Implied question: Nowadays, it is considered dangerous to eat [fish] shortly before it spoils, and also drinking afterwards water, which we say below that it is beneficial.

Answer #1: Perhaps nature changed, just like cures in the Gemara, which do not work nowadays.

Answer #2: Perhaps the rivers of Bavel were better for it (fish, than our rivers are).

Answer #3: Some say that "Kavra" does not refer to all fish. There is a fish called Kavra. It is different than other fish in these ways, like it says in Chulin 109b;

Citation (109b): The Torah forbade to us Girusa (a Tamei bird), and permitted the tongue of Kavra (which tastes like Girusa).

It is unreasonable to say that the tongues of all fish have the same taste.

Rashi's opinion: A second version in Rashi says "v'Gaf", for [if not] there is a loss, for they transport them without a cork;

Opinion #2: We can say that he must cover them due to Sheratzim. However, a cork is not needed, for a partial covering suffices. Perhaps new [oil] spoils [if it is not corked].

Reference: I explained this in the first Perek (2a DH Mshkin).

Observation: In our Mishnah, R. Yehudah is stringent [about Devar ha'Avud], and here he is lenient [to let others do it for an Avel].

Alternative text: Some texts say [that he needs to cork] "Kado" (his flask).

Assertion: R. Shimon ben Gamliel agrees to Rav Shisha brei d'Rav Idi's law, and forbids to an Avel [things permitted during Chol ha'Moed];

Even so, he agrees that where he is the only professional, it is permitted, in private.

Note: Rashash says that the next words begin a new Dibur, which explains that sharecroppers... do the work through others.

Explanation: [They do it through others] in order to avoid a loss for the one who hired them.

Opinion #1: Regarding his Avelus, we permit him himself if there is no one else who can do like him.

A professional for the Rabim, barber [.... or bathhouse attendant] for needs of the Rabim and the Regel, is permitted.

Opinion #2: Some say that we permit the Avel himself when one will not find others, like the words connote, "there is no professional there other than him." However, l'Chatchilah he must do through others.

Question: According to this, when donkey-drivers and ship captains are hired out to others, I do not know why below we do not require through others.

This is not difficult for the first opinion. There is no one who will do this like the professional donkey-driver, camel-driver or ship captain.