Joseph, a long time ago I wrote the exact same question in pencil in the side of my Gemara!

1) I wrote there that one may be able to say that Rashi agrees with the opinion of the Rambam, who does not make any distinction between fish and wild animals and birds. We see this in Hilchos Yom Tov 2:7, where the Rambam writes that fish, wild animals, or birds -- which are running free in large enclosures -- are Muktzeh and one may not hunt them on Yom Tov. We see that the Rambam prohibits not only fish but other animals. In addition, in 2:17, the Rambam writes that one may not give food or drink to all three types of creatures.

2) The Beis Yosef (Orach Chayim, near the beginning of 497) asks why the Rambam makes no distinction between fish and the others, even though the Mishnah does make a distinction. The Beis Yosef answers that the Rambam learns that it is only the first Tana in the Mishnah who holds that there is a difference between fish and wild animals and birds, while Raban Shimon ben Gamliel says that they are all the same. The Beis Yosef writes that the Rambam rules according to Raban Shimon ben Gamliel.

3) Therefore, I propose that Rashi learns like the Rambam: that according to the Halachic conclusion all creatures are equal, which is why Rashi writes "Ka Salka Da'atach Hashta," because he is explaining the Tana Kama but the Halachah does not follow the Tana Kama.

4) I later saw that the Tzelach here, by the author of the Noda bi'Yehudah, asks this question. The Tzelach answers that when Rashi writes "Ka Salka Da'atach Hashta," he means that at this stage we think that if there is a fence around the enclosure, even if the enclosure is large, one is still allowed to hunt the wild animals and birds. However, in the conclusion of the Gemara we change our position on this and say that the fence helps only for a small enclosure, not for a big one.

5) I also found a general rule, given by the Pnei Yehoshua in Bava Kama 22a on Rashi DH Mishum Mamono, to help us understand the general way of Rashi. He writes that Rashi in Shas writes many times "Ka Salka Da'atach" even though we stay with this explanation in the conclusion also. The Pnei Yehoshua also writes this rule at the beginning of Kidushin 78b, and the Vilna Gaon writes in Bi'ur ha'Gra (Choshen Mishpat 391:24) that Rashi writes "Ka Salka Da'atach" even though his explanation is true at the end of the discussion as well.

6) Guidance on learning Rashi:

Since we have seen above an important rule, given by the Pnei Yehoshua and the Vilna Gaon, concerning the way of Rashi in his commentary on Shas, I think it would be worthwhile to mention another couple of similar rules given by major Mefarshim on Rashi, and see how they compare with this rule. These are both rules that I have cited a few times in my answers to questions on Rashi, since a number of people find certain aspects of Rashi's approach confusing.

a) The first rule is given by the Beis Yosef (Orach Chayim 10, DH ul'Inyan Halachah), who writes that "Rashi is a Mefaresh and not a Posek." This is an important thing to know when we learn Rashi on the Gemara -- that we are not learning practical Halachah. That will come later, when we have understood the Gemara well, but if Rashi writes something that does not seem to fit with practical Halachah, this should not disturb us much, because Rashi saw his main role as helping us to understand the Gemara, while there are other Rishonim whose work was to decide the Halachah.

b) The second rule is given by the Tosfos Yom Tov in Peah 2:2. He writes that the way of Rashi in many places is to explain the Mishnah according to the original understanding of the Gemara. The Tosfos Yom Tov writes that the reason why Rashi does this is because the correct way of learning is to understand the Mishnah according to the initial approach of the Gemara before one sees what the final understanding of the Gemara is.

c) Now we see a third rule, given by the Pnei Yehoshua and the Vilna Gaon. They say that when Rashi in the Gemara writes "Ka Salka Da'atach," it is in fact often the conclusion as well.

d) Let us think about these three rules of Rashi that we have uncovered. First, we can point out how the rule of the Tosfos Yom Tov and the rule of the Pnei Yehoshua fit together. The Tosfos Yom Tov says that even though Rashi in the Mishnah does not say a word about it, often it can be that what he is writing does not remain at the end of the Sugya. The Pnei Yehoshua adds that even if Rashi writes that his comments here only apply for the beginning of the Sugya, it may be that in fact they apply for the end as well.

e) I think we are getting the idea already that the conclusion is not the most important thing in Rashi's eyes. What is more important is that we should understand what is happening in the Mishnah or Gemara at the present moment, the process. This is confirmed by the Beis Yosef who says that Rashi is not a Posek giving us the Halachic conclusions. Rather, Rashi is giving us a running commentary to help us understand the Gemara we are learning at the moment.

f) This also may help us understand the rule of the Pnei Yehoshua. Rashi writes "Ka Salka Da'atach Hashta." This means that Rashi is telling us what is important for us to know to understand the Gemara at the present juncture. Sometimes this understanding will remain at the end and sometimes it will not. That is not the crucial factor. The important thing is that we can understand the passage of the Gemara we are learning now, and do net get stuck, but are able to continue freely with the Sugya.

Dovid Bloom

Kol Tuv,

Dovid Bloom