Ruling on fishing with spears and hand grenades

Firstly:

There is no Sunnah to be followed with regard to fishing, and fish do not come under the heading of animals which must be slaughtered in a specific manner, or over which the name of Allah must be mentioned at the time of slaughter. But if one says the name of Allah before catching them, that is good and there is nothing wrong with it, as it is encouraged to mention the name of Allah over anything that is of any importance to a person. But there is no specific Sunnah concerning it, and it is not regarded as something that is to be slaughtered in a special manner, as mentioned above, because fishing is not subject to the same regulations that are prescribed with regard to slaughter and hunting land animals, such as saying Bismillah and takbeer. That is because the scholars are unanimously agreed that creatures that live only in water, such as fish and the like, are permissible without being slaughtered in a specific manner.

Secondly:

Fishing with spears and the like is permissible, if it is not possible to catch them in other ways, such as with  nets and so on, such as if the fish is big and can only be caught with a spear and so on. So the basic principle is that fishing with a spear is permissible. Allah, may He be exalted, says (interpretation of the meaning): “O you who believe! Allah will certainly make a trial of you with something in (the matter of) the game that is well within reach of your hands and your lances” [al-Maa’idah 5:94].

But the fisherman must pay attention to kindness in catching the fish, and try to choose the gentlest possible method of catching them, and the least likely to torment or cause undue hardship to whatever he catches; he should also avoid doing anything harmful to himself or others.

It was narrated from Shaddaad ibn Aws (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Allah has prescribed proficiency in all things, so if you kill, kill well, and if you slaughter, slaughter well. Let one of you sharpen his blade and spare suffering to the animal he slaughters.”

Narrated by Muslim (1955)

The basic principle with regard to preventing anything that may cause harm to oneself or others is the words of the Prophet (blessings and peace of Allah be upon him): “There should be neither harming nor reciprocating harm.”

Narrated by Ibn Maajah (2340); classed as saheeh by al-Albaani in Saheeh Ibn Maajah

And Allah knows best.