Owing to the problem of male infertility in the domesticated shrimp Penaeus monodon, this study was conducted to reveal the morphological events of an acrosome reaction (AR) of sperm of this highly valuable species. The AR observed in an in vitro incubation of sperm with egg water (EW) and that during actual spawning was compared. Under transmission and scanning electron microscopy, sperm taken from the female thelycum was composed of a posterior main body, a central cap and an anterior single spike. Upon contact with EW, the sperm underwent two phases of AR: acrosomal exocytosis and spherical mass formation. The former was composed of a degeneration of the spike, swelling of the cap region and rupture of the acrosomal pouch. The latter began with polymerization of materials within the subacrosomal region and ended with re‐configuration of the subacrosomal region into an electron‐dense spherical mass. The AR of the sperm observed during spawning revealed similar morphological events, with degeneration of the spike upon contact with the vitelline envelope and formation of the spherical mass while penetrating into jelly material produced by protruding cortical rods. The results suggest the presence of AR inducers derived from the vitelline envelope and cortical rods of the egg. This study forms the basis for an evaluation of infertility regarding to AR in the domesticated P. monodon male.

The activities of the enzymes N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) and the hormone melatonin were studied in the optic lobe of the subadult giant tiger shrimp Penaeus monodon. Compared with the level in other species, a relatively high level of NAT activity that was temperature- and pH-dependent were observed. The NAT enzyme had a relatively high maximum velocity (Vmax, 100 pmol/hr/micrograms protein) and low Michaelis constant (Km, 22 microM), when tryptamine is used as substrate. In contrast to the high level of NAT activity, HIOMT activity and melatonin levels were low in the optic lobe of the giant tiger shrimp. Sex differences in the levels of NAT activity and melatonin, which are observed in a freshwater species Macrobrachium rosenbergii, were not noticeable in the saltwater species P. monodon, at least not when they were in their subadult stage.

BackgroundPersistent infection of Penaeus stylirostris densovirus (PstDNV) (also called IHHNV) and its non-infectious inserts in the black tiger shrimp, Penaeus monodon (P. monodon) genome are commonly found without apparent disease. Here, we introduced the method of multiplex PCR in order to differentiate shrimp with viral inserts from ones with the infectious virus. The method allowed us to study the effect of pre-infection of IHHNV, in comparison to IHHNV inserts, on WSSV resistance in P. monodon.ResultsA multiplex PCR system was developed to amplify the entire IHHNV genome, ensuring the accurate diagnosis. Field samples containing IHHNV DNA templates as low as 20 pg or equivalent 150 viral copies can be detected by this method. By challenging the two groups of diagnosed shrimp with WSSV, we found that shrimp with IHHNV infection and those with viral inserts responded to WSSV differently. Considering cumulative mortality, average time to death of shrimp in IHHNV-infected group (day 14) was significantly delayed relative to that (day 10) of IHHNV-inserted group. Real-time PCR analysis of WSSV copy number indicated the lower amount of WSSV in the IHHNV-infected group than the virus-inserted group. The ratio of IHHNV: WSSV copy number in all determined IHHNV-infected samples ranged from approximately 4 to 300-fold.ConclusionThe multiplex PCR assay developed herein proved optimal for convenient differentiation of shrimp specimens with real IHHNV infection and those with insert types. Diagnosed shrimp were also found to exhibit different WSSV tolerance. After exposed to WSSV, the naturally pre-infected IHHNV P. monodon were less susceptible to WSSV and, consequently, survived longer than the IHHNV-inserted shrimp.

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