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Motherhood in the fish world

Don MacLean
Don MacLean

OUTDOOR WORLD BY DON MACLEAN

This weekend we have the opportunity to celebrate the mothers in our lives. Not only have they given us life but they have also nurtured and educated us along life’s journey.

While we don’t often think of maternal care in the fish world we often see it in other wildlife species. If you have ever been unfortunate to get between a mother moose, or bear, and their offspring then you know they will actively defend their young.

Examples of maternal care among fishes are not as extreme and, in reality, most fish species do not provide any form of parental care. This is especially the case for most marine fish where the eggs are simply released into the sea where they develop and hatch. However, there are a number of fish species where the females of the species actively play a role in nurturing their young.

While there are examples of maternal care in both fresh, and saltwater species, it is more commonly found in freshwater fishes. One group many of us will be familiar with is trout and salmon. When the female is ready to lay her eggs she begins by digging a nest in the stream bed by quickly fanning the gravel with her tail. This nest, known as a redd, is excavated to a depth deep enough to hold her eggs. Once the redd is completed the female releases her eggs. At this point the males fertilizes them with milt. Spawning completed, the female then covers the eggs with gravel.

Another element of female care found in trout and salmon is the amount of yolk each egg contains. As the embryos develop they feed on this yolk to provide energy until they are ready to swim up to begin feeding around this time of year.
Another local fish species which dig spawning nests is the lamprey. In this case the females move rocks by taking them in their mouth. When I fished the St. Mary’s River in Guysborough County it was a common sight to see lampreys’ redds the size of a washtub on the bottom of the river.

While protecting their eggs is one method female fish may use to ensure their young have some protection, other species have evolved other methods. Perhaps the highest level of survival is provided by those fish species where the females give birth to live young. This strategy is commonly found in aquarium fishes ranging from guppies and platies to swordtails and mollies.

One fish species that has developed a variety of maternal care to improve survival is the shark. They have evolved a complex life history where a variety of strategies have been developed to maximize survival of their offspring. Some sharks lay eggs, which are simply released into the sea. They are, however, covered in a tough egg case which provides some protection. In other shark species females have a hybrid system where they lay eggs, but retain them in their body until they hatch. When they are large enough the female releases them as free-swimming young.

Other species develop the embryos in their body and then give birth to free-swimming young. Blue sharks, which are commonly found off our coast, utilize this reproduction method. Young sharks are known as pups, and blue sharks have been recorded as giving birth to 134 pups.

So, maternal care can be found in one form or another across the animal kingdom. Make sure you celebrate the mothers in your life. Happy Mother’s Day.
 

Don MacLean is an outdoor writer and biologist who lives in Pictou County.

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