OpenUCT :: Browsing by Author "Cook, Peter"

Browsing by Author "Cook, Peter"

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Open Access
Acute and chronic effects of ammonia in the South African abalone, Haliotis midae Linnaeus (Mollusca)
(2006) Reddy-Lopata, Kasturi; Moloney, Coleen; Cook, Peter; Lopata, Andreas
Ammonia is the major end-product of protein catabolism in abalone, and is excreted into the surrounding water. Build-up of ammonia in abalone aquaculture systems can reach high toxic levels and impact negatively on farming operations. Ammonia levels therefore have to be regulated. Accurate estimates of toxic un-ionized ammonia (FAN) from the total ammonia nitrogen (TAN) measured by photometer test kits is crucial as inaccuracies could result in major losses of abalone on the farms. The accuracy and applicability of two frequently used photometer test kits (the Nesslers method and the Palintest method) were compared. The calculated TAN concentrations were regressed against the prepared standard ammonia concentrations in seawater for both methods. The predicted slope (β = 1) if the methods were 100% accurate was compared to observed slopes using the Nesslers (β=0.8327) and Palintest (β = 0.7507) methods. Both these test kits underestimated the TAN concentrations, but the Nesslers method was more accurate. Nitrites and nitrates are toxic to abalone at much larger concentrations than ammonia and exist at low concentrations in natural systems, therefore the sensitivity of their tests was not as important. Nitrites and nitrates were monitored using the Ferrous sulphate method and the Cadmium reduction method, respectively.
Open Access
Aspects of the respiratory metabolism of juvenile rainbow trout (Oncorhynchus mykiss) at sustained swimming speeds
(1993) Durholtz, Deon; Cook, Peter
A detailed description of the design of an apparatus suitable for investigations into the respiratory physiology of small nektonic organisms at various swimming speeds is presented. Juvenile rainbow trout (Oncorhynchus mykiss) were used to evaluate the performance of the apparatus. Twenty-four hour experiments indicated no detectable diurnal variation in the respiration rates of juvenile rainbow trout. Experiments investigating aerobic energy expenditure at sustained swimming speeds, through measurements of oxygen consumption rates, are described. Oxygen consumption was found to increase exponentially with increasing swimming speed. The influence of body size on this relationship was examined. The contribution of anaerobic metabolism at sustained swimming speeds was investigated.
Open Access
An assessment of the suitability of the galjoen, Coracinus capensis cuvier, for mariculture in South Africa
(1991) Van der Lingen, Carl David; Cook, Peter
The suitability of the galjoen, Coracinus capensis, for mariculture in South Africa has been assessed from both an economic and a biological viewpoint. In terms of economic criteria galjoen shows a high potential for culture, being widely known and highly regarded as a table fish. The restaurant trade in the southwestern Cape has been identified as a possible market showing a high demand for this species. Adult galjoen are readily available, hardy, and are easily maintained in captivity. A biochemical technique to determine the sex of live fish has been elucidated and allows sexual identification to be conducted for several months prior to and during the spawning season. Natural serial spawning with high fertilization occurs readily in captivity, with galjoen producing large numbers of good quality eggs during a single season. However induced spawning using two mammalian gonadotropins resulted in the production of poor quality eggs. The relationship between temperature and development time for fertilized galjoen eggs has been determined, and the lower lethal temperature for developing eggs was found to lie between 14° and 16°C. Newly-hatched larvae exhaust their endogenous food reserves rapidly and show a short time to irreversible starvation, with first-feeding beginning from 110 hours after hatching at 18°C. Galjoen larvae proved to be extremely difficult to rear. Although successful first-feeding on a few live food organisms was observed, mass mortality at 4-8 days and again at 12-15 days after first-feeding resulted in exceptionally poor survival. It is surmised that galjoen larvae have very stringent nutritional requirements which cannot be met by employing commonly-used live food organisms. Growth rate estimates for galjoen that survived past metamorphosis indicate that growth under culture conditions is similar to that in the natural environment. Certain biological attributes of the galjoen such as simple broodstock maintenance, ease of natural spawning in captivity and high fecundity select this species for culture. However the inability to mass rear larvae through to metamorphosis drastically reduces the suitability of this species, especially since larval rearing is the key to successful mariculture. In addition, the slow growth rate under culture conditions observed also selects against this species. Because of these last two factors, it is concluded that the galjoen is not a suitable species for mariculture in South Africa.
Open Access
Biochemical indicators of the transportation stress of the South Africa abalone (perlemoen), Haliotis midae, Linn.
(1999) Omolo, Samson Odira; Gade, Gerd; Cook, Peter; Brown, Alec C
Abalone exposed to air incurred greater metabolic and structural stress in muscle than do abalone at rest. Since foot and shell adductor muscle texture and flavor affect economic values of H Midae, the investigation sought evidence of differences attributable to transport of the commercial South African abalone based on environmental and exercise inducement. Tauropine dehydrogenase from Haliotis. midae muscle exhibits its highest activity 53.85 X 13.56 U g-1 wet weight in shell adductor muscle. The activities of octopine dehyedrogenase, strombine dehydrogenase or alanopine dehydrogenase in adductor muscle were very low. Therefore, tauropine dehydrogenase was isolated from adductor muscles for enzymatic determination oftauropine. Tauropine dehydrogenase was purified 8.5-fold with 47% recovery.
Open Access
Bioenergetics and growth of white steenbras, Lithognathus lithognathus, under culture conditions
(1991) Harris, Shael Anne; Cook, Peter
The bioenergetics and growth of white steenbras, Lithognathus lithognathus, under culture conditions were determined to assess its suitability for mariculture. Fish were captured by seine netting, from nearby estuaries and transported to the laboratory where they were successfully kept for the duration of the experimental period. The fish were initially fed on white mussels and then weaned onto a diet of commercial trout pellets. The bioenergetics of L.lithognathus was examined using a large, simple closed system respirometer in which nitrogen excretion and oxygen consumption were measured simultaneously. This system permitted the use of groups of fish for experiment which simulated aquaculture conditions. The effects of fish size, ration size and temperature on faecal and nonfaecal excretion, and on oxygen consumption of L.lithognathus were examined.
Open Access
The effect of chlorine, heat and physical stress on entrained plankton at Koeberg Nuclear Power Station
(1988) Huggett, Jenny A; Cook, Peter
The large volume of seawater used for cooling at Koeberg Nuclear Power Station contains many planktonic organisms which are exposed to heat, chlorine and physical stress during their passage through the system. Phytoplankton biomass, measured as chlorophyll a, was reduced by an average of 55.32% due to entrainment, and productivity was decreased by 38.30% on average, mainly due to chlorination. Zooplankton mortality averaged 22.34% for all species and 30.52% for copepods, the dominant group. The copepod Paracartia africana was used in laboratory experiments designed to simulate entrainment. Latent mortality was monitored up to 60 hours after a 30-minute application of stress factors (physical stress was not simulated), and approximately 75% of the total mortality occurred within the 30-minute period. Male Paracartia experienced higher mortalities than females. Extrapolation of these results predicts an overall entrainment mortality (including latent mortality) of 40% for copepods and 29.04% for total zooplankton, although the latter cannot be substantiated. Plankton entrainment at Koeberg was not considered to be overly detrimental to the marine environment because of the very localised area affected, rapid dispersion of heat and chlorine, rapid regeneration times of phytoplankton and some zooplankton, low abundance of commercially important species and potential recruitment from the surrounding productive Benguela upwelling region.
Open Access
Factors influencing the ranching of the abalone species Haliotis Midae along the Namaqualand Coast of South Africa
(2002) De Waal, S W P; Cook, Peter
The Namaqualand coast of South Africa has been targeted as a potential ranching area for the abalone Haliotis midae. A series of experiments and models were designed to: assess to what extent the area's babitat may support seeded juveniles, identify the characteristics of successful seeding sites, determine optimal seeding strategies, and investigate population dynamics and economics that may most influence commercial ventures. Most of the experiments took place on the north-west Namaqualand coast; others were carried out along the south-west coast near the Gouritz River.
Open Access
The influence of thermal polution on various aspects of the biology of three species of crab
(1983) Beviss-Challinor, Lesley Doreen Margaret; Cook, Peter
The construction of a nuclear power station on the west coast of South Africa will result in a large volume of heated effluent being discharged into the ocean, thus raising the temperature of the surrounding sea by a few degrees. The physiological effect that this hot water will have on three species of crab common along the west coast, is presented in this paper. Parameters of the energy equation C = Pg + R + Uₑₓ + F + Uₑ have been measured for adult Plagusia chabrus, Hymenosoma orbiculare and Cyclograpsus punctatus. It appears that rate-temperature responses increase with increase in temperature for all three species. Favourable water temperatures were found to be between 16°C and 21°C for the three species, with temperatures of 26°C being detrimental, especially during moulting in P. chabrus and H. orbiculare. The energy budget and energetic efficiencies are calculated for all the species and it appears that the increased temperatures around Koeberg Power Station will be beneficial to the adult crab species.
Open Access
Neuropeptide hormones from the eyestalks of Jasus Lalandii
(2000) Marco, Heather G; Gäde, Gerd; Cook, Peter; Brandt, Wolf F
The X-organ sinus gland complex, situated in the eyestalks of decapod crustaceans, are known to be a source of a variety of neuropeptide hormones that regulate a number of diverse physiological processes. This neuroendocrine complex was investigated in 3 crustacean species, viz. the European shore crab Carcinus maellas, and 2 spiny lobster species Jasus lalandii and Panulirus homarus by means of tissue immunocytochemistry and an enzyme-linked immunosorbent assay (ELISA). Positive immunoreactions, associated with the X-organ - sinus gland system only, were obtained with antisera raised against crustacean hyperglycaemic hormone (cHH) of the American lobster (Homarus americanus), the Mexican crayfish (Procambarus bouvieri) and the edible crab (Cancer pagurus), as well as with antisera raised against vitellogenesis-inhibiting hormone (VIH) of the H. americanus and moult-inhibiting hormone (MIH) of C. pagurus. This is the first time that the immunolocalisation of these 3 hormones have been studied in a single crustacean species. The chief results of this comparative immunocytochemical study showed that (1) neuropeptide hormones of the shore crab and the 2 spiny lobster species were sufficiently homologous in primary structure to be recognised by the heterologous antisera, thus, an indication of conserved peptide structures across the species and infraorder boundaries; (2) preabsorbed complexes of purified peptides and antisera from the edible crab did not produce any immunoreactions in tissue immunocytochemistry, nor in ELISA, thus, indicating the specificity of the anti-cHH and anti-MIH sera; (3) the anti-VIH serum demonstrated the ability to bind epitopes on cHH and MIH peptides and is, thus, not a specific antiserum in this study; (4) there is co-localisation of cHH, MIH, VIH immunoreactivity in the eyestalk neuroendocrine complexes of all 3 species studied which suggests that the different peptide hormones can be synthesized in the same neuronal cell bodies. This co-localisation of neuropeptides in the eyestalk of J lalandii was confirmed by a double-staining immunoflourescence experiment, and finally (5) immunoreactivity of antisera raised against cHH of H. americanus and MIH of C. pagurus was associated with distinct and unique peak fractions, following reverse-phase high pressure liquid chromatographic (RP-HPLC) separation of sinus gland extracts from J. lalandii. A total of 6 neuropeptide hormones belonging to the cHH/MIH/VIH peptide family were isolated, functionally characterised and sequenced from extracts of sinus glands from the South African west coast rock lobster, Jasus lalandii. This is the first complete report on these peptides from any species belonging to the Palinuridae infraorder.
Open Access
A new sabellid that infests the shells of molluscs and its implications for abalone mariculture
(2000) Ruck, Kevin; Cook, Peter
Infestations of sabellid polychaetes were found in South African farmed abalone in 1994. Growth experiments confirmed that infested abalone had reduced growth rates. Surveys of both the intertidal and subtidal region at various locations around the South African coastline revealed that the sabellid was endemic to the region. It occurred in a range of mollusc species, but some species were more susceptible than others. The fact that some molluscan species became infested with worms only when exposed to them in the laboratory suggests that environmental factors may play a role in controlling natural levels of infestation. Different host selection on the East Coast of South Africa suggests that there may be more than one species of worm. Larvae disperse by crawling and settle at the growing edge of the shell underneath the mantle. Although the larvae are benthic, there is limited transfer of larvae through the water column, which can result in export of larvae from infested tanks. The risks of dispersal are discussed in a farm management context. Abalone kept in more hygienic laboratory conditions tended to grow faster than in farm tanks and had lower levels of infestation by sabellid larvae. This was attributed to the sabellids being less fecund under these conditions. This was probably caused by lack of food as evidenced in a separate starvation experiment. Based on experimental observations and farm experience it was possible to make management recommendations to limit the effect of the sabellid Quantitative measurement taols to assess the impact and productivity of sabellid infestations were developed Management of infestations on a farm requires a combination of inhibiting transfer and productivity of the worm and also promoting growth of the abalone. However, the constant risk of exposure to natural populations of sabellids necessitates the development oJ a treatment to eradicate sabellid infestations. The use of microcapsules as a drug delivery mechanism was explored and holds promise. Gelatin microcapsules, oil immulsions and liposomes were experimented with. All formulations were successfully produced in the desired size range of 2-30 μm. In all cases the sabellid'l readily ingested the capsules. Various toxins were successfully added to the formulations, but none of the treatments were able to harm the sabellids. The problem appeared to be the short passage time within the guts and the inability of the sabellids to digest the outer encapsulating layers to expose the toxins. More research is required to find the correct combination of toxin and delivery mechanism.
Open Access
Physiology and energetics of the sandy-beach bivalve Donax serra Röding with special reference to temperature and chlorine tolerance
(1989) Stenton-Dozey, Jeanette Mary Edgeworth; Cook, Peter
This thesis examines the physiology and energetics of D. serra and considers physiological responses to elevated temperature and chlorine levels typical of sea water discharged from a nuclear power station.
Open Access
The role of enteric bacteria in the Abalone, Haliotis Midae
(1996) Erasmus, Jean Helen; Cook, Peter; Coyne, Vernon
The role of bacteria in the digestive tract of the abalone Haliotis midae was examined to determine whether bacteria aid hydrolysis of polysaccharides present in seaweeds which farmed abalone consume. The enteric bacteria were enumerated using culturable and total (DAPI) counts. The numbers of culturable bacteria fell between 3.5x10⁵ and 2.3x10⁸ cfu/g wet weight tissue. The DAPI counts were between 1.6x10⁹ and 5.1x10⁹ cells per gram of tissue. The numbers of bacteria differed between the crop, stomach and intestine. Electron microscopy showed that bacteria were present on the food and gut wall. No specialised structures, to aid adhesion of bacteria, were apparent on the gut wall. The isolated bacteria were identified to genus level using standard biochemical and morphological tests. The common genera identified were Vibrio, Alcaligenes, Flavobacteria, Pseudomonas and Aeromonas. The bacterial communities in each gut region varied, suggesting that both resident and transient bacterial populations are present in H. midae. Alcaligenes occurred mainly in the crop, while Vibrio species were predominant in the stomach and intestine. The bacterial isolates were tested for their ability to hydrolyse the polysaccharides alginate, laminarin, CMC, carrageenan and agarose. Bacteria able to utilise these polysaccharides belonged to the genera Flavobacteria, Pseudomonas, Vibrio, Alcaligenes, Bacillus and Enterobacteria. Many of the isolated bacteria were capable of utilising two or three of the substrates tested. Quantitative poly saccharase assays using the reducing sugar assays of Nelson (1944) and Somogyi (1952) and Gardner et al. (1988) were employed. These assays showed that bacteria from the crop exhibited the greatest degree of CMC and alginate hydrolysis. Bacteria from the intestine exhibited the greatest carrageenan and agarose hydrolysis. The endogenous enzymes produced by H. midae were examined using extracts of the hepatopancreas as it was found to be bacteria free. It was found that abalone synthesize a CMCase, laminarinase, alginase, carrageenanase and agarase. However, the synthesis of these enzymes was related to the diet of the abalone. Abalone fed Ecklonia (which contains relatively high concentrations of alginate and laminarin) exhibited significantly higher alginase and laminarinase activity than abalone fed Gracilaria. Similarly, abalone fed Gracilaria (which contains relatively high proportions of carrageenan and agar) produced significantly higher carrageenanase and agarase activity. Furthermore, these enzyme activities were found to be similar to those extracted from gnotobiotic abalone (obtained using the antibiotics chloramphenicol (250μg/ml), ampicillin (600μg/ml) and cefotaxime (250μg/ml)), indicating that polysaccharide synthesis occurs in the hepatopancreas of H. midae. Polysaccharase assays on gnotobiotic abalone were compared to assays on untreated abalone. Bacteria were found to significantly enhance the polysaccharase activity of alginase, laminarinase and agarase hydrolysis.
Open Access
The role of phytoplankton in the nutrition of the larvae of the giant freshwater prawn Macrobrachium rosenbergii (DeMan) (Crustacea : Palaemonidae)
(1985) De Boucherville Baissac, Pierre; Cook, Peter
The possible role of phytoplankton in the nutrition of the larvae of the prawn M. rosenbergii was investigated in this study which is conducted in two parts. In the first section of Part I, the utilization of the yolk and its lipids in the egg and first two larval stages was examined. It was found that the yolk lipids in the egg undergoes very little change during egg development and that these lipids provide for 94% of the metabolic requirements of the first stage larvae. In section two of part one, the changes in the lipids and fatty acids in larvae reared in phytoplankton rich cultures and in clear water were examined to determine whether the phytoplankton had any effect on the composition of these lipids. As no overall significant differences were found in the lipid and fatty acid compositions of larvae reared in phytoplankton rich or clear water systems, it was concluded that phytoplankton had no significant effect on the composition of lipids in M. rosenbergii larvae. In part two of the study the uptake and fate of dissolve ¹⁴C-glycine was examined. The uptake of ¹⁴C-glucose and ¹⁴C-labelled algal exudate was also examined. It was found that a mechanism for the uptake of these dissolved organic substances does exist in the larvae. It was also shown, however, that the dissolved organic compounds are not of major importance as a source of energy in the nutrition of the larvae. The possible role of dissolved organic compounds is discussed. It was concluded that phytoplankton does not play an important role as an energy source for the larvae of M. rosenbergii.
Open Access
Taxonomy and ecology of South African reef corals
(1993) Riegl, Bernhard; Branch, George M; Cook, Peter; Schleyer, Michael
This thesis provides a complete taxonomic review of South African hermatypic Scleractinian reef corals, a description of coral communities on northern Natal coral reefs, experiments isolating the influence of the most important abiotic factors forcing these communities and finally management suggestions for the marine reserves within which these reefs are situated, based on the results of the ecological investigation. The taxonomic part reviews the entire hermatypic scleractinian coral fauna of South Africa and Southern Mozambique, including also material from the Atoll Bassas da India in the Mozambique channel. The study of coral communities on Northern Natal coral reefs revealed major differences in the nature of the reefs and the community structure of the reef corals from typical coral reefs in the Inda-Pacific. The study lead to the assumption that wave-action and sedimentation are the most important abiotic factors influencing these coral communities. These hypotheses were experimentally tested in the field and in the laboratory, using indicator species for specific community types, as identified in the community study. Testing fragment survival of the hard coral Acropora austera confirmed the assumption that wave action is an important factor shaping coral communities by only allowing this species to dominate in depths greater than 18m. Four hard- and five soft coral species were used to quantify the effects of sedimentation on the coral communities. It was demonstrated that long-term sedimentation had greater influence on soft corals than on hard corals, leading to tissue necroses and local bleaching. These experiments confirmed the assumption that sedimentation is a major forcing factor on South African coral communities. The final part of thesis provides management options for the St. Lucia and Maputaland Marine Reserves focussing on conservation of the coral communities. The findings obtained in the ecological investigation allowed to identify which activities in the reserves have to be controlled in order to minimize damage to the coral communities by park visitors.
Open Access
Triploid induction in the South African abalone, Haliotis midae
(1997) Stepto, Nigel Keith; Cook, Peter
An investigation was undertaken to determine whether triploidy could be induced and improve the growth rate of the South African abalone, Haliotis midae. From the polar body counts at 17 °C the release times of polar body 1 and 2 were found to be at 12 - 15 min. post insemination (pi.) and 33-36 min. pi. respectively. Cytochalasin B (CB) (0.5mg. 1-¹ seawater) and elevated temperature (30 °C) were used as stresses to induce triploidy. CB induced 48.4% polar body 1 and 70.9 % polar body 2 triploid larvae at 20 hrs pi. At 120 hrs pi. induction rates were 55.5% and 62.4% respectively. Temperature induction was more successful, producing 92.9% polar body 1 and 86.4% polar body 2 triploid larvae at 20 hrs pi. This success was still evident at 120 hrs pi, where 71.1 % polar body 1 and 62.5% polar body 2 triploid larvae were produced. In the CB induction, where polar body 1 was retained, there was a pronounced production of tetraploid larvae (34. 2%). It appeared that CB affected the ova's resistance to polyspermy, which was found to be dependent on both CB concentration and the amount of excess sperm present. At 0.4 mg 1-¹ CB in seawater, 86.5% triploids and 0% tetraploids were produced. However, on the addition of sperm, 25.4% triploids and 69% tetraploids resulted. CB (0.5 mg 1-¹ ) in seawater produced 42.6%> tetraploids which, after the addition of sperm, increased even further to 50. l % pentaploids. Larval survival was found to be low overall with only 17% and 22% of control (diploid) animals surviving the rearing period, in the temperature and CB treatments respectively. The survival rates of the polar body 2 treatment were 11 % and 15% whilst those of the polar body 1 treatment were 7% and 11 %. Although these percentages indicated a difference in survival rates between the CB and temperature inductions, the actual numbers of larvae surviving were the same. The polar body 1 triploid larval survival was significantly less than both control and polar body 2 triploid animals.

Browsing by Author "Cook, Peter"

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