Roe a.k.a. hard roe is the eggs of female fish, enclosed in an ovarian membrane. Roe of some fish species is considered a great delicacy, the most famous being sturgeon roe. The processed salted roe of sturgeons is called caviar.
The ovarian membrane containing the individual eggs can be either cooked as a whole in salted water and eaten (eg sliced on toast with some onion), or the eggs can be squeezed out after first being frozen and thawed and eaten "raw": either plain or mixed with chopped onion and smetana, crème fraîche or whipped cream.
In picture above: tiny, whole fresh roe sacks of Baltic herring with a detail showing the individual eggs within.
Top-quality processed roe must be absolutely fresh, and the individual eggs unbroken. When bitten, they must burst easily and feel soft, not at all rubbery or hard. The roe must have a pleasant, not fishy, taste and scent, and there should not be extra liquid visible among the eggs.
Soggy roe with broken eggs should be avoided.
Because of its high fat content, roe is highly perishable and it should not be stored for longer than a couple of months in freezer and, after thawing, 2 - 3 days in the refrigerator, preferably at +3 °C, tightly sealed. But since the temperature of home refrigerators seldom is as low as this, roe should be eaten on the same day that it has been thawed, or stored for no longer than 1 - 2 days in refrigerator after thawing.
In Finland, the roe of rainbow trout (Oncorhynchus mykiss) is the most commonly consumed roe.
In picture on left: rainbow trout roe.
Also vendace (Coregonus albula) roe is highly praised: it is very delicious, but rather expensive. Outside the Nordic countries, it is sometimes sold under the name of "golden caviar".
Vendace roe is often replaced with the more affordable, yet almost as delicious, powan (Coregonus lavaretus) roe.
Other roes consumed include that of salmon (Salmo salar), burbot (Lota lota) and Baltic herring (Clupea harengus membras).
In picture on right: vendace roe.
Sometimes, although rather rarely, also pike (Esox lucius), smelt (Osmerus eperlanus), ruff/pope (Acerina cernua) and fourhorn sculpin (Myoxocephalus quadricornis) roe may be found on the fish counters.
In picture on left: fish roe comes in different colours and sizes Baltic herring roe on left and rainbow trout roe on right.
Some freshwater fish species especially pike, perch, burbot and ruff may carry the larvae of broad fish tapeworm (Diphyllobothrium latum), a parasite particularly common in the Baltic region, Russia and parts of North America. This parasite can also infect humans, attaching itself in the small intestine, causing symptoms like diarrhoea or constipation, abdominal pain, dizziness, loss of weight and anaemia. The
larvae are rather large in size (½ to 2 cm, or ¼" to ¾"), so they can be easily detected in the fish with naked eye.
However, if the fish or roe containing tapeworm larvae is properly cooked or frozen for a sufficient time (either for 24 hours at -18 °C or 72 hours at -10 °C), the infective larvae will be killed and no longer harmful to man. Usually only the people who fish for themselves and eat the flesh or roe of the fish raw or insufficiently cooked are at risk of being infected. Commercially sold roe at least in Finland is always carefully inspected and usually frozen. Nowadays the occurrence of the broad fish tapeworm is extremely rare in Finland.
Soft or white roe is the milt of male fish.
The roe of the crustacean or the invertebrate is called coral.
See a recipe for Christmas fish roe.