Science suggests there is more to the lateral line than we’ve suspected and may provide more than mere vibration detection.

An interesting mix of attributes we’ve always thought fish had – and new information that suggests it may detect form and assist in the recognition of prey.

“The lateral-line system is a unique mechanosensory facility of aquatic animals that enables them not only to localize prey, predator, obstacles, and conspecifics, but also to recognize hydrodynamic objects. Here we present an explicit model explaining how aquatic animals such as fish can distinguish differently shaped submerged moving objects. “

The authors present evidence in the form of heady mathematics which is completely offputting despite my math background, and my posts are unable to display mathematical symbols – requiring me to interpret the theorem with English…

First, a faithful shape recognition is only possible if the distance, D (is less than but approximately equal to) the submerged moving object’s body length, B; here, B (is approximately) 5 cm. Second, localization of the submerged moving object (SMO) is possible within a distance comparable to the length of the detect-ing lateral-line.

The above suggests that a baitfish could be recognized by a hungry 30” Striped Bass at a distance approximately the same as the Striper’s length. “Recognized” is the the human term describing the new stuff we don’t know and can’t describe. It’s possible that the frantic swimming of the bait may create a disturbance that registers with the predator’s lateral line from a greater distance – but it’s unable to “know” what made the motions.

It would seem that larger fish can detect (identify) motion-based food further away than smaller fish due to the increased length of its lateral line. It may partly explain why smaller fish rush forward to take the fly, they can see/feel it but can’t recognize it as food and need to close with it before identification is complete.

… and as they’ve already spent all those precious calories getting there first – why not give it an exploratory bite …

The real question is whether we’re only matching half the hatch. Silhouette and color are certainly part of the mix, but how much does the violent swimming motion of a dislodged Stonefly alter a fish’s perception of both the natural or its stiff imitation?

When drunk, humans can be coerced into sampling a two dimensional cardboard replica of a hamburger in part because it tastes identical to its three dimensional cousin, yet unimpaired they eat it anyways recognize it as inedible even at distance.

Makes an interesting thought to ponder. We’ve always seen motion of the fly or bait as part of the overall presentation. There’s not a great deal we can do other than pull it towards us fast or slow or add some device like tungsten beads or wiggle legs.

If the fly is presented upstream will the “dead drift” be as effective as the yanked fly as there’s less lateral line to engage – or should we present streamers broadside to the lateral line – giving us an even better chance of detection?

… and while I sort out all this new information should I be carving my caddis nymphs out of Gummy Worms as their gooey freshness resonates at the same pitch as a caseless Hydropsyche in full mating rut?

We allowed bobbers so long as we called them something different – and a Gummy Bear is artificial … Can the fly fishing world survive single, barbless, and sugary?

Tags: Lateral line, fish senses, gummy bear, stonefly, motion sensitive, fly fishing,