Hi All,
We know that in a fish head there are three sets of otolith called Sagitta, Asteriscus, and lapillus. In all teleosts - except the members of the families Cyprinidae and Siluridae - Sagitta is the largest and carries an ornamentation on its surface. In Cyprinidae, Sagitta is the very small and in Asteriscus it is the largest, while in Siluridae, Lapilus is the largest.
Could anybody explain to me why such differences occur?
Regards,
Laith A. Jawad
In general, it seems that fishes that live in structurally complex habitats – coral reefs, temperate mangroves, seagrass, etc. – tend to have larger and more complex sagittae, and relatively large lapilli and asterisci otoliths, compared to pelagic fishes. The theory is that as otoliths are parts of the critical senses of fishes – needed for balance, orientation, (hearing and even perhaps depth perception) etc. – the more complex a habitat and movements of a species, the larger and complex the otoliths are in shape to provide needed feedback to a fish. In contrast, high speed pelagic fishes such as marlin have very small (tiny) otoliths – a fish several metres long may have sagittae of only a few millimetres in any dimension - the pelagic environment is basically open spaces and the need for large otoliths is reduced.
it appears that differences in relative size and presence-absence can be related to behaviour, communication or location. Please have a look to Chesapeake Biological laboratory of the Maryland University for some info
http://www.cbl.umces.edu/~secor/manual/chap2.pdf
In general, it seems that fishes that live in structurally complex habitats – coral reefs, temperate mangroves, seagrass, etc. – tend to have larger and more complex sagittae, and relatively large lapilli and asterisci otoliths, compared to pelagic fishes. The theory is that as otoliths are parts of the critical senses of fishes – needed for balance, orientation, (hearing and even perhaps depth perception) etc. – the more complex a habitat and movements of a species, the larger and complex the otoliths are in shape to provide needed feedback to a fish. In contrast, high speed pelagic fishes such as marlin have very small (tiny) otoliths – a fish several metres long may have sagittae of only a few millimetres in any dimension - the pelagic environment is basically open spaces and the need for large otoliths is reduced.
The masses and the area sizes of the otoliths for the utriculus, sacculus, and lagena of 15 species of the Black Sea fishes are analyzed. Morphometrical otolith regularities are derived and their functional and ecomorphological explanations are suggested.
The otolith regularities are summarized in four otolith rules (if ecology is constant): 1) The masses of the otoliths gradually increase with the fish growth. 2) The mass ratio of the sacculus and utriculus or the sacculus and lagena otoliths does not change with the fish growth. 3) The ratio between the otolith area s and the otolith mass m is described by the exponential equation s = αm2/3. 4) The ratio between the otolith and macula sizes does not change with the fish growth.
Mathematical modeling of the otolith displacement responses to the acoustic and the instant force stimuli is performed. Based on the modeling the functional and ecomorphological explanations of the otolith regularities are suggested: 1) The greater is the otolith mass, the higher is the acoustic sensitivity at low frequencies and the sharper is the frequency response curve at its maximum. 2) The separation between maxima of the frequency response curves for the saccular and lagenar otoliths remains virtually constant with the fish growth . 3) The bottom and littoral fishes have better auditory capabilities than the pelagic fishes. 4) The sensitivity to vestibular stimuli for greater otoliths is higher but the response is slower. The corresponding acceleration resolution for greater otoliths is higher and the range of accelerations in which the otolith organ can operate is narrower. 5) The relative vestibular sensitivities of the utriculus, sacculus, and lagena otolith organs remain constant with the fish growth. 6) The otolith organs of the bottom and littoral fishes are tuned to different accelerations and possess different functional properties. The otolith organs of pelagic fishes are adapted to limited range of accelerations and are less sensitive to low accelerations as compared to the bottom and littoral fishes.
I agree with points made thus far, and would like to add one additional point. Predation has also been suggested as a factor determining otolith size. Echolocation of prey by citations and pinnipeds is thought to be correlated with otolith size. It’s possible that reduced size of the sagitta results from selection against larger size.
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