WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2026 35 Flowerhorns are hybrids within the Amphilophus group known for their vivid coloration, large body size, and high value in the aquarium trade (Figure 1). However, once introduced into natural ecosystems, they exhibit traits that promote ecological dominance (Nasution et al., 2022). These fish are notably aggressive, often monopolizing shelters, feeding sites, and breeding grounds (Herder et al., 2012). In closed systems such as Lake Sampaloc, this dominance has contributed to alterations in native fish assemblages, with small-bodied and endemic species experiencing marked population declines (Yan, 2023). Flowerhorns outcompete native species primarily through resource competition and territorial aggression, especially during spawning periods. Like many other members of the Cichlidae family, they demonstrate exceptional adaptability to a wide range of environmental conditions, including degraded or polluted habitats, which enhances their capacity to survive, reproduce, and establish thriving populations. Consequently, their invasive potential poses a substantial threat to native fish communities (Nasution et al., 2022). In addition, the Flowerhorn cichlid (Amphilophus spp.), being freshwater and benthopelagic, has also contributed to ecological pressures in invaded systems. In Lake Sampaloc, these fishes can reach a maximum length of 24.4 cm and are characterized by their bright orange or golden coloration in adults (from A. citrinellus ancestry), with mature males being larger, exhibiting elongated fins, and developing a distinct nuchal hump (Conkel, 1993). Flowerhorn cichlids are predominantly found in lakes and are omnivorous, feeding mainly on snails and small fishes, along with insect larvae, worms, and other benthic organisms (Yamamoto and Tagawa, 2000). Originally native to Central America, particularly Nicaragua and Costa Rica, they were introduced through the aquarium trade and subsequently escaped into natural waters (Nico et al., 2007). Lake Sampaloc is an inactive volcanic maar located at approximately 14°04’42” N, 121°20’03” E in San Pablo City, Laguna, Philippines (Figure 2). It is the largest among the seven crater lakes in the city, spanning approximately 104 hectares with a maximum width of 1.2 kilometers, a surface area of 1.04 km², and a maximum depth reaching 27 meters (LLDA, 2005; Duka et al., 2024). The lake’s relatively small catchment area of 26 hectares contributes to a prolonged water residence time of up to four years, fostering stable stratification and unique limnological dynamics. Hydrologically, Lake Sampaloc receives water inputs primarily from precipitation, subsurface springs, and surface runoff, while outflows occur via seepage, evaporation, and discharge through Sabang Creek (Duka et al., 2024). Located within a tropical monsoonal zone, it experiences distinct wet and dry seasons that drive seasonal changes in temperature, nutrient concentration, and aquatic productivity (Tamayo-Zafaralla et al., 2013). Biologically, Lake Sampaloc supports a moderately diverse fish assemblage, with twelve recorded species representing three orders and eight families (Briones et al., 2016). This community comprises Fenced and Feral: Farming and Spread of Flowerhorn (Amphilophus spp.) in Lake Sampaloc, Philippines Hannah Nicole C. Gasmen and Janice A. Ragaza (CONTINUED ON PAGE 36) FIGURE 1. A detailed view of a Flowerhorn cichlid highlights its vibrant gold coloration derived from Midas cichlid inheritance, a trait prized in the aquarium trade but impactful in the wild. Photo: H.N. Gasmen. FIGURE 2. A view of Lake Sampaloc providing context for the distribution of fish pen aquaculture. Photo: H.N. Gasmen.
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