinephelus marginatus?

The interaction between cultured barber goby Elacatinus figaro (cleaner fish) and the dusky grouper Epinephelus marginatus, and the efficiency of the cleaner fish in removing ectoparasites were evaluated. When the interaction between these two species was observed, cleaner fish showed a preference for the largest groupers. In a second trial, treatments: TWC (Control) – two groupers without a cleaner fish, T1C – two groupers with one cleaner fish, T3C – two groupers with three cleaner fish and T6C – two groupers with six cleaner fish were tested in four replicates. After 8 days, monogeneans were removed and identified as Neobenedenia melleni. The highest mean abundance of parasites was found on the groupers in the TWC group (37 parasites per host) and the lowest on those in the T6C group (4.1 parasites per host). By increasing the number of cleaner fish, a higher cleaning efficiency was obtained, as observed in T6C, where almost 90% of the parasites were removed. Possibly, this removal would have been complete if the number of cleaners had not been reduced in the treatments due to the mortalities observed. This study demonstrates the possibility of using gobies to remove monogeneans and in improving grouper health.     

Ulcerative dermatitis in wild dusky grouper Epinephelus marginatus (Lowe) from Libyan waters

In the period 2013–2015, wild dusky grouper, Epinephelus marginatus (Lowe), caught in Libyan coastal waters and ranging in size from 42 to 92 cm in total length, were observed to have distinctive skin lesions of unknown aetiology. Histopathologically, the lesions comprised a multifocal, unilateral or bilateral dermatitis, involving the epidermis, superficial dermis and scale pockets, and sometimes, in severe cases, the hypodermis. Severe lesions had marked epidermal spongiosis progressing to ulceration. Healing was observed in some fish. Bacteria and fungi could be isolated from severe lesions, although they were not seen histopathologically in early‐stage lesions. By contrast, metazoan parasite eggs were observed in the dermis and epidermis of some fish with mild and moderate dermatitis. Unidentified gravid digenean trematode parasites carrying similar eggs were also seen within the blood vessels of the deep and superficial dermis. The cause of this distinctive condition, termed dusky grouper dermatitis (DGD), and its potential impact upon already threatened Mediterranean wild dusky grouper populations and upon cultured grouper more widely have yet to be established.     

Prevalence of nematode parasite,Contracaecum, in Nile tilapia,African catfish and Barbus species in Lake Hawassa,Ethiopia

A cross‐sectional study was conducted from November 2017 to March 2018 at Lake Hawassa to determine the prevalence of larval Contracaecum infestation in Nile tilapia, (Oreochromis niloticus), African Catfish (Clarias gariepinus) and Barbus species (Barbus intermedius). Fifty‐two point six per cent (52.6%) previous prevalence and 5% precision were used to estimate the sample size. Accordingly, a total of 383 randomly sampled fish species comprising of 163 (42.6%) C. gariepinus, 159 (41.5%) O. niloticus and 61(15.9%) B. intermedius were examined. The length and weight of each sampled fish were recorded. All the sampled fish were examined for the evidence of Contracaecum parasites in Hawassa University Veterinary Parasitology and Pathology Laboratory. Chi‐square values and comparison of proportions were used to analyse the data. The overall prevalence of Contracaecum parasites of fish population was 31.6%. The distribution of parasite was significantly affected by fish species (p = .000), sexes (p = .018), length (p = .003) and weight classes of fish (p = .026). As a hygienic problem and gutting activity conducted at the sides of the Lake Hawassa and distribution of discarded fish wastes for surrounding piscivorous birds by butchers and other people, the life cycle of Contracaecum parasite was perpetuated. Thus, the parasite is of zoonotic significance. Therefore, awareness creation activities for societies and control of fish parasites should be conducted in the study area.     

Natural outbreak of Streptococcus agalactiae (GBS) infection in wild giant Queensland grouper, Epinephelus lanceolatus (Bloch), and other wild fish in northern Queensland, Australia

Ninety‐three giant Queensland grouper, Epinephelus lanceolatus (Bloch), were found dead in Queensland, Australia, from 2007 to 2011. Most dead fish occurred in northern Queensland, with a peak of mortalities in Cairns in June 2008. In 2009, sick wild fish including giant sea catfish, Arius thalassinus (Rüppell), and javelin grunter, Pomadasys kaakan (Cuvier), also occurred in Cairns. In 2009 and 2010, two disease epizootics involving wild stingrays occurred at Sea World marine aquarium. Necropsy, histopathology, bacteriology and PCR determined that the cause of deaths of 12 giant Queensland grouper, three wild fish, six estuary rays, Dasyatis fluviorum (Ogilby), one mangrove whipray, Himantura granulata (Macleay), and one eastern shovelnose ray, Aptychotrema rostrata (Shaw), was Streptococcus agalactiae septicaemia. Biochemical testing of 34 S. agalactiae isolates from giant Queensland grouper, wild fish and stingrays showed all had identical biochemical profiles. The 16S rRNA gene sequences of isolates confirmed all isolates were S. agalactiae; genotyping of selected S. agalactiae isolates showed the isolates from giant Queensland grouper were serotype Ib, whereas isolates from wild fish and stingrays closely resembled serotype II. This is the first report of S. agalactiae from wild giant Queensland grouper and other wild tropical fish and stingray species in Queensland, Australia.     

The risk of parasite transfer to juvenile fishes by live copepod food with the example Triaenophorus crassus and Triaenophorus nodulosus

Natural zooplankton is a potential food resource for juvenile fish in fish farms as it is a good source of fats, carbohydrates, and protein. However, it is also a potential source of parasites and pathogens. The present study was conducted (1) to estimate the risk of parasite transfer by live copepod food under intensive farming conditions using the parasites Triaenophorus crassus and Triaenophorus nodulosus as example and (2) to look for strategies to avoid parasite infestation of juvenile fish.An easy and routinely applicable aniline blue staining method was developed to check the infestation levels of copepods with procercoids during the on-growing season of juvenile fish. From the copepod species occurring in zooplankton Cyclops spp. was infested frequently (9.4 ± 12.0%, maximum 38.7%), Diaptomus spp. infrequently (1.5 ± 1.6%, maximum 3.2%), Daphnia spp. never. Juvenile grayling, Thymallus thymallus, and corgonids, Coregonus sp., which had been fed with natural zooplankton revealed infestations rates with T. crassus of circa 5%, with T. nodulosus of circa 10%. As the occurrence of procercoids in the zooplankton was temporary limited, Triaenophorus infestation can be avoided by using artificial food instead of live copepods during the risky season.To prevent parasite infestation of juvenile fish methods were investigated to eradicate procercoids from copepods by chemical treatment (sodium chloride, hydrogen peroxide, citric acid treatment) and by freeze-thawing methods. Chemical methods failed to remove procercoids. In fish, which had been fed with frozen thawed zooplankton, no Triaenophorus spp. infestation was observed. Their survival rates were similar as in the control fed with live zooplankton, however the weight of the fish was significantly lower.     

Growth performance and disease resistance against Vibrio vulnificus infection of novel hybrid grouper (Epinephelus lanceolatus × Epinephelus fuscoguttatus)

Groupers are economically important for aquaculture in Thailand. A novel hybrid grouper (Epinephelus lanceolatus × Epinephelus fuscoguttatus) has been successful cross‐bred; therefore, the present work aimed to assess the hybrid's traits. The growth performance, strength and tolerance to a pathogenic bacterial infection of this hybrid were compared with its parent species, tiger grouper and giant grouper. The results of all measured growth parameters indicated that the hybrid strain grew fastest followed by giant and tiger grouper respectively. The expressions of the growth‐related genes, insulin‐like growth factor (IGF) I and II, were also analysed in fish muscle and liver which are the main target organs in fish growth regulation. Among tested species, similar expression patterns of IGF‐I and IGF‐II were detected in both organs. The levels of these genes in liver and muscle of hybrid and giant grouper were higher than those of tiger grouper comparable with the growth manner. After challenge with Vibrio vulnificus, the immunological parameters, clearance time of Vibrio in haemolymph and survival was measured to verify the fish immunity. Leucocyte number, lysozyme activity and the ability to eliminate the pathogen were very high in hybrid and giant grouper while these parameters were lower in tiger grouper. Correspondingly, the mortality rate of tiger grouper was higher than others and % survival at the end of observation time (15 days post challenge) was lowest in infected tiger grouper. Altogether, the results suggested that the hybrid grouper has desirable traits that will improve cultured grouper.     

Infection and pathology in Queensland grouper,Epinephelus lanceolatus, (Bloch), caused by exposure to Streptococcus agalactiae via different routes

Since 2007, 96 wild Queensland groupers, Epinephelus lanceolatus, (Bloch), have been found dead in NE Australia. In some cases, Streptococcus agalactiae (Group B Streptococcus, GBS) was isolated. At present, a GBS isolate from a wild grouper case was employed in experimental challenge trials in hatchery‐reared Queensland grouper by different routes of exposure. Injection resulted in rapid development of clinical signs including bilateral exophthalmia, hyperaemic skin or fins and abnormal swimming. Death occurred in, and GBS was re‐isolated from, 98% fish injected and was detected by PCR in brain, head kidney and spleen from all fish, regardless of challenge dose. Challenge by immersion resulted in lower morbidity with a clear dose response. Whilst infection was established via oral challenge by admixture with feed, no mortality occurred. Histology showed pathology consistent with GBS infection in organs examined from all injected fish, from fish challenged with medium and high doses by immersion, and from high‐dose oral challenge. These experimental challenges demonstrated that GBS isolated from wild Queensland grouper reproduced disease in experimentally challenged fish and resulted in pathology that was consistent with that seen in wild Queensland grouper infected with S. agalactiae.     

Temporal and Spatial Variations of Ectoparasites on Cage‐reared Channel Catfish,Ictalurus punctatus,in Tamaulipas,Mexico

Studies in cage‐cultured fish have reported spatial and temporal variations on parasite prevalence; however, most of these studies have been carried out in cold water and marine environments. Channel catfish, Ictalurus punctatus, is the main floating cages‐raised species used in intensive fish culture in Tamaulipas. In Mexico, there are no seasonal reports on fish parasites in this type of cage system. The aim of the present study was to determine the prevalence and mean intensity of ectoparasites of cage‐cultured channel catfish in a year. Fish were sampled bimonthly from six locations in Tamaulipas and measured and evaluated for ectoparasites. Results showed the presence of two gill‐dwelling metazoans, Ligictaluridus floridanus and Ergasilus cerastes and one skin‐dwelling protozoan, Trichodina sp.; a pattern characterized by peaks in prevalence in early autumn for L. floridanus and late autumn for E. cerastes was observed. In addition, geographic location had a significant effect on the prevalence of L. floridanus and E. cerastes. It was also observed that presence of these parasites was not associated with any fish mortality. To our knowledge, this is the first seasonal study on ectoparasite prevalence on channel catfish reared in cages in México.     

Microbiota of yellow grouper (Epinephelus awoora Temminck & Schlegel, 1842) fed two different diets

The rapidly growing yellow grouper industry has experienced relatively severe bacterial disease problems in China. The proliferation of pathogens in fish can be suppressed by commensal microbiota. In this background, we used nested polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE) and sequence analysis to investigate microbiota in the skin, gills and intestines, including adherent bacteria and non‐adherent bacteria in yellow grouper fed with natural diet and complete feed. A total of 21 bacterial species were identified using phylogenetic analysis. The γ‐Proteobacteria group (81.0%, 17 species) dominated the bacterial communities in yellow grouper completely. Others belonged to Firmicutes (9.5%, two species), Actinobacteria (4.75%, one species) and Verrucomicrobia (4.75%, one species). The higher similarities (above 91%) of the DGGE band patterns in skin, gill and intestinal‐non‐adherent bacteria between two groups of fish indicated that existed more stable microbial communities existed in these specifically ecological niches in yellow grouper. However, considerable differences existed between two intestinal‐adherent bacteria (IAB) samples; that is, compared with natural diet fed yellow grouper, higher bacterial apparent species richness and possibly less abundance existed in IAB in fish fed with complete diets, probably indicating that the community structures in IAB were affected easily and significantly by diet.     

Quantitative trait locus mapping of growth‐related traits in inter‐specific F1 hybrid grouper (Epinephelus fuscoguttatus × E. lanceolatus) in a tropical climate

Growth‐related traits are the main target of genetic breeding programmes in grouper aquaculture. We constructed genetic linkage maps for tiger grouper (Epinephelus fuscoguttatus) and giant grouper (E. lanceolatus) using 399 simple sequence repeat markers and performed a quantitative trait locus (QTL) analysis to identify the genomic regions responsible for growth‐related traits in F₁ hybrid grouper (E. fuscoguttatus × E. lanceolatus). The tiger grouper (female) linkage map contained 330 markers assigned to 24 linkage groups (LGs) and spanned 1,202.0 cM. The giant grouper (male) linkage map contained 231 markers distributed in 24 LGs and spanned 953.7 cM. Six QTLs affecting growth‐related traits with 5% genome‐wide significance were detected on different LGs. Four QTLs were identified for total length and body weight on Efu_LG8, 10, 13 and 19 on the tiger grouper map, which explained 6.6%–12.0% of the phenotypic variance. An epistatic QTL with a reciprocal association was observed between Efu_LG8 and 10. Two QTLs were identified for body weight on Ela_LG3 and 10 on the giant grouper map, which explained 6.9% of the phenotypic variance. Two‐way analysis of variance indicated that the QTL on Efu_LG13 interacts with the QTLs on Ela_LG3 and 10 with large effects on body weight. Furthermore, these six QTLs showed different features among the winter, summer and rainy seasons, suggesting that environmental factors and fish age affected these QTLs. These findings will be useful to understand the genetic structure of growth and conduct genetic breeding in grouper species.     

Occurrence of trypanosomiasis in net‐cage cultured groupers (Cromileptes altivelis and Epinephelus fuscoguttatus) in Nanshan port of Sanya,Hainan province,China

In the present study, reported was an unidentified trypanosome that caused massive mortalities of cultured humpback grouper, Cromileptes altivelis (Valenciennes, 1828) and brown‐marbled grouper, Epinephelus fuscoguttatus (Forsskål, 1775) in the net‐cages in Sanya, China, and some general pathological features of E. fuscoguttatus after experimental infection of the trypanosome. Before dying in the net cages of diseased fish, listlessness and anorexia were the observable symptoms. The blood of the diseased fish was light‐coloured in comparison with that of healthy one. E. fuscoguttatus experimentally infected with this trypanosome are with different degrees of engorgement in gill lamella, liver, spleen and kidney. Tissue lesion and necrosis were observed in liver and spleen of diseased fish.     

Nanoemulsions with oleoresin of Copaifera reticulata (Leguminosae) improve anthelmintic efficacy in the control of monogenean parasites when compared to oleoresin without nanoformulation

This study compared the in vitro anthelmintic activity of Copaifera reticulata oleoresin (200, 400, 600, 800 and 1,000 mg/L) and of nanoemulsions prepared with this oleoresin (50, 100, 150, 200 and 250 mg/L) against monogeneans on the gills of Colossoma macropomum. The major compounds present in the oleoresin of C. reticulata were γ-macrocarpene (14.2%), α-bergamotene (13.6%), β-selinene (13.4%) and β-caryophyllene (11.7%). All concentrations of the nanoemulsion and the oleoresin without nanoformulation showed anthelmintic efficacy against monogeneans, and higher concentrations led to more rapid parasite mortality. Structural damages to the tegument of the parasites exposed to C. reticulata oleoresin were observed with scanning electron microscopy. At two hours of exposure, fish showed 100% tolerance to all nanoemulsion concentrations used in the in vitro assays, whereas 100% mortality was shown in the fish exposed to the oleoresin without nanoformulation after one hour. The results of this study suggest that nanoemulsions with oleoresin of C. reticulata have advantages in the control and treatment of monogenean infections in C. macropomum when compared to the oleoresin without nanoformulation. In addition, since nanoemulsions with the C. reticulata oleoresin are safe to control monogeneans, the efficacy of these nanoformulations may be assayed in therapeutic baths to treat C. macropomum infected by monogeneans.     

Fish hosts of the freshwater mussel Unio foucauldianus Pallary, 1936

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Soy protein concentrate as an alternative in replacement of fish meal in the feeds of hybrid grouper,brown‐marbled grouper (Epinephelus fuscoguttatus) × giant grouper (E. lanceolatus) juvenile

Hybrid grouper juveniles (body weight, 6.1 ± 0.7 g) (brown‐marbled grouper, Epinephelus fuscoguttatus × giant grouper, E. lanceolatus) were fed with six isoproteic (50% crude protein) and isolipidic (12% crude lipid) feeds containing different levels of soy protein concentrate (SPC) in replacement of fish meal (SPC at 20%, 30%, 40%, 50% and 60% protein) and control feed (SPC0) for 6 weeks. Hybrid grouper juveniles were cultured in 100‐L fibreglass tank equipped with flow‐through water system and fed twice a day to apparent satiation level. The highest and lowest growth was recorded in fish fed SPC20 and SPC60 respectively. However, growth of SPC20 was not significantly higher than those fed SPC0, SPC30, SPC40 and SPC50 (p > .05). A decreasing growth trend was observed with the increasing level of SPC from feed SPC40 to SPC60. A noticeable better feed utilization was also observed in fish fed SPC0, SPC20, SPC30, SPC40 and SPC50 compared to fish fed SPC60 (p < .05). The fish condition factor, hepatosomatic index, viscerosomatic index and whole body proximate content of the fish were not affected by the graded levels of SPC. However, the body lipid content was significantly lower in fish fed SPC40 to SPC60 (p < .05). The apparent digestibility coefficient (ADC) of protein and lipid was significantly higher in fish fed SPC0 and SPC20 compared to other dietary treatments (p < .05). Based on the regression analysis on specific growth rate, the study suggests that the hybrid grouper grow best at 21.4% and can utilize up to 50% inclusion level of SPC in protein without significantly affect their growth and its body condition.     

Early‐stage sea lice recruits on Atlantic salmon are freshwater sensitive

Sea lice are significant parasites of marine and brackish farmed fishes. Freshwater bathing is a potential control option against numerous sea lice species, although has been viewed as futile against those that are capable of tolerating freshwater for extended periods. By comparing freshwater survival times across host‐attached stages of Lepeophtheirus salmonis (Krøyer), a key parasite in Atlantic salmon farming, we show the first attached (copepodid) stage undergoes 96–100% mortality after 1 h in freshwater, whereas later attached stages can tolerate up to 8 days. Thus, regular freshwater bathing methods targeting the more susceptible attached copepodid stage may successfully treat against L. salmonis and potentially other sea lice on fish cultured in marine and brackish waters.     

Local adaptation studies and conservation: Parasite–host interactions between the endangered freshwater mussel Unio crassus and its host fish

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Use of neem oil (Azadirachta indica) to control caligid copepod infestation on Asian seabass (Lates calcarifer)

Asian seabass (Lates calcarifer) culture in marine cages have been developed rapidly in Malaysia. The high intensity of culture might facilitate several disease infection including caligid infestation. This study was conducted to evaluate the effect of neem oil (Azadirachta indica) against caligid parasites on seabass. The prevalence and clinical pathogen of Caligus infection has been described through a sampling of 150 fish from floating cage at different cultured periods. Acute toxic tests with different concentrations of neem oil were carried out on the parasite and fish host. Results revealed that the 96‐hr median lethal concentration (LC₅₀) of Caligus and fish (10.3 ± 2.5 g of body weight) were 2 and 20 ppm respectively. The in vivo test indicated that 10 ppm of neem oil could result in 100% antiparasitic efficacy within 96 hr. These results therapeutically demonstrated the efficacy of neem oil in caligid control.     

What causes cannibalization‐associated suffocation in cultured brown‐marbled grouper,Epinephelus fuscoguttatus (Forsskål, 1775)?

During culture of grouper, cannibalism is a frequent phenomenon that usually causes economic loss. Grouper culture often requires grading to prevent size‐dependent cannibalism. In comparison with orange‐spotted (Epinephelus coioides) and giant grouper (E. lanceolatus), failure to swallow prey during cannibalism is frequently observed in brown‐marbled grouper (E. fuscoguttatus). The cannibal cannot engulf the entire prey and the two fish ultimately end up dying together. Herein, we attempted to compare morphometric differences among orange‐spotted, giant and brown‐marbled grouper. We established a cannibal–prey total length (TL) relationship for brown‐marbled grouper: TL_prey=0.71 TL_cannibal−1.75. According to the equation, a difference of approximately 50% in TL is a threshold to use for grading the grouper. This value is much larger than that used (30%) in orange‐spotted and giant grouper, and this size difference results in a higher incidence of failed cannibalism attempts in brown‐marbled grouper. It is our belief that the standard grading method will fail to produce as good an effect in brown‐marbled grouper as is seen in orange‐spotted and giant grouper. Therefore, in addition to grading, other manipulations such as satiation feeding, nutritional supplementation and optimal stocking densities should be applied to reduce cannibalism of brown‐marbled grouper.