Susceptibility of Tiger Shrimp (Panaeus monodon) against Vibrio harveyi on various Molt Stage and Osmolarity

Vibrio harveyi causes disease of tiger shrimp (Penaeus monodon) aquaculture in East Kalimantan. This research aimed to investigate the susceptibility of tiger shrimp on various molt stage and osmolarity, and determine the salinity (osmolarity) of water that can reduce the risk of V. harveyi attack. Shrimp age of 1.5 months was maintained in 4 aquariums with salinity 29.72 ‰, 26.07 ‰, 22.35 ‰ and 17.79 ‰, then challenged with V. harveyi. After 7 and 14 days, osmolarity of haemolimph was observed with automatic osmometer and Digital Roebling Osmometer. The susceptibility of tiger shrimp to V. harveyi was evaluated based on clinical symptoms, pathological anatomy of shrimp and density of V. harveyi (TPC) in the hepatopancreas. Osmolarities of shrimp haemolymph at premolt, postmolt, and intermolt stage were 575.30-812.60; 534.00-788.80, and 566.20-795.60 mOsm/l H2O, respectively. The lowest bacterial content in the premolt stage was maintained at a salinity 22.35 ‰, and the highest one was obtained in postmolt stage at 29.72 ‰. The molting and postmolt stage were the most susceptible to V. harveyi attacks. The results suggested that the shrimp maintained at 22.35 ‰ salinity was less susceptible to V. harveyi.

Epidermal collagenase activity and its induction by 20-hydroxyecdysone in the fiddler crab Uca pugilator

The epidermal collagenase activity and its induction by 20- hydroxyecdysone in Uca pugilator were investigated. Zymographic electrophoresis showed four bands of collagenase activity, 16, 19, 22 and 29 kDa in molecular weight, with the former two accounting for 60% and 36%, respectively, of the total collagenase activity. The collagenase activity varies during the molting cycle. Among the molt stages tested, Premolt Stage D0 exhibited the highest epidermal collagenase activity for both the 16 and 19 kDa isoenzymes and, as the molt stage proceeded, the enzymatic activity of these two isoenzymes decreased, with the lowest activity for both found in Premolt Stage D3-4. Injection of 20-hydroxyecdysone significantly induced the activity of the 16 kDa collagenase in the epidermis of Uca pugilator, suggesting that the activity of this isoenzyme is under molting hormone control. Although 20-hydroxyecdysone injection did not result in a statistically significant increase in the activity of the 19 kDa isoenzyme, a tendency of the induction was nonetheless demonstrated. This is the first report on epidermal collagenase activity and its induction by the molting hormone in a crustacean.