Salinity ranges of some southern African fish species occurring in estuaries

The recorded salinity ranges of 96 fish species occurring in southern African estuaries are documented. Factors influencing the tolerance of fishes to low and high salinity regimes are discussed, with most species tolerant of low rather than high salinity conditions. This is important since most systems are subject to periodic freshwater flooding, especially during summer. The penetration of freshwater teleosts and elasmobranchs into estuaries is examined and the occurrence of marine fishes in rivers documented. Mortalities arising from salinity extremes in southern African estuaries are discussed, with temperature a key factor initiating such fish kills. Only eight fish species have been recorded spawning in estuaries although the fry of many species are attracted to estuarine waters. It is concluded that a small percentage of southern African fishes have succeeded in utilizing estuaries and this may be attributed to the paucity of strong osmoregulators     

Faecal analysis suggests generalist diets in three species of Western Cape cordylids

Climate has been proposed as an explanation for the present-day distribution of closely-related melanistic and non-melanistic cordylid species in the southwestern Cape of South Africa. However, diet may also contribute towards shaping geographic distributions. We present preliminary data on diet composition based on analyses of faecal pellets of Cordylus cordylus (non-melanistic), C. niger (melanistic) and C. oelofseni (melanistic). Coleoptera were the most common prey ingested both in summer and early spring for all species, followed by Hymenoptera for all species in summer. The overlap in other arthropod taxa ingested was low across species and seasons, suggesting an opportunistic component to their foraging behaviour.We distinguished plant matter in faecal samples of all species in all seasons, reflecting either voluntary or accidental ingestion. The results of this study suggest that the generalist diets of these cordylid species should not constrain their distributions despite the common preference for coleopterans.     

勺鸡、石鸡和天鹅血液生理指标的比较研究

采用常规方法对人工饲养的3种鸟类(勺鸡、石鸡、天鹅)血液中的血红蛋白、红细胞沉降率、红细胞平均体积、红细胞比容、血细胞数及白细胞分类6项生理指标进行了测定。结果表明：天鹅的红细胞总数、血红蛋白含量、血小板总数、红细胞比容、红细胞体积最大,勺鸡次之,石鸡最小；红细胞沉降率石鸡最大,勺鸡次之,天鹅最小；白细胞总数及各类白细胞所占的比例3种鸟类之间差别不明显,白细胞体积天鹅最大,石鸡次之,勺鸡最小。种属不同是导致3种鸟血液生理常值差别的主要原因。     

Dental microwear of sympatric rodent species sampled across habitats in southern Africa: Implications for environmental influence

Dental microwear textures have proven to be a valuable tool for reconstructing the diets of a wide assortment of fossil vertebrates. Nevertheless, some studies have recently questioned the efficacy of this approach, suggesting that aspects of habitat unrelated to food preference, especially environmental grit load, might have a confounding effect on microwear patterning that obscures the diet signal. Here we evaluate this hypothesis by examining microwear textures of 3 extant sympatric rodent species that vary in diet breadth and are found in a variety of habitat types: Mastomys coucha, Micaelamys namaquensis and Rhabdomys pumilio. We sample each of these species from 3 distinct environmental settings in southern Africa that differ in rainfall and vegetative cover: Nama‐Karoo shrublands (semi‐desert) and Dry Highveld grasslands in the Free State Province of South Africa, and Afromontane (wet) grasslands in the highlands of Lesotho. While differences between habitat types are evident for some of the species, inconsistency in the pattern suggests that the microwear signal is driven by variation in foods eaten rather than grit‐level per se. It is clear that, at least for species and habitats sampled in the current study, environmental grit load does not swamp diet‐related microwear signatures.     

Residency and small-scale movement behaviour of three endemic sparid fishes in their shallow rocky subtidal nursery habitat,South Africa

The residency and small-scale movements of early juveniles (<175 mm fork length) of three sparid fish species were examined in the shallow subtidal zone along a 500 m stretch of rocky coastline near Schoenmakerskop (Eastern Cape Province, South Africa). A total of 12 blacktail (Diplodus capensis), 12 zebra (Diplodus hottentotus) and six white musselcracker (Sparodon durbanensis) were tagged using visible implant elastomer (VIE) tags. Underwater observations in four shallow rocky subtidal gullies and adjacent areas were made using snorkeling gear on a total of 37 days spanning 13 field trips over spring low tide periods between January and August 2006. The VIE tagging method was well suited to individually tag small juvenile fish with minimum disturbance. In general, the degree of residency of juveniles in the shallow rocky subtidal zone was species specific and dependent on the size of individuals. Juvenile zebra displayed the highest degree of residency followed by white musselcracker and blacktail, with re-sightings recorded on 53%, 40% and 10% of observation days, respectively. The high degree of residency by early juvenile sparids renders them vulnerable to localized coastal perturbations and climate change.     

Validation of the periodicity of growth zone formation in the otoliths of four fish species from the Upper Zambezi ecoregion,southern Africa

In the Upper Zambezi and Okavango ecoregions, Brycinus lateralis, Hepsetus cuvieri, Schilbe intermedius and Serranochromis macrocephalus are important in subsistence fisheries, while S. intermedius and S. macrocephalus are often caught in commercial catches. Despite their importance, there is little information on their age and growth and age validation. Growth zone deposition rate in otoliths of B. lateralis, H. cuvieri, S. intermedius and S. macrocephalus was validated as annual using edge analysis in this study. Annual deposition of growth zones was corroborated by a fluorochrome marking experiment. Both methods demonstrated that one growth zone was deposited annually. Edge analysis demonstrated that the highest proportion of opaque zones was detected between August and December, most likely as a result of slow growth during lower temperature water during the preceding winter. With growth zone deposition validated as annual, future research should focus on determining the growth, maturity and mortality rates of these species, parameters which are important for their management.