World Aquacluture Magazine - September 2020

30 SEP TEMBER 2020 • WORLD AQUACULTURE • WWW.WA S.ORG grouper. The retail market of Sabah grouper seems to be very competitive, with a low profit margin, but the retail price of leopard coral grouper behaved differently. An interesting question that requires more research is why the retail market prices of leopard coral grouper did not go down with its wholesale prices? One possible explanation is that consumers were using the prices of Sabah grouper as a reference point for pricing leopard coral grouper. Obviously, as an alternative to wild coral reef fish, the Sabah grouper can meet the public’s demand for seafood, conserve life in the ocean, and preserve other coral fish. It is a win-win situation that addresses the concerns of environmentalists with coral reef fish trade in Hong Kong (Warren-Rhodes et al . 2003). The fish is a substitute for the far more expensive wild groupers and eliminates the need for natural grouper fish fry. Complaints by Environmentalists against the Sabah Grouper Some local green groups have raised the question of people releasing Sabah groupers into the sea for religious purposes. Critics worry that released Sabah groupers will become voracious giant fish preying on smaller local fish and cause an ecological disaster (Mul- doon and Chiam 2013, Kao 2018a, 2018b). Is that concern credible? Scientists from the Borneo Marine Research Institute have studied sexual maturation and gonadal development in the Sabah grouper and found that hybrids are fertile, with gonads normal in size and structure, gametes normal in size and zygotes viable. Sexual maturity was observed in individuals 70-90 cm TL (Luin et al . 2013). Furthermore, Ching et al . (2018) reported the first observation in a fish laboratory of the natural spawning of the Sabah hybrid since its first production in 2006. Natural spawning, triggered by a sudden change of water depth from 3.0 to 1.5 m, occurred between January and April 2016. The water temperature in the holding tanks was very warm, around 27 C. Broodfish of the Sabah grouper had been reared in the hatchery for ten years and weighed from 12 to 20 kg, corresponding to lengths of 80 to 95 cm. It is therefore not an impossibility that the Sabah groupers released into the sea for religious purposes could reproduce and establish their population in the wild. The average seawater temperature around Hong Kong from June to October ranges from 26 to 30 C, favoring gonad maturation and reproduction. The Outcome of Some Marine Fish Introductions Some marine fishes have been introduced into new ecosystems, both intentionally for pest control, to improve fisheries or as baitfishes and unintentionally through natural range extensions, movement of fishes through canals, transport in ballast water, accidental release by aquarists, or from aquaculture. However, few of these introductions have resulted in the establishment of self-sustaining reproductive populations (Baltz 1991, Randall 1987). Of the marine fishes that have been become established after introduction, examples include the peacock hind Cephalopholis argus and the blue-lined snapper Lutjanus kasmira . Both were introduced intentionally into the Hawaiian archipelago to enhance nearshore fisheries (Randall 1987). The peacock hind nowmakes up more than 80 percent of large piscivore biomass on many coral reefs in the Main Hawaiian Islands (Dierking et al . 2009) while the blue- lined snapper is now the second most abundant fish in numbers and biomass over hard substrate in Hawaii (Friedlander et al . 2002). One non-native marine fish introduction that has attracted a lot of attention in recent years has been that of two species of Indo- Pacific lionfish ( Pterois volitans and P. miles ) (Hixon et al. 2016). Before that time, there had been no documented cases in which an introduced marine fish had become a major invasive threat (Albins and Hixon 2013). Introduced to Florida coastal waters in the mid-1980s (Morris andWhitfield 2009), the most likely vector being releases or escapes frommarine aquaria (Hare andWhitfield 2003, Semmens et al. 2004), Pterois volitans and P. miles have, over the past three decades, extended their range to the tropical and subtropical Western Atlantic, the Gulf of Mexico and the Caribbean Sea as far south as Venezuela (Schoffield 2009, Schofield 2010). More recently, Ferreira et al . (2015) reported the first lionfish record for the Brazilian coast and showed that the individual collected is genetically linked to the invasive Caribbean population. In approximately 30 years, lionfish have dramatically expanded their non-native distribution range to an area of roughly 7.3 million km 2 (Ferreira et al . 2015). The large number of adults observed and the occurrence of juveniles indicate that lionfish are established as breeding populations at their sites of invasion. In their invaded range, densities of more than 390 lionfish/ ha have been reported, compared to 26.3 lionfish/ha in their native range (Green and Côté 2009, Kulbicki et al . 2012). Because of their rapid range expansion and exponential population growth (Albins and Hixon 2013), lionfish are causing serious concern and have become a conservation priority. In recent years, studies have been directed towards assessing the ecological impact of the lionfish invasion. Albins and Hixon (2008) showed that single lionfish reduced recruitment of Bahamian native fish by 79 percent on small experimental reefs in as few as five weeks. The effects of invasive lionfish on native coral-reef fish abundance is nearly three times greater than that of a similarly FIGURE 4. Average monthly wholesale prices of Sabah grouper and leopard coral grouper (HK$/kg), 2010 to 2019.