Changing Form and Function for a Changing Environment

General Fish Adaptations

Bluegills contain numerous adaptations that allow them to live in aquatic niches.  Some structures found in most all fish species include jaws, an endoskeleton, and gills.  As time has passed, bluegills have evolved specific structures that allow them to gain nutrients, avoid predators, and  reproduce successfully. 

Gills of a Mature Bluegill (Image taken by Author)

Bluegill Adaptations: Movement

Bluegills have the ability to travel and turn at different angles and speeds because of synchronized fin movements.  To move forward, they use caudal fins, soft dorsal fins, body undulations, and pectoral fins.  The speed of forward motion depends directly on the abducting and adducting fins.  A slender body negates resistance as bluegills can essentially slice through water.  To turn, this species relies heavily upon the angular orientation of their pectoral fins.  These large, flexible fins can also allow bluegills to brake quickly.  In many ways, the degrees of maneuverability facilitates them to forage and escape predators with great efficiency.  Other incredible sensory adaptations have allowed bluegills to succeed throughout aquatic ecosystems in North America. 

Bluegill Adaptations: The Sensory System

Unfortunately for bluegills, water is not a favorable median for sensory reception.  Some fish, including bluegills, contain a lateral line that detects vibrations and other pressure changes.  Bluegills have hair cells within their lateral line and inner ears that act as receptors for these vibrations and variations in pressure.  For instance, if a predator approaches, a bluegill can likely sense the water displaced by the fins of the predator.  In comparison, possible food sources can also be detected.  It is true, however, that bluegills depend heavily on sight to gain their nutritional needs.  The structure of their eyes is comparable to other chordates like humans.  They detect objects through stimulation within their eyes and perceive the object to be a predator, prey, or any other object with their nervous system. Optimal sight occurs during daylight hours as the light allows more contrast between an object and its background.  Other physiological adaptations allow them to forage resourcefully.

Structure of a Bluegill (Image taken by Author)

Bluegill Adaptations:  Foraging

The mouth of a bluegill is very small (8.0 mm in diameter) (Spotte, 2007).  Still, the mouth's size fits its purpose.  Instead of feeding on gastropods like fish species with larger mouths, bluegills tend to consume smaller species.    When near a possible food item, bluegills expand their pharynx to suck the item into their tiny mouths.  These adaptations permit bluegills to be so successful in capturing prey, avoiding predators, and competing with other species to gain resources.   

Foraging Bluegill (Image Taken by Author)

 

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