Biology and pathogenicity of the gill monogenean of grouper (Epinephelus coioides) cultured in the Philippines
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2005-03Page views
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Abstract
The diplectanid monogenean Pseudorhabdosynochus lantauensis was the most abundant parasite recovered from the gills of cultured orange-spotted grouper (Epinephelus coioides) in the Philippines. The morphology of P. lantauensis is described. Morphometric analysis showed this species has smaller measurements when compared with other related species previously reported from Hong Kong, Malaysia and Indonesia. This species is characterized by having an overlapping dorsal bar and a short copulatory organ.
The life cycle of this gill monogenean is also described. One mature parasite lays at least 10-22 eggs/day. Eggs are oval in shape (0.021-0.120 mm) with a spiral filament attached to one end. Eggs hatch into free-swimming larvae (oncomiracidia) within 2-6 days at 30°C and 30 ppt. The rate of development of various eggs of one hatch is not uniform, that is, some hatch in 2 days while others take 6 days. The oncomiracidium can attach to the grouper host within 2 hr. Upon attachment, the oncomiracidium metamorphoses to an adult parasite in 4-7 days. The parasite becomes fully mature and lays eggs in 7 days. Without a host, the oncomiracidium dies in 4-8 hr. The life cycle is completed in 13-20 days (egg to oncomiracidium in 2-6 days; oncomiracidium to adult parasite in 4-7 days; and adult to fully mature and egg laying parasite in 7 days).
The effects of salinity and temperature on the hatching rate of eggs were investigated to estimate biological characteristics of the gill monogenean. Results showed that at 30°C the rate of egg hatching was 85% at 10 ppt, 92% at 20 ppt and 98% at 30 ppt. No hatching was observed at 0 and 60 ppt. Egg hatching was 75% at 25°C, 86% at 30°C and 67% at 35°C in seawater (30 ppt).
The pathogenicity of the gill monogenean on healthy grouper juveniles was studied. Results showed that a level of 5,000 parasite eggs placed in aquarium with 20 fish resulted in 85% mortality of the fish, 2,000 eggs/20 fish caused 60% mortality, 1,000 eggs/20 fish resulted in 50% mortality and 500 eggs/20 fish resulted in 35% mortality. No mortality was observed at the control (0 egg/20 fish) group. The hematocrit level of the highest infection group (5,000 eggs/20 fish) was lower than those of the other treatment groups. Histopathological analysis revealed that the gills filaments of infected grouper challenged with 5,000 eggs/20 fish showed extensive hyperplasia and hypertrophy.
Suggested Citation
Erazo-Pagador, G. (2005). Biology and pathogenicity of the gill monogenean of grouper (Epinephelus coioides) cultured in the Philippines. In K. Nagasawa (Ed.), Recent Advances in Diagnosis and Prevention of Fish and Shrimp Diseases in Southeast Asia (pp. 295–308). Tigbauan, Iloilo, Philippines: Aquaculture Department, Southeast Asian Fisheries Development Center.
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9718511732Related items
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Temporal changes in innate immunity parameters, epinecidin gene expression, and mortality in orange-spotted grouper, Epinephelus coioides experimentally infected with a fish pathogen, Vibrio harveyi JML1
Amar, Edgar C.
; Faisan, Joseph P., Jr. ; ; Pakingking, Rolando V., Jr. (Elsevier, 2017)
Changes in innate immunity parameters and epinecidin mRNA transcript levels were examined to characterize the non-specific immune response of E. coioides to pathogenic V. harveyi JML1 isolated from affected cage-cultured fish. After fish had been injected with bacteria at a dose causing 30% mortality, blood and tissue samples were collected at 0, 6, 12, 24, 48, 72, 96, 120, and 240 h post-infection (hpi) for assessment of indices such as the oxidative burst (OB) and phagocytic index (PI) of head kidney cells, and lysozyme activity (LYS) and total immunoglobulin (Total Ig) levels of the plasma. The epinecidin mRNA transcript levels (EGE) from skin, gills, liver, kidney, and spleen tissues were also determined by gelbased RT-PCR. Lastly, daily mortality (DM), liver total bacterial load (TBC), and presumptive Vibrio count (TVC) were monitored up to 240 hpi. The results revealed that bacteria proliferated rapidly in fish tissue, reaching peak densities at 24 hpi for both TBC and TVC but was on a downward trend thereafter. The pattern in fish mortality closely correlated with TBC and TVC. Total Ig, OB, and PI in E. coioides were suppressed in the early part of infection when V. harveyi load was high but recovered and later increased as bacterial density declined. LYS and EGE were consistently high and their activities were not hampered by bacterial infection. The study demonstrated that V. harveyi JML1 interacts with E. coioides by transiently inhibiting some immune parameters resulting in mortalities. However, consistently high LYS, upregulated EGE, and resurgent PI, OB and Total Ig conferred resistance and subsequent recovery in the fish. The study provides new insights on the interaction between E. coioides and V. harveyi JML1 that can aid in formulating health management strategies for groupers. Further studies on prophylactic interventions to enhance the innate immune response in grouper during infection with V. harveyi JML1 are suggested. -
Detection and identification of viral pathogens of grouper (Epinephelus malabaricus) cultured in Thailand
(Aquaculture Department, Southeast Asian Fisheries Development Center, 2005-03)A virological survey was conducted in brown-spotted grouper (Epinephelus malabaricus) cultured in cages, earthen ponds and pens from April 2001 to January 2002 on the east and south coasts of Thailand. The adult grouper samples exhibited a wide range of clinical signs beginning from darkening of body color with focal distension of the skin to red boil skin, and to appearance of red spot ulcers on the body and head. Diseased fry to juvenile grouper showed darkening of body color and swirling movement. Thirty-five isolates of viruses were obtained from using freshwater fish cell lines, SSN-1 and EPC. These isolates could be grouped into two different groups of fish viruses. One viral group has been identified as a betanodavirus, which belongs to genotype RGNNV (redspotted grouper nervous necrosis virus). RT-PCR tests in this betanodavirus using specific primers to SJNNV (striped jack nervous necrosis virus) were negative, while specific primers to RGNNV showed positive RT-PCR product. The second viral group could be identified as an iridovirus. This grouper iridovirus had some level of similarities to RSIV (red sea bream iridovirus). One set of specific primers for RSIV could give positive PCR product, while the second set of specific primers gave negative PCR result. The grouper iridovirus was found different from Ranavirus. Betanodavirus could infect both adult and fry to juvenile stages of the grouper and seemed to have more significance during November to January or during the dry and cold season in Thailand. The grouper iridovirus seems to cause disease in adult size of the fish with low level of mortality and seems to infect the fish predominantly in August and September or during rainy season in Thailand. These findings indicate that two different viruses are associated with grouper and identified each as Betanodavirus and grouper iridovirus. The new isolate of grouper iridovirus has some level of variations in nucleotide sequences when compared with RSIV gene. There is a need to do more molecular study of this new isolate of grouper iridovirus as well as its pathogenesis. -
Distribution of nervous necrosis virus in orange-spotted grouper Epinephelus coioides with asymptomatic infection
(Japanese Society of Fish Pathology, 2007)Distribution of nervous necrosis virus in asymptomatically infected orange-spotted grouper Epinephelus coioides was determined by PCR assay in this study. Fourteen different tissues and organs were collected from apparently healthy groupers including seven individuals of broodstock and 17 juveniles with body weight ranging from 4 to 12 kg and from 2 to 9 g, respectively. No cytopathic effects were found in E-11 cells inoculated with filtrates of sample homogenates. However, all the broodstock and juveniles were positive by nested PCR test except for one juvenile. One hundred percent detection rate of the virus was obtained only from the brain.
