Characterization of protease activity in developing discus Symphysodon aequifasciata larva Alexander Chong, Roshada Hashim, Leng-Choy Lee & Ahyaudin bin Ali SchoolofBiologicalSciences,UniversitiSainsMalaysia,Minden,Penang,Malaysia Correspondence: AlexanderChong,SchoolofBiologicalSciences,UniversitiSainsMalaysia,11800,Minden,Penang,Malaysia. E-mail: alex@usm.my Abstract The activity of different protease classes was moni- tored in developing discus (Symphysodon spp.) larvae using a combination of biochemical assays and substrate SDS±PAGE techniques. Results showed the presence of alkaline proteases of serine proteasessuchastrypsinwithasignificantincrease in activity levels detected beginning 3days after hatching. Other alkaline proteases such as metallo- proteases and chymotrypsin, a type of serine prote- ase, were only detected in older larval stages, at around 20±30days after hatching. Acidic protease activity was very low during the first 20±25days of development before showing a significant (P , 0.01) rise. This is despite the formation of a stomach observed 10days after hatching. Based on the development of the protein digestive system ob- served, the use of microdiets to replace Artemia shouldbeconsidered25daysafterhatching. Keywords: discus, larva, protease, development, characterization Introduction Theprocessofraisingfishlarvatothejuvenilestage hasbeenidentifiedasamajorbottleneckinattempts to increase production of numerous fish species (Alves, Specker & Bengston 1999; Turano, Davis & Arnold 2000). Most of the problems are associated with nutrition (Planas & Cunha 1999). The use of bothlivefeedanddrymicrodietsfacesseveralprob- lems needing to be addressed. Artemia and rotifer usage, for instance, are often hampered by high cost,irregularsupplyandtheneedforinfrastructure and labour to enable mass production (Lavens & Sorgeloos 2000). Although dry micro particulate feed has been proposed in numerous reports as a possible replacement, limited success has been reported in selected species (Charlon & Bergot 1984; Person-Le Ruyet, Alexandre, Thebauld & Mugnier 1993; Cahu, Zambonino-Infante, Escaffre, Bergot & Kaushik 1998; Yufera, Pascual & Fernandez-Diaz1999).Inmostcases,earlyweaning of larvae to dry diets resulted in higher mortality and decreased growth as compared with continuos feeding with live feed (Verreth, Torreele, Storch & Segner 1987; Dinis 1992; Jones, Kamarudin & Le Vay 1993; Cahu, Zambonino-Infante, Quazuguel & Le Gall 1999). Nevertheless, the potential of micro diets is huge if properly developed, as its' com- position can be controlled to allow for reliable production of high-quality larvae (Buchet, Zambonino-Infante & Cahu 2000). Culture of tropical fishes to supply the global aquarium trade is an important source of income for several Asian countries (Ng & Tan 1997). The discus (Symphysodon spp., Cichlidae) is one of the mostpopularandvaluablefreshwaterspeciesbeing intensively cultured in Malaysia, Thailand, Singa- poreandIndonesia.Tradingofthisfishischaracter- ized by high price and strong demand for export of newly developed strains. Despite its commercial value, there is a lack of research on nutritional aspects of discus needed to develop a feeding strat- egy for intensive culture (Chong, Hashim & Ali 2000). Discus larvae can rely solely on the bodily mucussecretionproducedbybothparentfishasfirst exogenous feed for around 30days after hatch Aquaculture Research, 2002, 33, 663±672 ß 2002 Blackwell Science Ltd 663