So, what Makes a fish a “fish?” If you’re not familiar with the differences you are not alone, and the answers may surprise you. Fishes come in a wide variety of shapes, colors and sizes. Yet, not all creatures that swim in our oceans, lakes, rivers, and streams fall under the “fish” classification. So, how do you properly identify a fish? Well, here’s a guideline – fishes have three important traits in common: 1. they live in water, 2. they have fins, and 3. they use gills to get their oxygen from the water.
A prime example of this is the shark , which is technically classified as a fish, while the dolphin is considered a sea mammal , and a member of the whale family. The nuances that separate these two animals are quite subtle. A dolphin and a shark differ in several ways; a dolphin relies upon breathing in oxygen more like a human than a fish. In other words, the animal must “come up for air,” in order to survive. A shark, on the other hand, does not. It breathes through its gills to obtain oxygen from water. A dolphin is a mammal made up of skeletal bone, while a shark’s skeletal structure is not comprised of bone at all, but made up entirely of hard cartilage.
Fertilization and Reproduction:
Some fishes like sharks, reproduce by internal fertilization . This means the male deposits sperm into the female fish, where the eggs are fertilized inside of the mother. These fishes are called live bearers , which means that they give birth to live young, not egg hatchlings.
Most fishes reproduce by a process known as external fertilization . This means a female fish releases her eggs into the water, where they are fertilized by sperm from a male. This process is called spawning . Most species of salmon spend part of their lives in the salt water of the Pacific Ocean, but they will soon travel many miles into fresh water streams and rivers to spawn. Along the journey, their bodies change to a brilliant red color. Females release eggs along the gravel bottom, where they are fertilized by males. Sadly, both males and females die after spawning – their life journey is complete. The young fish hatch and spend a year in the fresh water before traveling out to sea. Two to three years later, the salmon return to the river as breeding adults. They spawn, and the cycle continues.
Many fishes develop bright colors during their breeding seasons. In most fish species, the male is more colorful than the female. He uses his bright colors to attract females, and the color also makes it easier for fishes to recognize species members.
Eggs and Hatching:
Fish eggs may hatch anywhere between several days to many weeks of spawning, depending on their specific species, water temperature and other varying circumstances. Eggs range in size from a barely visible, microscopic sized dot, all the way to the size of a large coin. Some eggs float in open water, while others are heavier and sink to the bottom. Eggs on the bottom may clump together in masses, or even stick to various objects. Some fishes place eggs on the undersides of rocks or on sticks in the water. Some eggs simply fall into the spaces between surrounding rocks and pebbles.
Many fishes travel to special areas or locations where conditions are just right for spawning and protecting their eggs. For some species, this might be a matter of moving a few yards ahead into a stream, or into shallow water in a lake. But for others it can mean a life journey of thousands of miles. Many fishes simply release their eggs and sperm into the water, paying no attention at all to the fertilized eggs, but other fishes build nests and fiercely guard the eggs and young. In a few species the adults carry eggs on their bodies. Some fishes actually keep the eggs in their mouths until they hatch.
Generally, when young fishes hatch they may look very different from the adults. A newly hatched fish may be nearly transparent, but in a few days they develop colors, patterns, etc. Juvenile fresh water fishes tend to resemble their parents, but most salt water fishes develop in larval stages. These larval fish species drift freely in the open sea and many are very bizarre looking, with odd shapes or long trailing fins!
Fishes usually spawn during a particular time of year. In fresh water ponds and lakes, late spring and early summer are excellent times to observe fishes making nests and laying eggs. It’s also a good time to observe hatchlings (baby fishes) schooling together. So if you want to plan an observation trip, that’s the time to do it! These kinds of outings make great field trips for kids because they’re fun as well as educational.
The world of fishes is one of our most vast and complex of our entire planet, and not to be dismissed or underestimated. Sadly, as many fishes and sea mammals decline in numbers, these losses will have a very negative impact on our ecosystems around the globe. It is only through education and awareness that we can learn how to protect these lives and this precious home we all call Earth.
Source by Dawn Lambros