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Are Trout Colorblind?

It is a myth that trout are colorblind.  In fact, many shallow water fish of both oceanic and fresh water systems such as the trout or salmon have well defined color vision and can even see colors that we humans are not capable of seeing.  The trout’s vision traits evolved as it did in other animals as a mechanism to allow them to better separate potential food items from the background.  For example, in a watery habitat the background may be located at the bottom of the water which is normally a tarnished olive to green color or the background could even be the water itself.  When looking horizontally through clear water, the background appears to the trout as a pale, silvery blue color.  This phenomenon is known as background space light and is caused by the scattering of blue light as it passes through the water.  In water with a lot of suspended algae, the background space light is typically found to be a greenish yellow color whereas in bog water, the background space is more likely to appear a reddish brown color.

One of the reasons many fishermen use flies or lures with strong coloration is to make them stand out more against the background space light and attract fish.  The red and yellow fish lures and flies are quite popular among many fishermen today for this reason.  Fluorescent colors are also quite popular as they stand out stronger than most lures and flies and have highly fluorescent shades that are very attractive to salmon and trout in the area making them much more likely to bite.

Trout can distinguish colors with ease and do not usually discriminate between very fine shades of any color for selective feeding purposes, rather they may discriminate between four or five shades of color varying from the palest shade to the darkest when feeding.  The reason for their lack of color hyper-sensitivity is that since their food organisms vary slightly in color, if the trout were too sensitive to color much of the food would get away.

Interestingly enough, It has also been found that those shades of color consisting of more chroma ( meaning it appears to be more intense than the color of the natural) are more attractive to selective trout.  Along with being able to better find food this way, the fact that trout see further into the ultraviolet range than humans do (they see colors that are not visible to us), could be another reason for why they are more attracted to the colors with more chroma.  This also means that the watery environment the trout reside in could be influencing the transmission of specific colors.  In addition to this, skylight varies during the day.  In morning and evening it contains more red resulting in reds, oranges and browns standing out more during this time.

The rods and cones in a trout’s eyes physically swap places at both the start and end of daylight.  In the evening, the cones which give rise to color response but need high light levels to operate are withdrawn into the surface of the retina and the rods obtrude.  At dawn this action is reversed.  How the trout’s brain assesses the combined cone response and what the fish experiences as a result of this response is still something that scientists are trying to figure out.  However, it is definitely clear that fish such as the trout possess the mechanism for full color vision as we humans know it, and with somewhat a higher range than what we can even comprehend.

Are Sharks Afraid Of Dolphins?

Sharks are not necessarily afraid of dolphins.  Nor are dolphins often found killing or attacking sharks.  There have been a few instances where a dolphin has taken on a shark that is relatively small in order to defend itself. Rumor has it that the myth that sharks are afraid of dolphins may have come from an incident that took place at a seaquarium in the 1950’s when a sandbar shark showed too much interest in the birth of a Bottlenose Dolphin calf, and as a result three of the adult male dolphins ganged up on the shark, butting it in the gills and stomach until it finally died.

During the 1960’s the United States Navy also trained Bottlenose Dolphins to incapacitate large sharks by butting them in their gill pouches.  The dolphins quickly learned to attack certain species of sharks such as the Sandbar shark or the Lemon shark but still seemed to be afraid to try and take on a Bull shark.  It should be noted that bull sharks are about the same size and shape as the dolphins and that in the wild the Sandbar and Lemon sharks are not typically found to attack dolphins, whereas the Bull shark has been found to attack the dolphins in the wild.  This suggests that dolphins may be able to sense which types of sharks pose a threat and which do not.

For the most part sharks and dolphins leave each other alone.  However, Some 75% of wild dolphins show some degree of shark scarring, and we usually only see the ones who were fortunate or strong enough to get away.

Is It Safe To Eat Cod While Pregnant?

Although there are some fish that pregnant women should stay clear of altogether, cod is among one of the species of fish that is considered okay and safe to eat while pregnant.  Many women eat fish during their pregnancy as a way to load up on good nutrients such as protein, vitamin 3 and omega 3 fatty acids, all of which are essential for a baby’s development.  However the downside to eating fish s that almost every single kind of fish often includes traces of Methyl mercury.  This compound is known to be harmful in high doses to an unborn developing nervous system.  Generally it is usually the larger predator fish which accumulate the highest levels of this mercury however.

Eating fish can be quite beneficial for pregnant women and their developing babies.  Just a few of the many benefits that incorporating fish into their diet are as follows:

  • Prevents high blood pressure as well as pre-eclampsia.  (Pre-eclampsia is a combination of symptoms during pregnancy that include high blood pressure, edema, swelling and changes in reflexes.)
  • Enhances the baby’s brain development
  • Promotes the birth of a full term baby with a higher and healthier birth weight

The United States Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) in past years has issued newer guidelines for how women who are trying to conceive, are pregnant, nursing mothers, or who have young children can help limit their exposure to mercury in fish.  It is also now recommended that these women eat no more than 6-12 ounces a week of canned tuna and other cooked fish.  However some types of fish are safe to be consumed twice a week and include the following:

  • Cod
  • Salmon in all forms (except from the Great Lakes)
  • Farmed trout
  • Rainbow trout
  • Flounder
  • Sole
  • Haddock
  • Herrings
  • Sardines
  • Mahi mahi
  • Perch
  • Farmed cat fish
  • Striped bass
  • Tilapia
  • Pilchards
  • Shrimp
  • Scallops
  • Crab
  • Oysters
  • Clams
  • Mussels
  • Crayfish
  • Canned mackerel

Fish that should be avoided altogether include:

  • Swordfish
  • Shark
  • King mackerel
  • Tilefish (Golden and/or white snapper)
  • Tuna steak (Fresh and frozen)
  • Spanish Mackerel
  • Marlin
  • Grouper
  • Large mouth bass
  • Small mouth bass
  • Walleye
  • Northern Pike
  • Lake Whitefish
  • Bowfin
  • Salmon from the Great Lakes
  • Gar
  • Toxic species such as the puffer fish, blowfish and sea squab

Since these fish are at the top of the food chain, it usually means that they also contain the highest levels of mercury.

A few other ways pregnant women can ensure reducing harm to their babies is to follow these tips when including fish or other types of seafood into their diet:

  • Never eat raw fish or raw shellfish such as oysters, clams, mussels or sushi.  They can harbor several serious viruses.
  • Limit golden or white snapper, tuna steak and albacore tuna (white tuna) to 1 serving per month.
  • Canned tuna should be limited to 1-2 6 ounce cans a week.  This is considered safer than eating fresh tuna.
  • Limit your consumption of fish caught by friends and check local safety advisories for guidelines.  If you cannot find this information try to limit your total fish consumption to 6 ounces per week.

Another risk that pregnant women run by eating seafood is a type of bacteria that is known as Listeria.  This bacterium is found everywhere and can cause a food borne illness known as Listeriosis, which is extremely dangerous for a pregnant woman and her unborn baby.  This food borne illness has been known to cause premature delivery, miscarriage and even fetal death.  A pregnant woman is more susceptible to Listeriosis because of the normal pregnancy changes that affect her immune system during this time.

Furthermore, Listeria is an unusual bacteria in that they can grow at refrigeration temperatures of 40 degrees or below.  Only cooking kills them.  Therefore it is crucial to follow these safety tips:

  • Never refrigerate smoked seafood unless it is cooked in a dish such as a casserole.
  • Refrigerated smoked seafood includes: salmon, trout, whitefish, cod, tuna, and mackerel.
  • Canned fish and shelf stable smoked seafood is safe to eat.
  • Clean your refrigerator on a regular basis.
  • Use perishable, ready to eat, and precooked items as soon as possible.

Listeriosis may cause flu like symptoms such as fever, chills, diarrhea, muscle aches, and upset stomach.  It can take a few days or in some cases even a few weeks to appear.  If you think that you may have Listeriosis it is important to contact your health care provider immediately.  Especially if you believe you may have eaten a contaminated product.

Can Sharks Live in Fresh Water?

For most shark species, spending a day in fresh water would be similar to placing us humans on the moon without a spacesuit.  They most likely would not be able to survive due to the inhospitable surrounding environment.  One of the main problems that would pose a serious threat to sharks in this case is the process known as osmosis.  Osmosis refers to when a fluid moves through a semi-permeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of liquid on both sides of the membrane.  In this case, the dissolved substances involve sodium and chloride.

Because sharks evolved in salt water, they are equipped with salty bodies.  Even sharks in fresh water contain more than twice the amount of salt and chloride as other fish that are more common among freshwater.  In theory, sharks that are placed here should burst like a balloon when it is overfilled with air, given the osmosis effect; however since they urinate a lot they are able to avoid this problem.

The sharks take in a lot of extra water however they excrete much of it as urine that is diluted and has a rate of over 20 times that of typical saltwater sharks.  What this means is that their kidneys are required to work harder than normal, thus utilizing additional energy.  Much like humans that have become accustomed to life in low oxygen regions, sharks in fresh water appear to adapt to what would seem to be formidable conditions.

Although there have been several studies over the years that have determined that there are in fact some species of sharks residing in freshwater environments, relatively few sharks spend a substantial amount of time here.  In fact, river shark populations are now at dangerous lows.  Bull shark’s population numbers are higher since they often move between fresh water and salt water environments.  Other species of sharks however, that are more adapted to life in lakes and rivers are faced with having to withstand both natural and human induced problems within their habitats.  Problems that these sharks face include changes in temperature, oxygen, mineral content, and other climate changes.  Human activities such as damn building, water modifications such as irrigation and the introduction of pollutants to the water all pose a serious threat to these particular species of shark.

Can Trout Swim Upstream?

Trout are indeed capable of swimming upstream.  Biologically speaking, most trout swim upstream in response to sex hormones when it is time for them to spawn.  This causes them to first seek highly oxygenated water to fight the current.  There is also a fairly complicated evolutionary history behind the trait of trout swimming upstream.  This fish initially started out as a freshwater fish.  However, as time went on their ancestors moved into brackish rivers and finally into oceans.  Because they evolved in freshwater, the eggs could still only survive in fresh water.  As a result every year the trout ancestors were required to move from the ocean back into the freshwater when it was time to reproduce.

However as trout moved through the oceans they gradually began to discover new rivers and streams located in new countries, as well as streams that had just formed on their own with time.  The trout began to breed in these new streams and some of them never moved back to the oceans.  As a result today there are a lot of different types of trout and while most do still move back to the oceans after they hatch, some live their entire lives in freshwater environments.  Some species of trout such as the Steelhead are able to do either, with some individuals returning to the oceans while others starve in the freshwater where they are born.

Because all trout ancestors evolved to swim from the ocean back up the freshwater streams, most species of trout can still be found doing so today.  Even those trout that have never left the freshwater begin to feel the urge to move and swim higher upstream.  Some trout species never swim upstream, and instead opt for clean water which many times is located downstream.

Do Salmon Die After Spawning?

It is true that many salmon do in fact die after spawning.  There are many various species of Pacific salmon spawning semelparously.  The word Semelparous refers to the reproductive strategy of an organism. A species is considered semelparous if it is characterized by a single reproductive episode before death.  In truly semelparous species, death after reproduction is simply a way of life and is part of an overall strategy that includes putting all available resources into maximizing reproduction at the expense of future life.  About 90 to 95% of all Atlantic salmon also die following their first spawning, however some survive to spawn two or three more times.  As many as four spawning have been reported in some cases.  The surviving salmon, predominantly female, return to sea to feed between spawning.

However this does not indicate why the survivors were able to make it, whether they somehow are better able to withstand the freshwater than their cohorts, or if they just manage to have enough food reserves to get them back to sea and back to full health is still in question.  It is suggested however that most that die do so as a result of possibly using all of their energy to return to their home stream for making eggs and digging up the nest.  During this time most salmon stop eating when they return to freshwater and as a result have little no energy left for a return trip to the ocean after spawning.

After these salmon die, other animals have been known to eat them.  However humans do not.  If the dead salmon are not consumed after dying, they decompose and add nutrients to the stream.  Some common species of salmon that have been known to die often after spawning include the Chinook and Coho salmon.  They may be less palatable since they do not feed during their spawning runs, which cause their muscle tissues to begin to break down.  Fish that usually do not die after spawning and are generally found to be in much better condition during spawning include fish such as the steelhead, brown trout and brook trout.

Do Cod Live in Fresh Water?

Cod mostly reside in salt water however a few species are considered freshwater fish.  Many cod live throughout most of the UK waters, although are generally seen as a winter fish in the south.  They are found in the Northern Atlantic Ocean.  Areas with the greatest amount of cod fishing include Newfoundland, Labrador, New England, Novia Scotia, Iceland, Alaska, Florida, The Mediterranean Sea, Indian Ocean, and The Gulf of Valdez.

The Eastern freshwater cod also known as the Eastern cod are a large and striking predatory freshwater fish of the Macculooochella genus and Perchichthyidae family that have been known to reside in the coastal Clarence River system of north eastern New South Wales.  These freshwater cod are closely related to the Murray cod of the Murray Darling river system and are considered an icon of the Clarence River system.  As a long-lived, slow growing species, these freshwater cod are threatened by poachers, habitat degradation and natural catastrophic events such as bushfires.  These are just a few reasons that they are now protected by law.

Are Trout and Salmon Related?

It is true that trout and salmon are related.  In fact, they are so closely related that fishermen and scientists often have a difficult time classifying the individual species.  Both fish are classified as “an oily fish”.  Technically Trout are a species of freshwater and saltwater fish and Salmon belong to some of the same family as trout.  However unlike most trout, most salmon species spend most of their lives in salt water and are not usually found in fresh water on a regular basis.

In 1989 DNA tests showed that the rainbow trout also known as the steelhead really isn’t a trout at all, and the fish was reclassified as a salmon.  Likewise, the Atlantic salmon was then not determined to be a salmon after all, and reclassified as a trout.

The salmon and trout family is quite large and also includes great game fish such as the trout, salmon, chars, and grayling.  It also includes baitfish such as the whitefish and ciscoes.  This family is native to cool/cold streams and lakes throughout Europe, Northern Asia and North America and has also been known to reach as far south as Northwest Mexico and Northern Africa.

Some of the main species of salmon include the following:

  • Adriatic trout
  • Atlantic trout
  • Brown trout
  • Cutthroat trout
  • Flathead trout
  • Hucan salmon
  • Kokanee salmon
  • Land-locked trout
  • Maramorta trout
  • Ohrid trout
  • Pacific salmon
  • Rainbow trout
  • Sevan trout
  • Steelhead salmon

Are Sharks Mammals Or Fish?

Sharks are not mammals.  Rather, they are a species of fish because they have a skeleton that is entirely composed of cartilage and is equipped with tough, leathery, scale less skin.  These skeletons differ greatly from those of the bony fish or other terrestrial vertebrates.  Cartilage is flexible, durable and has about half the amount of density as bones.  As a result this helps to reduce the skeleton’s weight and conserves energy.  Sharks also lack a rib cage which would result in its own weight crushing it if it were placed on land.  Sharks do not have lungs that breathe air; they breathe oxygen by passing water over their gills.  These creatures have highly streamlined bodies.

The earliest known shark dates as far back as 420 million years ago.  Since that time, sharks have diversified into 440 different species ranging in size and length.  A shark’s teeth are embedded in the gums rather than directly affixed to the jaw and are constantly replaced throughout its life.  The jaw’s surface and its gill arches need extra support due to its heavy exposure to physical stress and its need for strength.

shark

In sharks, the respiration and circulation process takes place when deoxygenated blood travels to the creature’s two chambered heart and then pumps blood to the gills via the ventral aorta artery where it branches into afferent brachial arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the efferent brachial arteries which come together to form the dorsal aorta.  The blow flows from this aorta throughout the body.  The deoxygenated blood then flows through the posterior cardinal veins to enter the posterior cardinal sinuses.  It is here that the blood then enters the heart ventricle then causing the cycle to repeat.

Unlike mammals which are warm blooded creatures, most sharks are cold blooded meaning that their internal body temperature matches that of their ambient environment.  Another thing that makes sharks differ from other mammalian species is the way in which they digest their food.  A shark has an extremely short intestine.  This short length of the intestine is achieved by the spiral valve with multiple turns within a single short section instead of a long tube like intestine that many mammals possess.  The valves provide a long surface area that requires food to circulate inside the shark’s short gut until it has been fully digested, when remaining waste products pass into the cloaca.

shark

Most sharks are ovoviviparous, meaning that their eggs hatch in the oviduct within the mother’s body and that the egg’s yolk and fluids secreted by glands in the walls of the oviduct help nourish the embryos.  The young continue to be nourished this way until they hatch.  Differing from sharks, mammals give birth to live young and feed them with milk from their mammary glands. There have also been two cases where sharks have reproduced asexually; another difference compared to mammals as mammals are now the only major group of vertebrates in which asexual reproduction has not yet been observed.

Are Salmon Carnivores, Herbivores, or Omnivores?

Salmon are generally considered to be omnivorous creatures that will eat just about anything.  They mostly feast upon plants and/or plant material but have also been known to eat smaller fish from time to time and in some cases may even be found eating their own eggs.  What a salmon eats also depends on their age, species and location.

When salmon are young and still residing in freshwater they eat tiny zooplankton and adult invertebrates.  However, this too varies upon the species.  For instance, young Coho salmon typically feed during the day and have been found to prefer aquatic insects often found at the surfaces of a stream such as mayflies, caddis flies and stone flies.  While the young Chinook salmon often prefers plankton it locates off of the river floor as well as terrestrial insects and small crustaceans.  Another food source that is not uncommon for young salmon is found on overhanging riparian plants.  Larvae and insects feeding upon this vegetation often fall into the stream allowing the salmon to add this to, to their diet.

As a salmon matures and eventually leaves the freshwater to venture off into the ocean, their diet may begin to change.  While Chum and Sockeye salmon prefer to continue eating zooplankton and occasionally other small adult fish, other species have been known to begin eating larger fish and aquatic insects.  This often includes shrimp, surf smelt, sand lance, crab, herring, amphipods, and krill.  When salmon return to freshwater to spawn, feeding efforts virtually stop as a means to conserve more energy for the journey upstream to produce eggs and dig a nest.

While salmon are hungry little creatures that can be found feasting upon plankton and the like, there are plenty of things that are ready to feast upon the salmon.  This fish is a hearty staple for humans and also a favorite treat for birds, bears, sea lions, dolphins and other large predatory fish.

Salmon kept on farms are often fed things such as mixtures that contain ground up fish, and/or other organisms from the ocean, as well as food sources with a soy base.  Something that should be considered about salmon who are kept on farms is that they may come with a couple of hazards.  Salmon that were farmed and fed on vegetable rather than animal proteins may be lacking in Omega-3, which is one of the main reasons salmon are so healthy for a human diet.  Farmed salmon are also usually highly susceptible to sea lice, a relentless parasite that has been known to spread throughout the salmon farm in the blink of an eye and that can also be spread into the wild if the farmed salmon have been kept in connecting waters.

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