291
indicating that the best gliding performance can be achieved when the fl ying fi sh
glides nearly parallel to the sea surface. As the lateral dihedral angle of the pectoral
fi ns decreases, the lift coeffi cient slightly increases. In addition to the enlarged
pectoral fi ns, the large pelvic fi ns have an important role in enhancing the lift-todrag ratio and longitudinal static stability. The enhancement of the lift-to- drag ratio
from the pelvic fi n is attributed to the jet-like fl ow existing between the pectoral and
pelvic fi ns. For both solid and water surfaces, the drag coeffi cient decreases and
thus the lift-to-drag ratio increases as a result of the ground effect, indicating that
the fl ying fi sh obtains substantial advantages by gliding close to the sea surface. The
ground effect is more pronounced for the water surface, which has a slip boundary
condition,” (Park and Choi 2010 ).
7.2 Fish Fin Spines and Rays
According Alben et al. ( 2007 ), “since fi ns provide the structural interface between
the fi n muscles and the fl uid environment, understanding the mechanics of fi n function is an essential component of a complete analysis of how locomotor forces are
transmitted by fi sh to the aquatic environment,” (Alben et al. 2007 ). Therefore, fi sh
fi ns as specifi cally designed and macrostructured formations are the most intriguing
subjects for developing fi sh-bioinspired robotic devices. However, at the microlevel
of their structural organization other biocomposite-based constructs – spines and
rays – are of great interest to biological materials scientists as well as experts in
bionics and biomimetics. In Osteichthyes, most fi ns may have rays or spines. “Fin
ray structure in ray-fi nned fi shes (Actinopterygii) largely defi nes fi n function.
Fin rays convert the muscle activity at the base of the fin to shape changes
throughout the external fi n web,” (Taft and Taft 2012 ). Despite their critical functional signifi cance, very little is known about the relationship between form and
function in this key vertebrate structure. Such feature as segmentation of rays is the
main difference that separates them from spines, which are usually sharp and stiff.
Additionally, rays appear generally as fl exible structures which may be branched.
A fi sh fi n may contain only soft rays, only spiny rays, or a combination of both.
Since the nineteenth century (Krukenberg 1885 ; Harrison 1893 ), the structure of
fi sh fi n rays was under investigations. This topic has continued to attract the attention
of researchers in early twentieth century (Goodrich 1904 ) and continues to this day.
The diversity of dermal fi n rays is excellently described in the classic paper by
Edwin Goodrich entitled “ On the Dermal Fin - rays of Fishes - Living and Extinct ”
(Goodrich 1904 ). He mentioned that real dermal rays are absent in Amphioxus and
the Cyclostomes. The ray-like structures fi gured and described by various authors
in the larva of Amphioxus (Willey 1890 ) are elongated epidermal cells. In the
Cyclostomes, on the other hand, the fi ns are supported by delicate cartilaginous
rays, prolongations of the neural and haemal arches of the axial endoskeleton
(Goodrich 1904 ).
7.2 Fish Fin Spines and Rays
indicating that the best gliding performance can be achieved when the fl ying fi sh
glides nearly parallel to the sea surface. As the lateral dihedral angle of the pectoral
fi ns decreases, the lift coeffi cient slightly increases. In addition to the enlarged
pectoral fi ns, the large pelvic fi ns have an important role in enhancing the lift-todrag ratio and longitudinal static stability. The enhancement of the lift-to- drag ratio
from the pelvic fi n is attributed to the jet-like fl ow existing between the pectoral and
pelvic fi ns. For both solid and water surfaces, the drag coeffi cient decreases and
thus the lift-to-drag ratio increases as a result of the ground effect, indicating that
the fl ying fi sh obtains substantial advantages by gliding close to the sea surface. The
ground effect is more pronounced for the water surface, which has a slip boundary
condition,” (Park and Choi 2010 ).
7.2 Fish Fin Spines and Rays
According Alben et al. ( 2007 ), “since fi ns provide the structural interface between
the fi n muscles and the fl uid environment, understanding the mechanics of fi n function is an essential component of a complete analysis of how locomotor forces are
transmitted by fi sh to the aquatic environment,” (Alben et al. 2007 ). Therefore, fi sh
fi ns as specifi cally designed and macrostructured formations are the most intriguing
subjects for developing fi sh-bioinspired robotic devices. However, at the microlevel
of their structural organization other biocomposite-based constructs – spines and
rays – are of great interest to biological materials scientists as well as experts in
bionics and biomimetics. In Osteichthyes, most fi ns may have rays or spines. “Fin
ray structure in ray-fi nned fi shes (Actinopterygii) largely defi nes fi n function.
Fin rays convert the muscle activity at the base of the fin to shape changes
throughout the external fi n web,” (Taft and Taft 2012 ). Despite their critical functional signifi cance, very little is known about the relationship between form and
function in this key vertebrate structure. Such feature as segmentation of rays is the
main difference that separates them from spines, which are usually sharp and stiff.
Additionally, rays appear generally as fl exible structures which may be branched.
A fi sh fi n may contain only soft rays, only spiny rays, or a combination of both.
Since the nineteenth century (Krukenberg 1885 ; Harrison 1893 ), the structure of
fi sh fi n rays was under investigations. This topic has continued to attract the attention
of researchers in early twentieth century (Goodrich 1904 ) and continues to this day.
The diversity of dermal fi n rays is excellently described in the classic paper by
Edwin Goodrich entitled “ On the Dermal Fin - rays of Fishes - Living and Extinct ”
(Goodrich 1904 ). He mentioned that real dermal rays are absent in Amphioxus and
the Cyclostomes. The ray-like structures fi gured and described by various authors
in the larva of Amphioxus (Willey 1890 ) are elongated epidermal cells. In the
Cyclostomes, on the other hand, the fi ns are supported by delicate cartilaginous
rays, prolongations of the neural and haemal arches of the axial endoskeleton
(Goodrich 1904 ).
7.2 Fish Fin Spines and Rays