Most fish is high in the particular types of fats referred to as "Omega-3" fatty acids.
These fats are essential to the human diet as we do not synthesize them biologically,
and we must either consume the particular Omega-3s that our bodies require, or their precursor fatty acids which the body converts into the fats we use.
These "fish oil" variety of these fats are originally manufactured by algae, and eventually are incorporated into the fish as they move up the food chain.
The two most widely spoken of are abbreviated as DHA and EPA. These two Omega-3 fatty acids are currently being studied as they are now considered very healthful fats,
alongside monounsaturated fats such as olive oil. Omega-3 fatty acids however may be better for you than you realize.

Omega-3 fatty acids are required nutrients for prenatal development. While a baby will derive his or her nutrition from the mother's body,
a pregnant woman should consume enough Omega-3 fatty acids to satisfy both her and her baby's requirements.
The most critical Omega-3 fatty acid is DHA (Docosahexaenoic acid).
Found throughout the body, it is a key structural fat and is integral in the development of the retina, the brain, and the heart.
In fact, approximately 97% of all omega-3 fatty acids found in the brain is DHA as well as 93% of the omega-3 fatty acids in the eyes is DHA.1-2
Many medical professionals believe that DHA is key to maintaining a healthy pregnancy and the consumption of DHA during pregnancy and
breastfeeding has shown a direct relationship with increased mental processing (i.e. IQ score) of the child.3-4
The most common question I hear (which I had a hard time finding the answer to back then) is "How much DHA should I take when pregnant or breastfeeding?"
The simple answer is:

300mg of DHA, not "Omega-3 fatty acids."5-6 Since Omega-3 fatty acids tend to stay in the bloodstream over time,
this requirement can usually be met by consuming two to three portions of fatty fish per week (such as wild salmon, sardines, or any other deep water fatty fish)
or by taking Omega-3 Supplements during pregnancy. Some people prefer to take supplements to lower the possible risk of contaminants in certain fish.
Physicians suggest that women who are pregnant or who intend to become pregnant should avoid Swordfish, Shark, Mackerel, and Tilefish,
and should limit their intake of White Albacore Tuna to less than 6oz per week due to the potential for contaminants (mercury, PCBs, etc., which move up the food chain and concentrate in the large predatory fish).