By Dr. NEKF
Knowing about the fish you are going after can help improve your odds as a fisherman. For instance, by studying the striped bass’ anatomy you can glean clues about characteristics and behaviors. Comparative anatomy is a science that compares the differences and similarities of organ systems between species. For example, a fish has a set of nostrils like a human does, yet, unlike a human, they are only used for smell, and not breathing. However, most fish just have a set of holes through which water flows. Yet, unlike most fish, a striped bass has a pair of nostrils on each side that maintain a connection between the nostrils and the mouth, like in humans. This actually allows for smell and taste to be integrated and shows us that the striper, as a fish, relies on smell and taste a lot more than vision to navigate through its world of water.
The nervous system of the striper, Morone or Roccus saxitilis, consists of a forebrain, midbrain, brain stem, spinal cord, and nerves. It operates mostly on instinct that is programmed into its nervous system. In addition the nervous system and organism as a whole operates on a reflex basis depending on environmental stimuli. The brain has a very small cortex, therefore it does not have advanced capabilities for memory and emotions as we know them. That is why they seem to “forget” and can at times hit a lure again shortly after being released. However, they seem to exhibit learned behaviors and can associate certain events or things with food or danger. In addition, pain processing appears to be minimal due to the absence of pain processing centers in the brain’s miniscule cortex. That is not to say that they do not react to injury or to things that we would term painful. Their nervous system is not adapted for them to feel or “experience” pain as we humans do, and some studies imply that they have basic behavioral reactions (reflex reactions) to painful stimuli. We, however, put an emotional descriptor onto a painful stimulus and call it pain and presumably “feel’ it on a much richer level. The brain of a fish is not as complex as ours, including how it relates to the interpretation of pain. Regardless, it is our responsibility as conscientious fishermen to minimize the pain and trauma that we inflict on fish.
The nerve tracts for smell are well developed in stripers yet the visual cortex (that part of the brain dedicated to vision) is small. It is no surprise that a striper, therefore, has a keen sense of smell, but not as keen as Anguilla rostrata, the American eel. A study once showed that eels responded to 1 billionth of a drop of alcohol in a pool. It is thought that striped bass, like salmon, can smell their place of birth and this is what guides them on their quest to spawning grounds. It is also why using scented artificial baits makes a lot of sense. In addition to smell, a striper has taste buds on its lips, tongue, and over most of its mouth. Stripers literally swim in a sea of smells and chemicals. They are therefore very adept at chemoreception. These are all good reasons why you must make sure that your lures and baits are free of foreign smells and tastes, ie. sunblock, bug spray, cologne, perfume, soap, etc.
Vision in a striped bass is not as keen as its other senses and is used mostly for short range encounters. However, its retina contains an ample population of rod receptors and some cone receptors allowing vision to be similar to ours. The rod receptors enable the fish to see in low light conditions whereas the cones allow color vision. The eyes are large and are set slightly forward and upward on the head. This enables some binocular vision and facilitates looking up at its prey from below. The lens is round and does not flatten to focus light on the retina like our eyes. However, the lens can be moved closer to or further away from the retina to focus an image. Fish also do not have eyelids because their eyes are constantly in water and won’t dry out. Six small muscles very similar to ours control movement of the eyeball. Because of its large eyeball size and density of rod receptors on its retina, a striper’s visual system allows it to be an excellent nocturnal hunter.
Striped bass have a wide color visual range, especially during daylight. A recent study from the Virginia Institute of Marine Science (1) has shown that stripers are sensitive to a large part of the color spectrum and their retina is sensitive to very rapid movements. The middle of their spectrum sensitivity is yellow and yellow green. This means their peak response was to the color yellow. Is it any wonder that chartreuse colored lures work well? According to VIMS researcher Andrij Horodysky, "Nothing in the wild is ever chartreuse, but the color is right smack dab in the middle of a striper's visual range. They can see it really well."
Researchers also found that during daylight hours the retinas of striped bass, as compared to weakfish, respond much better to light of red wavelengths yet both fish do not respond to red wavelengths at night. Another fascinating fact is that the rods and cones, the two sensory nerve cells of the retina, actually migrate and change position on the retina in accordance with day and night. This circadian rhythm also changes to adapt to seasonal differences. During the daylight hours, cones migrate to the surface of the retina to allow color vision and acuity while the rods take a back seat, literally. During the waning hours of light and nighttime, the reverse happens with the greater density of rods affording low light vision and contrast discrimination.
In a camera, shutter speed is the speed at which light is allowed through an aperture setting. In fish, this speed is called “flicker fusion frequency” and is measured by a technique used in humans called electroretinography. Essentially, the amplitude and frequency of nerve impulses from the retina are measured in response to stimulation inputs. In striped bass, their “shutter speed” is fairly rapid, measuring around 50 cycles per second, almost as fast as humans (about 60 cps). This enables them to see large and fast moving prey similar to menhaden. This is in contrast to weakfish with a fusion frequency half that of the striper: 25 cps. In addition, weakfish have a visual spectrum that is optimal at lower wavelengths when compared to bass. These two factors allow weakfish to see contrast better than color and slower moving prey. This enables them to see in low light conditions and small prey that inhabit the night such as shrimp and small fish. In addition, being more sensitive to the lower end of the light spectrum, weakfish can see in ultraviolet.
For fish to see optimally, water clarity is essential. Murky waters force fish to use senses other than vision and can account for the disparity found in research of the stomach contents of stripers. Due to their visual capabilities, you would expect to see a preponderance of large fast swimming forage in their stomach. Quite the contrary was found in murky waters as their bellies were filled with juvenile crustaceans and shrimp. It seems that in turbid waters, stripers are forced to feed in contrast to the evolutionary development of their visual system. Researchers are now raising different questions: Is it the prey per meter amount or the number of prey they are able to see in our bays that is important for survival of these visual predators? If they can’t see their prey ideally, how can they optimally eat it?
M. Saxitilis does not have external ears, yet it has an exquisite capacity to hear sounds, especially since sound travels faster in water (3200 mph) than in air (769 mph at sea level, at 70 degrees F). That’s about 4600 feet per second, faster than the muzzle velocity of most high-powered rifle cartridges. Stripers, like most fish, use the lateral line system to sense vibration and movement. They have internal ears that detect sound and transmit information as to spatial orientation and balance. Therefore they can sense water current, other fish, prey, and other objects, including lures that make noise and vibrational sounds.
Looking in a striper’s mouth you will notice several clues as to its eating behavior. It does not have teeth in the real sense of the word as in the case of a bluefish. It has roughened areas on the upper and lower jaw, and two parallel elongated patches on the back of the tongue. The teeth are abrasive, rather than cutting, as anyone with “Striper-thumb” knows. Therefore, these teeth are not meant for chopping or cutting, like the bluefish, but for holding and grasping its prey. The mouth is very large and ends immediately into the esophagus or muscular tube that empties into the stomach. As you study the striper’s mouth, it is apparent that it was meant to engulf and swallow its prey whole. Since it is primarily piscivorous or fish eating, it must take its prey head first or else the fins and dorsal rays would become lodged in the bass’ throat. Its stomach has large folds in it or rugae that increase the surface area to hasten digestion. Once a bass engorges itself and fills its stomach, it will lie low until the food is digested and then again feed.
The body of a striped bass displays power and strength. It’s large tail and muscular body enables it to stem strong currents or swim quickly for shorts bursts. However, it also means that is must eat to sustain strength and stamina. Therefore it is no secret that M. saxitilis has a voracious appetite. In addition, its large size means a large amount of muscle mass. When a muscle contracts and exerts energy, it generates an “oxygen debt” and an overproduction of lactic acid. This can change the pH of tissues and cause damage to muscle cells. Metabolic changes can even usher in death. In addition, variations in the fish’s environment can alter stress-related death. High water temperatures (as in the summer months), lower salinity, and decreased oxygen saturation can adversely effect a fish's survival due to the stress of being caught. In striped bass, temperature, salinity, and fish size have been shown to be the three most important factors affecting survival in catch-and-release programs. Larger fish engage an angler longer and are harder to handle. A larger fish also has a greater ratio of body mass to gill surface area and therefore has a more difficult time paying back its “oxygen debt” incurred during a fight. In other words, it can’t efficiently get rid of carbon dioxide generated via muscular exertion and re-oxygenate tissues fast enough. This can result in deadly metabolic changes. The weight of their bodies out of water can cause injury to their vital organs if held improperly. Larger fish also tend to swallow bait resulting in getting deeply hooked, a potentially lethal situation. The odds of a striped bass dying are more than 15 times if it is deeply hooked (gut)! Lastly, exposing a fish to air, especially if it is warm, will increase their stress-related mortality.
Knowing all you can about the fish you target can aid in bait or lure selection and increase your chance of success. Oftentimes just observing how a fish is anatomically built can give you clues as to its behavior. The striped bass is just such a fish. It is the premier game fish in our New England waters. As conscientious fishermen, we should consider the above information when fishing and handling these sentient beings. Each time I successfully release a striper I am reminded of what the famed fly fisherman Lee Wulff wrote in 1938; "A good gamefish is too valuable to be caught only once". Follow sound catch and release guidelines and protect our precious resource. Happy fishing and good luck!
1. Horodysky AA, Brill, RW, Latour RJ. Visual function in Chesapeake Bay sport and prey fishes: Summer flounder, Bluefish, Cobia, and Atlantic Menhaden. Virginia Inst. of Marine Sciences, Project RF 06-08, Sept. 1, 2007.