I want to start right out by stating the obvious; these fish are not called "sperm layers!" So what does that tell us? Referring to egglaying freshwater tropical fishes as matriarchal would seem to be a bit of an overstatement. Let's just say that the moms are the leaders of this pack! The term "egglayer" is very misleading. Take a look at the chart for a moment. "Submerged bubblenester;" that part about the nest makes it sound like it could have something to do with laying eggs. But what about "maternal mouthbrooder," or "egg hanger?" If you are feeling confused, it is not without good reason. What the term egglayer really means to us is that the female's eggs have left her body before they are fertilized (in contrast to female livebearers, whose eggs are internally fertilized). After this has taken place, there are countless variations on the theme as to what happens to them next. For example: some eggs sink and others float; some eggs are sticky, and adhere to the surface they land on, while others are free to move with the currents. But, the one thing they all still have in common is that the eggs are outside of the female. So, what happens next? Fertilization must necessarily occur very soon after the eggs have left the body of the female. That's easier said than done! Take Lake Tanganyika, for example. Would you agree that it can reasonably be described as a big lake? If your eggs are the non-adhesive floating variety, you're going to need a male that is smart, fast, and a bit of a sharpshooter. What's that, a wave?! It is up to the prospective dads to figure out how to get their sperm to the right place at the right time. The idea of those spermatophores is starting to sound pretty good right about now. The point I'm trying to make here is that in order for the balance of nature to be achieved, egglaying moms need to produce many times more eggs than livebearing moms in order to increase the likelihood that at least some of them will be fertilized, and that even a few of those will survive to adulthood. No matter what strategy an egglayer is using, the challenge to reproduce themselves consumes most of their energy. Let me take you on a brief trip into the "uncharted territory" of hermaphrodites, meaning that one animal contains both male and female sexual organs. The Checkerboard Cichlid (Discrossusfilamentosus) is protogynous; they are all born female, with the most aggressive turning into the dominant male. There are proteandrous species which are all born male, and then some become females. An example of this is the Amphiprion bicinctus, a marine Clown Fish. In simultaneous hermaphrodites, one animal
Modern Aquarium - Greater City A.S. (NY)
functions as both a male and a female at the same time, thereby producing eggs which are selffertilized. There is a family of 100 or so airbreathing snails called Lymnaeids, which are an example of this. Gradual hermaphrodites change from one sex to the other within the course of their lives. Some of the livebearing fishes do this. Let's not forget the asexual, or parthenogenic species, of which Rivulus marmoratus, a killifish from South and Central America, is an example. Their eggs develop without being fertilized! I'm sure there are other examples of strange bedfellows, but you get the idea! There are many moms in the fish world who maintain an air of secrecy. We have no idea how they reproduce. They arrive in our aquariums as a consequence of having been "wild-caught." Why, after so many years of fish being kept in tanks, do we still have "mystery moms?" Maybe it's because the tank environment is not similar enough to their natural environment for them to feel comfortable enough to engage in their inherent breeding behaviors. They might need a little mothering themselves, from Mother Nature! Maybe they need a square mile of open water. Maybe they take their cue from the sound of empty snail shells clacking together, or the smell of urine from one of their natural predators, or the sight of a ray of sunshine illuminating the substrate at just the right angle! There must be countless esoteric "triggers" which we can only guess at, and that will never occur in an aquarium. Some of these moms will keep their secrets for all time. There may even be a whole type of fish mom that we haven't even discovered yet! A Few Closing Thoughts We are fooling ourselves if we think that we have even begun to understand these breeding behaviors. For us to call them "strategies" is to mock them. They have their origins in a place more deep and mystical than our minds will ever be able to probe. Even so, fish and their behaviors will always fascinate and taunt us, calling us to look ever closer, and then closer still. And so we will. "To travel hopefully is a better thing than to arrive." Robert Louis Stevenson, 1881 By the way, do you remember Luna, the gravid molly? Turn the page if you would like to see the fruits of her labor. She spells it out for us more clearly than words can, that every day is Mother's Dayl
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