English Translation
They were biting like crazy yesterday.
The English sentence is completely missing the meaning of the cloze-word {{いやぁ}}. The closest meaning of いやぁ in this context is “well…” in English. It’s an interjection with several different meanings:
いやぁ、昨日は雨に降られてねぇ。（あめにふられて）= My plan was ruined by the rainy weather yesterday. – いやぁ in this context means “It was terrible”, “Oh no!” or “Oh my…”
いやぁ、恐縮です。= I’m so flattered and honored to receive such a nice word/award/present. – いやぁ in this context means “flattering” and it is a bit overwhelming.
Mary: 昨日の釣りはどうだった？(How was your fishing yesterday?) → Tom: いやぁ、昨日は入れ食いでねぇ。(Well, it’s unusual but I could catch fish after fish.)
いやぁ is derived from いや or 嫌, which originally means “no” or “to hate” as a denial expression. The first rainy case with いやぁ implies that the speaker didn’t expect it would rain yesterday. So, it’s a denial. The second case suggests that “I’m not such a wonderful person to have a nice word etc. from you”. This is also a denial. The third fishing case inserts いやぁ (Well…) to make Tom’s tone down in order to be more humble. We, Japanese, don’t show off our achievements. This is how a small negation いやぁ works.
入れ食い is originally a fishing term. 入れ食い = 入れる + 食う (くう) or 食べる (たべる) = once you cast a line into a pond/river/sea (= 入れる), fish after fish eat the bait (= 食う).
Please be noticed that 入れ食い is also used in sexual context. – e.g. Tom went to a party and many women there tried to hook up with him. Or 入れ食い is a kind of scam in business. – e.g. That customer is so naïve that he buys everything I recommend to him.