Bruce Ajari: Find freshwater shrimp, and trout likely near
April 22, 2009
Humans love shrimp, and trout are certainly similar when it comes to freshwater shrimp or scuds. Scuds are found in many lakes and some streams in our region that tend to be a little more alkaline in nature.
Shrimp require high levels of dissolved calcium in the water in order to develop and maintain their chitinous exoskeleton, which is frequently shed. Aquatic environments that support populations of shrimp are also home to a variety of other aquatic invertebrates, including mayflies, midges, damselflies, caddisflies, dragonflies and stoneflies, all of which are prominent trout food sources.
Freshwater shrimp or scuds are members of the Class Crustacea, Order Amphipoda. Worldwide there are about 800 freshwater species. Representatives of two families, Gammarus and Hyalella, are common to many north temperate freshwater ecosystems. The Hyalella is the most common in the Sierra Nevada and grows to around a half-inch in length.
When present, these creatures provide an excellent and abundant food source for trout. Trout often grow very quickly in size due to their presence. Russ Wickwire, former area Department of Fish and Game biologist in the 1970s and 1980s, once told me of the phenomenal growth rate of fish in Frenchman Reservoir ascertained by the department at that time. He told me that fish introduced in the spring would grow seven inches by the fall. That’s an amazing growth rate.
Prime scud habitat usually has thick mats of vegetation in shallow shoals or a littoral zone of a lake or stream. They also seek cover in rocky or woody debris areas within the shallow water zone. Scuds are omnivorous in feeding behavior but seem to have a preference for detritus (decaying plant matter or animal matter). Their body coloration will match that of the habitat they are living or hiding in so individuals from the same water body can range from very light olive green to dark brown.
Mating can occur several times during the late spring to fall months, with water temperature having the most influence on the initiation of mating courtship. During reproduction the females will often be carried on the backs of the males. Females can release several to more than 50 eggs per brood.
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The eggs are carried in a brood pouch or marsupium located on the underside of the thorax area. Fertilized eggs are typically bright orange in color. All crustaceans undergo regular molts as they outgrow their hard exoskeleton. Newly molted scuds are easily recognized by their semi-transparent light blue or baby blue coloration.
When present, scuds can make up the bulk of a trout’s diet. As a result, when you find that they are present, you should definitely try a fly that imitates them. Fish imitations in a size No. 10 to No. 18 on either a floating line or a sinking fly line in anywhere from around 8 feet to right on the bank. You may be pleasantly surprised.
” Bruce Ajari is a Truckee resident and regular fishing columnist for the Sierra Sun and other area newspapers.