Family: Amblyopsidae

cavefishes

Introduction:

The Percopsiformes

(trout-perches, sand rollers, pirate perchers, and cavefishes)

Fig. 1. Comparative external morphology of amblyopsid species (drawing by John

Ellis; from Romero, 2003b)

        The Amblyopsidae is one of the three families of the Order Percopsiformes.  The oldest fossils of this Order date back to the Paleocene Paskapoo Formation (between 62 and 60 MYA) in Western Canada (Murray and Wilson 1996).  The Percopsiformes may be remotely related to the codfishes (Gadiformes) and toadfishes (Batrachoidiformes).  These are fishes small in size (less than 20 cm or 8 in) characterized by a mosaic of primitive and advanced characters that include some primitive ones such as adipose fin and advanced ones such as a pelvic girdle located further back from the cranium when compared with most other fishes.  They also have fewer fin spines and ray-supported dorsal and anal fins, each usually with one to four anterior soft spines.  If the pelvic fins are present, they are located in a subabdominal position behind pectorals, with three to eight soft rays.  Their body is covered with cycloid or ctenoid scales.

        Percopsiformes are found in North America, from Alaska and the Great Lakes drainage to the south and eastern United States.  All species are freshwater with two species found in swamps, one as a facultative cave dweller, and four species are obligatory cavernicoles.  They are opportunistic predators that eat a variety of food items and at least one species is cannibalistic.  Besides all species being solitary, little is known except for particular behaviors studied among cave fishes (see below).  At least two of the non-cavernicolous species are nocturnal.  They are oviparous but nothing else is known as to make further generalizations.  Spawning (at least for the non-cavernicolous species) takes place in the Spring.  Fecundity tends to be low.

This order is usually divided into two suborders: 1. Percopsoidei, characterized by the presence of an adipose fin and a complete lateral line; they are represented by one family (Percopsidae or trout perches) with one genus and two species; and, 2. Aphredoderoidei, characterized by the absence of an adipose fin and includes two families: Aphredoderidae (pirate perch, one species) and Amblyopsidae (swamp and cave fishes, four genera and six species) (Romero 2003).  One of the facts that has been very controversial about the phylogeny of this order is that they show primitive conditions such as the presence of an adipose fin, which suggests character reversal in their evolutionary history.  Some have suggested that the amblyopsids should be placed in a separate suborder: Amblyopsoidei.  The monophyly of the Percopsiformes has been questioned by Rosen (1985) and Patterson and Rosen (1989).  Murray and Wilson (1999) proposed to remove the amblyopsid family from it and created a new order: Amblyopsiformes.

The Amblyopsidae

NON-TROGLOMORPHIC SPECIES

There is only one non-troglomorphic species of Amblyopsidae

Comparative characteristics are summarized in Table 1 below.

The swamp fish, Chologaster cornuta Agassiz, 1853

This is the only species of the amblyopsid family that is not found in the hypogean environment and, therefore, is considered to be fully epigean.  However, its study is helpful in order to discern the evolution of the family as a whole.  This species shows a stark contrast between its dorsally brown and ventrally creamy white colorations.  Individuals of this species also show three narrow, dark stripes on each side, one on lower side wide at front, narrow at rear; and two black streaks along back before dorsal fin separate to encircle dorsal fin.  They have a dusky black band in the dorsal fin while the caudal fin is clear near the base, often black in the center.  They have 9 to 12 dorsal soft rays, 9 to 11 branched caudal rays, and 9 to 10 anal soft rays.  They lack pelvic fins.  Other morphological characters include small eyes, 0 to 2 rows of papillae on caudal fin and visible pink gills.  Males have an appendage on the dorsal surface of the snout which have been implicated in courtship and in chemoreception, but neither hypotheses has been verified (Ross and Rohde, 2003).  This is the only amblyopsid species living along the Atlantic Coastal Plain; it is found from the Roanoke River drainage in southeast Virginia to Altamaha River drainage in central Georgia (Cooper and Rohde, 1980; Rohde and Pernell, 1994; Figure 2).  Typical habitats are waters well-shaded by vegetation and debris in swamps, ponds, ditches, and slow streams (but not in caves) (Shute et al. 1981).  Water temperatures where they are found never exceed 23°C.  Although this species is locally common, it is hard to spot because both being largely nocturnal and found in heavily vegetated waters (Rohde and Pernell 1994, p. 139; Ross & Rohde, 2003).  They feed mostly at night, on small amphipods, aquatic insects, cladocerans, ostracods, and copepods.  They reach sexual maturity atve been given to this species: C. cornutus and C. avitus.  one year of age.  Spawning takes place in March and April and they may live up to two years.  There is no evidence that they are gill brooders (Ross and Rohde, 2003).  Two synonims have been given to this species in the past: C. cornutus and C. avitus 

(Drawing by E.S. Damstra, published in Romero, 2003a).

Fig. 2. Distributional map of the Amblyopsid species (After Bergstrom, Nolti, and Holtsford 1995)

Table 1. Summary information on the amblyopsid species of fish. Sources: Robison & Buchanan 1988, Page & Burr 1991,  Means & Johnson 1995, Pflieger 1997, Romero 1998a,b,c, Romero & Bennis 1998.

* Branched