June is high season for fish spawning—fish that mate in colder waters are finishing, while those that prefer warmer water for their eggs are just starting. Soon, the summer waters will be full of tiny immature fish called “fry.” Before that can happen, though, the expectant parents have many hurdles to overcome: fish eggs are just as sensitive as adult fish are to the amount of oxygen in the water, and need both oxygen and the correct temperature to develop properly, yet they cannot move to greener pastures if they aren’t getting what they need. In addition, fish eggs are excellent food for all manner of predators, including other fish, and are eagerly gobbled up when found. Let’s take a look at some strategies fish use to protect their eggs from these dangers.
Many species of fish, including bass, sunfish and crappies, create nests for their eggs. The male will find a suitable spot, sometimes close to other males, and use his fins to fan away sand and silt to form a bowl-shaped depression at the bottom of a lake or river. He hangs out around his nest, waiting for a female to come along and lay eggs in his nest (she may lay anywhere from 2,000 to 100,000 eggs). When she does, he fertilizes the eggs and then spends the next 3-7 days doing nothing (not even eating!) except tending the nest: he fans water over the eggs to be sure they have enough oxygen and to keep them clean, and he aggressively defends his nest against predators. He’ll even pick up items that have drifted in amongst the eggs and move them away. He will guard the nest until the young fry have headed out on their own.
Minnows use a variety of strategies: fathead minnows, for example, are similar to sunfish in that they create a nest under a log or rock, defend it, and care for the eggs. Other minnows will lay their eggs in areas with a current of oxygenated air, choosing to deposit their eggs in crevices between rocks to keep them safe from predators. This method of egg-laying is similar to that of our state fish, the walleye.
Many fish, however, do not care for their eggs at all—so how do they keep their eggs safe? Yellow perch choose an area with an aerating current, and deposit their eggs in long, jelly-like strands that could be up to 6 ft. long. These strings of eggs catch on plants and rocks, and the parents do not provide any care or protection, yet perch eggs are seldom eaten. Scientists think that the gel that surrounds the eggs contains some kind of undesirable component that discourages other animals from eating them.
Other fish, such as freshwater drum, quillback and sturgeon, rely on sheer numbers of eggs to ensure that some will survive. Drum spawn in river channels where the current is strong enough to provide enough oxygen to the developing eggs; the males make deep rumbling noises to attract mates. A female can produce up to 500,000 eggs in one season—a necessity, as the eggs are simply laid in the water and left to be carried away in the current with no protection. Most of these eggs are eaten, but the large number of eggs mean at least a few will survive. Drum eggs develop quickly; they hatch in one or two days, and the fry are ready to eat and swim in another two days. This helps the young find cover from predators less than a week after their eggs are laid.
Ironically, no matter how much care a parent fish heaps upon its eggs, once the young fish leave the nest many become prey for older fish, even those of their own species. It is possible that a father bass, for example, could spend a week or two of his life protecting his offspring, and then end up eating them later in the summer. But the energy a fish puts into protecting its young no doubt helps many more of them survive and grow to adulthood. While no strategy is perfect, the abundance of fish in our waters tells us that parents will be parents, even if they are fish, and that while parents have different ways of protecting their young, they all work.
Join us at Kroening Interpretive Center in North Mississippi Regional Park for the following nature programs: Free Family Fundays: Come by on Sunday afternoons anytime between 1-4 p.m. for a free family program, all ages welcome: River Sandcastles on June 11, Fairy Fun on June 18, and Games on June 25. Reservations are not required for the above free programs. Call 763-694-7693 for info.