No description available.

No description available.

This study was undertaken to try to delay gonadal maturation of pink salmon for one year beyond their normal two year life cycle. This would allow these fish to spawn in years of low or nonexistent escapement and possibly increase these "poor" year populations. Three experiments were conducted to investigate the efficacy of the antigonadotropic drug, methallibure, in inhibiting gonadal maturation in pink salmon. Gonadosomatic index, oocyte diameter, and stages of cell maturation in the testis and oocyte maturation in the ovary were measured. The first or pilot experiment involved a range of doses of methallibure (0.10 mg., 0.32 mg., and 1.0 mg./gm./2wks.) to determine the optimal dose for subsequent experiments. All doses had only a slight slowing effect on maturation. This result and possible undesirable effects of higher doses prompted the decision to use the 0.10 mg./gm. dose for subsequent experiments. The second or long-term experiment investigated the effects of methallibure and a constant 12 hours light:12 hours dark photoperiod on gonadal maturation of males and females for a period of ten months. Methallibure completely inhibited testicular maturation by preventing the transformation of primary into secondary spermatogonia. Ovarian maturation, however, was only slowed. The treated ovaries possessed oocytes in the oil globule stage while control ovaries had oocytes in the secondary yolk globule stage. Methallibure had an antithyroidal effect under natural photoperiod but not under constant 12L:12D photoperiod or at a high dose (1.0 mg./gm). Stress from kidney disease may have been operative in this effect. Methallibure also slowed the rate of increase in body weight. The constant 12L:12D photoperiod slowed gonadal maturation in both males and females. It is suggested that a specific day-length and an endogenous rhythm stimulate the initiation, maintenance, and termination of gonadal maturation and that the seasonal daylength fluctuations function as a synchronizer. The difference in effect of methallibure on males and females may be due to treatment beginning prior to the start of testicular maturation but after the start of vitellogenesis. To investigate this possibility, methallibure treatment was begun at successive intervals prior to the start of vitellogenesis in the third or sequential experiment. This treatment had no effect on ovarian maturation which suggests that the females are less sensitive to methallibure than are the males. Treatment with a higher dose started early in juvenile life may inhibit ovarian maturation. From this study, only the males could be delayed and, therefore, possibly spawn in "poor" years. However, Funk and Donaldson (1972) were able to achieve the same goal by maturing males in the year of hatching, thus making a three year program impractical. The value of a long program would be the delay of ovarian maturation since Funk et al. (1973) were unable to advance maturation of females by one year. / Science, Faculty of / Zoology, Department of / Graduate

Anadromous pink salmon undergo several migratory movements between different habitats during their life history. These migrations are accurately timed on a seasonal basis. Annual rhythms or seasonally-timed events may result from interactions between daily rhythms and annual changes in environmental factors. Therefore, knowledge of daily behavioral rhythms in pink salmon may improve our current poor understanding of the seasonal timing of its migrations. Hence, the objective of this study was to investigate, in a seasonal context and mainly under laboratory conditions, diel rhythms of ecologically-relevant behavior in juvenile pink salmon, and their timing mechanisms. Fry emergence from a simulated gravel redd in fresh water was mainly nocturnal below 13°C. Diel emergence timing was synchronized with the onset of night, but was affected by temperature in a non-linear manner. Temperature affected negatively the duration of the intra-gravel alevin stage and the rate of emergence. Nocturnal emergence was considered an anti-predator adaptation. Fry exhibited mainly nocturnal rhythms of swimming activity and of vertical distribution during the first week after emergence. However, a gradual shift from a nocturnal to a diurnal swimming activity rhythm occurred 7 to 13 days after emergence, when wild fish are residing in estuaries and adjacent coastal waters. Coincident with this shift was an increasing tendency of the fry to swimnnear the water surface during the day. This suggested a weakening of their negative phototactic response during this period. Thereafter, the fish usually displayed diurnal rhythms of swimming activity and nocturnal rhythms of vertical distribution. The ontogenetic shift in the phase of the activity rhythm and in photobehavior was considered adaptive for schooling and feeding during the day. Wild fry fed mainly during daylight hours in littoral areas of two marine bays. However, their feeding rhythms varied among study sites. Laboratory experiments showed that hunger level affected fish feeding rate and ration consumed positively. Fish fed continuously on live copepods under idealized laboratory conditions. During a 12-h session they rapidly (< 30 min) filled their stomachs with prey; thereafter, they maintained their stomachs full by feeding at a rate that balanced the rate of evacuation of prey from the stomach. Hence, I concluded that pink salmon have flexible feeding activity rhythms, which may permit opportunistic exploitation of prey, and feed at a relatively low hunger threshold. This feeding strategy may explain in part their relatively high growth rates in nature. During the periods corresponding to their juvenile coastal and pelagic ocean phases, the fish exhibited generally diurnal rhythms of swimming activity and of aggression, and nocturnal rhythms of vertical distribution in response to simulated seasonal photoperiodic and temperature changes. These rhythms were synchronized with the artificial light-dark (LD) cycle throughout most of the year. Some parameters of these rhythms varied on a seasonal basis, but not according to the Aschoff-Wever model. Mean swimming speed, the degree of diurnalism of the swimming activity rhythm, and the timing of the daily peak of the rhythms were affected by daylength. Hence, photoperiod might be an important proximate factor that pink salmon use to time their oceanic migration on a seasonal basis. Some data suggested the existence of an endogenous, circadian activity rhythm, and thus a daily "clock", in pink salmon. However, this remains uncertain. The free-running period of their activity rhythm was not related negatively to constant light intensity, as predicted by the Circadian Rule. The LD cycle affected directly swimming activity (masking), rather than entraining an endogenous circadian system. Since the activity rhythm of pink salmon does not possess a strong endogenous component, it is doubtful that the seasonal timing of its migrations results from interactions between a circadian clock and seasonal changes in environmental factors. However, the flexibility and inter-individual variability of their behavioral rhythms may be adaptive responses to the instability and heterogeneity of the marine environment. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

No description available.

No description available.

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No description available.

Two fungi that cause disease on onion in the Mid Murray region of South Australia were investigated. These were Fusarium oxysporum f. sp. cepae, the cause of damping off of seedlings, wilting in the field, and basal rot in storage, and Phoma terrestris, which causes pink root. The aim of the study was to investigate resistant or tolerant cultivars and crop rotations as possible management strategies for these diseases. Several Fusarium spp. were isolated from onion roots and bulbs in the field, onion bulbs in storage, soil, and onion seed. All isolates were tested for pathogenicity by various means, however, none caused disease and therefore could not be identified conclusively as F. oxysporum f. sp. cepae. As a result research on Fusarium was discontinued. Pink discolouration was detected on onion roots in commercial crops at Bowhill, South Australia, and isolation of P. terrestris from roots was attempted. Several published and novel methods were employed with variable success. Only one of the published methods yielded P. terrestris, but results were inconsistent. Two methods developed in this study permitted isolation of P. terrestris. In both cases, infested plant material was incubated on wheat straw agar (WSA), which turns pink in the presence of P. terrestris. One method involved soaking surface sterilised pink-pigmented wheat straw in solution, at approximately 24ºC for 2 days, and then spreading 1 ml of the resulting suspension on acidified potato dextrose agar (APDA) and incubating for a further 7 to 10 days. The second method involved dispensing warm sterile water into a plate of pink-pigmented WSA, agitating the plate, and spreading 1 ml aliquots onto APDA, and incubating for 7 to 10 days. One isolate of P. terrestris, shown to be pathogenic to onion was used in subsequent experiments. Several brown onion cultivars commonly grown in the Mid Murray region of South Australia, or marketed as tolerant to pink root, were examined for susceptibility to infection by P. terrestris. Seven cultivars were tested in vitro, and seedlings of eight cultivars were grown in a greenhouse for 4 months in soil naturally infested with P. terrestris. Selected cultivars were also evaluated in the field. Of the cultivars tested, none was significantly less susceptible to infection by P. terrestris than any other as indicated by pink pigment on WSA. Cereals such as wheat, oat and barley, as well as lucerne and canola, are grown in rotation with onion to provide ground cover, to minimise soil erosion and reduce inoculum of pathogens between onion crops. As the susceptibility of these rotation crops to P. terrestris was not known, several were tested in the field and in the greenhouse for their ability to act as hosts for P. terrestris. Likewise, the potential of weeds commonly found in onion fields to act as hosts of P. terrestris was investigated. Less P. terrestris was detected in the roots of plants of oat cultivars Marloo and Swan, as well as barley cultivars Galleon and Schooner than of most other crops tested and, thus, these cvs were considered less likely to act as hosts of P. terrestris. Weeds such as Brassica tournefortii, Portulaca oleracea and Oxalis pes-caprae collected from the field were infected by P. terrestris, whereas P. terrestris was not detected in the roots of Chenopodium album. In summary, new methods for isolation of P. terrestris were identified and may, with further development, aid in research on pink root. The onion cultivars tested in this study did not differ in susceptibility to pink root, but more cultivars should be tested. P. terrestris infected a range of other crops and weeds, and it is recommended that further work is conducted in this area to facilitate cultural management of onion crops to minimise build up of inoculum in the soil. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1473377 / Thesis (M.Ag.Sc.) -- University of Adelaide, School of Agriculture, Food and Wine, 2009