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The present study examined the pharmacokinetics and bioavailability of oxytetracycline (OTC) in vannamei shrimp (Penaeus vannamei) after intra-sinus (10 mg/kg) and oral (10 and 50 mg/kg) administration and also investigated the net changes of OTC residues in the shrimp after the thermal, acid and alkaline processing methods. The hemolymph concentrations of OTC after intra-sinus dosing were best described by a twocompartment open model. The oral bioavailability was found to be 48.2 and 43.6% at doses of 10 and 50 mg OTC/kg, respectively. The peak hemolymph concentrations after 10 and 50 mg OTC/kg doses were 3.37 and 17.4 lg/ml; the times to peak hemolymph concentrations were 7 and 10 h. The elimination half-lives were found to be 15.0 and 11.5 h for the low and high dose, respectively. The residual OTC was rapidly eliminated from muscle with the elimination half-life value of 19.4 and 15.4 h, respectively, for the groups treated with doses of 10 and 50 mg/kg. The residual OTC levels in the muscle fell below the MRL (0.2 lg/g) at 72 and 96-h post-dosing at dose levels of 10 or 50 mg/kg, respectively. Residual OTC levels in muscle and shell were approximately 20-50% lower in the thermal treatment such as boiling, baking and frying. By the acid treatment, OTC residues were reduced to [80%, while those were reduced to around 30% by alkaline treatment.

White spot syndrome virus (WSSV) is highly pathogenic to penaeid shrimp and has caused significant economic losses in the shrimp farming industry in Thailand. Genotyping analysis was done in 124 WSSV isolates from cultured Pacific white shrimp

White feces syndrome and acute hepatopancreatic necrosis disease (AHPND) are serious diseases that have recently been noted in Pacific white shrimp (Litopenaeus vannamei). Vibrio bacteria and 6 species of fungi (Aspergillus flavus, A. ochraceus, A. japonicus, Penicillium sp., Fusarium sp., and Cladosporium cladosporioides) were isolated from shrimp naturally infected with white feces syndrome. Antibiotics have been used to treatment the disease for many years, but these have been ineffective and have resulted in drug residue problems for the shrimp industry. In this study, an alternative method was tested for its efficacy in controlling these pathogens. The crude extract of galangal (Alpinia galanga Linn.), an herbal medicine, inhibited the growth of 8 vibrio species of the pathogen, V. parahaemolyticus (EMS/AHPND) in particular. The results also showed that 0.5 mg/ml of the galangal extract was a concentration that produced the strongest inhibition of the fungi A. ochraceus. Naturally infested shrimp L. vannamei were fed 2 and 4% (v/w) portions of the herb extract for 12 days and their progress was compared with that of a control group (no herb extract). At the end of the feeding trial, the numbers of total Vibrio spp. and the incidence of fungi infestation in the hepatopancreas and intestines of treated shrimp were significantly lower than that in the control group (P<0.05). Furthermore, the survival rates for the treatment groups, after injections with V. parahaemolyticus (EMS/AHPND), were significantly higher than that of the control group (P<0.05). Based on these results, we can report that the galangal extract has antimicrobial properties that are applicable as bio-medicinal agents against white feces syndrome and AHPND. Therefore, in the future this herb should be an alternative to chemotherapeutic agents that are being used in the shrimp industry.

The anti-microbial activity of galangal (Alpinia galanga Linn.) is well known. In this study, the feeding of galangal crude extract was investigated for its effect on preventing the infectious diseases Vibrio harveyi and white spot syndrome virus in Pacific white shrimp (Litopenaeus vannamei). A commercial diet mixed with galangal ethanol extract was fed to shrimp for 1 or 2 months. In the first month of feeding, the growth rate of the galangal extract diet group was lowered compared with that of the control diet group, possibly because the shrimp required time to acclimatize to the galangal diet. After 2-months of feeding, the growth of the shrimp in terms of body weight, specific growth rate and survival rate of the galangal diet group did not differ significantly (P > 0.05) from that of the control diet group. The clearance ability was evaluated by counting the bacterial cells in the hemolymph of shrimp injected with V. harveyi in the abdomenal segment. The number of V. harveyi in the hemolymph of the galangal diet group was significantly lower than that in the control diet group (P < 0.05), indicating the higher clearance ability of the galangal diet group. The oral administration of galangal extract enhanced the resistance of Pacific white shrimp against V. harveyi and white spot syndrome diseases, as demonstrated by the significantly higher survival rate of the galangal diet group. These results suggested that galangal is useful as an alternative to chemotherapeutic treatment to solve the problems created by residual antibiotics in shrimp.

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The present study examined the influences of industrial chitin extraction processes on the residual oxytetracycline (OTC) and oxolinic acid (OA) in shrimp carapaces and shells. The drugs were orally administered by catheter to the kuruma shrimp (Penaeus japonicus) and vannamei shrimp (Penaeus vannamei). The shrimps were sampled at 6-h post-dosing and their carapaces and shells were collected and used as raw material in the chitin extraction. Residual OTC levels in raw materials were 9 -18 fold higher than the maximum residue limit (MRL) (0.2 µg/g). The residual OTC was reduced 10 -30% by washing treatment. By the acid treatment with HCl, the OTC residues were reduced >98%. The deproteinized material contained negligible levels of OTC. Residual OA levels in raw materials was much higher (134 -376 fold) than the MRL (0.03 µg/g). The residual OA was reduced considerably (34 -68%) by washing treatment. By the demineralization, the residual OA could not be detected in both shrimp carapaces, while the levels of OA residues were determined more than MRL in shells. In the deproteinized materials, no residual OA were detected. Finally, residual OTC and OA could not be detected in the chitin materials for both shrimps.