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178 The Southwestern Naturalist vol. 28, no. 2
<br />relative fecundity from their data and derived a range of ca. 600 to 2,000
<br />ova/cm SL (X = 1,166 t 490.6).
<br />Injuries and Disease.-Incidence o[ injury and disease was remarkably
<br />Righ in razorback suckers Gom Lake Mohave (Table 5), another possible
<br />indication o[ great age and/or stress for the population. A large number of
<br />individuals were blind in one or both eyes, and 11.5% of fish so afflicted had
<br />their orbit(s) totally overgrown with epidermis. A progressive deterioration
<br />was indicated, with eyes first becoming opaque, then swollen and protrud-
<br />ing from the skull, followed by rupture and shrinkage into the orbit, and
<br />overgrowth by skin. The reasons for this condition are unknown, but unit)
<br />about 1976 an eye fluke was a major problem in trouts in the Colorado
<br />River (Loudermilk, pers. comm.). In 1973, B. D. Roselund (LiSF~NS, pers.
<br />comm.) found some bacteria (Aeromonas hydrophila) in aqueous humor of
<br />two infected eyes, plus large numbers of the protozoan hyxosoma sp. in
<br />macerated tissues of the choroid-sclera region. Four of eight eyes (four fish)
<br />examined in 1974 also yielded Myxosoma sp. G. Hoffman (USFWS) could
<br />not identify the spores, which "measured 7.5 X 9 µ in face view," and were
<br />probably undescribed (Roselund, pers. comm.). Few Eish appeared ema-
<br />ciated, even when to[a11y blinded, indicating a highly developed gustatory
<br />system (Miller and Evans, 1965). Deformations o! the vertebral column also
<br />were relatively common, as were infestations of parasitic copepods (Lernaea
<br />sp.). Roselund (USFWS, pers. comm.; also in 4Vydoski et al., 1980 and Ano-
<br />nymous, 1981) similarly recorded Lernnea sp., and also identified an internal
<br />monogenetic trematode of the suborder Polyopis[ocotyles, pathogenic proto-
<br />zoans of the genera lchthyophthirius and Myxosoma (see above), and patho-
<br />genic bacteria o[ the genera Aeromonas and Pseudomonas from razorback
<br />suckers in Lake Mohave. Mpoame (1981) found remarkably few parasites in
<br />his sample from that take. One of 18 Eish had a cestode (Isoglaridacris bul-
<br />borirrus), and 17 hosted immature nematodes of the genus Darnitoides.
<br />Higher incidences of gross bacterial infections and external lesions were in
<br />samples taken during or following breeding. These maladies were conspicu-
<br />ously low in pre-breeding fish in 1982. External damage from tubercles of
<br />males and from contact with the bottom presumably lead to these secondary
<br />infections.
<br />Attempted Recovery of the Species.-In ]974, the USFWS commenced
<br />experimental propagation of razorback suckers at ~l'illow Beach National
<br />Fish Hatchery (Toney, 1979). As already discussed, progeny from the 1979
<br />and 1975 stocks provided growth and size data (Fig. 3), information on size
<br />at sexual maturity, embryological and larval developmental sequences
<br />(Minckley and Gustafson, 1982), and a few escaped into Lake Mohave. Some
<br />of these young fish were retained for breeding purposes, and they, plus addi-
<br />tional brood stock Erom Lake Mohave, were moved to Dexter National Fish
<br />Hatchery in 1981, where 20,000 [ingrrlings (about 8 cm TL) were produced.
<br />Some o[ these were stocked into historic habitats in Arizona. Additional
<br />adults were obtained in 1982, more than 1.8 million larvae were produced,
<br />and survivors were released in appropriate habitats (Table 6; Johnson, ]982).
<br />triable populations will hopefully result from these reintroductions, espe-
<br />cially in stream reaches were non-native fishes are rare. If reproduction con-
<br />May 1983 Minckley-Status of Razorback Sucker 179
<br />Teel.e 5.-Incidence of ¢arasiles and disease in razorhazA suckers from Lake Alohave, Arizona-
<br />Nn~ada, 1974J982, Percentages are in ¢annlheses and do rsol equal IOtW' since some fish had more
<br />than one aJJlirtion.
<br />Condi,ion 1975 1976 1977 1979 19A0 19A1 19A2 Toial
<br />Blind (right eye only) i 1 9 5 2 6 28 39 95
<br /> (i4.7) (i9.1) (21.7) (28.6) (19.4) (19.4) (13.6) (15.8)
<br />Blind (IeG eye only) 6 8 1 0 5 16 39 79
<br /> (7.7) (17.0) (4.9) (0.0) (16.1) (9.7) (15.6) (12.3)
<br />Blind in bosh eyes 5 4 2 0 1 12 I6 91
<br /> (6.4) (8.5) (8.6) (0.0) (93). (7.2) (6.4) (6.8)
<br />Curvature of spinal 9 2 2 0 4 4 7 22
<br />column (3.8) (4.9) (B.6) (0.0) (12.9) (2.4) (2.8) (9.7)
<br />Eternal lesions 2 1 0 1 1 17 1 23
<br /> (2.6) (2.1) (0.0) (14.9) (9.2) (10.3) (0.4) (3.8)
<br />External wmerous 6 1 0 0 2 9 5 18
<br />tissues (7.7) (2.1) (0.0) (0.0) (6.4) (2.4) (2.0) (3.0)
<br />Bacterial infections 12 17 9 2 9 29 3 76
<br /> (15.4) (36.2) (39.1) (28.6) (29.0) (14.5) _(1.2) (12.6)
<br />Lcmara sp. 9 S 6 2 9 19 no 43'
<br /> (11.6) (6.4) (26.1) (28.6) (12.9) (11.5) data (12.3)
<br />Total Fish 78 47 23 7 31 165 205 601
<br />'Based on !51 fish, 1915-81.
<br />times to fail, we will at least have some riverine stocks o[ this long-lived
<br />species to study in further attempts to alleviate its precarious situation.
<br />Dtscusslon ena SuMMeRV.-The razorback sucker population in the lower
<br />Colorado River drainage is now reduced to scattered individuals in all but
<br />Lake Mohave, Arizona-Nevada. That population consists o[ large, slowly-
<br />growing fish, which are proposed to be nearly 30 years old, presumably hav-
<br />ing hatched when the reservoir -was filling in the early 1950s. The species
<br />remains abundant in Lake Mohave, comprising about 12.5ga of all Fishes
<br />taken by trammel netting in the period 1974-82. No recruitment into the
<br />population has been detected in that period, despite repeated observations of
<br />spawning. Ova are fertile since fertitized eggs and hatched larvae have been
<br />recorded in nature, and hatchery and laboratory production of the species
<br />has been achieved. There are no data, however, on the percentages of ova
<br />which are fertile, or ova survival to the larval sage. Nevertheless, sex ratios,
<br />sexual dimorphism, and fecundity all indicate the fish to be reproductively
<br />capable despite high incidences of injury and disease.
<br />A pattern exists that large, presumably old, fish persist for many years in
<br />reservoirs. They did so in Roosevele Lake from 1915 to near 1950, and in
<br />Saguaro Lake from 1930 to past 1949 (but not until 1966). They now appear
<br />to be disappearing from Lake Mead, which was closed in 1935, and Lake
<br />Havasu, closed in 1938. They remain common in Lake Mohave, which
<br />began filling in 1950, yet there is no evidence o[ subsequent, successful
<br />reproduction in that reservoir. It is notable in this regard that Wallis (1951)
<br />considered razorback suckers far less abundant in the newl}~-impounded
<br />Lake Mohave than in Lake Mead, indicating that a strong year class had not
<br />yet been produced in the former reservoir. He considered the species "to be
<br />holding its own and reproducing abundantly in Lake Mead." These data
<br />
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