World Aquacluture Magazine - September 2020

36 SEP TEMBER 2020 • WORLD AQUACULTURE • WWW.WA S.ORG Tilapia can promote the growth of microorganisms. Ensuring the growth of phytoplankton through fish excretion is also important because phytoplankton supply the needed oxygen in the ecosystems. Moreover, soil and water quality can be enhanced because the movement of tilapia facilitates nutrient cycling (Bosma and Tendencia 2014, New and Valenti 2017). Challenges inCultivatingTilapia Although tilapia is ideal for aquaculture due to its sturdiness and adaptability, it may still cause problems in ecosystems such as competition, disease or hybridization. As tilapia are efficient feeders, they can compete with or consume the larva or juvenile fish of endemic species. As they can grow and reproduce quickly, they may outnumber many slower-growing endemic species, thus leading to the reduction or even extinction of native populations. In Lake Victoria in Africa, the Nile tilapia caused a decline in species population, genetic diversity, and to some extent wiped out the endemic species in the area (Loiselle 1994, Bagarinao 1999, Angienda et al. 2011, Cuvin-Aralar 2016). In the Galapagos Islands, where many endemic species can be found, the introduction of tilapia became a serious threat to the environmental structure of the island (Toral-Granda et al . 2017). Tilapia often forage on the sediment surface and make water turbid, thus blocking sunlight, which is necessary for plants and animals. Although considered predominately a freshwater fish, some species can survive and adapt to brackishwater and seawater conditions. In the United States, some tilapia were able to adapt to the hypersaline Salton Sea. The adaptation rapidly reduced the population of the only native species of fish in the sea, the tiny desert pupfish, considered an endangered species since 1986 (Courtenay 1989, Swift et al. 1993). Tilapia can serve as a vector or serve as a reservoir of an existing pathogen. Because tilapia is adapted to tropical environments, low temperatures affect its immune system, making it prone to many diseases (Deines et al. 2016). Hybridization refers to interbreeding either with native or previously introduced and similar AIS in the area. The Oreochromis genus has an increased survival rate that promotes expansion of its invasive range. Hybridization can reduce the genetic diversity of the population (Juliano et al. 1989, Guerrero 2002, Anonymous 2016). Moreover, AIS that have become established in an area can pose risks for the rich biodiversity of a particular ecosystem (McCrary et al. 2007). Thus, tilapia cultivation in aquaculture and open waters must be checked thoroughly to prevent damage to endemic species and to avoid structural alteration of aquatic ecosystems (Canonico et al. 2005). Milkfish Like tilapia, milkfish has become a stable food source since its introduction to the Philippines around 800 years ago. Marketable size ranges from 15-18 cm in males and weighs at 150-300 g (Cultured Aquatic Species Information Programme 2007). Milkfish are found in clear, shallow and saline tropical waters where temperature is greater than 20 C, especially on well-developed coral reefs. They also frequently enter estuaries and rivers. Milkfish has positive effects for food production and enhancement of water bodies. Opportunities inMilkfishAquaculture Since its introduction as a foodfish, milkfish has become one of the favored species for cultivation in the Phillipines. Milkfish eat a wide range of natural food items such as phytoplankton, zooplankton and fish larvae. Awell-developed epibranchial organ allows adult milkfish to digest plant material (Bagarinao 1994). Although milkfish is a marine species, they can be cultured in a variety of aquatic environments due to their euryhaline tolerance (Bagarinao 1999). Since 1997, global annual production for this fish has increased considerably. By 2005, production was 539,774 t, valued at US$ 616 million, with the Philippines being the world’s top producer (270,341 t), followed by Indonesia (230,424 t) (Cultured Aquatic Species In- formation Programme 2007). Most of the harvest is processed into value-added forms such as dried, marinated, smoke fermented with rice, and canned or bottled in different styles. A recently improved strain of milkfish characterized by its F 1 having a golden color attained through selective breeding has been reported in Taiwan. Although this fish is not yet out in the market, it may contribute significantly to worldwide milkfish production (Cultured Aquatic Species Information Programme 2007). These milkfish are grown through mariculture using fish cages. The milkfish supply dropped in May 2018 due to massive fish kill. The release of permits for fish pen operations was initially halted by the municipal government. In 2019, BFAR hopes to seize giving permits to reduce water pollution (Photo: E.J. Morata). Carps are sold concurrently with other freshwater fish (catfish, in the background) in General Santos City Public Market, General Santos City, Philippines (Photo: E.V. Morata, Sr.).