In the Gambia, fish is an important diet of the people that provide protein and could be used in diverse ways.

Fish and fish oil contain two fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), according to William E Connor and Sonja L Connor at the division of Endocrinology, Diabetes and Clinical Nutrition, Department of Medicine, Oregon Health & Science University, Portland.

The major dietary sources of these two fatty acids, according to them are fish and shellfish, which is from both salt water and fresh water. DHA can also be synthesized in the body from the n-3 fatty acid -linolenic acid, which is present in some vegetable oils and some nuts as well as seeds. However, this synthetic step is relatively inefficient.

DHA is 22 carbons long and has 6 double bonds with the n-3 configurations. It is the most prominent fatty acid in the brain, retina, and spermatozoa and is necessary for vision, cognition, and sperm motility. DHA is especially rich in the neurons and synaptosomes of the cerebral cortex, where it occupies the
number two positions of membrane phospholipids. In premature infants, whose formula contained DHA balanced with n-6, arachidonic acid, vocabulary and motor performance increased and vision improved.

Of interest also is the fact that dietary DHA can be incorporated into monkey brain phosophilipids later in life as well as during development.
With this background, a logical question is: "Would fish consumption retard the decline in cognitive function that might otherwise occur in an elderly
population? Fish and fish oil, according to the Portland university information,  have a high content of DHA and its 20-carbon precursor EPA.

Studies to answer this question were begun in the 1990s. In a typical study, the investigators estimated the amount of fish in the diet or measured the
composition of the plasma fatty acids at baseline, which provided an index of fish consumption. Cognition was estimated at baseline with follow-up years
later to correlate any change in cognition with the baseline fish consumption, plasma fatty acids, or both.

In the past, some studies were positive and some were negative. A recent report from the Framingham Heart Study showed that persons with plasma phosphatidylcholine DHA in the top quartile of values had a significantly (47%) lower risk of developing all-cause dementia than did those in the bottom quartile Significantly greater protection was obtained from consuming 2.9 fish meals per week than from consuming 1.3 fish meals per week.