Aspects of the biology of aestivation in Bulinus (Physopsis) africanus (Krauss) (Gastropoda, Pulmonata)
- Authors: Heeg, J. (Jan)
- Date: 1973
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21054 , http://hdl.handle.net/10962/6178
- Description: Aestivation, a period of dormancy during hot, dry conditions, is known to occur in both the Prosobranchia and the Pulmonata among freshwater Gastropoda. While there have been numerous accounts, mainly by field ecologists concerned with bilharziasis control, of the survival value of aestivation in the Gastropoda, little is known of its underlying physiological mechanisms. Results of investigations into the physiological basis of aestivation in the freshwater Prosobranchia, confined to the family Ampulariidae, have been conflicting, fundamental differences having been shown to exist between different species of the genus Pila . Only a single comprehensive study, that by von Brand and his coworkers on the planorbid snail Australorbis glabratus*, forms the basis of our knowledge of the aestivation process in the aquatic Pulmonata. In view of the conflicting results obtained in investigations on freshwater Prosobranchia, the general applicability of the findings for Australorbis glabratus to other freshwater Pulmonata was open to question. The present investigation on the planorbid snail Bulinus (Physopsis) afriaanus, a species known to be a successful aestivator, was prompted by the obvious need for a further comprehensive study on an aquatic pulmonate species . The results presented here show that aestivation in this species is a definite physiological state, characterised by a depression of the metabolic rate, which not only aids in husbanding the snails I metabolic resources. during the enforced starvation which must necessarily accompany aestivation, but also constitutes a form of resistance adaptation to the transient high temperatures which aestivating snails are bound to encounter. Loss of body water is shown to be important in initiating aestivation, but it is also the factor most likely to prove lethal during the course of aestivation. The results confirm and extend the earlier findings for Australorbis glabratus. The results are discussed in the context of our present knowledge of aestivation in other Gastropoda, both aquatic and terrestrial, and also in relation to other forms of resistance adaptation. As expected, the investigation raises more questions than it answers, thus directions for further research, arising out of the present findings, are suggested.
- Full Text:
- Date Issued: 1973
- Authors: Heeg, J. (Jan)
- Date: 1973
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21054 , http://hdl.handle.net/10962/6178
- Description: Aestivation, a period of dormancy during hot, dry conditions, is known to occur in both the Prosobranchia and the Pulmonata among freshwater Gastropoda. While there have been numerous accounts, mainly by field ecologists concerned with bilharziasis control, of the survival value of aestivation in the Gastropoda, little is known of its underlying physiological mechanisms. Results of investigations into the physiological basis of aestivation in the freshwater Prosobranchia, confined to the family Ampulariidae, have been conflicting, fundamental differences having been shown to exist between different species of the genus Pila . Only a single comprehensive study, that by von Brand and his coworkers on the planorbid snail Australorbis glabratus*, forms the basis of our knowledge of the aestivation process in the aquatic Pulmonata. In view of the conflicting results obtained in investigations on freshwater Prosobranchia, the general applicability of the findings for Australorbis glabratus to other freshwater Pulmonata was open to question. The present investigation on the planorbid snail Bulinus (Physopsis) afriaanus, a species known to be a successful aestivator, was prompted by the obvious need for a further comprehensive study on an aquatic pulmonate species . The results presented here show that aestivation in this species is a definite physiological state, characterised by a depression of the metabolic rate, which not only aids in husbanding the snails I metabolic resources. during the enforced starvation which must necessarily accompany aestivation, but also constitutes a form of resistance adaptation to the transient high temperatures which aestivating snails are bound to encounter. Loss of body water is shown to be important in initiating aestivation, but it is also the factor most likely to prove lethal during the course of aestivation. The results confirm and extend the earlier findings for Australorbis glabratus. The results are discussed in the context of our present knowledge of aestivation in other Gastropoda, both aquatic and terrestrial, and also in relation to other forms of resistance adaptation. As expected, the investigation raises more questions than it answers, thus directions for further research, arising out of the present findings, are suggested.
- Full Text:
- Date Issued: 1973
Some aspects of the effect of temperature on the respiratory and cardiac activities of the Cichlid Teleost Tilapia mossambica
- Authors: Josman, V
- Date: 1971
- Subjects: Fishes -- Effect of temperature on , Cichlids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5859 , http://hdl.handle.net/10962/d1012613
- Description: The importance of the cichlid teleost Tilapia mossambica as a protein source, coupled with its remarkable adaptability, has resulted in its introduction into many water systems throughout the tropical, sub-tropical and even temperate regions of the world. However, its successful exploitation of these waters is dependent very largely upon the value of minimum temperatures and their duration. For e.g. Long et al (1961) has drawn attention to the tremendous mortalities of T. mossambica that occur in shallow water bodies during the precipitous temperature decreases that accompany the winter monsoons in Vietnam and other eastern countries, even at temperatures as high as 14 or 16º C. Coehe (1967) does not recommend stocking with T. mossambica where temperatures are not above 14º C all the time. Ailanson et al (1962) conclude, after an experimental study, that low temperatures (13º C or lower) in South African highveld dams in winter are certainly an important factor in the extensive mortalities of T. mossambica that have been reported from these dams. Jubb (1961) also reports that this species is often killed during a severe winter in Rhodesia. Intro., p.1.
- Full Text:
- Date Issued: 1971
- Authors: Josman, V
- Date: 1971
- Subjects: Fishes -- Effect of temperature on , Cichlids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5859 , http://hdl.handle.net/10962/d1012613
- Description: The importance of the cichlid teleost Tilapia mossambica as a protein source, coupled with its remarkable adaptability, has resulted in its introduction into many water systems throughout the tropical, sub-tropical and even temperate regions of the world. However, its successful exploitation of these waters is dependent very largely upon the value of minimum temperatures and their duration. For e.g. Long et al (1961) has drawn attention to the tremendous mortalities of T. mossambica that occur in shallow water bodies during the precipitous temperature decreases that accompany the winter monsoons in Vietnam and other eastern countries, even at temperatures as high as 14 or 16º C. Coehe (1967) does not recommend stocking with T. mossambica where temperatures are not above 14º C all the time. Ailanson et al (1962) conclude, after an experimental study, that low temperatures (13º C or lower) in South African highveld dams in winter are certainly an important factor in the extensive mortalities of T. mossambica that have been reported from these dams. Jubb (1961) also reports that this species is often killed during a severe winter in Rhodesia. Intro., p.1.
- Full Text:
- Date Issued: 1971
A contribution to the benthic biology of some southern African lakes
- Authors: Boltt, R E
- Date: 1969
- Subjects: Aquatic biology -- Africa, Southern Benthos -- Africa, Southern Lake animals -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5836 , http://hdl.handle.net/10962/d1009521
- Description: The benthos of Lake Sibayi, Lake Nhlange, Lake Shengesa and Lake Sifungwe has been sampled by means of a van Veen grab of bite area 0.225m². Except for Lake Shengesa, the substrates of the lakes have been investigated visually by SCUBA divers. Some quantitative sampling, using underwater techniques, has been carried out in Lake Sibayi. In general, the substrate of the lakes consisted of two types, either fine sand with an average particle size of 3.2 phi, or mud with a median phi value of less than 6. The sandy substrata was usually rich in fauna, and the mud usually poor. Lake Sibayi , which is freshwater (135 ppm Cl¯) has estuarine and freshwater species in the benthos. Some of the species, notably Grandidierella lignorum and Apseudes digitalis, show an uneven pattern of distribution with respect to depth. Lake Nhlange is a brackwater lake (3.4‰ salinity) and has mainly an estuarine fauna. Many of the species are different from those found in Lake Sibayi. There is some evidence that the benthic fauna of the lake has increased its range in depth in the years following a flood in January 1966. Only chironomid larvae were found in the benthos of Lake Shengesa. The greater part of the substrate of this lake consisted of a highly organic mud mainly derived from burnt grassland around the periphery of the lake. Lake Sifungwe, which is connected to Lake Nhlange, has a halocline at about 9 metres. The fauna of the benthos has more species than lake Nhlange. There is some evidence to suggest that LGC fauna invades deeper water in summer, and is driven into shallower water in winter because of the fluctuating level of anaerobic conditions below the discontinuity layer. The benthic fauna of the lakes has been compared with that of the estuaries reported on by the Cape Town Ecological Survey. experimental studies on G. lignorum, a species present in Lake Sibayi, suggested that the physiological responses of material from an estuary normally at 35‰ salinity (Kowie River estuary) and from lakes which are normally of low salinity (Groenvlei 2.5‰ salinity, Lake Sibayi) were not different. Studies on substrate choice, and pressure, indicated that these factors do not affect the distribution pattern of G. lignorum in the substrate. Studies on light orientation responses and the effects of rates of carbon dioxide increase of about 20 mm HgC0₂/hr or more, suggest that these may be the principle factors affecting the distribution of G. lignorum in the benthos of Lake Sibayi. Some supporting evidence for the presence of changing pC0₂ has been found. A discussion of the importance of dynamic events at the substrate/water interface is given.
- Full Text:
- Date Issued: 1969
- Authors: Boltt, R E
- Date: 1969
- Subjects: Aquatic biology -- Africa, Southern Benthos -- Africa, Southern Lake animals -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5836 , http://hdl.handle.net/10962/d1009521
- Description: The benthos of Lake Sibayi, Lake Nhlange, Lake Shengesa and Lake Sifungwe has been sampled by means of a van Veen grab of bite area 0.225m². Except for Lake Shengesa, the substrates of the lakes have been investigated visually by SCUBA divers. Some quantitative sampling, using underwater techniques, has been carried out in Lake Sibayi. In general, the substrate of the lakes consisted of two types, either fine sand with an average particle size of 3.2 phi, or mud with a median phi value of less than 6. The sandy substrata was usually rich in fauna, and the mud usually poor. Lake Sibayi , which is freshwater (135 ppm Cl¯) has estuarine and freshwater species in the benthos. Some of the species, notably Grandidierella lignorum and Apseudes digitalis, show an uneven pattern of distribution with respect to depth. Lake Nhlange is a brackwater lake (3.4‰ salinity) and has mainly an estuarine fauna. Many of the species are different from those found in Lake Sibayi. There is some evidence that the benthic fauna of the lake has increased its range in depth in the years following a flood in January 1966. Only chironomid larvae were found in the benthos of Lake Shengesa. The greater part of the substrate of this lake consisted of a highly organic mud mainly derived from burnt grassland around the periphery of the lake. Lake Sifungwe, which is connected to Lake Nhlange, has a halocline at about 9 metres. The fauna of the benthos has more species than lake Nhlange. There is some evidence to suggest that LGC fauna invades deeper water in summer, and is driven into shallower water in winter because of the fluctuating level of anaerobic conditions below the discontinuity layer. The benthic fauna of the lakes has been compared with that of the estuaries reported on by the Cape Town Ecological Survey. experimental studies on G. lignorum, a species present in Lake Sibayi, suggested that the physiological responses of material from an estuary normally at 35‰ salinity (Kowie River estuary) and from lakes which are normally of low salinity (Groenvlei 2.5‰ salinity, Lake Sibayi) were not different. Studies on substrate choice, and pressure, indicated that these factors do not affect the distribution pattern of G. lignorum in the substrate. Studies on light orientation responses and the effects of rates of carbon dioxide increase of about 20 mm HgC0₂/hr or more, suggest that these may be the principle factors affecting the distribution of G. lignorum in the benthos of Lake Sibayi. Some supporting evidence for the presence of changing pC0₂ has been found. A discussion of the importance of dynamic events at the substrate/water interface is given.
- Full Text:
- Date Issued: 1969
Some aspects of the ecology of the citrus red mite, Panonychus citri (McGregor), in the Eastern Cape Province
- Authors: Keetch, D P
- Date: 1969
- Subjects: Citrus -- Diseases and pests -- South Africa -- Eastern Cape Plant mites -- Ecology -- South Africa Citrus red mite Citrus red mite -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5860 , http://hdl.handle.net/10962/d1012630
- Description: The citrus red mite, Panonychus citri (McGregor), is a relatively new pest to South African citriculture, the first recorded injury to citrus trees was from Rustenberg, Transvaal in 1950 (Smith 1953). In the U.S.A. the biology of this mite has been studied by Quayle (1938), Prendergast (1938), English and Turnipseed (1941), DeBach (1947), DeBach et al. (1950), Ebeling (1959) and Jeppson et al. (1957,1961). However, in South Africa little information is available concerning the ecolopy of the citrus red mite. The majority of the literature pertaining to P. citri in Republic, (Smith (1953), Mentz (1954), Stofberg (1959), Schwartz (1965) and Brodrick (1965) is of a descriptive nature, and mainly concerned with the chemical control of the mite. The only biological investigation on the development of P.citri, and the effect of insecticides and insect predators on its biology, under South African conditions, was made by van Rooyen (1966) at Zebediela, Transvaal. In the control of citrus pests, such as the citrus red mite, that need for a better understanding of their ecology has been well emphasised by DeBach (1951) and Griffiths (1951). DeBach (1951) in particular, stressed the danger of the continued reliance on insecticidal treatment as the only method of nest control, and has pointed out that persistent chemical applications may only serve to intensify the pest problem. He has suggested that a closer study of the environment of the pest species could provide a solution to the problems now encountered as a result of insecticidal control measures. Intro., p. 1-2.
- Full Text:
- Date Issued: 1969
- Authors: Keetch, D P
- Date: 1969
- Subjects: Citrus -- Diseases and pests -- South Africa -- Eastern Cape Plant mites -- Ecology -- South Africa Citrus red mite Citrus red mite -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5860 , http://hdl.handle.net/10962/d1012630
- Description: The citrus red mite, Panonychus citri (McGregor), is a relatively new pest to South African citriculture, the first recorded injury to citrus trees was from Rustenberg, Transvaal in 1950 (Smith 1953). In the U.S.A. the biology of this mite has been studied by Quayle (1938), Prendergast (1938), English and Turnipseed (1941), DeBach (1947), DeBach et al. (1950), Ebeling (1959) and Jeppson et al. (1957,1961). However, in South Africa little information is available concerning the ecolopy of the citrus red mite. The majority of the literature pertaining to P. citri in Republic, (Smith (1953), Mentz (1954), Stofberg (1959), Schwartz (1965) and Brodrick (1965) is of a descriptive nature, and mainly concerned with the chemical control of the mite. The only biological investigation on the development of P.citri, and the effect of insecticides and insect predators on its biology, under South African conditions, was made by van Rooyen (1966) at Zebediela, Transvaal. In the control of citrus pests, such as the citrus red mite, that need for a better understanding of their ecology has been well emphasised by DeBach (1951) and Griffiths (1951). DeBach (1951) in particular, stressed the danger of the continued reliance on insecticidal treatment as the only method of nest control, and has pointed out that persistent chemical applications may only serve to intensify the pest problem. He has suggested that a closer study of the environment of the pest species could provide a solution to the problems now encountered as a result of insecticidal control measures. Intro., p. 1-2.
- Full Text:
- Date Issued: 1969
Studies on the biology of the Cape chestnut psylla paurocephala Calodendri Moran (in press) and the South African citrus psylla Trioza Erytreae (Del Guercio) (Homoptera : Psyllidae)
- Authors: Moran, V C (V. Cliff)
- Date: 1968
- Subjects: Citrus -- Diseases and pests -- South Africa , Psylla
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5867 , http://hdl.handle.net/10962/d1012883
- Description: Citrus is grown as a commercial crop in several areas surrounding Grahamstown in the Eastern Cape Province of South Africa. Twelve miles South-west of Grahamstown is an orchard of about 6000 trees on the farm "Mosslands". This orchard attracted attention as the insect pests of citrus have been kept at a sub-economic level by natural biological control since 1949. This orchard is completely surrounded by indigenous bush and originally the object of this study was to see, in how far, the insect fauna of the indigenous bush was infuencing the biological control which had been achieved in the orchard. As citrus is a member of the family Rutaceae, four indigenous plants in this family, which occured in the indigenous bush, were chosen for a closer study of their associated insect fauna. This study continued for a year during which time a bewildering number of insects and their parasites were collected and it was realized that only an investigation of a very specific aspect of the problem could possibly yield meaningful results. As a starting point, therefore, Trioza erytreae (Del Guercio) (Homoptera: Psyllidae), the South African citrus psyllid, was singled out. This psyllid was found on citrus at "Mosslands" and was also found on all but one of the indigenous rutaceous plants. It was chosen for study because of its polyphagous habit and because very little is known of the biology of this economically important species in South Africa. Also very little work has been done on the Psyllidae generally. Intro., p. 1.
- Full Text:
- Date Issued: 1968
- Authors: Moran, V C (V. Cliff)
- Date: 1968
- Subjects: Citrus -- Diseases and pests -- South Africa , Psylla
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5867 , http://hdl.handle.net/10962/d1012883
- Description: Citrus is grown as a commercial crop in several areas surrounding Grahamstown in the Eastern Cape Province of South Africa. Twelve miles South-west of Grahamstown is an orchard of about 6000 trees on the farm "Mosslands". This orchard attracted attention as the insect pests of citrus have been kept at a sub-economic level by natural biological control since 1949. This orchard is completely surrounded by indigenous bush and originally the object of this study was to see, in how far, the insect fauna of the indigenous bush was infuencing the biological control which had been achieved in the orchard. As citrus is a member of the family Rutaceae, four indigenous plants in this family, which occured in the indigenous bush, were chosen for a closer study of their associated insect fauna. This study continued for a year during which time a bewildering number of insects and their parasites were collected and it was realized that only an investigation of a very specific aspect of the problem could possibly yield meaningful results. As a starting point, therefore, Trioza erytreae (Del Guercio) (Homoptera: Psyllidae), the South African citrus psyllid, was singled out. This psyllid was found on citrus at "Mosslands" and was also found on all but one of the indigenous rutaceous plants. It was chosen for study because of its polyphagous habit and because very little is known of the biology of this economically important species in South Africa. Also very little work has been done on the Psyllidae generally. Intro., p. 1.
- Full Text:
- Date Issued: 1968
Hydrobiological studies on the Vaal River and some of its tributaries, including an introduction to the ecology of Simulium in its lower reaches
- Authors: Chutter, F M
- Date: 1967
- Subjects: Freshwater biology Freshwater animals Freshwater ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5841 , http://hdl.handle.net/10962/d1010499
- Description: The studies on the Vaal River and its tributaries presented here, were carried out for a variety of reasons. Prominent among them were several of immediate practical importance, such as the need to know the pollution status of waters which ultimately form the major supply for the Witwatersrand urban and industrial complex, and the need for background data on a stretch of the river which was to be insecticided to control a Simulium pest. However the results of such work can often be used for wider purposes. In this thesis they are used to examine the major factors thought to govern the distribution and abundance of the invertebrate Metazoa in the river. Introduction, p. 2-3.
- Full Text:
- Date Issued: 1967
- Authors: Chutter, F M
- Date: 1967
- Subjects: Freshwater biology Freshwater animals Freshwater ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5841 , http://hdl.handle.net/10962/d1010499
- Description: The studies on the Vaal River and its tributaries presented here, were carried out for a variety of reasons. Prominent among them were several of immediate practical importance, such as the need to know the pollution status of waters which ultimately form the major supply for the Witwatersrand urban and industrial complex, and the need for background data on a stretch of the river which was to be insecticided to control a Simulium pest. However the results of such work can often be used for wider purposes. In this thesis they are used to examine the major factors thought to govern the distribution and abundance of the invertebrate Metazoa in the river. Introduction, p. 2-3.
- Full Text:
- Date Issued: 1967
A contribution to the respiratory physiology of three South African freshwater pulmonate snails, Bulinus (Physopsis) Africanus (Krauss), Bulinus (Bulinus) Tropicus (Krauss), and Lymnaea Natalensis Krauss
- Authors: Alberts, I E
- Date: 1966
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:20965 , http://hdl.handle.net/10962/5696
- Description: From Introduction: The use of chemical molluscicides in the control of schistosome transmitting snails has been largely based on empirical studies of toxicity, rather than on a clear understanding of basic physiology and biochemistry of snail hosts. It is therefore possible that purely physiological studies may in themselves provide information which could be of value in the development of more effective mollucicides. In this investigation an attempt has been made to understand some aspects of the respiratory physiology of three species of fresh-water pulmonate snails, all of which are of medical and veterinary importance in the Republic of South Africa. Bulinus (Physopsis) africanus (Krauss) is the intermediate host of Schistosoma haematobium, the causative organism of human schistosomiasis (Bilharziasis). Bulinus (Bulinus) tropicus (Krauss) is the intermediate host of the conical flukes Calicophoron calicophorum and Paramphistomum microbothrium and of the liver fluke Fasciola hepatica, while Lymnaea natalensis Krauss is the intermediate host of the liver fluke Fasciola gigantica.
- Full Text:
- Date Issued: 1966
- Authors: Alberts, I E
- Date: 1966
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:20965 , http://hdl.handle.net/10962/5696
- Description: From Introduction: The use of chemical molluscicides in the control of schistosome transmitting snails has been largely based on empirical studies of toxicity, rather than on a clear understanding of basic physiology and biochemistry of snail hosts. It is therefore possible that purely physiological studies may in themselves provide information which could be of value in the development of more effective mollucicides. In this investigation an attempt has been made to understand some aspects of the respiratory physiology of three species of fresh-water pulmonate snails, all of which are of medical and veterinary importance in the Republic of South Africa. Bulinus (Physopsis) africanus (Krauss) is the intermediate host of Schistosoma haematobium, the causative organism of human schistosomiasis (Bilharziasis). Bulinus (Bulinus) tropicus (Krauss) is the intermediate host of the conical flukes Calicophoron calicophorum and Paramphistomum microbothrium and of the liver fluke Fasciola hepatica, while Lymnaea natalensis Krauss is the intermediate host of the liver fluke Fasciola gigantica.
- Full Text:
- Date Issued: 1966
The salinity tolerance of some Eastern Province fish in relation to their known distribution
- Authors: Hofmeyr, Hendrik Petrus
- Date: 1966
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21165 , http://hdl.handle.net/10962/6684
- Description: The tolerances to sea water, sodium chloride and sodium sulphate of various cichlid, cyprinid and anabantid species which occur naturally in or near the Eastern Province region of Southern Africa, were determined, and correlated with their distribution ranges. Of the nine freshwater species tested, only Tilapia mossambica is able to disperse through the sea and is therefore the only member of the secondary division (Myers 1937) present in this region. The remaining species are possibly all limited to the use of freshwater links for dispersal between river systems. Death of fish in sea water and in sodium chloride is chiefly due to loss of osmotic control, but in solutions of sodium sulphate a pronounced toxic effect is responsible for death. In all the solutions used, an inverse relation between survival time and concentration is present. No evidence of any cells specialised for salt excretion was found in the gills of fish exposed to various salt concentrations.
- Full Text:
- Date Issued: 1966
- Authors: Hofmeyr, Hendrik Petrus
- Date: 1966
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21165 , http://hdl.handle.net/10962/6684
- Description: The tolerances to sea water, sodium chloride and sodium sulphate of various cichlid, cyprinid and anabantid species which occur naturally in or near the Eastern Province region of Southern Africa, were determined, and correlated with their distribution ranges. Of the nine freshwater species tested, only Tilapia mossambica is able to disperse through the sea and is therefore the only member of the secondary division (Myers 1937) present in this region. The remaining species are possibly all limited to the use of freshwater links for dispersal between river systems. Death of fish in sea water and in sodium chloride is chiefly due to loss of osmotic control, but in solutions of sodium sulphate a pronounced toxic effect is responsible for death. In all the solutions used, an inverse relation between survival time and concentration is present. No evidence of any cells specialised for salt excretion was found in the gills of fish exposed to various salt concentrations.
- Full Text:
- Date Issued: 1966