THE EFFECT OF AGITATION AND TURBULENCE OF THE GROWTH MEDIUM ON THE GROWTH AND VIABILITY OF MICROCYSTIS

SUMMARY

Observation of natural blooms of Microcystis, suggested that increased turbulence plays a role in retarding bloom formation of Microcystis. In laboratory experiments the influence of turbulence mediated by a magnetic stirrer on the growth and viability of Microcystis in batch cultures was determined. The different turbulences (0, 25, 75, 126, 209 and 314 cm sec^?1 linear velocity) had no effect on the growth rate. There was a highly significant correlation between the linear velocity and percentage viability as determined by a plating and serial dilution method. The viability ranged from 0,8% for stationary cultures to 99,2% for vigorously stirred (314 cm sec^?1 linear velocity) cultures.     

REVERSED VERTICAL MIGRATION OF PLANKTONIC CRUSTACEANS IN A EUTROPHIC LAKE OF HIGH pH

SUMMARY

Two studies of the diel vertical migration of zooplankton in the hyper-eutrophic Hartbeespoort Dam, revealed that both in summer when the lake was anaerobic below 15 m depth, and in winter, when homogeneous, aerobic conditions existed throughout the water column, a major portion of the zooplankton standing crop displayed a reversed migration tendency. The clado-cerans Daphnia pulex and D. longispina, and the copepod Thermo-cyclops oblongatus were the species involved. There was no evidence to sugest that interspecific interference, a phenomenon recently found to have caused reversed vertical migration in the rotifer Asplanchna priodonta, was responsible for the unusual movements recorded in the present study, since the species concerned were by far the total biomass and size dominants of the population.     

The origin of the dog revisited

Abstract

The most widely accepted hypothesis of the origin of the dog, Canis familiaris, is that the dog is a domesticated gray wolf, Canis lupus. This paper reviews the evidence for this conclusion, finds many unanswered questions and conceptual gaps in the wolf origin hypothesis, and explores the alternative hypothesis that the most likely ancestor of the domestic dog was a medium-size, generalist canid.     

ON THE STATUS OF CLARIAS GARIEPINUS (BURCHELL) IN LARGE MAN-MADE LAKES IN RHODESIA

SUMMARY

Data from some large man-made lakes in Rhodesia suggest that the populations of Clarias gariepinus have declined in these lakes. The reasons for this are not clear although commercial fishing does not appear to be responsible.     

POPULATION STRUCTURE OF TWO LABEO SPECIES IN THE HENDRIK VERWOERD DAM AS DETERMINED BY GILL NET SAMPLING

SUMMARY

A series of seven gill nets was used to sample populations of two Labeo species in the Hendrik Verwoerd Dam. Selection curves were computed for these nets and were used to define size and age structure of the two populations; these populations differ markedly, in that the moggel Labeo umbratus has a greater proportion of mature fish, while Labeo capensis (the Orange River Labeo) showed a more normal size and age distribution. Bio-mass curves closely follow the size distribution, while the fecundity of both species is highest in the larger size groups. These data were used to speculate on a fish exploitation strategy for the dam.     

A CONCEPTUAL MODEL OF A SILTATION SYSTEM IN SHALLOW LAKES WITH LITTORAL VEGETATION

SUMMARY

In shallow lakes a siltation system develops when wind driven water turbulence erodes the lake floor, silt is resuspended and transported by means of waterdrift into the littoral vegetation. Here, due to the resistance of the vegetation, the turbulence is reduced and the silt deposited. Through this mechanism, the prevailing winds have a major rôle in the erosion and siltation pattern, lake morphology, vegetation pattern and in the mixing of water and nutrients from the open water and the reedswamp and vice versa. The model explains the uneven distribution of vegetation at the lakes Neusiedlersee (Austria) and Chilwa (Malawi) satisfactorily, if one assumes a positive correlation between siltation and reedswamp growth and spread.     

BATHYMETRIC STUDIES ON THE PONGOLO RIVER FLOODPLAIN

SUMMARY

Thirteen of the major pans on the Pongolo river floodplain have been studied. Most are shallow (>2.5 m) and regularly lose up to 70% of their water each year, although few dry out. Floods inundate considerable areas (1000 ha) around pans situated in the flatter parts of the floodplain. Whilst inundated, these areas provide an allochthonous energy and nutrient source for the pan and, as the water levels recede, the exposed Cynodon dactylon (L.) Pers lawns provide grazing for cattle. The suitability of the various pans for fish production is discussed.     

A LIMNOLOGICAL INVESTIGATION OF LAKE LIAMBEZI,CAPRIVI

SUMMARY

A general investigation was carried out on Lake Liambezi to characterize the limnological features of the lake. The lake, 101 km² in area and situated within the tropics, was found to be shallow and bordered by reed swamps, particularly on the south-western shore. It was polymictic and consequently oxygen levels were high at all depths. Transparency was such that photosynthesis occurred to the bottom. Conductivity ranged from 17,3 to 41,2 mSm^?1 and the waters were moderately alkaline. Transfer of organic detritus from the reed swamp into the open water has resulted in the presence of high levels of organic nitrogen and phosphorus whilst ambient levels of inorganic forms were low. Planktonic chlorophyll a concentrations ranged between 1 and 104 μg l^?1 and Microcystis was the dominant phytoplankter. The dominant zooplankter was Bosmina. The important species of phytoplankton and zooplankton are listed and include two new species of blue-green algae which are described. The lake was found to be generally similar to most shallow tropical African lakes with a wide diversity of food sources for fish. Progressive encroachment by Salvinia appears to hamper access to fishing areas and the fishery potential is threatened.     

OBSERVATIONS ON THE THREE ALLOPATRIC POPULATIONS OF THE MALUTI MINNOW,OREODAIMON QUATHLAMBAE (BARNARD) WITH NOTES ON ITS EVOLUTION,ECOLOGY, SPAWNING,AND CONSERVATION

SUMMARY

Meristics and pigmentation of specimens of Oreodaimon quathlambae from the three known populations were compared to determine whether the species has experienced divergent evolution. Pigmentation was found to vary substantially but meristics counts did not. A proposal is made-to recognise three varieties of the species: Tsoelika-na, Senqu, and Moremoholo.

A review of the possible evolution of the species and the Drakensberg ecosystem suggests that the decline of the minnow is due to its exclusive adaption to a disappearing habitat.

Examination of what is known of the fish's life history and the history of the host rivers implies that competition from trout is a secondary cause of extermination of the endangered minnow. Environmental degradation poses a greater threat to the survival of the species.

Speculation is offered that O. quathlambae is a crevice spawner.

A report on the current conservation status and research is given along with management recommendations. Recent surveys have discovered another isolated population on the Tsoelikana River.     

THE HABITATS AND HABITAT PREFERENCES OF CLARIAS GARIEPINUS (PISCES: CLARIIDAE) IN A CLEAR COASTAL LAKE (LAKE SIBAYA,SOUTH AFRICA)

SUMMARY

The habitat preferences of the sharptooth catfish, Clarias gariepinus, in a clear coastal lake, Lake Sibaya, are described. Larval and small juvenile catfish inhabit flotsam and the rootstocks of plants in very shallow marginal areas. Larger juveniles inhabit densely-vegetated marginal pools, and may venture into open areas at night. Adult catfish (over 350 mm TL) occupy offshore areas, where their density is highest in terrace and sheltered bay habitats, and least in slope and profundal habitats. Adult catfish undergo a diel migration into shallow water at night and into deeper water during the day which is more marked at low lake levels. The methods used to capture catfish, and the main habitats in Lake Sibaya, are also described.     

TAXONOMIC BIBLIOGRAPHY OF VASCULAR AQUATIC PLANTS IN SOUTHERN AFRICA

SUMMARY

The length mass relationship for a Labeo capensis population is described by the equation M = 0,0134 L^2'999 where 2,999 represents a constant the value of which indicates isometric growth. There is very little difference between the length/mass relationship for males and that for females and this is similar to the results found by Mulder (1973) for L. capensis in the Vaal River. The length/mass relationships for gravid males and females are different from that of the population as a whole indicating that maturity does result in a change of the body form which is in accordance with the results of Mulder (1973).

A modified formula to take into account, small length intervals of an age group, is used to calculate the relative condition factor for Labeo capensis from the Caledon River for a consecutive “winter” and “summer” period. The results show that the conhd1t10ni for Labeo capensis of the 0⁺, 1⁺ and 2⁺ age groups is better in the summer period than in the winter period, whereas in the older age groups 3⁺ to 5⁺ the condition in winter is better than in summer. This can be attributed to the attainment of sexual maturity at the age of 3⁺ years and the presence of large quantities of fat deposited in the body during the winter months, which are then utilised for the development of the gonads prior to spawning. These results are similar to those obtained for the same species by Mulder (1973) in the Vaal River and by Bloemhof (1974) in the Hardap Dam.     

Responses of cats to petting by humans

Abstract

There is evidence that different gland areas in animals of the cat family have different functions. This study showed that nine cats gave more positive and fewer negative responses to petting by their owners in the temporal region (between the eyes and ears), the reverse to petting in the caudal region (around the tail), with the perioral (chin and lips) and non-gland areas intermediate. This suggests that cats prefer being petted in certain body areas.     

Development of a Target cell-Biologics-Effector cell (TBE) complex-based cell killing model to characterize target cell depletion by T cell redirecting bispecific agents

T-cell redirecting bispecific antibodies (bsAbs) or antibody-derived agents that combine tumor antigen recognition with CD3-mediated T cell recruitment are highly potent tumor-killing molecules. Despite the tremendous progress achieved in the last decade, development of such bsAbs still faces many challenges. This work aimed to develop a mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) modeling framework that can be used to assist the development of T-cell redirecting bsAbs. A Target cell-Biologics-Effector cell (TBE) complex-based cell killing model was developed using in vitro and in vivo data, which incorporates information on binding affinities of bsAbs to CD3 and target receptors, expression levels of CD3 and target receptors, concentrations of effector and target cells, as well as respective physiological parameters. This TBE model can simultaneously evaluate the effect of multiple system-specific and drug-specific factors on the T-cell redirecting bsAb exposure–response relationship on a physiological basis; it reasonably captured multiple reported in vitro cytotoxicity data, and successfully predicted the effect of some key factors on in vitro cytotoxicity assays and the efficacious dose of blinatumomab in humans. The mechanistic nature of this model uniquely positions it as a knowledge-based platform that can be readily expanded to guide target selection, drug design, candidate selection and clinical dosing regimen projection, and thus support the overall discovery and development of T-cell redirecting bsAbs.     

Tourist impact on Tibetan macaques

Abstract

Ecotourism is a growing sector of the tourism industry, but few studies to date have quantified its impacts on local people, tourists and wildlife. We present a preliminary study on threat and affiliative behaviors of two groups of free-ranging Tibetan macaques (Macaca thibetana) as a function of habituation and tourist presence. Data indicate that the less habituated group spent less time within sight of tourists compared with the more habituated group. The more habituated group engaged in frequent affiliative behaviors while within sight of humans, whereas affiliative behavior was not observed in the less habituated group. The general pattern of threats consisted of adults primarily threatening juveniles and juveniles primarily threatening humans, possibly due to redirection. No clear pattern of threats as a function of tourist density emerged. Tourist feeding, although discouraged, potentially provided a catalyst for some aggression. Future research will focus on clarifying which human behaviors evoke specific threat responses from monkeys. These data will be used to refine the existing management plan for this monkey population.     

BOOK REVIEWS

SUMMARY

Scale studies indicated that the annulus is a reliable year mark. A linear relationship existed between scale radius and body growth enabling back calculations to be made. The growth rate of males in Doorndraai Dam were similar to findings in the Incomati and Limpopo systems by Gaigher 1969 and Potgieter 1974 for the same species. The average sex ratio was one male to 1,8 females and was similar to that of the above river systems. Males reached sexual maturity at 12 cm while females matured at a length of 15 cm. The spawning season extended from late September to after December. Fecundity increased with an increase in length from 3 600 ova for a 15,4 cm fish to 8 500 for a 30,9 cm fish. T. rendalli fed extensively on macro-phytic vegetation when it was available, otherwise they became facultative feeders.     

草原革蜱和森林革蜱幼虫的形态学研究

将采自不同地区的草原革蜱Dermucentor nuttalli Olenev和森林革蜱Dermaeentor silvarumOlenev成虫在实验室中培养,对所获幼虫的形态特征用生物统计方法进行分析。结果证明,革蜱幼虫的一些形态变异很大,同一种革蜱采自不同地区或不同雌虫所产的幼虫的个体变异甚至比种间变异还大。所以,前人根据个别地区少量材料所描述的上述幼虫形态特征及所做的检索表,不能广泛适用。作者分析了大量材料后,找出上述两种幼虫较稳定的鉴别特征。根据假头宽和盾板长可以区分草原革蜱和森林革蜱;按照肩毛(Sc)和第一对背中毛(Cd₁)的长度可以把上述两种幼虫与我国北部分布的其他三种革蜱(边缘革蜱、银盾革蜱和网纹革蜱)区别开来。     

灭幼脲引起两种幼虫表皮组织病变的显微观察

本文研究了灭幼脲引起黄粉(虫甲)(Tenebrio mclitor)和粘虫(Mythimna separata)幼虫的中毒征象和组织学病变.低剂量能引起幼虫蜕皮障碍,但看不到明显的组织学病变.高剂量处理,不仅引起了严重的中毒征象,而且伴有明显的组织学病变:内表皮生长停滞,真皮细胞排列异常,在内表皮和真皮细胞之间出现附加层和球状颗粒.对这些现象进行了较细致的讨论.     

棉铃虫对氮的消耗和利用

在25℃下分别用棉叶/桃和人工饲料饲养棉铃虫(Heliothis armigera),测定幼虫对食物中氮的利用效率,以及通过棉铃虫不同发育期的氮流.除棉叶/桃组2—3龄幼虫的氮累积速率低于4龄幼虫外,两组幼虫对食物中氮的消耗速率、虫体氮的累积速率(毫克氮/毫克千重/天)和幼虫含氮百分率均随幼虫龄期的增加而降低.氮的排出速率(毫克氮/毫克干重/天)在2—3龄期间趋于降低,但4龄以后略有升高,幼虫发育后期的粪便含氮百分率也趋于升高.因此,幼虫在4龄以后对食物中氮的利用效率显著降低,表明它对氮的需要逐渐减少.人工饲料的含氮量约比棉桃高70%,但棉叶/桃组幼虫对氮的同化效率却比人工饲料组幼虫高10%左右.两组雌蛹—成虫的氮转化率在71—74%之间.雌蛾含有的氮约有37%(人工饲料组)—45%(棉叶/棉桃组〕用于繁衍后代.本试验提供的资料结合含糖量和含水分较多的寄主植物器官对幼虫有较好营养效应的假设可以比较合理地解释棉铃虫在田间的为害习性.