Tafsir Ibn Kathir (abridged)
Ismail ibn Kathir
The Blessings and Signs of Allah
Allah says, pointing out His mighty power in creating different things, how He has created the two seas (kinds of water). The fresh, palatable sea (kind of water) refers to the rivers which flow among people, rivers great and small according to people's needs in all regions and areas and lands. This water is sweet and palatable for whoever wants to drink it.
وَهَـذَا مِلْحٌ أُجَاجٌ
and that is salty and bitter. means, unpalatable. This is the ocean in which the big ships sail, and is salty and undrinkable. Allah says:
وَهَـذَا مِلْحٌ أُجَاجٌ
(and that is salty and bittery.) Then Allah says:
وَمِن كُلٍّ تَأْكُلُونَ لَحْماً طَرِيّاً
(And from them both you eat fresh tender meat,) meaning, fish.
وَتَسْتَخْرِجُونَ حِلْيَةً تَلْبَسُونَهَا
(and derive the ornaments that you wear.) This is like the Ayah:
يَخْرُجُ مِنْهُمَا الُّلؤْلُؤُ وَالمَرْجَانُ فَبِأَىِّ ءَالاءِ رَبِّكُمَا تُكَذِّبَانِ
(Out of them both come out pearl and coral. Then which of the blessings of your Lord will you both (Jinn and men) deny) (55:22-23).
وَتَرَى الْفُلْكَ فِيهِ مَوَاخِرَ
And you see the ships cleaving, means, they travel through it, plowing through the water with their beak-shaped bows. Muja0hid said, The wind drives the ships, and the wind cannot drive any ships except the big ones.
وَلِتَبْتَغُواْ مِن فَضْلِهِ
that you may seek of His bounty, means, through your journeys to engage in trade from one land to another.
وَلَعَلَّكُمْ تَشْكُرُونَ
and that you may give thanks. means, that you may give thanks to your Lord for subjugating this mighty creation -- the sea -- to you, so that you can travel through it as you wish and go wherever you want, and nothing stops you؛ His power has subjugated for you whatever is in the heavens and on earth, and all of this is by His grace and mercy.
In the next verse: وَمِن كُلٍّ تَأْكُلُونَ لَحْمًا طَرِيًّا وَتَسْتَخْرِجُونَ حِلْيَةً تَلْبَسُونَهَا (And from each, you eat fresh meat, and derive ornaments that you wear - 35:12), it is being said that one gets fresh meat, that is, fish to eat from both waters, sweet or brackish. In this verse, by alluding to fish as meat, the hint released is that fish is meat, already halal by itself. One does not have to slaughter it. This is contrary to the case of the animals found on land. Unless one slaughters them with the name of Allah, they do not become halal. Fish does not have this condition. It is meat, ready to eat. And the word: حِلْيَةً (hilyah) means ornament and refers to pearls. The verse tells us that the way pearls are found in brackish waters, they are also found in sweet waters, something contrary to the general belief, since it is well known that pearls are harvested from the brackish water of the seas. However, the reality is what is evident from the words of the Qur'an that they form in both - yes, much less in sweet waters and far more in the brackish waters of the sea. That they are found in seas excessively contributed to the popular belief that pearls come only from brackish waters.
By using the masculine form in the last word: تَلْبَسُونَهَا (talbasunaha: that you wear), a hint is being released that the use of pearls is permissible for men as well - contrary to gold and silver, the use of which as an ornament is not permissible for men. (Ruh-ul-Ma’ ani)
God first created man from the elements of the earth. By dividing human beings into men and women, God caused the human race to multiply. This exemplifies the power of the Creator. At the time when a child starts developing in his mother’s womb, he finds that all the factors essential to his growth are provided without asking. This shows that the Creator of the child knew his requirements beforehand, otherwise how could He have made such perfect arrangements in advance? The same is true of a man’s age. Nobody has the power to determine his own life-span. It appears that this lies wholly in the hands of an external Being. He takes away one person at a young age, while He gives another a longer life. In all these events, nobody has any say, except God. Then, how can it be proper for a man to have fears or entertain hopes of any being other than God?
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.