|Sardinella tawilis being sold in a market.|
Harengula tawilis Herre, 1927
Sardinella tawilis (the freshwater sardinella, freshwater herring, or bombon sardine), is a freshwater sardine found exclusively in the Philippines. It is the only member of the genus Sardinella known to exist entirely in fresh water. Locally, they are known in Filipino as tawilis.
S. tawilis is a small fish reaching up to 15 cm and weighing less than 30 g. Like other members of their family, they have laterally compressed bodies with bellies covered in tough, scale-like scutes. They have a single, triangular dorsal fin and a forked caudal fin. They possess long, slender gill rakers in their mouths.
Range and distribution
S. tawilis populations are found only in a Taal Lake in Batangas province on the island of Luzon in the Philippines. The third-largest lake in the Philippines is in the caldera of an ancient volcano. Before recent history, the lake was but an extension of the entirely marine Balayan Bay. Major eruptions in the 18th century essentially sealed the lake from the sea, eventually leading its waters to become fresh water. S. tawilis is believed to be one of a few former marine species trapped within the lake that have evolved into purely freshwater species.
S. tawilis, like members of its family, is an epipelagic filter feeder, using its gill rakers to strain plankton from the water while it swims with its mouth open. They roam the lake in large schools, just below the surface as the volcanic (and thus sedimentary) nature of the lake limits their plankton food to the surface.
The freshwater sardinella prefers to ingest larger prey, such as adult copepods, supplemented with rotifers and water fleas. During the summer months when the density of smaller copepods were much higher, their stomach contents consisted primarily of calanoid copepods, which are larger than the copepods blooming during this time. This suggests some partial control over prey selection exhibited by the fish, as opposed to simple filter-feeding.
Etymology and taxonomic history
Sardinella is the diminutive of the Greek sarda, meaning literally "little sardine".
The species was originally identified and named in 1927 as Harengula tawilis by Albert William Herre, the Chief of the Fisheries Division of the Bureau of Science in Manila. The species was later moved to the more appropriate and taxonomically accurate genus, Sardinella.
Importance to humans
Despite its threatened status, stocks in Lake Taal have been commercially fished for several decades. The fish is a widely popular food fish in the Philippines, and tons are shipped to most of the major cities in the country. Local supermarkets and wet markets usually have a tray or pile dedicated solely to the species.
The species is commonly referred to as tawilis in the local language of Tagalog. On the island of Cebu, one of the many places where tawilis is shipped, the native Cebuano name for the fish is tunsoy.
In addition to raw consumption, tawilis is also processed into various food products. It is one of the many fish species dried, salted, and sold as daing in the country. They are also smoked and bottled in oil, and sold commercially.
Because of several factors, the species is threatened by overfishing. As with all species consisting of a single population in one location, a local extinction event will lead to species extinction. As the population of the Philippines grows, the demand will be greater for tawilis, possibly overfishing the lake's stock population.
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