Agonostomus monticola

mountain mullet

Type Locality:

Jamaica (Bancroft 1834, pp. 367 in Cuvier 1836).

Etymology/Derivation of Scientific Name

Synonymy

Miller (2005) regards A. hancoki Seal, from the Galapagos Islands, as a synonym of A. monticola; Meek and Hildebrand (1916) placed A. nasutus Gunther in synonymy with A. monticola.

Characters

Maximum size: 722 mm (Anderson 1957).

Coloration: Ground color brownish black above, scales with dark outlines. Larger individuals with silver lateral band about scale rows 5 and 6 below first dorsal fin. Scales above approximately the third row from bottom on sides with golden coloration; ventral surface below this plain white. Scales below silvery band with heavy dark margins, appearing like a dark lateral band, forming dark blotch near base of caudal fin. Iris golden, reddish above, dusky before and behind pupil. Cheeks, underside of head and lower lip white. Fins yellowish; pectoral pale, usually with black blotch at base; second dorsal and caudal dusky outer edge; yellow in pelvic and anal especially bright and clear (Carr and Giovannoli 1950).

Counts: 10 anal fin rays; 2 anal fin spines in adults (Murdy 1983); lower limb of first gill arch having 17-20 gill rakers (Hubbs et al. 1991). Dorsals IV-I, 8. 40-42 in lateral series to end of body; about 12 in transverse series from origin of 2^nd dorsal to anal (Carr and Giovannoli 1950)

Body shape: Body elongate, not very compressed (Carr and Giovannoli 1950).

Mouth position: Upper lip terminal (Murdy 1983); lower jaw rounded, without symphyseal knob (Hubbs et al. 1991).

External morphology: Scales ctenoid (Hubbs et al. 1991). Snout not projecting beyond upper lip; two widely separated dorsal fins (Miller 2005). Lateral line inconspicuous (Carr and Giovannoli 1950). No visible adipose tissue around eye (Stevenson 1976; Murdy 1983; Hubbs et al. 1991).

Internal morphology: Teeth on lower jaw in continuous band; teeth present on palate (Miller 2005); stomach not gizzard-like (Carr and Giovannoli 1950).

Distribution (Native and Introduced)

U.S. distribution: Found along the Atlantic and Gulf coasts through the Caribbean to Columbia and Venezuela in South America (Hubbs et al. 1991).

Texas distribution: Has been found great distances upstream in various streams from Trinity to the Rio Grande and is a common inhabitant of the lower Rio Grande (Hubbs et al. 1991). Warren et al. (2000) list the following drainage units for distribution of Agonostomus monticola in the state: Sabine Lake (including minor coastal drainages west to Galveston Bay), Nueces River.

Abundance/Conservation status (Federal, State, NGO)

Populations in southern drainages considered vulnerable (Warren et al. 2000). Rare and scattered (Rohde 1980).

Habitat Associations

Macrohabitat: Adults and subadults move into tropical and subtropical streams, often

to the headwaters; young occurring at sea and found drifting in currents hundreds of miles from shore (Rohde 1980). Juveniles live in lower river courses; adults occur mainly in the upper parts of clear tributaries having strong currents and rocky bottoms at elevations as high as 1500 m (Cruz 1987; Miller 2005).

Mesohabitat: Rheophilic, fast, strong swimmer often associated with swift currents and possibly near large boulders; found in abundance or at rest in deeper pools of stream below falls and rapids (Carr and Giovannoli 1950). Over river beds of large granitic type rocks and crystal clear waters (Cruz 1987). According to Cruz (1987), preference for tributaries rather than main river channel (Rio Platano, Honduras) may result from the greater occurrence there of terrestrial insects and facility to capture these in less turbulent conditions.

Biology

Spawning season: September - December, based on collection of larval specimens taken off the Bahamas, Florida, and lower Georgia coasts (Anderson 1957). Occurs in June, in El Salvador, Central America (Hildebrand 1925). Spawning usually occurs during rainy season in Jamaica, West Indies (Aiken 1998).

Spawning habitat: Anderson (1957) suggested that adults spawn in offshore, marine waters; young (taken from mid-November to late January) remaining there for a period of time before moving inland.

Spawning Behavior: NA

Fecundity:  Oviparous, eggs are pelagic and non-adhesive (Breder and Rosen 1966). A ripe female specimen collected in the Rio Platano, Honduras, had 300,000 eggs in 75 g of gonadal weight (Cruz 1987). In Jamaica, West Indies population fecundity was 340,000 eggs for 25 g ovary (Aiken 1998).

Size at maturation: In Jamaica, West Indies population minimum size at maturity for females was 123 mm fork length (FL) and 96 mm FL for males. Mean size at maturity for females was 165.8 mm FL (S.D.) = 1.61) and for males was 148.4 mm FL (S.D. = 2.97; Aiken 1998).

Migration: Catadromous species with young collected from marine waters and large specimens collected from freshwater (Myers 1949; Anderson 1950; Rhode 1980; McDowall 1988). Prejuvenile stages of A. monticola frequently captured along main river (Rio Platano, Honduras), but showed seasonality in their occurrence suggesting migration (January seems to be preferred month) of the prejuvenile stages up the river (Cruz 1987).

Growth and Population structure:  In the Rio Platano, Honduras, length-weight relationship similar for both sexes. Largest specimens collected: female, 215 mm SL and 222 g; male, 125 mm SL and 47 g.; smallest specimens collected: female, 41 mm SL and 1.7 g; male, 50 mm SL and 3.2 g. Slight dominance in frequency of females over males greater than 100 mm SL (Cruz 1987). In Jamaica, West Indies population females outnumbered males 1.2:1. Mean lengths of males and females captured were 129.4 mm (S.D. = 5.56) and 160.4 mm FL (S.D. = 0.70), respectively (Aiken 1998).

Longevity: NA

Food habits: Presumably a filter feeder (Rohde 1980); opportunistic feeder, largely carnivorous, feeding on crustaceans, a variety of insects (mainly aquatic), and algae (Torres-Navarro and Lyons 1999). Mainly carnivorous; insectivorous species consuming variety of insects (especially aquatic forms); apparently no difference in diet of three size classes: prejuveniles consuming Odonata (25% of diet), Hymenoptera (14%), freshwater shrimp (8.9%), other taxa present in smaller proportions; juveniles ingesting Odonata (33%), unidentified animal material (16%), Atya (6.4%); adults fed on unidentified animal material (20.5%), Atya (19.7%), Odonata (16.6%), Characidae (17.8%; Cruz 1987). Agonostomus monticola in Jamaica, West Indies found to be chiefly insectivorous feeder; major food items found in stomach contents in ranked sequence were insects, freshwater prawns, plant detritus and algae (Aiken 1998).

Phylogeny and morphologically similar fishes

Subfamily Gestraeinae; similar to species of Mugil; apparently the only species in genus Agonostomus inhabiting the western Atlantic area; in western Atlantic Joturus appears to be most closely related among other mugilid genera (Rohde 1980). Agonostomus monticola is similar in appearance to the white mullet (Mugil curema), also known in fresh water, and to the striped mullet (M. cephalus), which is well known for ascending rivers for great distances. Agonostomus can readily be distinguished from Mugil by lacking an adipose eyelid and in having a relatively thick lower lip, fewer gill rakers (17-20 on the lower limb of the first arch vs. 25 or more in Mugil), and considerable brown pigmentation on the body (Boschung and Mayden 2004). The sea-stage young (description based on larvae up to 35 mm) of Agonostomus monticola resemble the sea-stage young of both Mugil curema and M. cephalus, in general appearance, the most noticeable difference being that A. monticola appears far more slender and has a longer caudal peduncle; observed under magnification, presence of ctenoid scales separates A. monticola from these two species of Mugil (Anderson 1957).

Host Records

Monogenea: Ancyrocephalidae - Ancyrocephalus sp., Microcotylidae - Microcotylidae gen. sp.; Trematoda: Allocreadiidae - Creptotrema agonostomi; Haploporidae: Saccocoelioides sogandaresi, Ascocotyle (Ascocotyle) tenuicollis; Nematoda: Cystidicolidae - Spinitectus agonostomi, Camallanidae - Procamallanus (Spirocamallanus) jalisciencis (Salgado-Maldonado et al. 2004).

Commercial or Environmental Importance

This mullet is a favorite food fish which is sought after locally, though difficult to catch (Miller 2005); most in demand for food, in Honduras (Cruz 1987).

[Additional literature noting collection of this species from Texas locations includes, but is not limited to the following: Schlict (1959).]

References

Aiken, K.A. 1998. Reproduction, diet and population structure of the mountain mullet, Agonostomus monticola, in Jamaica, West Indies. Environ. Biol. 53(3):347-352.

Anderson, W. W. 1957. Larval forms of the freshwater mullet (Agonostoma monticola) from the open ocean off the Bahamas and South Atlantic Coast of the United States. U. S. Fish Wildl. Serv. Fish. Bull. 120, 57:415-425.

Breder, C.M., Jr., and D.E. Rosen. 1966. Modes of Reproduction in Fishes. T.F.H. Publications, Jersey City, N.J. 941 pp.

Cuvier, G. 1834. The Animal Kingdom: arranged in conformity with its organization. G.B. Whitaker, London. 680 pp.

Carr, A. F., Jr. and L. Giovannoli. 1950. The fishes of the Choluteca drainage of southern Honduras. Occ. Pap. Mus. Zool. Univ. MI 523:1-38.

Cruz, G.A. 1987. Reproductive biology and feeding habits of Cuyamel, Joturus pichardi and Tepemechin, Agnostomus monticola (Pisces: Mugilidae) from Rio Platano, Mosquitia, Hondurus. Bulletin of Marine Science 40(1):63-72.

Hildebrand, S. F. 1925. Fishes of the Republic of El Salvador, Central America. Bull. U. S. Bur. Fish., 41:237-287

Hubbs, C., R. J. Edwards, and G. P. Garrett. 1991. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Texas Journal of Science, Supplement 43(4):1-56

McDowall, R. M. 1988. Diadromy of Fishes: Migration between Freshwater and Marine Environments. Timber Press, Portland, OR. 308 pp.

Meek, S. E. and S. F. Hildebrand. 1916. The fishes of the fresh waters of Panama. Field Mus. Nat. Hist. Publ. 191, Zool. Ser. 10(15):217-374.

Miller, Robert Rush. 2005. Freshwater Fishes of Mexico. The University of Chicago Press, Chicago. 490 pp.

Murdy, E.O. 1983. Saltwater fishes of Texas: a dichotomous key. Texas A&M University Sea Grant College Program, College Station. 220 pp.

Myers, G.S. 1949. Usage of andromous, catadromous and allied terms for migratory fishes. Copeia 1949(2):89-96.

Rohde, F. C. 1980. Agonostomus monticola (Bancroft), Mountain mullet. pp. 778 in D. S. Lee, et al. Atlas of North American Freshwater Fishes. N. C. State Museum Natural History, Raleigh, i-r+854 pp.

Salgado-Maldonado, G., Mercado-Silva, N., Cabañas-Carranza, G., Caspeta-Mandujano, J. M., Aguilar-Aguilar, R., Iñiguez-Dávalos, L. I. Helminth Parasites of Freshwater Fishes of the Ayuquila River, Sierra de Manantlán Biosphere Reserve, West Central Mexico. Comparative Parasitology. 71(1):67-72.

Schlict,F.G. 1959. First records of the mountain mullet Agonostomus monticola (Bancroft) in Texas. Texas J. Sci. 11:181-182.

Stevenson, H.M. 1976. Vertebrates of Florida. University Presses of Florida, Gainsville. 607 pp.

Torres-Navarro, C. I. and John Lyons. 1999. Diet of Agonostomus monticola (Pisces: Mugilidae) in the Rio Ayuquila, Sierra de Manantlan Reserve, Mexico. Rev. Biol. Trop. 47(4):1087-1092

Warren, M.L. Jr., B.M. Burr, S. J. Walsh, H.L. Bart Jr., R. C. Cashner, D.A. Etnier, B. J. Freeman, B.R. Kuhajda, R.L. Mayden, H. W. Robison, S.T. Ross, and W. C. Starnes. 2000. Diversity, distribution and conservation status of the native freshwater fishes of the southern United States. Fisheries 25(10):7-29.