The Birds and the... Fish?

Our oldest son is four years old and I have to admit: "the talk" has never even crossed my mind. He's a preschooler for heaven's sake! But, sadly, they do grow up way too fast, and I learned this morning that my husband and I need to be better prepared. For your reading pleasure, our family breakfast conversation:

Setting: In the kitchen at the bar. On one end of the counter is a new ten-gallon fish tank with only five survivors from the original cast of nine. Aaron and Nicole (aka: Daddy and Mommy) are chatting over a cup of coffee. Big Boy is eating his fourth slice of toast and has chocolate sprinkles (a Dutch breakfast treat--don't worry, we made him eat eggs, apple, and peanut butter toast before breaking out the sprinkles) from ear to ear. Baby is putting squares of peanut butter toast in his hair.

Nicole: Hey, look at that! I think our tiger barbs are getting a little friendly.

Aaron: That would explain why the big one has been so aggresive chasing the other fish away. Mimicking amorous male fish: 'Can't a guy get a little alone time with his lady?'

Nicole: Laughs. Look, the shark is jealous. Mimicking the shark: 'You never hang out with the guys anymore! She's got you wrapped around her little fin...'

Aaron: You know, if they do mate, the other fish will probably eat the eggs. Do tiger barbs lay eggs?

Big Boy: What's mate?

Aaron and Nicole exchange meaningful glances.

Nicole: Ahem. Why don't you field this one daddy?

Aaron: Well, Sweetie, that mommy and daddy fish love each other very much and I think they would like to make some baby fish.

Nicole: Aghast. I think you could have avoided this conversation entirely by saying that they were just snuggling.

Aaron: Oh.

Big Boy: How do they make baby fish?

Nicole: Knew that was coming. Reaches over to Baby and begins to tickle his knees.

Baby: Laughs hysterically.

Nicole: Sorry honey, mommy can't hear you.

Baby: Continues to giggle.

Aaron: Begins to tickle Big Boy, too. All-out tickle fest ensues. Topic of "mating" is happily forgotten. Until next time...

Oh my goodness, that was close. Any suggestions/help/advice for round two? I know my son--he won't forget! Can't I just freeze him at this sweet little age???