Indonesian researcher discovers alternative sedation for live fish

MANILA, Philippines - Clove oil is the best alternative for sedating live grouper (lapu-lapu) before they are placed in aquariums in restaurants. 

This finding by Indonesian researcher Wahyu A. Nugraha of the Department of Marine Science of the Trunojoyo University in Kamai, Bangkatan, Indonesia is significant for fishermen who could command higher prices for the grouper they catch and deliver live to restaurants. 

Nugraha’s study, supported by the Southeast Asian Regional Center for Research and Graduate Study in Agriculture (SEARCA), was deemed by SEARCA director Dr. Gil C. Saguiguit Jr. as a significant development that would eventually reduce, if not eliminate, cyanide fishing in Indonesia, the Philippines and much of Southeast Asia. Nugraha conducted the study while pursuing his MS in fisheries program at the University of the Philippines Visayas under SEARCA scholarship. 

The Nugraha study is the first analysis of the impact of clove oil on grouper, a premium fish species that diners want live in most Asian restaurants. 

Previous studies on clove oil impact on fish covered such species as rabbit fish (locally known as danggit), largemouth bass (apahap), sea bass, Atlantic salmon, Senegal sole (dapa), and gilthead sea bream. 

Saguiguit said finding an alternative to cyanide as an anesthetic for coral reef fish like grouper is necessary to minimize what had been described by the study of Johannes and Riepen in 1995 as “excessive collateral environmental damage.” 

Technically, cyanide fishing is banned in Indonesia and in the Philippines but the ban has not stopped coral reef fishermen from using the chemical in capturing premium fish species demanded by the markets in Hong Kong, China, Singapore, Malaysia, Japan, the Philippines, and Indonesia.

“While an overdose results in the death of the target organism, a properly calibrated squirt allows a diver to easily remove the anesthetized animal from its refuge in a reef, often after some breakage of the corals surrounding the refuge,” Nugraha explained. 

The impact of clove oil as anesthetic in fishing is similar to the effect of the technology developed by Filipino marine scientist Bonifacio Comandante who made it possible for fish to be subjected to suspended animation without water before they are delivered to the markets. 

“This study investigated the possibility of using clove oil as an alternative for cyanide in fishing. Tests were done by recording the stunning and recovery times for grouper (Epinephelus fuscoguttatus) and measuring the bleaching percentage and change in zooxanthellae density in Porites lutea relative to 10 grams per liter (g/L) cyanide, which is normally used in cyanide fishing,” Nugraha said. 

In brief, Nugraha said the average stunning time of grouper E. Fuscoguttatus was reduced exponentially but the recovery time increased as the concentration of clove oil is raised.  

“At 30 g/L, clove oil had a similar stunning effect as cyanide. All small fishes exposed to clove oil for up to 30 minutes recovered but none survived after 60 minutes of exposure,” the researcher stressed. 

Clove is known to most Filipinos as the main ingredient of the aromatic cigarette Gudang Garam and Bentoel. 

Clove oil is distilled from the crushed stems, buds, and leaves of the clove tree Eugenia caryophyllata, Nugraha said, and for centuries, it has been used as a topical anesthetic in Indonesia.   

The primary active ingredient in clove oil is the phenolic compound eugenol, which makes up 70-90 percent of all the clove oil sold in Indonesia. 

Nugraha said using 30g/L of clove oil assures the safe recovery of grouper after 30 minutes and their eventual transport to buyers. 

Clove oil does not dissolve completely in water and for this reason, it has to be combined with hot freshwater at a 1:9 ratio, with the solutions prepared every other day during the period of study in Komodo Island, Indonesia. 

On the other hand, cyanide can be mixed with seawater at a concentration of 10 grams per liter.

But for Komodo Island, the concentration used varied between one half and one tablet per liter, with each tablet containing about 10 grams of cyanide.