The black line inside the fish flesh is:Fishy line

The fishy line is the sensory organ of fish to feel the flow of water. On the back of the fish spine there is a kind of fish scales called lateral line scales, on the top of the lateral line scales there are many neatly arranged small holes, and directly with the fish inside the ichthyophore, and some of the smell of the outside environment, such as the earthy smell of the water through the small holes directly attached to the ichthyophore.

The ichthyic threads of grass carp, crucian carp and carp are more obvious and easy to take out, while the ichthyic threads of marine fish are not as obvious as those of freshwater fish. It is mainly used to sense the stimulation to the outside world, the strength of the odor. "Fishy line" will carry some of the earthy flavor of the water, after the removal of natural can remove part of the fishy

Fish deodorization method:

Try to choose to kill now eat, fish fish fishy taste is mainly caused by trimethylamine did not get oxidized, and in the fish is still alive, this oxidation is always maintained!

The fish smell is mainly caused by the fact that trimethylamine has not been oxidized while the fish is still alive, and this oxidation is always maintained when the fish is still alive.

The best thing to do after handling the fish is to choose two hours before stewing, because the fish is dead will produce some harmful substances, this material can be discharged in two hours or so, if the fish is handled after the start of cooking, may increase the content of the harmful substances in the body, and wait for two hours before doing not only a reduction in the content of harmful substances, fishy flavor is not so big.

Reference: Baidu Encyclopedia - Fishy Thread