Pick Our Brain - December 2012

What’s the difference between delta smelt and the ones I can find in the freezer section of the grocery store?

Delta smelt is a small slender-bodied smelt, about 5 to 7 cm (2.0 to 2.8 in) long, of the Osmeridae family. Endemic to the upper Sacramento-San Joaquin estuary of California it mainly inhabits the low salinity zone of the estuary.

Smelts are a family of small fish that look similar to sardines and anchovies. They are found both in freshwater and in coastal areas of the Pacific and Atlantic oceans. They are also found in the North American Great Lakes, and seas of the northern part of Europe. Many migrate from the ocean to fresh water areas during their spawning season. Certain species of smelt like longfin smelt (Spirinchus thaleichthys) and delta smelt (Hypomesus transpacificus) stay primarily in fresh or brackish water.

There are also several other species of smelt in California waters. The smelt most commonly found in California markets is the rainbow smelt (Osmerus mordax) from the Great Lakes or eastern United States. Night smelt (Spirinchus starski) and surf smelt (Hypomesus pretiosus) are also caught commercially in California and are sometimes found fresh in local markets. Both delta smelt and longfin smelt are endangered species and cannot legally be caught or sold in California.

Longfin smelt is an estuarine fish that typically measures 3.5 to 4.3 inches standard length, although third-year females may grow to almost 6 inches. Longfin smelt are found in the Sacramento-San Joaquin estuary but generally prefer areas with higher salinities than delta smelt. They can be distinguished from other smelts mainly by their long pectoral fins.

The rainbow smelt is slender and cylindrical. It has a silvery, pale green back and is iridescent purple, blue, and pink on the sides, with a light underside. When full grown, the rainbow smelt is between 7 and 9 inches long and weighs about 3 ounces. It was introduced to Michigan’s inland waters from the East Coast as food for stocked salmon in 1912, soon escaped to Lake Michigan and the other Great Lakes, and from there has made its way to various other places.

The surf smelt is primarily a marine species that is occasionally found in estuaries. While the maximum size is about 10 inches, the average is more like 6 inches. They spawn in the surf zone of certain beaches from California to Alaska and are sometimes caught there in large numbers. Surf smelt provide an important commercial and sport fishery in Northern California.

Night smelt are similar in appearance to longfin smelt. The maximum length of night smelt is 9 inches but they are generally a little smaller than surf smelt. As the name suggests, they spawn at night along many of the same beaches where surf smelt spawn and are caught by both sport and commercial fishers.