Does fish oil require a Hashgacha:^[1]

The oil of a non-Kosher fish is likewise Biblically non-Kosher.^[2] Accordingly, all fish oil products require a Hashgacha to verify that the oil is derived from a Kosher fish. Fish oil is added in many foods such as Vitamins, medicines. The following will discuss the various non-food products that contain fish oil and their Hashgacha status.

Dental Floss:^[3] Many types of Dental floss are waxed with fish oil. Nevertheless, dental floss does not require a Hashgacha being that one is not eating the oil and has no intent to swallow it.

Fish oil medicine for one who is sick:^[4] It is permitted for one who is sick to the point of being bedridden [Choleh Sheiyn Bo Sakana] to drink fish oil for treatment of his illness, even if his illness does not involve danger, and even if the fish is certainly not Kosher.^[5] Nonetheless, it is best to enter the oil into a capsule and only then swallow it.^[6] Likewise, if there is Kosher fish oil available, then one must buy it even if it is very expensive.^[7] Practically, today there are various companies of Kosher fish oil available on the market and hence it is forbidden to use a fish oil that does not contain a  Hashgacha.

Omega 3 fish oil capsules: Based on the above Poskim, it is understood that there is no allowance for one who is currently healthy to drink fish oil that does not contain a proper Hashgacha. Nonetheless, some Poskim^[8] rule that one may swallow fish oil capsules without a Hashgacha even if he is currently healthy. This is permitted even if one knows the fish oil derives from non-kosher fish. However, if there is Kosher fish oil available, then one must buy it even if it is very expensive.^[9] Practically, today there are various companies of Kosher fish oil capsules on the market and hence it is forbidden to take fish oil capsules that does not contain a  Hashgacha.

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[1] Hakashrus 11:21-22

[2] Rama Y.D. 83:5, in contrast to Tzir of the fish which is only Rabbinically forbidden, as ruled in Michaber 83:5

[3] Hakashrus 11:21 in name of Rav Elyashiv

[4] See Yabia Omer 2:12

[5] Dvar Moshe 1:8, brought in Darkei Teshuvah 155:25; Halef Lecha Shlomo Y.D. 22; Divrei Chaim 2:52; Salmas Chaim 2:20; Yabia Omer 2:12

The reason: As it is permitted for a sick person to benefit from non-Kosher food in an irregular way, and it is irregular to drink oil. [ibid; see Y.D. 155:3]

[6] Rama 155:3; Mahariy Halevi 1:62; Yabia Omer ibid

[7] Dvar Moshe 1:8, brought in Darkei Teshuvah 155:25

[8] Yabia Omer 2:12 based on the fact that swallowing a capsule is not Derech Hanaah, and the Shach 155:13 who rules that when it’s not Derech Hanaah, then a non-Kosher food that is permitted in benefit is permitted even for a healthy person.

[9] Dvar Moshe 1:8, brought in Darkei Teshuvah 155:25