Striped bass larvae, native to the Shubenacadie River, catch invertebrates in darkness using mechanoreception via lateral line neuromasts. The neuromast total increased from 17 at first feeding (5 to 7 dph) to 135 by the juvenile stage (27 dph). A 5 mM neomycin dose ablated neuromasts, confirmed by fluorescent and confocal microscopy. In feeding trials, larvae with and without functional neuromasts were offered Artemia salina in darkness or light. To identify ontogenetic changes in feeding, experiments were repeated at 10, 13, 17, and 20 dph. In darkness, neomycin treated larvae caught fewer prey (~5 Artemia h-1 at all ages, p<0.05) than larvae with intact neuromasts (10 dph, 16 Artemia h-1; 20 dph, 72 Artemia h-1). In light, neomycin did not affect feeding, indicating no deleterious side-effects. Neomycin did not damage olfactory or taste cells judged by FM1-43FX and calretinin staining. The results support the contribution of mechanoreception to non-visual feeding. / Master's thesis

No description available.

The effect of Plagiorchis elegans cercariae on the vertical distribution of second, third, and fourth instar larvae of Aedes aegypti in the water column was studied in the laboratory. Under daytime conditions and in the absence of the parasite, larvae divided their time between the top and bottom of the water column. At night larvae spent the majority of their time at rest at the top of the column. In the presence of P. elegans cercariae larvae spent more time at rest at the surface under daytime conditions but increased their active time at the bottom under nighttime conditions. The presence of cercariae elicited escape and grooming responses and tended to reduce and fragment feeding activity.

Filter-feeding black fly larvae in lake outlet streams convert suspended bacteria and algae into benthic biomass, available to fish. Positive correlations between larval abundance and both bacterioplankton and phytoplankton were significant at the p < 0.10 level among 5 outlet streams of varying trophic status in the Eastern Townships of Quebec, and either food type alone explained &sim;28% of the variance in larval abundance among streams (Chapter 1), suggesting bacterioplankton and phytoplankton to play similar roles in larval distribution. However, when larvae were removed from 3 of 6 oligotrophic outlet streams examined in the Mauricie region of Quebec, calculated ingestion rates revealed larvae to ingest roughly 20 times more phytoplankton carbon than bacterial carbon (Chapter 2). Phytoplankton ingestion rates were high enough to satisfy daily carbon requirements, but bacterivory was low (Chapter 2), indicating that bacterial biomass contributes little to black fly diets in most systems, and will be less useful than phytoplankton biomass when using food to predict larval distribution. The majority of bacteria in streams form a carbon link to fish through sediment food webs, rather than through black fly larvae.

No description available.

The effects of food availability and the presence of the parasite, Plagiorchis elegans, on the probability of Aedes aegypti preimagos to transform from one immature stage to the next over consecutive 24- or 48-hour periods of time were determined. Under conditions of low food availability, 24- and 48-hr transition probabilities of all larval instars, to the next were reduced. Increases in food availability reversed this process, causing significant decreases in same-stage transition probabilities. However, as transition to successive stages increased among first, second, third and fourth instars, there was concomitant significant increase in first and fourth preimago mortality. Addition of Plagiorchis elegans cercariae caused significant decreases in the 24 and 48-hour same-state probabilities for all pre-imago stages. Successive stage transitions for first, second and third instars were significantly increased while those of fourth instars and pupae were significantly decreased following exposure to the parasites. The mortality of all preimago stages significantly increased with exposure to parasite, but was highest among fourth instars and pupae. There were strong food-by-parasite interaction effects among first, second and third instars. Differences in transition probabilities increased with increasing food levels between controlled and parasite-exposed groups. The opposite was true for fourth instars and pupae. While there was no significant interactive effect between food and the presence of the parasite on pupae regardless of food concentration, this was not true for mortality probabilities among fourth instars. Significantly more fourth instars died in response to parasite exposure and there were significant interactive effects of food and parasites on the probability of fourth instars transformation to pupae over 48 hrs.

The effects of food availability on the population structure of Aedes aegypti in the presence and absence of Plagiorchis elegans cercariae were studied in the laboratory. Under conditions of low food availability and in the absence of the parasite, larval population levels cycled at 40 day intervals. Cycles were initiated by the periodic build-up and decline of fourth instar larvae. These major competitors for food resources appear to be responsible for the release of a cascade of events which allowed the intermittent flow through of larvae from the first to the third instar. Under both optimal and suboptimal conditions of food availability, the introduction of high densities of P. elegans cercariae resulted in a decrease in the production of adult mosquitoes. Although the parasite reduced competition by preferentially removing fourth instar larvae and hastened the development of surviving instars, such survivors were exposed to the effects of the parasite as soon as they reached the fourth instar.

The buoyancy (or density = mass volume-1) of marine larval fish is influenced by their nutritional status, starved larvae being less dense than fed larvae of like age. Buoyancy has, therefore, been proposed as an indicator by which to assess the nutritional condition of marine fish larvae in experiments and in situ. It has also been hypothesized that larval fish experiencing advanced starvation will exhibit increased density due to water loss resulting from osmoregulatory breach and failure. The magnitude of osmoregulation-related changes in density has not been examined and its influence on interpretations of nutritional condition and vertical distributions are unknown. Through a series of controlled laboratory experiments performed on larvae of cod (Gadus morhua L.), I developed evidence that osmoregulatory breach and failure has a strong positive effect on the density of larval fish, and that this effect on density is not limited to larvae experiencing advanced stages of starvation. These effects of osmotic breach and failure are sufficient to obscure effects resulting exclusively from nutritionally caused changes in density. Hence, if not identified and controlled these osmotically driven density changes can bias parameterization of buoyancy-related condition indices. I developed methods for isolating nutritional and osmotic effects. This facilitated the calibration of a nutritionally based density index with which to evaluate the nutritional state of cod larvae. Comparison of the calibrated density assay with a suite of widely used indices of condition (morphometric, behavioural and biochemical) showed density to be superior in its capacity to correctly classify larvae with respect to their nutritional state. The density index was also less subject to bias resulting from uncontrolled changes in larval size. A linear regression model based on these findings was developed to assess the relationship between density as an index of condition and near-term larval

This thesis has examined the influence of the environment on aspects of the acute stress response in juvenile and pro-larval Acipenser fulvescens.The acute stress response was examined in grouped and isolated juveniles. Catecholamines significantly increased in both treatments one minute post-stress and plasma glucose was significantly higher in isolated as compared to grouped fish one minute post-stress. In the second series of experiments fertilized eggs of A. fulvescens were raised at 9, 12 & 15°C. Chromaffin-like cells were studied using light and electron microscopy techniques. Development of renal tissue was also examined in these treatment groups. Two populations of chromaffin-like cells were identified, one in close association with the proximal tubule of the kidney, and the other in close association with the neural tube. Results suggest this latter population were immature pheochromoblast like-cells. Development of renal tissue followed a predictable pattern that was most rapid in the 15°C treatment.

As water depth increased, fourth instar larvae of the mosquito Aedes aegypti required progressively more time to reach the pupal stage, more individuals died or were disabled and the resulting adults were significantly smaller. Water depth affected females more severely than males and the developmental time of larvae was affected more than adult mass. Time spent by fourth instar female larvae in the feeding zone during the first five hours predicted the time to subsequent pupation. Thereafter, mean feeding time was a determining factor of subsequent adult mass. With increasing water depth, both the prepupal resting period and mean time spent in the feeding zone per feeding bout increased, whereas behavior frequency (determined by an activity index) decreased.