Ear Structure of Deep-Sea Fishes

Recent paper:

Deng, X., Wagner, H.-J., and Popper, A. N. (2011). The Inner Ear and its Coupling to the Swim Bladder in the Deep-Sea Fish Antimora rostrata (Teleostei: Moridae). Deep Sea Research, part I, 158:27-37. LINK

Benthopelagic deep-sea fishes dwell between 1000 and 5000 meters. At these depths there is little or no light, food is scarce, and there are considerable distances between individuals. Thus, we hypothesize that these fishes have evolved acoustic communication and auditory specializations. Since such fish rarely can be taken alive, the only way to study their hearing is to extrapolate from anatomical studies.

We are interesting in a broad range of deep-sea fish species, currently we have several active projects on three families of benthopelagic deep-sea fishes:

I. Comparative studies of the morphology and ultrastructure of the inner ears in nine species of deep-sea Macrouridae fishes.

Fig. 1 - Dorsal view of brain and ears of C. armatus
 
Fig. 2 - Saccular macula of C. rupestris

The Macrourid fishes, often called rat-tails and grenadiers, are the most abundant species in the bethopelagic fauna. This group of fishes is very successful in deep-sea environments in that they can be found in all deep-sea areas on the earth and occupy a wide range of depths. The nine species included in this study are Coryphaenoides rupestris, C. mediterraneus, C. leptolepis, C. armatus, C. brevibarbis, C. guentheri, C. profundicolas, Nezumia aequalis, and Coelorhyncus occa. These species range in depth from 1000 meters to 4000 meters.

Figure 1 shows a whole view of the brain and ears of C. armatus. These macrourid species have relatively large saccules and ellipsoid shaped otoliths. The orientation of the hair cell ciliary bundles in the saccule is similar to that found in the Atlantic cod (Gadus morhua) (Dale, 1976), and in the deep sea Gadiform Bregmaceros (Popper, 1980), with a bi-directional vertical pattern in the middle, and a gradual shift to a bi-directional horizontal pattern at both ends (Fig.2).

The lagenae of the Coryphaenoides have lagenar otoliths that are often shaped like a saddle with different patterns of fluting along the edges (Fig. 3). Up to one-half to three-quarters of each macula surface is not covered by the otolith, but rather by the otolith membrane which extends beyond the otolith (Fig. 4)

 
  Fig. 3 - Lagena of C. rupestris Fig. 4 - Lagena macula and otolith of C. rupestris

II. Anatomical study of a gadiform deep-sea fish Antimora rostrata

The blue antimora (Antimora rostrata) is a bathypelagic morid cod obtained at 2,500 m depth. Its inner ear has a number of unique morphological and ultrastructural features. The walls of the three otolithic end organs are rigid and partially sclerotic, with tight attachments to all of the surrounding bones. The saccule in this species has a very large and heavy otolith (Fig.5). The saccular macula (epithelium), which is exceptionally thin and long, is in three distinct segments, and can also be divided into eight regions according to the hair cell bundle orientation (Fig.6).

 
  Fig. 5 - Left and right ears of Antimora rostrata
   
 
  Fig. 6 - Left saccular macula of Antimora rostrata



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