Typescript, etc. / Digitized by Kansas State University Libraries

Typescript, etc. / Digitized by Kansas State University Libraries

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Call number: LD2668 .T4 1929 S31

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The aim of this study was to improve the rearing of common clownfish Amphiprion percula, by weaning juveniles from a live feed to a formulated feed as early as possible, while still maintaining good growth and survival. The growth response of A. percula to a formulated dry feed was initially investigated. There was no difference in growth rate of juveniles fed a formulated feed, and the formulated feed supplemented with either Artemia or a Donax serra / Penaeus indicus combination. Amphiprion percula readily consumed the formulated feed, and the fishmeal/casein combination appeared an acceptable protein source. As the amount of protein included in a diet can have a profound effect on growth, the optimal dietary protein level for juvenile A. percula was investigated by feeding semipurified diets containing graded levels of protein, ranging from 40-65%. There was no difference in the growth rates of juveniles fed the various diets, however all diets promoted good growth with an average weight gain of 419%, and thus for the purposes of this study the diet formulation was deemed adequate. The histological study of the digestive system of larval A. percula revealed that the alimentary canal was advanced at hatching and that larvae start exogenous feeding immediately. Three days after hatch (DAH) the yolk sac is completely absorbed. In the hind-gut epithelium of 5-day-old larvae small supranuclear inclusion vacuoles appear, suggesting pinocytotic digestion, and by 7 DAH gastric glands are established in the epithelium of the stomach. Nine DAH supranuclear inclusion vacuoles appear in the epithelium of the mid-gut, indicating extracellular digestion and absorption across the lumen. As pinocytotic digestion of protein is less efficient than extracellular digestion, especially in the case of formulated feeds, it was hypothesised that the digestive system of A. percula could only effectively digest formulated feeds 9 DAH onwards. The two weaning experiments designed to test this hypothesis revealed that A. percula was able to utilise the formulated feed, without reduction in survival, from 7 DAH onwards. However, in terms of growth, the optimal time to wean juveniles from the live feed to the formulated dry feed was between 15 to 20 DAH. As A. percula accept a formulated feed and can benefit nutritionally from it, the dependence of larvae and juveniles on live feed can be reduced. This study has shown that the rearing of A. percula can been simplified and improved by weaning from 7 DAH with no reduction in survival, and from 15 to 20 DAH with no reduction in growth.

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

The effect of impoundment size on fish has been investigated. Investigators have reported that greatest growth has taken place in large in some instances and in small impoundments in others. The effect of varying space on the cichlid Aequidens pulcher Gill, was examined in four tanks of equal volume. Each tank was divided into two replicates in the compartment ratios 9:3:1 and each contained 90:30:10 fish respectively. A higher density tank had twice the fish number in all compartments and had lowest growth due to either reduced oxygen availability, increased biomass, increase in activity or stress due to small nearest neighbour distances. Fish in a tank with mirrors on all compartment walls had a reduced growth possibly due to visual stress compared to a control lacking mirrors. A further tank had twice the surface area of the control, a greater distance between nearest neighbours and greatest fish growth. Growth was significantly greater, at the 95 percent confidence limit, in all small compartments of tanks and activity was significantly greater in large compartments. In an identical treatment design to that of the control fish were shown to lose weight while being starved. The fish in the larger compartments were more active and lost most weight. A strong suggestion that the lower growth rate in large compartments was due to greater activity, possibly this was related to the total available swimming space per fish. Fish aggression was greatest in small compartments and decreased over time, possibly as a result of conditioning. / Science, Faculty of / Zoology, Department of / Graduate

Otolith growth in young fishes occurs with a circadian periodicity, resulting in a concentric growth record of calcareous material. The resultant sequence of daily growth increments is often punctuated by prominent checks (discontinuities). Yet little is known of those variables that may control or modify the production of one increment per day and/or checks. The objective of this thesis was threefold: 1) to assess the influence of some environmental variables on daily increment production 2) to develop a mechanism and explanation for check formation 3) to interpret the otolith microstructure of wild fishes in terms of knowledge gained from the first two objectives. The influence of light and temperature on daily increment formation was the subject of the first experiment. Tetracycline injected into juvenile starry flounders (Platichthys stellatus) was incorporated into the periphery of the sagittal otoliths within 24 h. The resulting band, visible under ultraviolet light, was used as a dated mark on the otolith growth increments. This technique was used to verify that increments were laid down on a daily basis, both in field and laboratory environments. Sub-daily increments were visible in otoliths of fishes reared under most environmental conditions. The production of daily increments in juvenile starry flounders preconditioned to a natural environmental regime was unaffected by photoperiod or temperature fluctuation, suggesting the presence of an internal circadian rhythm. Juvenile steelhead trout (Salmo gairdneri) and starry flounders were reared 64-76 d under various experimental feeding regimes to determine if feeding periodicity influenced the production of daily growth increments on the otoliths. Both species produced daily increments when fed thrice daily, daily or once every three days, as well as through 26-32 d of starvation. Daily growth increments were also deposited in vateritic ("crystalline") otoliths, which comprised 27% of the trout sagittae sampled. Feeding frequency affected increment appearance and the incidence of subdaily increments in trout, but not in flounders. The difference in effect was probably due to the higher metabolic rate of trout. Increment deposition in all flounders was far more variable than in trout, and some flounders apparently ceased increment formation altogether. Since the results of the first two experiments were apparently contrary to some previous studies, I suspected that age may interact with light and/or temperature to influence otolith growth. Plainfin midshipman, Porichthys notatus, were reared in the laboratory under three environmental regimes to determine the influence of certain variables upon otolith growth increment formation. Both larval and juvenile midshipman were used to test diel cycles and constant conditions of light and temperature. In the absence of a diel photoperiod, daily growth increments were not formed upon hatch. However, after an acclimation period of 2-3 wk, an endogenous circadian rhythm became evident, resulting in daily increment production. With increasing age, the influence of light as a zeitgeber decreased, while daily increments became more prominent in all environments. Temperature fluctuation affected increment appearance, but did not entrain increment deposition. Periods of stress can disrupt daily growth increment formation on a fish otolith, producing a check (discontinuity). Calcium-45 was used to monitor calcium deposition on the sagittae of coho salmon, Oncorhynchus kisutch, during periods of check formation. "5Ca deposition on the otolith continued for 12 hr after transfer from a5Ca water. When stress was applied during fl5Ca immersion, tt5Ca deposition was reduced. However, stress applied immediately after transfer from a5Ca water had no effect on U5Ca deposition. Stress indirectly disrupted *5Ca deposition on the otolith through a reduction in branchial uptake of calcium. Check formation was not associated with resorption of otolith calcium. "Lunar" growth patterns have been observed in the otoliths of many marine fishes. I examined the otolith microstructure of juvenile starry flounders sampled from a monitored environment for evidence of lunar periodicity. Three types of biweekly cycles were observed in all of the flounder otoliths; two of the cycles were correlated with a tidal modulation of the environment. Through a multiple regression model, much of the day-to-day variability in daily increment width could be explained by daily variations in temperature, salinity and tidal mixing. My results suggest that a 15-d increment width cycle was entrained by the interaction of a 15-d tidal cycle with temperature and salinity. The same tidal cycle/temperature interaction probably produced a semi-lunar pattern of increment contrast. However, the presence of otolith checks formed at weekly and/or biweekly intervals could not be so explained, although checks were consistently formed on the new and full moons. / Science, Faculty of / Zoology, Department of / Graduate

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