What do fish eat?


Illustration by Yana Volkovich

“What do fish eat?”

I turned around in my chair and looked in the direction of my office door where my colleague was staring at me with questioning eyes. His question came as a complete surprise to me. I did not know how to react. What do fish eat? Was this some sort of riddle? Was it a play of words? Was it a general question about the diet of marine species? The question sounded simple, but I had no idea what it meant. I could not imagine what could have prompted it. My guess was that it was some sort of strange joke.

“You are from Iceland, right?” my colleague asked after having given up on waiting for an answer to his original question.

“Yes,” I replied hesitantly, unable to comprehend how that fact had anything to do with the original question. I put my joke theory aside, unless my nationality had something to do with the pun.

“Then you must know something about the diet of fish,” my colleague claimed. By now I was certain that this was not a joke, my colleague looked too serious.

“Well, I guess it depends on the type of fish,” I answered rather unconvincingly. “I guess that some eat plankton and others maybe eat shrimp. I must however admit that I know very little about the diet of fish. My priority is for fish to be part of my diet rather than bothering about what they themselves eat.”

My lack of knowledge on the subject was no understatement. If I had ever learned about it in biology class, I had certainly forgotten all about it by now. I was also surprised about being asked this question by my colleague. We were both PhD students in rather non-biological subjects — I in computer science and he in mathematical logic. The subject of the diet of fish was not really a common one in our part of the university.

“But fish in tanks?” my colleague continued. “Goldfish. What do they eat?”

“Fish food,” I guessed. “I guess.”

I was surprised how unconvincing my answer sounded. In particular in the light of how obvious it was. The logician should not need the help of a computer scientist to reach that conclusion. I wondered again whether it was some sort of logical trick question. Maybe a non-obvious question that asked for a non-obvious answer.

“That’s what I thought as well,” my colleague answered, nodding his head.

We remained silent for a while. My colleague stared out of the window, looking as if he was thinking very deeply about something. This was obviously no logical trick question, my colleague looked too serious. I was curious to know what this was all about, since the whole situation was rather absurd.

“Why do you ask?” I asked my colleague to try to satisfy my curiosity.

“My flatmate has gone on a trip for a few days and she left me a note to remind me to feed the fish,” my colleague replied. “However, she said nothing about what I should feed them, when, or how much. I am a bit puzzled. I don’t know what to do.”

My colleague did indeed look puzzled and a little helpless.

“Are you sure that there is no fish food in the vicinity of the tank?” I asked, rather skeptical that my colleague’s assignment was as complex as he seemed to think.

“I looked for some, but found nothing,” my colleague admitted and sighed. “What does fish food look like, anyway?”

As I had never kept fish myself I had limited knowledge of fish food. I recalled a moment from my childhood, seeing a friend of mine mince some sort of mixture of green leaves for his fish. That was all I knew about keeping fish.

“As far as I know, fish food is some sort of minced leaves in a small cylindrical container,” I suggested trying not to sound more knowledgeable than I really was.

“That’s what I thought as well,” my colleague replied. “But I could see no such thing anywhere close to the fish tank.”

It struck me how hopeless my colleague looked when confronted with this problem. I knew him as the authentic genius who could find a solution to any question that came up in the field of mathematical logic. However, to this elementary problem of pet keeping, he could not find an answer. I decided to help him by continuing to point out the obvious.

“Why don’t you go to a pet shop and ask for fish food?” I suggested and felt the same embarrassing sensation of silliness I always got when I answered an obvious question put forward by a professor in the classroom.

“That’s a good point,” my colleague replied and seemed relieved for a while before returning to his previous hopelessness. “Where do I find a pet shop?”

I thought about it for a while but I could not remember ever having passed a pet shop in the three years I had lived in Amsterdam. In my defense, I had never needed anything from a pet shop, so I guessed it was normal that I had not noticed any — even if I had passed one.

“No clue. I do not recall having seen such a shop,” I admitted. “As I said before, I have very limited knowledge of these fishy matters. When it comes to me and fish food, it is the fish that is the food and I am the one who is doing the eating.”

“So, I guess the logical conclusion to all of this would be that if I should try to make use of your experience in these matters, it would make sense for me to eat the fish,” the colleague deduced, smiling. He was apparently not too worried about not having found a sensible solution to his problem.

“You are the logician,” I replied. “I will not argue against your reasoning in this case. However, you might want to google a pet shop before you prepare dinner.”

“Thanks! I’ll figure something out,” my colleague said as he left my office. “In the worst case scenario I could find a good goldfish recipe.”

I could not but wonder if he was going to have fish for dinner.

*****

“Ta-da! Guess what this is?”

I turned around in my chair and looked in the direction of my office door where my colleague stood smiling with a small cylindrical container in his hand, which to me looked likely to contain dried parsley.

“Dried parsley?” I replied.

“Fish food?” my colleague asked as he handed me the cylindrical container.

“No, dried parsley,” I reiterated.

“Are you sure it is not fish food?” my colleague asked, the smile disappearing from his lips.

“Yes, I am very sure. This is a spice used to flavor fish before putting it in the oven, not something used to feed it.”

“But say someone fed this to fish, would it hurt them?”

Again, I did not have the right experience to answer my colleague’s question. In fact, I did indeed doubt that anyone had the right experience to answer that question. Yet.

“I’m not sure,” I replied. “I know however that parsley is ideal if you want to cook fish in the oven. Did you feed parsley to the fish?”

“Err, yes,” my colleague replied awkwardly.

“Why?”

I almost could not resist laughing at my colleague’s misfortune. I tried to hold it back though, since my colleague did not seem to share my joyfulness.

“I went home with your description of fish food in mind. I looked around the house for a container full of minced dried leaves. This was the only thing that matched that definition.”

“Did you find the parsley close to the fish tank?”

“Well, not that close to the fish tank, it was in a cupboard in the kitchen.”

“Maybe between the salt and pepper?” I asked unable to hold back a nasty grin.

“Well, perhaps not between them,” my colleague replied. “But in the same general area. Well, the same shelf.”

“It did not occur to you that since the container was on the same shelf as the salt and pepper that it might be some sort of spice used for cooking?”

“No, not really. That did not occur to me. I guess I was so determined to find fish food that I did not think about that.”

“So, you gave the fish parsley?”

“Yes,” my colleague replied, looking rather awkward. He seemed to be realizing the mistake he had made.

“Did they eat the parsley?”

“Like candy,” my colleague replied, smiling as if he was recalling some good old memory from the past.

“And they are still alive?”

“Well, they were alive when I left for the office this morning.”

“Not floating on their back close to the surface?”

“Not floating on their back close to the surface.”

“Interesting!” I said. “Maybe parsley is a decent food for fish after all. However, if I were you, I would still google a pet shop. Just in case long term parsley consumption does have some unexpected side effects for goldfish.”

“I will. Thanks for the advice,” my colleague replied as he left my office with the parsley in one hand and a smile on his face.

*****

“Is it normal that fish change color?”

I turned around in my chair and looked in the direction of my office door where my colleague was standing for the third consecutive day asking a fish related question. Although I was getting used to weird questions, this one was the weirdest one so far.

“Pardon?” I asked to make sure I had heard correctly.

“Is it normal that fish change color?”

I had probably heard correctly. At least I had heard the same thing twice in a row. I thought of the parsley, and of lollipop-green goldfish swimming in a tank.

“Well, I think that some marine animals can change colors in order to assimilate their surroundings and thereby avoid being eaten by other marine animals,” I answered even though I was sure that my colleague’s question was not about the general adaptability of marine life.

“I mean goldfish. Is it normal that they change color. From yellow-ish to green-ish?”

“Green-ish goldfish, you say. Have the parsley eating goldfish changed colors?” I asked, trying to hold back the laughter that was boiling inside me. “Have they turned green?”

“Err, yes,” my colleague answered nervously.

“But they are alive?”

“Yes, alive. But green.”

Once again I had to admit that my colleague’s problem was far beyond my core competence.

“I must admit that I have limited experience of the effect of feeding parsley to goldfish. I cannot say if this color change is a normal reaction or not,” I said with as straight a face as I could maintain. “I can however confirm that oven baked fish with parsley does not change colors. Or at least it does not turn green.”

“Oh well,” was all my colleague had to say before going back to his office.

*****

“Do you have Sipser?”

I turned around in my chair and looked in the direction of my office door where my colleague had once again appeared with a question on his lips. It took me a while to digest the question. The question was abnormally normal. The question was somewhat understandable, did not involve color-changing, parsley-eating goldfish and made sense in the context of an office space inhabited largely by mathematicians, logicians and theoretical computer scientists.

“You mean `Introduction to the Theory of Computation’?” I asked just to be sure I had heard correctly, and was not missing some hidden connection to either the diet or metamorphosis of goldfish.

“Yes,” my colleague confirmed. “I need to look up a definition.”

I handed him the book and told him he could take it with him and return it when he was done. He thanked me and prepared to return to his own office.

“By the way, how did it go with the goldfish?” I asked before he could leave the office. “Did they survive the parsley?”

“Well, yes,” my colleague answered awkwardly. “They remained green for a week. My flatmate got a shock when she returned. She thought I had killed the fish and replaced them with green ones.”

“But they recovered?”

“Yes. They are now back to their golden yellow color.”

“Did you ask her about the fish food?”

“Well, yes,” my colleague answered and blushed slightly but did not seem to have any intention of elaborating on that answer.

“And?” I asked to try to drag the story out of him.

“Well, the thing is that the box with the fish food was on top of the note that she left me. I thought it was some sort of spice so I put it in the fridge.”

“The fridge?”

“Well, yes,” my colleague replied and paused before continuing. “How is it going with the upper bound of that algorithm you were studying last week, by the way?”

I smiled. My colleague had apparently had enough of fish related discussion for the time being.

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