No description available.

<p> Three new virus diseases are described in larvae of the midge, Chironomus plumosus. The intracellular development of one of these, CpV-1, in the fat body and muscle of this insect is given in detail. In addition, the ultrastructure of the virion is described. Classification of the known icosahedral cytoplasmic DNA viruses is discussed. </p> <p> The development of a cytoplasmic polyhedrosis virus in the midgut is examined. Observations are discussed in relation to knowledge concerning other polyhedrosis viruses, and possible evolutionary pathways among them. </p> <p> A cytoplasmic polyhedrosis of the fat body is described for the first time. The ultrastructure of the viral capsid is compared to that of the bacteriophage X 174. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.

This thesis was conducted to evaluate the potential of obtaining yellow perch eggs and fry by controlling the reproductive cycle of broodfish and the techniques used to rear the resulting fry. Chapter 1 is a review of literature pertaining to yellow perch culture and related topics. Chapter 2 is a study of yellow perch broodstock exposed to a 6-month, artificial photothermal cycle and injected with LHRHa and pimozide to induce spawning. The mean gonadosomatic index for manipulated females was 24.2% and the mean fertility of eggs from manipulated females was 26.5%. The fertilization rate was significantly greater among strip-spawned females than tank spawned females (p < 0.05). The time to ovulation after injection showed a negative correlation (r2 = 0.505) with the mean oocyte diameter of manipulated females. Chapter 3 is a study comparing the performance of larval yellow perch reared in a recirculating system fed only live rotifers (T1), in a recirculating system fed live rotifers and an artificial diet (T2) and in a greenwater system (T3). Survival was low in all treatments. The specific growth rate did not differ among treatments over the first 6 days. The percentage of fry with inflated swimbladders and absorbed yolksacs did not differ by day 6. While T3 larvae began ingesting food earlier than T1 and T2, the percentage of fry ingesting food did not differ among treatments by day 6 (p >0.1). The total percentage of skeletal deformities was greater in T3 than either T1 or T2 (p < 0.05) and may have been due to excessive handling of T3 larvae during hatch-out. Chapter 4 outlines the costs associated with a yellow perch hatchery designed around photothermally manipulated broodstock. This hatchery model produces four separate spawns annually, yielding 644,000 fingerlings year-1. Including start-up, fixed and variable costs, such a facility can produce 3" (76mm) fingerlings for $0.20 fingerling-1 for the first 5 years of operation, $0.16 fingerling-1 for the second 5 years and $0.06 fingerling-1 after 10 years. / Master of Science

The major bottleneck during the domestication of the white-margined sole Dagetichthys marginatus in South Africa has been low larval survival. The cause of this is not clear but considering current literature on flatfish culture and more specifically soleid culture, nutritional deficiencies are hypothesized to be the main possible cause. Following the importance of nutrition, the first aim of the research was to use an ontogenetic developmental approach to develop a species specific larval feeding strategy. Ontogenetic development of D. marginatus showed that weaning will take place at much later ages than other soleids currently being farmed. This makes the partial replacement of Artemia with a suitable inert diet in co-feeding strategies very important to cut the cost associated of live food production. This leads on to the second aim, in which an 'in vitro' approach was used to model the digestibility of Artemia, which could ultimately contribute towards designing inert feeds with similar digestibility characteristics to Artemia in the future. Obtaining nutrients from food is closely linked to the functional status of the digestive tract, the support organs and the external morphological characteristics required for the ingestion of live or inert feeds. Considering both morphological and physiological ontogenetic development, it is clear that D. marginatus follow a similar pattern to other soleids. Larvae can successfully feed on Artemia as early as 3 days after hatching but exhibit a slow metamorphosis into the juvenile stage when compared to other soleids. The absence of any detectable acidic protease activity during the first 45 days of development and the importance of exogenous enzymes from Artemia all points to limited capacity to digest artificial diets. Prior to modelling the 'in vitro' digestion of Artemia, digestive enzyme activity at different pH's were modelled using functional forms from the normal distributive category of functions. / As there is no substantiated information for the general effects of pH on enzyme activity in the literature for finfish larvae, three species occurring in the same bio-geographical region of Dagetichthys marginatus, namely Sarpa salpa, Diplodus sargus capensis and Argyrosomus japonicus were used to investigate this effect. The fitted parameters, namely the optimal pH and sigma (the slope around the optimal pH) showed two interesting results. When using a negative log likelihood ratio test to test for differences between species for a particular enzyme, the optimal pH for alkaline proteases (7.67), lipase (8.03), amylase (7.69) and phosphatase (9.84) activity was the same for all three species. Furthermore, the study illustrated the potential to detect dietary shifts during ontogenetic development based on changes in enzyme activity around the optimal pH using the sigma parameter. Sarpa salpa showed increased amylase activity and a decrease in protease activity around the optimal pH with increased size, corresponding to a change in diet from zooplankton to algae. The 'in vitro' modelling approach taken in this study was based on known enzyme interactions and dynamics which makes the results very interpretable. from Artemia is achieved based on gut evacuation time and enzyme levels. This 'in vitro' study furthermore clearly indicates the importance of exogenous enzymes from Artemia, contributing as much as 54 percent to protein digestion and 64 – 72 percent to carbohydrate digestion. This was however, only an initial investigation, and further expansion of the model is required to achieve a complete understanding of Artemia digestion and ultimately partial replacement with artificial diets. A feeding strategy for D. marginatus should therefore follow those of other farmed soleids, although there will be a general delay in implementation due to slower development. Problems can thus be solved and improvements made by transferring technology from other soleids to D. marginatus.

Call number: LD2668 .T4 1956 O32 / Master of Science

Call number: LD2668 .T4 1965 L332 / Master of Science

No description available.

Due to high mortality encountered by marine fish larvae during their first weeks of life, small changes in the number of individuals surviving through this period can cause large fluctuations in year-class strength. Larval Red Drum (Sciaenops ocellatus) are dependent upon structured estuarine habitat to avoid predation. A study of post-settlement larval Red Drum distribution in a subtropical seagrass meadow in Mission-Aransas Estuary, Texas, USA indicates that larvae settle over approximately two months. Abundance of larger settled larvae was significantly different among sites. The areas of highest larval abundance varied temporally, indicating that the entire extent of the seagrass bed is utilized. Regression analysis of abiotic environmental factors did not explain why larvae were more abundant at particular sites. To characterize the structure and variability of the fish species assemblage that Red Drum encounter upon settlement, larvae and juveniles were captured in the seagrass meadow during weekly collections. Of the 32 fish species collected, seven represented 92% of the assemblage. Multivariate species analysis indicated that collections widely separated in time and space shared the lowest Bray-Curtis similarity. Because Red Drum settle over a relatively long period and co-occur at body sizes known to cause cannibalism under laboratory conditions, I tested combinations of small and large Red Drum larvae at various field-realistic densities and at different levels of seagrass habitat structure to determine potential for cannibalism. Artificial seagrass did not protect small (5 – 6 mm SL) larvae from cannibalism, but natural dense seagrass had a protective effect relative to edge habitat. The final component of this research examined the emergent impacts of a common predator pinfish (Lagodon rhomboides) on mortality and cannibalistic interactions between small and large Red Drum larvae. Both pinfish and large Red Drum larvae alone readily consumed small Red Drum in all seagrass habitat structures tested. However, the combined treatment of pinfish and large Red Drum together led to reduced mortality of small Red Drum. Predation can significantly affect Red Drum survival during the post-settlement period, and multiple predators may have a protective effect on the smallest settlers if predation pressure is re-directed towards a larger size class. / text

The Large Copper butterfly, Lycaena dispar, is extinct in Britain and rapidly declining in the rest of Europe, due predominantly to loss of its wetland habitats. In the Netherlands the sub-species L. d. batavus is at the edge of its range in Northern Europe and, as with most marginal butterflies, has more specialised food plant and habitat requirements than the core populations of L. d. ruti/us. The aim of this study was to investigate some of the reasons for its continuing rarity, particularly looking at the reasons for its specialisation on Rumex hydrolapathum in a fen land habitat, whilst L. d. ruti/us is more generalist and utilises a range of Rumex species. Laboratory experiments reveal that L. d. batavus has retained its ability to feed on other Rumex species, without detriment to their overall survival and can utilise these alternative host plants more efficiently than their natural host plant. This indicates that plant chemistry is not responsible for their lack of utilisation in the wild. Field experiments have also shown these potential hosts can support larvae, throughout each of their larval stages, to maturity within a natural habitat, with no significant differences in survival rates compared with R. hydrolapathum. Investigations into adult female oviposition preferences were undertaken. Females showed a willingness to oviposit on alternative Rumex and expressed no preference for any particular plant species. There are plans to re-establish L. dispar into Britain in the near future, dependent upon the location of a suitable donor population. Allozyme electrophoresis work on L. dispar and several of its captive colonies, has revealed that the wild Dutch, and one captive population, have sufficiently high levels of genetic diversity that may enable a reestablishment programme to go ahead with a captive colony, if necessary.