A member of the Herring family (Clupeidae), cultriventris is a brackish to fresh water fish native to the Black, Azov and northern Caspian Seas and nearby lakes and rivers, while grimmi and engrauliformis live in central and southern Caspian only. All can grow to just over 5-1/2 inches, engrauliformis a little longer, and are major fish for canning in the region. I have also seen some cans of Latvian Baltic sprats labeled Kilka, but that isn't right. The photo specimen, which was salt pickled, was 5 inches long and weighed 3/4 ounce. The largest in the batch was 6 inches and weighed 1-1/8 ounces.
Caspian stocks have recently dropped 50% due to an American comb jelly named Mnemiopsis leidyi eating all their food and the fishery is now endangered. This also happened to the Black Sea but another American jellyfish named Beroe ovata came allong and ate most of the Mnemiopsis. This solution is likely to be applied in the Caspian. Beroe eats only Mnemiopsis and disappears when they are all eaten.
More on Herring Family.
Canned Kilka: Kilka is mostly canned in oil or tomato sauce or smoked and canned in oil. The major exporter is Iran, so you aren't likely to see much of it in the U.S. until the current sword rattling is a thing of the past.
Meanwhile some Latvian Baltic sprats are roasted and made up in tomato sauce, and even labeled "Kilka". I've had them and they're quite edible. Of course the bulk of sprats are smoked and canned in oil. These fish are so closely related substitution is not a problem.
Salt Pickled Kilka: This form is available in some markets serving a Russian community - the photo specimen came from Jon's Marketplace in Glendale CA. Salt pickled kilka are much like salt pickled herring, just nearly an ounce, rather than nearly a pound.
Prep: Like herring, salt pickled Kilka should be soaked in water for some hours before eating or using in a recipe to cut salt content. 6 hours should be fine, even less if you reduce it to fillets.
Yield: 1-1/4 pound yielded 11-1/4 ounces of fillet (55%).
Filleting: You may wish to fillet this fish rather than eat it "head guts and feathers", especially for use in recipes This is easier than you might think. When doing this procedure it is fastest to do one step on all the fish before going to the next step. I do the filleting before soaking to reduce salt.