I phoned a Halacha hotline, but the connection was not very clear. I have a 23liter aquarium with several small fish, a filter, air pump, and water heater. The first question I had asked was regarding BORER. The female fish is expected to give birth, and typically she eats her young. I was advised to separate the young and place them in a separate bowl. If I understood the rav on the phone correctly, this is prohibited due to BORER. I had wanted to ask the rav about the prohibition of harming animals and if there is also a positive mitzva of saving animals also. The second question I had wanted to ask was regarding the air pump, which from time to time stops pumping air because the plastic tubes disconnect. I had asked the rav on the phone if I could reconnect the tubes on shabbos. The rav asked me if the air pump puts in a lot of air into the aquarium. And I Of course told him that the pump DOES put in a lot of air. The rav therefore said this is also prohibited. Please advise me as the phone connection was not very good. Thank you.
Yes, there is a positive mitzva to save animals, but in this case, not at the expense of transgressing Shabbat. Regarding the pump, yes it's a problem to fix the pump on Shabbat, but I imagine the fish can manage fine if you fix it right after Shabbat.