Why is the term דגה frequently used to refer to Egyptian (Nile) fish?

Question

I ran a word search using Snunit's tool on the appearance of the word דג in the Bible. The search revealed 17 occurrences, and all of them had that word or some form of the word such as דגים (plural noun) or דגי (plural possessive / adjective.)

The version דגה occurs 11 times in various forms including the possessive plural form דגת.

The word דגה tends to be used relating to the fish in Egypt (the Nile). Examples:

• Shemot 7:18

וְהַדָּגָה אֲשֶׁר-בַּיְאֹר תָּמוּת, וּבָאַשׁ הַיְאֹר; וְנִלְאוּ

Referringto the fish in the Nile

Bemidbar 11:5

זָכַרְנוּ, אֶת-הַדָּגָה, אֲשֶׁר-נֹאכַל בְּמִצְרַיִם, חִנָּם; אֵת הַקִּשֻּׁאִים, וְאֵת הָאֲבַטִּחִים, וְאֶת-הֶחָצִיר וְאֶת-הַבְּצָלִים, וְאֶת-הַשּׁוּמִים מִצְרַיִם, לִשְׁתּוֹת מַיִם מִן-הַיְאֹר

Again, referring to the fish in Egypt

Yechezkel (Ez.) 29:4

וְנָתַתִּי חחיים (חַחִים) בִּלְחָיֶיךָ, וְהִדְבַּקְתִּי דְגַת-יְאֹרֶיךָ בְּקַשְׂקְשֹׂתֶיךָ; וְהַעֲלִיתִיךָ, מִתּוֹךְ יְאֹרֶיךָ, וְאֵת כָּל-דְּגַת יְאֹרֶיךָ, בְּקַשְׂקְשֹׂתֶיךָ תִּדְבָּק.

Again, referring to the Nile's fish.

There are a few other examples.

Mind you, this term is used in other places unrelated to the referring to Egypt or the Nile. But, it seems that when the Bible does refer to Nile fish, it this term. Why is that?

Is there a difference in meaning between the two terms, in general, even in the other situations where דגה is used?

Answer 1

According to milon.co.il, the word דגה means

כלל הדגים

which I would translate as the collective term "all fish" kind of like how the word "humanity" means "all humans". So, for example

וְהַדָּגָה אֲשֶׁר-בַּיְאֹר תָּמוּת

means "the entirety of fish-hood in the river will die."

An example of another pair of words in Hebrew which exhibit a similar pattern is (שיר, שירה). A "שיר" is a single song, while "שירה" means "song" as in "They lifted their voices in song."