Bands against stripes on the backs of mackerel, Scomber scombrus L.

Abstract

A thin band of re£ecting platelets overlies the central parts of the light and dark stripes found on each side of the dorsal surfaces of the body of the mackerel (Scomber scombrus L.). When this ¢sh has its anteroposterior axis horizontal and its mid-dorsal and mid-ventral lines in the same vertical plane,V, the surfaces of the re£ecting platelets in these bands are within a few degrees of being vertical. These surfaces are, however, tipped about 178 from plane V towards the tail. In the angular distributions of radiance commonly found in the sea, the re£ections from these bands can mask parts of the pattern of light and dark stripes seen by neighbours in ways that depend on the orientation of the ¢sh in the external light ¢eld and the position of the ¢sh relative to its neighbours. With this arrangement, when the ¢sh changes its orientation and/or its velocity with respect to neighbouring ¢sh, this is signalled to its neighbours as changes in the patterns of brightness of its dorsal surfaces. Relatively small changes in roll, pitch and yaw can produce large changes in appearance and, as vision is a most important sense in the mackerel, it seems likely that these changes are important for signalling.

Contrasting stripes are a widespread feature of group living in birds, mammals and fishes

“…This may suggest that stripes are important in the confusion effect, horizontal lines serving to reduce the ability of predators to judge the speed and direction of prey [23]. Denton & Rowe [20] further suggest that stripes in the mackerel Scomber scombrus help to coordinate shoaling behaviour, because stripes are perceived differently with changes in body orientation (although they referred to the vertical stripes of the dorsal side of a fish's body). Once again, therefore, the association of grouping with these stripes suggests that both confusion and coordination effects may play an important role for these species.…”

“…In such species, a role of sexual selection as a driver of such body patterns may be dismissed, as these marks are shown year-round by both males and females in otherwise sexually dichromatic species that display both breeding and non-breeding plumages [17]. Whether the stripes in other social taxa, in particular the contrasting bands on the bodies of some social mammals, such as gazelles [18], or the stripes of different species of fish [19][20][21][22] play a role in coordination remains unclear.…”

Spectral sensitivity of juvenile chub mackerel (Scomber japonicus) in visible and ultraviolet light

“…Since UV is scattered so effectively by water, visibility in the UV range is thought to offer a private channel for interspecies communication (Losey et al 1999;Kodric-Brown and Johnson 2002;Cummings et al 2003). At oblique angles (seen by a shoaling fish in more or less parallel alignment behind another) of light incidence, Atlantic mackerel are strongly reflective in the near-UV range (Denton and Rowe 1998). Therefore, if the reflectance pattern of chub mackerel is similar to that of Atlantic mackerel, then juvenile chub mackerel could follow other individuals in a shoal using their UV sensitivity, without being detected by predators that lack UV sensitivity.…”

Pigments, Patterns, and Fish Behavior

“…Indeed, this preferential shoaling was strongest in the striped morphs in these studies. Denton and Rowe 58 suggested that stripes help coordinate shoaling behavior because the way stripes are perceived changes with body orientation. Cleaning behavior and stripes: Several studies have suggested a role for stripes in another cooperative interaction: cleaning behavior.…”