SARDINES and anchovies may seem like ordinary fish found in markets and on dinner tables, but scientists say they hide a surprising diversity of species, many of which are being uncovered in Philippine waters.
Japanese ichthyologist Harutaka Hata of the Okinawa Institute of Science and Technology cited new taxonomic studies revealing previously overlooked sardine and anchovy species, highlighting the Philippines as an important center of marine biodiversity.
Hata specializes in the biology, ecology, and systematics of Clupeiformes, a group of fish widely consumed around the world. In 2019, he was part of the research team that described Sardinella pacifica, a species first identified from Manila Bay.
“Most sardines are schooling in shallow coastal water and mainly feeding on plankton. However, the species of Clupeiformes are surprisingly varied in their morphology and biology,” Hata said during the lecture “From Inland Streams to Seas (FINS): Twin Lectures on Fish Ecology and Systematics,” organized by the UST Department of Biological Sciences.
Apart from being served fresh as sushi or sashimi in Japanese restaurants, sardines are also consumed worldwide as dried, smoked, or canned fish.
Hata also highlighted the presence of Sardinella melanura, a sardine species native to the Philippines. He noted its distinctive black spot on the tail fin, which is so recognizable that it has earned the nickname “Pikachu.”
Despite their global importance, taxonomic studies on sardines and anchovies slowed after major reference works were published in the late 20th century, he said.
Much of Hata’s research begins in fishing ports and public markets where specimens are readily available. During field surveys, he examined sardines and anchovies from fishing ports in Japan and Malaysia, including Penang, where anchovies are sometimes caught incidentally in prawn fisheries.
Through genetic analysis and detailed comparisons of body features, Hata found that several fish once considered a single species were actually made up of multiple distinct species.
“Genetic analysis and more detailed morphological observation discover many more species that were overlooked. Clupeiformes has been shown to be a group with much higher species diversity than previously known.”
Earlier studies identified about 400 species of Clupeiformes, but Hata has described 64 additional species since 2015.
The Philippines may still harbor undiscovered species. Because the archipelago’s islands were never connected to surrounding landmasses even during periods of lower sea levels, unique sardine and anchovy lineages may have evolved in isolation, he said.
Ken Maeda, also from the Okinawa Institute of Science and Technology, discussed how fish migrate between freshwater and marine environments during different stages of their life cycles. He has worked with Philippine partners on projects that supported the discovery and description of new goby species, including one found in Palawan.
Maeda noted that Okinawa, where much of his research takes place, is geographically closer to Manila than Tokyo, even if there are no direct flights.
Although the island is best known for coral reefs, Okinawa also has hundreds of small freshwater streams, he said. In one stream only 6.7 kilometers long, researchers have recorded 268 fish species, showing how even small habitats can support high biodiversity.
“There are many different patterns of fish migration,” Maeda said. “Migration between the sea and freshwater is called diadromous migration.”
Diadromous migration can be classified into anadromous, catadromous, and amphidromous migration.
Anadromous fish such as salmon spawn in freshwater before migrating to the sea, while catadromous species such as freshwater eels spawn in the sea but grow in freshwater. Amphidromous fish, including gobies, spend different stages of their life cycles in both environments.
“The difference between anadromous and amphidromous migration is the timing of the upstream migration,” Maeda said. “Anadromous fish migrate to the river only for reproduction, while amphidromous fish migrate to the river after hatching to continue growing.”
Maeda’s fieldwork has revealed surprising details about fish development. In year-long beach sampling, researchers collected about 12,000 fish individuals, with gobies making up 86 percent of the total.
Some goby larvae begin drifting downstream shortly after dark. Sampling data show larval numbers rising in the evening and peaking around midnight, suggesting eggs hatch at night and larvae reach the sea within hours in Okinawa’s short rivers.
Using microscopic rings in ear bones called otoliths, Maeda and his team traced the origins of some larvae and found they might have been born farther south in warmer waters during winter months, when spawning is not observed locally.
Meada said ocean currents originating east of the Philippines might have carried some of these larvae northward to Okinawa.
The two lectures were delivered on Feb. 11 at the UST Main Building. Regis Avalo Jophiel L. Lim With reports from Justin Jacob S. Urag
