Pseudobarbus asper

Jim A. Cambray - Albany Museum, Somerset Street, Grahamstown, 6139 South Africa

Common names: Smallscale redfin (E), Kleinskub-rooivlerkie (Afrikaans).

Conservation status: As a species in no immediate danger although populations are reduced by habitat degradation and excessive water abstraction especially during droughts.

Identification: Member of the Cyprinidae, one of seven redfin minnows in the genus Pseudobarbus. It is a member of a monophyletic lineage of flexible-rayed redfin minnows (Skelton, 1988). D III-IV + 7, A III + 5, LL 37-40 small scales. The primary dorsal ray is both simple and flexible. Its sister species is Pseudobarbus afer which only occurs in the Cape Fold Mountain Belt. P.sper has a single pair of barbels and compared to its sister species the intestine is considerably longer and involuted. The males are easily recognizable during the breeding season with a dark red fins and breeding tubercles on the head. This species can grow to 80mm SL (females) and 83mm SL (males).

Distribution: This species has penetrated into the arid Karoo sections of both the Gamtoos and Gourits River system and both populations live up to the DFC motto, "DESERT FISHES RULE: To boldly thrive where no other fish (= "Pseudobarbus") can make it!" They have "left behind" the rest of the Pseudobarbus species which occur in perennial, clear Cape Fold mountain streams and one species in the mountain streams of the upper Orange River in Lesotho

Abundance: This species can be locally very abundant, and during droughts can be found in the thousands in isolated riverine pools that are drying up. It is a species that is adapted to "booms and busts" in population numbers.

Habitat and Ecology: This species has been studied in detail (Cambray, 1990a,b, 1991a,b, 1994a,b,c,d: Cambray & Bruton, 1994: Cambray & Hecht, 1995). It occurs in turbid, eutrophic waters with silt to boulder substratums in the Karoo. It is a minnow and small size is known to be an adaptation to a highly variable environment as it makes new food sources available by allowing ready access to spatially restricted habitats. It also has a long gut relative to its sister species which feeds mainly on invertebrates. Juveniles inhabit sheltered areas such as erosion gullies and vegetated areas in streams. It has a life history style more similar to Barbus anoplus than the other six redfin minnows (Cambray, 1994d). That is its life history style enables it to colonize habitats of a temporary nature with alternating "booms and busts" in population size. In the Karoo sections of both the Gamtoos and Gourits Rivers this minnow has to be adapted to a riverine system with very erratic flows, prolonged droughts, devastating floods and high silt loads. Therefore traits such as early maturation in the first year of life, high reproductive effort, more than one clutch per year, quick growth and short inter-brood interval in phase with the optimal times of the year, would be advantageous for a small, short-lived species. Can have a life span of up to 3 years compared to its sister species, P. afer with up to 6 years.

Reproduction: The combination of life-history attributes, gonadosomatic index, fecundity, egg size, investment per clutch, number of clutches per season and reproductive lifespan was found to be different for the Pseudobarbus species which lives in the arid interior, P. asper, than for the species, P. afer, which inhabits the more perennial rivers of the Gamtoos River system. Pseudobarbus asper attains maturity within one year at 41-42mm SL (male) and 43mm SL (female) unlike its sister species in the oligotrophic Cape Fold mountain streams which attain maturity at a similar size but only after 2 years. P. asper has both an early maturity and a high reproductive rate which enables it to quickly recolonize areas. It has a relatively higher fecundity (4770 for a 64mm SL) compared to 3911 for a considerably larger female (73.1 mm SL) of the sister species, P. afer. In addition more of the ova in P. asper were closer to a mature size (35%) than those in P. afer (20%). P. asper also has considerably smaller mature ova, 1.3 mm than does P. afer (1.8mm). Cambray (1994d) suggested that the variability in egg size in the two environments of the Gamtoos River system played an important evolutionary role and this plasticity has partially lead to the ability of P. asper to colonize the arid interior. At first feeding larval P. asper are smaller (6.6mm TL) than P.afer (8.99 mm TL) and also develop to this stage three days earlier, in comparative laboratory studies at the same temperature (Cambray, 1994d). Even the nuptial tubercles on the heads of male P. asper are reduced both in size and number compared to those on P. afer (Cambray, 1994a).

This reproductive strategy probably evolved in a seasonally fluctuating riverine environment and has been shown to be advantageous to this species ability to colonize intermittent streams in arid regions (Cambray, 1994d). Peak spawning usually occurs after periods of steady rainfall. They undertake spawning migrations to riffle areas where the non-adhesive eggs occur between the boulders (Cambray, 1994d). There is a protracted reproductive season of five to six months, November to March/April during which an individual fish can have multiple clutches (Cambray, 1994d). Multiple clutches per season would also be advantageous in arid areas and decreases the chances of one or more generations being lost due to unfavourable conditions. All of the Pseudobarbus species studied to date are non-guarders of their non-adhesive eggs and young, open substrate, benthic spawners on coarse boulders and have photophobic free embryos.

Pseudobarbus asper has been able to adapt and survive in the highly variable Karoo streams of two river systems due to its ability to become an altricial form distinct from the more precocial form of P.afer which has life-history attributes which are adapted to the relatively stable, clear mountain streams.

Threats: Habitat degradation, excessive water abstraction and impoundments and weirs limiting longitudinal migrations which aid in repopulating areas after prolonged droughts.

Conservation action: The various Departmental Conservation agencies should have trained staff to monitor fish populations and be able to react when signs show deterioration of the environment.

Conservation recommendations: As with any freshwater fish species in South Africa there is a need to consider fish reserves that will protect this gene pool for the future. Areas should be identified now so that introduction of non-native species can be restricted and also habitats can be conserved.

Literature:

Cambray, J.A. 1990a. Fish collections taken from a small agricultural water withdrawal site on the Groot River, Gamtoos River System. Southern African Journal of Aquatic Science 16(1/2): 78-89.

Cambray, J.A. 1990b. Adaptive significance of a longitudinal migration of juvenile freshwater fish in the Gamtoos River System, South Africa. South African Journal of Wildlife Research 20(4): 148-156.

Cambray, J.A. 1991a. The effects of fish spawning and management implications of impoundment water releases in an intermittent South African river. Regulated rivers: Research and management 6: 39-52.

Cambray, J.A. 1991b. Comparative scanning electron microscopy studies of the egg envelopes of six African Barbus and three Pseudobarbus species (Cyprinidae). In: (ed.) D. Hoyt, Larval fish recruitment and research in the America's proceedings of the thirteenth annual fish conference: 21-26, May 1989, Merida, Mexico. NOAA Technical Report NMFS 95, pp. 109-119.

Cambray, J.A. 1994a. Seasonal occurrence and distribution of nuptial tubercles in two African minnows, Pseudobarbus afer (Peters, 1864) inhabiting clear water, and Pseudobarbus asper (Boulenger, 1911) inhabiting turbid water (Cypriniformes, Cyprinidae). Annals of the Cape Provincial Museums (Natural History) 19(2): 149-170.

Cambray, J.A. 1994b. Adaptive significance of sex ratio differences of African minnow species. Journal of African Zoology 108(4): 335-351.

Cambray, J.A. 1994c. Effects of turbidity on the neural structures of two closely related redfin minnows, Pseudobarbus afer and P. asper, in the Gamtoos River system, South Africa. South African Journal of Zoology 29(2): 126-131.

Cambray, J.A. 1994d. The comparative reproductive styles of two closely related African minnows (Pseudobarbus afer and P. asper) inhabiting two different sections of the Gamtoos River system. Environmental Biology of Fishes 41: 247-268.

Cambray, J.A. & Bruton, M.N. 1994. Evolutionary trade-off between egg size and egg number in a sister species pair of redfin minnows, Pseudobarbus afer and P. asper (Osteichthyes: Cyprinidae). Ichthyological Exploration of Freshwaters 5(4): 305-320.

Cambray, J.A. & Hecht, T. 1995. Comparison of the growth of two closely related redfin minnows, Pseudobarbus afer (Peters, 1864) and P. asper (Boulenger, 1911) (Pisces, Cyprinidae), in the Gamtoos River System, South Africa. Journal of African Zoology 109(4): 349-376.

Skelton, P.H. 1988. A taxonomic revision of the redfin minnows (Pisces, Cyprinidae) from southern Africa. Ann. Cape Prov. Mus. (nat. Hist.) 16(10): 201-307.

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