| Freshwater Sardinella | |
|---|---|
| Sardinella tawilis being sold in a market. | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Clupeiformes |
| Family: | Clupeidae |
| Subfamily: | Incertae sedis |
| Genus: | Sardinella |
| Species: | S. tawilis |
| Binomial name | |
| Sardinella tawilis (Herre, 1927) |
|
Sardinella tawilis (sometimes obscurely referred to as the Freshwater Sardinella) is a freshwater sardine found exclusively in the Philippines. It is unique in that it is the only member of the family Clupeidae that is known to exist entirely in freshwater. Locally, they are known in Filipino as tawilis.[1]
Contents |
S. tawilis are 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.[1]
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 used to be the caldera of an ancient volcano.[2] 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 non-saline. Sardinella tawilis is believed to be one of a few formerly-marine species trapped within the lake that have evolved into purely freshwater species.[1]
S. tawilis, like members of its family, are epipelagic filter feeders, using their gill rakers to strain plankton from the water while they swim with their mouths 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.
S. tawilis prefer to ingest larger prey, such as adult copepods, supplemented with rotifers and water fleas. It has been found that during the summer months when the density of smaller copepods were much higher, S. tawilis 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.[3]
Little is known about their reproduction.[4] It is known that the Taal population spawns during the months of April to July, when surface temperatures are highest.[3]
Sardinella is straightforwardly derived from the Greek "sarda", literally "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.[1]
Despite its threatened status,[5] tawilis 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".[1]
In addition to raw consumption, tawilis are also processed into various food products. Tawilis 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 most probably lead to species extinction. As the population of the Philippines grows, there will be greater demand for tawilis, possibly overfishing the lake's stock population.