Background for Teachers
TPW Magazine, September 2009
This month we're making a fun twist on going back to school -- fish school! You'll find features on Texas freshwater fish (found in streams, rivers and lakes) and saltwater fish (found in the Gulf). There are some fun facts strewn throughout the article on fish adaptations and differences between freshwater and saltwater fish, and most importantly, messages about conservation.
Do you remember going fishing with Grandma or Grandpa? Does an unhurried day on a river or lake, with the occasional excitement of a fish on the line sound like fun to you? Were you curious about those fish you tried to catch?
Texans love to fish and, with miles of beautiful coastline, bays, rivers lakes and streams we have an abundance of both saltwater and freshwater fish to enjoy. Check out the listed sportfish species. Sportfish are those fish whose populations are protected under the watchful eye of biologists and game wardens. TPWD scientists monitor the quantity and quality of these fish populations to set fair rules for how many, what size and when these fish may be harvested by the public and by commercial fisheries. After careful study with surveys in many waterways, fisheries staff recommend rules for harvesting fish. Fish regulations are then set by the Parks and Wildlife Commission and enforced by game wardens. Some of these fish populations are replenished or stocked through the efforts of state or federal fish hatcheries. Texas Freshwater Fisheries Center, Sea Center Texas and other fish hatcheries around the state not only raise and stock fish, but offer tours of their facilities.
Some Texas fish, like the San Marcos gambusia and the Comanche Springs pupfish, are found nowhere else in the world. Texas also has endangered or threatened fish species. One very interesting threatened fish, the paddlefish, is a relic from pre-dinosaur times with some fossils of paddlefish found to be over 300 million years old. These amazing fish can grow to 7 feet long and resemble sharks in that they have no scales and have cartilaginous skeletons. But, they are gentle giants and eat plankton that they filter from the water as it flows over their gill rakers. Students will enjoy learning about these fish which are being raised and reintroduced to some of our east Texas rivers.
Because fish have amazing adaptations for survival, they engage students' interest and stretch their understanding of the natural world. How do different kinds of fins and different body shapes make some fish speed through the water like a bullet to attack prey or help them dart quickly in a short space to elude a predator? Why do different species of fish have different mouth shapes? A fish's mouth shape is adapted to the food it eats. A fish whose mouth slants upward might attack prey from underneath. A fish whose lower jaw is flat probably feeds on or near the bottom.
How can coloration camouflage a fish to help it survive? Southern flounder can change its coloration to blend in with the muddy or sandy bottoms of bays. Bright silvery fishes live in areas where light reflects off their bodies making them harder to see and confusing predators. Many fish have two-tones or "countershading." Their lower bodies are light colored so when seen from underneath, they blend in with the sun shining into the water; and are darker on their upper bodies so when seen from above, they blend in as the water gets deeper. Some fish have "disruptive coloration" of stripes or spots to blend into their surroundings. The bright red color of some fish, such as a red snapper, actually make it harder to see under water. Red is barely visible in deep water!
Fish have a protective coating called "slime" that covers their bodies and helps prevent infections. When handling live fish, it is important to wet your hands to minimize any disturbance to their slime coating and gently return fish to water.
How long do fish live? Determining the age of wild animals is very difficult, but research is producing some of the answers. Similar to reading tree growth rings, fisheries biologists have learned to read the growth rings formed in the scales, fin spines, ear bones (otoliths), and vertebrae of fish to determine age. During periods of rapid growth, the rings are far apart, but when growth is retarded, as in winter, the rings are close together. By counting the areas of concentrated rings, the biologist can tell how many winters have passed. This aging method is more accurate in the North, where seasonal temperatures are extreme, but it is not completely accurate since conditions other than winter are known to retard growth occasionally.
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The watery world of fish is both fascinating and a vital resource for people. The health of fish and humans is intricately tied together. People must consider how their actions affect water. Did you know that it could take up to 50 years for a styrofoam cup to dissolve in the water or that it can take up to 600 years for fishing line to dissolve? Tin cans take 50 years to dissolve and plastic six-pack rings take 400 years to dissolve. In addition to some very careless trashing of our waterways, debris can enter through run-off from rain and can be blown by wind. Excess fertilizers run off lawns, down storm drains and into waterways. These nutrients overfeed algae and plants in lakes, rivers and streams and eventually choke out fish and other biotic life. Our actions, intentional and unintentional, impact fish and wildlife. What about people whose towns use that water for drinking? What is good for fish is good for people. And what is bad for fish is usually bad for people. Each person has a responsibility to keep our waterways clean.