“Spring rise” of whaleworm (Anisakis simplex; Nematoda, Ascaridoidea) third-stage larvae in some fish species from Norwegian waters

The seasonal variation in the infection of saithe (Pollachius virens), cod (Gadus morhua), and redfish (Sebastes marinus) from a coastal area of central Norway with Anisakis simplex third-stage larvae (L3) was studied over a period of 1 year. In all three host species there was an increase in the abundance of the parasite in spring, with a peak appearing in March and April. Cod displayed the most distinct seasonal variation, showing a clear abundance peak in April. The abundance peak in April for redfish was not as pronounced. In saithe the abundance over the seasons was less prominent, with a maximum appearing in March and another increase in abundance occurring during July. It is apparent that the causes behind the pattern of infection observed in this study are complex. However, possible explanatory mechanisms are discussed. Arguments are propounded to suggest that the increased supply of parasite eggs from northward-migrating whales in addition to the general spring bloom of plankton constitute the most important factors governing the phenomenon of “spring rise” in A. simplex L3 in the study area. Received: 4 February 2000 / Accepted: 25 February 2000     

Growth of whaleworm (<Emphasis Type="Italic">Anisakis simplex</Emphasis>, Nematodes,Ascaridoidea, Anisakidae) third-stage larvae in paratenic fish hosts

The growth of Anisakis simplex L3 larvae in the three paratenic hosts saithe ( Pollachius virens), cod (Gadus morhua) and redfish (Sebastes marinus) was studied based on material collected off the island of Vega on the west coast of Norway over a period of 1 year. In all three fish species, a positive correlation between the length of larvae and the age of the fish was shown. The number of large larvae, here defined as L3>28 mm, increases with increasing age of the host. These findings clearly indicate an accumulation of large L3 larvae and larval growth in the fish host. The larvae were additionally grouped according to the tissue--muscle, liver or other viscera--they were located in. When the average lengths of the three groups of larvae were compared, the gadoids saithe and cod had somewhat higher values for L3 larvae found in the liver. Redfish, on the other hand, which store fat to a relatively higher degree in the viscera, had the highest average length of larvae in this tissue. The lowest average values in all three species were found in the musculature. These trends suggest that the growth of A. simplex L3 larvae is positively correlated with the fat content of the tissue in which it is encapsulated. Of the three host species included in this study, saithe seemed to be the best suited for A. simplex L3, as the growth rate and average length of the parasite was greatest in this species. The growth and average length of L3 was least pronounced in redfish while cod held an intermediate position.     

Experimental infections of copepods and sticklebacks Gasterosteus aculeatus with small ensheathed and large third-stage larvae of Anisakis simplex (Nematoda, Ascaridoidea, Anisakidae)

Free-swimming ensheathed larvae of Anisakis simplex were shown experimentally to be ingested by the copepods Oitona similis and Acartia tonsa and by the nauplii of barnacles Balanus sp. The larvae did not grow in the copepod hemocoel. Experimental infections of various malacostracans were unsuccessful. Sticklebacks Gasterosteus aculeatus are naturally infected with larvae of A. simplex in coastal brackish water. Such sticklebacks may have acquired the infection by eating either a crustacean host or third-stage larvae (L3) from fish. Experimental infections of cod Gadus morhua with L3 from viscera of herring Clupea harengus showed that about one-third of the ingested larvae passed through the cod alimentary tract and were extruded whole but dead. Experiments showed that larvae from herring viscera survived and remained infective after at least 6 weeks in brackish water and seawater and that L3 from herring viscera were ingested by sticklebacks (and flounder Platichthys flesus), where they reencapsulated on the viscera; the L3 were alive 2 years later. Received: 21 March 2000 / Accepted: 21 June 2000      

An in vitro study of lipid preference in whaleworm (Anisakis simplex,Nematoda, Ascaridoidea,Anisakidae) third-stage larvae

The behavioural response of nematodes to chemical stimuli has been extensively investigated in some free-living and plant parasitic species. However, in animal parasitic species, little is yet known, particularly in regards to marine forms such as the whaleworm (Anisakis simplex). Previous studies showed that A. simplex L3-larvae tend to prefer fish tissue with high lipid content. The intention of this study was to investigate the behaviour of A. simplex L3 in response to different concentrations of fish lipid in further detail. This was done by an in vitro study based on larvae from cod (Gadus morhua). Ten larvae were placed in each of the culture containers containing agar that was separated into three segments of equal size. Three categories of agar were used containing 0, 2 and 7 % cod liver oil. A total of 900 larvae were included. The study consisted of three parts: The purpose of experiment I was to establish whether different lipid concentrations influenced the migration pattern at all. Experiment II was intended to examine whether A. simplex L3-larvae were able to actively search for lipids. Experiment III was set up to analyse the short-distance dispersion of the L3-larvae. Experiment I indicated that the L3-larvae move randomly but do not stop randomly since the tendency to move out of the start area was inversely correlated with lipid concentration. Experiment II indicates that the larvae are almost unable to select areas of high lipid concentrations when more than a few centimetres away. Experiment III showed that the L3-larvae prefer high-fat content and can seek it out over short distances.     

Occurrence of anisakid nematodes in Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and Greenland cod (<Emphasis Type="Italic">Gadus ogac</Emphasis>), West Greenland

Anisakid nematodes commonly infect gadids, and are of economic and aesthetic importance to the commercial fishing industry in Greenland as some species are pathogenic to humans. However, very little is known about the occurrence of these parasites and their impact on the hosts in Greenland waters. During a survey in 2005, stomach sample of 227 Atlantic cod (Gadus morhua) and 64 Greenland cod (Gadus ogac) was collected in Godthaab and Sisimiut fiord systems in West Greenland waters. All cod were dissected for stomach contents and anisakid nematodes were removed from the visceral cavity. Third stage larvae (L3) of three anisakid species were found, including Contracaecum osculatum (Rudolphi, 1802), Anisakis simplex (Rudolphi, 1809) and Hysterothylacium aduncum (Rudolphi, 1802). Molecular identification by PCR-RFLP indicated the presence of A. simplex s.s. and the sibling species C. osculatum B and C. The prevalence of infection by C. osculatum was higher in Greenland cod (84.3%) than in Atlantic cod (73.9%) whereas the prevalence of A. simplex showed an opposite pattern (Greenland cod 8.3%; Atlantic cod 24.2%). Only one G. morhua (1.0%) was infected by H. aduncum. No gender specific difference in both nematode species regarding prevalence of infection and mean infection intensity was evident, and there was no relationship between fish condition and the intensity of nematode infections. Standardised for size, capelin-eating cod were in better condition and more heavily infected than fish subsisting on alternative prey at the point of collection. Hence, nematode infections in the two gadids seem governed in part by feeding behaviour, and capelin appears a significant source of larval anisakids.     

Distribution of Anisakis simplex in fish caught in the Ligurian Sea

A total of 822 individuals of 5 fish species were sampled in the western coastal area of the Mediterranean Sea and examined for the presence of Anisakis simplex larvae in the body cavity, muscle, and viscera. A. simplex mean intensity (mI) and prevalence (Pr) values were very high in the common scad (Trachurus trachurus; Pr 80–100%, mI 19.3–36.8) and the blue scad (T. picturatus; Pr 80–100%, mI 18.2–70.7), moderate in the blue whiting (Micromesistius poutassou), and low in the red mullet (Mullus barbatus) and the striped mullet (M. surmuletus). The larval burden was strongly related to host length in the common and blue scad. Received: 23 December 1999 / Accepted: 17 January 2000     

Acetylcholinesterase secreted by Anisakis simplex larvae (Nematoda: Anisakidae) parasitizing herring,Clupea harengus: an inverse relationship of enzyme activity in the host–parasite system

Acetylcholinesterase (AChE) is a key enzyme involved in nerve impulse transmission in both vertebrates and invertebrates. In addition to neuromuscular AChE, many parasitic nematodes synthesize AChE in secretory glands and release the enzyme into their external environment. In this study, we evaluate the activities of both somatic and secreted AChE from larvae (L3) of the parasitic nematode Anisakis simplex, and compare these to the AChE activity in its host, herring, Clupea harengus. A. simplex larvae were obtained from a herring sampled in three areas of the southern Baltic. Enzyme kinetics were determined for excretory/secretory (E/S) products and somatic extracts of larvae as well as for herring muscle tissue. The results reveal that mean AChE activity is approximately fourfold higher in E/S products and eightfold higher in somatic extracts of post-secretory A. simplex larvae than in host muscle tissue. The level of AChE activity in nematodes is inversely related to the enzyme activity in their hosts, i.e. reduced AChE activity in herring was accompanied by increased enzyme activity in its parasites. The physiological function of AChE secreted by parasitic nematodes has been widely discussed in the literature, and numerous roles for this form of enzyme have been suggested. The results of our investigation indicate that AChE secretion by A. simplex larvae may constitute an adaptive mechanism that promotes survival under adverse environmental conditions. Larvae probably increase secretion of AChE in response to a direct and/or indirect effect of neurotoxic compounds. This is the first report of such a phenomenon in A. simplex.     

Anisakis spp. in European hake, Merluccius merluccius (L.) from the Atlantic off north-west Africa and the Mediterranean off southern Spain

We studied the parasitization by Anisakis spp. in European hake (Merluccius merluccius) of 40–52 cm from the Atlantic off north-west Africa and the Mediterranean off southern Spain. Infection parameters differed: The fish from the Atlantic showing a prevalence of 87.97% and a mean intensity of 4.69, while, in those from the Mediterranean, these were 41.27% and 1.73, respectively. In both samples the two-third larval stage types were isolated: Anisakis simplex sensu lato and Anisakis larvae type II, with prevalence of 85.71% and 30.83% in fish from the Atlantic and 41.27% and 1.59% for those from the Mediterranean, respectively. In both samples, the prevalence of larvae in viscera was clearly higher than in the muscle tissue. We also observed an increase in parasitization with increasing host length, those ≥ 46 cm having the highest prevalences (94.87% for those from the Atlantic and 58.33% for those from the Mediterranean; p<0.03). This paper is dedicated to the memory of Prof. Dr Ignacio Navarrete López-Cózar, DVM, recently deceased.     

The life cycle of<Emphasis Type="Italic"> Anisakis simplex</Emphasis> in the Norwegian Deep (northern North Sea)

Copepoda (Calanus finmarchicus n=1,722, Paraeuchaeta norvegica n=1,955), Hyperiidae (n=3,019), Euphausiacea (Meganyctiphanes norvegica n=4,780), and the fishes Maurolicus muelleri (n=500) and Pollachius virens (n=33) were collected in the Norwegian Deep (northern North Sea) during summer 2001 to examine the importance of pelagic invertebrates and vertebrates as hosts of Anisakis simplex and their roles in the transfer of this nematode to its final hosts (Cetaceans). Third stage larvae (L3) of A. simplex were found in P. norvegica, M. muelleri and P. virens. The prevalence of A. simplex in dissected P. norvegica was 0.26%, with an intensity of 1. Prevalences in M. muelleri and P. virens were 49.6% and 100.0%, with mean intensities of 1.1–2.6 (total fish length 6.0–7.2) and 193.6, respectively. All specimens of C. finmarchicus and M. norvegica examined were free of anisakid nematode species and no other parasites were detected. P. norvegica, which harboured the third stage larvae, is the obligatory first intermediate host of A. simplex in the investigated area. Though there was no apparent development of larvae in M. muelleri, this fish can be considered as the obligatory second intermediate host of A. simplex in the Norwegian Deep. However, it is unlikely that the larva from P. norvegica can be successfully transmitted into the cetacean or pinniped final hosts, where they reach the adult stage. An additional growth phase and a second intermediate host is the next phase in the life cycle. Larger predators such as P. virens serve as paratenic hosts, accumulating the already infective stage from M. muelleri. The oceanic life cycle of A. simplex in the Norwegian Deep is very different in terms of hosts and proposed life cycle patterns of A. simplex from other regions, involving only a few intermediate hosts. In contrast to earlier suggestions, euphausiids have no importance at all for the successful transmission of A. simplex in the Norwegian Deep. This demonstrates that this nematode is able to select definite host species depending on the locality, apparently having a very low level of host specificity. This could explain the wide range of different hosts that have been recorded for this species, and can be seen as the reason for the success of this parasite in reaching its marine mammal final hosts in an oceanic environment.     

New locality records for third-stage larvae of Anisakis simplex (sensu lato) (Nematoda: Ascaridoidea) in euphausiids Euphausia pacifica and Thysanoessa raschii from Prince William Sound, Alaska

Five euphausiid species (n=41,037) were collected in October 1997 from Prince William Sound, Alaska, and examined for parasites. New locality records are claimed for third-stage larvae (L3) of whaleworm Anisakis simplex (sensu lato) in two (0.019%) of 10,437 Thysanoessa raschii, and in one (0.013%) of 7,443 Euphausia pacifica. The L3 were about 19.5, 21.3 and 30.5 mm long. L3 were absent from 8,026 T. inermis, 10,302 T. longipes and 4,829 T. spinifera collected at the same time, and from 6,648 euphausiids representing the five species collected in July 1998. No individual harboured more than one parasite—a whaleworm L3, the ellobiopsid Thalassomyces fagei, a trypanorhynchid (tetrarhynchid) cestode (probably Nybelinia sp.), or a possible rhizocephalan. Controversy regarding the number of moults that occur in the egg of marine ascaridoids is discussed briefly.     

A recombinant enolase from Anisakis simplex is differentially recognized in natural human and mouse experimental infections

A 1,963-bp cDNA was isolated from an Anisakis simplex cDNA library by immunoscreening with a hyperimmune rabbit serum raised against a crude extract of A. simplex L3 larvae. The open reading frame encodes a putative protein of 436 amino acid residues, which exhibits high similarity (70–80%) to enolase molecules from various other organisms, including helminth parasites. After subcloning and expression of the A. simplex cDNA in PGEX-4T-3, the resulting glutathione S-transferase fusion protein, purified by glutathione-Sepharose-4B chromatography, showed functional enolase activity. The immunogenicity of the recombinant A. simplex enolase was analyzed by immunoblotting using sera obtained from (a) mice immunized with crude extracts (CE) of A. simplex, or other nematode species, (b) mice immunized with excretory–secretory (ES) antigens from A. simplex, or (c) mice infected with L3 larvae by the intraperitoneal route. In addition, we used ELISA, to investigate the presence of IgG1 and IgE antibodies against this molecule in sera from patients infected with A. simplex. Mouse sera obtained after infection with L3 or raised against CE antigens, but not sera raised against ES antigens, showed strong reactivity with the recombinant A. simplex enolase. We also obtained good reactivity in Western blotting with sera from mice immunized with CE antigens from Ascaris suum and Toxocara canis, but not with sera from mice immunized with CE antigens from Trichuris muris, Trichinella spiralis or Hysterothylacium aduncum. In contrast to the experimental infections/immunizations in mice, we were unable to detect anti-enolase IgE antibodies in sera from human patients infected with A.simplex (15 sera), and the levels of anti-enolase IgG1 antibodies in these sera were low and apparently nonspecific. These results seem to indicate that, during natural infection in humans, A. simplex larvae do not offer sufficient antigenic stimulus to induce anti-enolase antibodies.Note: Nucleotide sequence data reported in this paper were submitted to the GenBank, EMBL and DDBJ databases under the accession number AJ496792.     

Hysterothylacium aduncum (Rudolphi, 1862) infection in cod from the Oslofjord: Seasonal occurrence of third-and fourth-stage larvae as well as adult worms

Hysterothylacium aduncum infections in cod from the Oslofjord were followed for 1 year. The recovered worms were grouped according to developmental stage [third-stage larvae (L3), fourth-stage larvae (L4) and adult worms] and according to location (in the gut or encapsulated on the viscera). The cod were found to be infected withH. aduncum (all stages lumped) throughout the whole year, with the prevalence approaching 100%. The abundance of the parasites (mean number per fish studied), however, was clearly lowest during the summer months. L3 and L4 recovered from the intestine dominated most of the time but showed a very clear peak during late winter and early spring. L3 recovered from the body cavity was the only stage that showed a clear peak during the summer months. Adult worms, although adult worms were present in very small numbers throughout the year, they tended to peak in May and then again in December and January. Since there did not seem to be a correlation between the accumulation of L3 in the body cavity and the length or age of the fish, the possibility of self-infection whereby the larvae reenter the gut and continue to develop into L4 and then into adults, is discussed.     

Occurrence and molecular identification of Anisakis spp. from the North African coasts of Mediterranean Sea

Larval forms of the genus Anisakis were reported infecting several fish species from the North African coasts of central Mediterranean Sea. Polymerase chain reaction–restriction fragment length polymorphism (PCR-RFLP) analysis was used to investigate the occurrence of larval forms of different Anisakis species in teleost fishes and squid from North African coasts of the Mediterranean Sea and to establish the geographical and host range of these parasites in this area. A total of 282 Anisakis larvae were identified by PCR-RFLP from 13 teleost fish species and one cephalopod species captured at different sites off the Algerian, Tunisian and Libyan coasts. The type I larvae were found with a frequency of 93.62% and were identified as belonging to the following species: Anisakis simplex s.str., Anisakis pegreffii, A. simplex s.str/A. pegreffii hybrids and Anisakis typica. The type II larvae were found to belong to Anisakis physeteris, with the frequency of 6.38%. The record of A. simplex s.str/A. pegreffii hybrids, previously recorded from the Spanish and Portuguese Atlantic coasts and the Alboran Sea, extends their geographic distribution to the Tunisian coasts. The occurrence of A. simplex s.str. and hybrids away from their known area of distribution may predict the successful use of Anisakis larvae for tagging Scomber scombrus fish stocks for fisheries management purposes. Moreover, the results reported provide valuable information regarding the diversity of Anisakis species in the study area, indicating that several Anisakis sibling and morphospecies coexist in the North African coasts of the Mediterranean Sea.     

Records ofIxodes vespertilionis,I. simplex andArgas vespertilionis (Ixodoidea: Ixodidae,Argasidae) from German bats (Chiroptera)

An investigation of the tick fauna of bats in the Federal Republic of Germany revealed three species:Ixodes vespertilionis, I. simplex andArgas vespertilionis. I. simplex was recorded for the first time in Germany. The occurrence ofI. vespertilionis andI. simplex in Germany is compared with the distribution of their host species.     

Parasitic helminth fauna of the cutlass fish,<Emphasis Type="Italic"> Trichiurus lepturus</Emphasis> L., and the differentiation of four anisakid nematode third-stage larvae by nuclear ribosomal DNA sequences

The helminth fauna of the gastrointestinal tract and abdominal cavity of cutlass fish, Trichiurus lepturus L., off the Taiwanese coast of the north-western Pacific was investigated. The following helminths were found: (1) nematodes—Anisakis simplex, Hysterothylacium aduncum, Porrocaecum decipiens, Raphidascaris trichiuri; (2) digeneans—adult Lecithochirium trichiuri; and (3) cestodes—plerocercoids of Proteocephalus spp. The third-stage larvae of these four anisakid nematodes were characterized genetically using a molecular approach. The nuclear ribosomal DNA region spanning the first internal transcribed spacer (ITS-1), the 5.8S gene and the second internal transcribed spacer (ITS-2) was amplified and sequenced. Based on the sequence differences, a PCR-based restriction fragment length polymorphism method was established for the unequivocal delineation of the four species. Phylogenetic analysis showed that H. aduncum clustered with P. decipiens, whereas A. simplex was not closely related to these according to the nucleotide sequences of all rDNA.     

Experimental infection/transmission of sculpins (Myoxocephalus scorpius) and cod (Gadus morhua) by sealworm (Pseudoterranova decipiens) larvae

Five serial transmission experiments with sealworm larvae were carried out. Pseudoterranova decipiens third-stage larvae (L₃) were transferred via a stomach tube from sculpin to cod, from cod to sculpin, from sculpin to sculpin, and from cod to cod. After a minimum of 37 days the recipient fish were killed and the numbers of surviving P. decipiens larvae were recorded. P. decipiens transferred to sculpins showed the greatest rate of survival. Received: 25 September 1996 / Accepted: 30 October 1996     

Monoclonal antibodies against diagnostic Anisakis simplex antigens

Five monoclonal antibodies (UA2, UA3, UA5, UA6, and UA8) specific for Anisakis simplex are described. All are IgG1/κ monoclonal antibodies, except for UA2, which is an antibody IgM/κ. The molecular weights of the major components recognized in immunoblotting are 48 and 67 kDa (UA2); 139 kDa (UA3 and UA5; same epitope); 35, 38, and 139 kDa (UA6); and 205 kDa (UA8). UA2 was the only monoclonal antibody to recognize both components of an excretion-secretion antigen preparation and antigens in the excretory cell and esophageal glands of third-stage A.␣simplex larvae; antigens in the excretory cell were also recognized by UA3 and UA6. Cross-reactivity studies using a hyperimmune polyclonal rabbit serum reacting with various ascaridoid nematodes indicated that the antigens captured by our monoclonal antibodies were specific for A. simplex. Finally, comparative studies of our monoclonal antibodies and An2 (the only monoclonal antibody currently available for serodiagnosis of human anisakiasis), based on the calculation of multiples of normal activity for human anisakiasis sera, indicated that our monoclonal antibodies (and particularly UA3) recognized antigens that are good candidates for serodiagnostic purposes. Received: 13 February 1997 / Accepted: 16 March 1997     

Myosin isoforms in red and white muscles of some marine teleost fishes

Summary The myosin content from red and white muscles of three marine fish species, saithe (Pollachius virens. L), haddock (Melanogrammus aeglefinus, L.), both members of the familyGadidae, and capeline (Mallotus villosus, M.) of the familyOsmeridae, was analyzed electrophoretically.Analysis of the native myosin by electrophoresis under non-dissociating conditions revealed two isoforms in red muscles, and three or four in white muscles. The white muscles of the two closely related species had a similar pattern of isoforms.Myosin from the slow red muscles had two types of light chain, LC1S and LC2S, and myosin from the fast white muscles three, LC1F, LC2F, and LC3F. The pattern of light chains in both types of muscles was species-dependent. All the light chains from fish myosins were more acidic than those of the rat diaphragm used as standard.One main type of heavy chain was detected in each kind of muscle. In white muscles of saithe there was an extra band, present in minor amounts. The heavy chains from white muscle myosin had lower electrophoretic mobilities than those from red muscle, and the mobilities of all of them were intermediate between those of the heavy chains type IIa and I of rat diaphragm myosin.In our opinion, there are probably more isomyosins in fish muscles than those detected in the present work and their presence is obscured by comigration with the main types.     

Larval development of Aelurostrongylus abstrusus (Nematoda, Angiostrongylidae) in experimentally infected Cernuella (Cernuella) virgata (Mollusca, Helicidae)

The larval development of the cat lungworm Aelurostrongylus abstrusus was studied for the first time in the helicid mollusc Cernuella (Cernuella) virgata, in order to know its performance as intermediate host (I.H.). This snail is very common in the north-west of Spain. First-stage larvae (L1) of A. abstrusus were obtained by the Baermann–Wetzel method from the faeces of a naturally infected cat. Then, 120 specimens of C. (C.) virgata were infected with 500 L1/snail and maintained under laboratory conditions (20±2 °C). Every 2 days, from day 8 to day 76 post-infection (p.i.), three snails were killed in order to study the larval development of the parasite. Morphological features of the different larval stages were also recorded. The apparent rate of penetration of L1 into the snail foot was 65.5%, but only 4.78% completed their development to the infective stage (L3). The total number of larvae was 49.8±28.8 larvae/snail and the average number of L3 was 23.9±18.4 L3/snail. The first L2 and L3 were observed on day 12 and day 18 p.i., respectively. From day 52 p.i. onwards, all larvae were at the infective stage in the snail. Considering those results, it was concluded that C. (C.) virgata is a suitable I.H. for A. abstrusus.     

Experimental susceptibility of some reef fish species to Benedenia lutjani (Monogenea: Capsalidae), a parasite of Lutjanus carponotatus (Pisces: Lutjanidae)

The susceptibility of species of lutjanid, lethrinid and serranid fish to infection by either larval or post-larval (juvenile and adult) specimens of the capsalid monogenean Benedenia lutjani Whittington and Kearn (1993) was examined experimentally. Four species of lutjanids became infected when exposed to larvae of B. lutjani, but three species of lethrinids and four species of serranids were not susceptible to larvae under the same conditions. Variability in the intensity of infection by larvae occurred within and between lutjanid species. Few post-larval specimens of B. lutjani transferred between individuals of the specific host Lutjanus carponotatus (Richardson 1842) in 60-l aquaria and none transferred between specimens of L. carponotatus in a 7,500-l concrete tank. These results indicate that transfer of post-larval B. lutjani between individuals of the specific host is unlikely to occur in the wild. Other lutjanid species did not become infected when exposed to specimens of L. carponotatus infected heavily by post-larval B. lutjani, but two lethrinid species were susceptible to infection under the same conditions. These data indicate that different factors may mediate host-specificity for larval and post-larval B. lutjani. Received: 3 July 2000 / Accepted: 14 September 2000