Aquaculture in Tanzania is represented primarily by the culture if seaweeds, Kappaphycus alvarezi and Eucheuma denticulatum as source of carageenan for food additives. During the 1950s, there was considerable effort to establish freshwater pond culture of tilapia in the country, but the projects proved to be unfeasible due to robust capture fisheries in lakes and rivers and a lack of transportation and infrastructure to access distant markets. There has been some culture of penaeid shrmp in brackish ponds, and renewed interest in pond culture of tilapia. A number of species are being cultured experimentally, including milkfish, giant clams (Tridacna gigas) and pearl oysters Pinctada margaritifera.