Growth and mortality of the chinese clam (chione gnidia) were examined in the Estuary of La Cruz, Sonora, Mexico from 1987 to 1989. Clams were reared in trays in two habitats of the Estuary of La Cruz, the pool and the canal, where four experiments were carried out. In experiment 1 growth and mortality under two densities and two environments was assessed. Experiment 2 yielded information on growth and mortality of clams growing on four different substrates and at two densities. Experiment 3 assessed growth and mortality in high density conditions, and experiment 4 assessed growth after a period of growth stagnation. In all cases, highly significant differences in growth and mortality were observed between environments. The pool was found to be the place where higher total growth and least mortality occurred. However, the sizes achieved by clams in the pool suggest that the Estuary of La Cruz is not a suitable environment for the cultivation of this clam, and that the introduction of C. gnidia in this area is not feasible under present habitat conditions.

<p> Daily ring formation has been validated for a variety of fish species, but there is little known information or data on ageing young of year Alligator Gar (<i>Atractosteus spatula</i>). Artificially spawned Alligator Gar fry with a known spawn date, hatch date, and swim-up date were stocked into two ponds at Tishomingo National Fish Hatchery and reared from 9 to 91 days post-hatch. Up to 10 individuals were sampled each week, and age in days was estimated from counts of presumptive daily rings in the otoliths (sagittae, lapilli, and astericsi). Mean daily ring count and known age were closely related to swim-up (sagitta r² = 0.98, lapillus r² = 0.99, asteriscus r² = 0.93) indicating that daily ring deposition occurred in the otoliths of Alligator Gar 2 days after swim-up. Daily increment counts were accurate through 73 (sagitta), 86 (lapillus), however accuracy for asteriscus was very low throughout 86 days from swim-up. Age-bias plot for the lapillus visually showed no bias between readers. The resulting regression of ring counts against known age (age = -0.96 + 1.03*estimated age) was applied to wild caught Alligator Gar collected in the summer of 2013 from Lake Texoma, Oklahoma, to estimate spawn dates. Spawn dates seem to coincide with rising pool elevation of Lake Texoma and water pulses of tributaries.</p>

One of the main environmental impacts of salmon aquaculture activities in the Bay of Fundy is the alteration of sediment chemistry as a result of the large amount of organic waste that accumulates below fish pens. To investigate these impacts, vertical profiles of delta13C, delta 15N, Corg, Corg:Ntot, FeHC1 , MnHCl, Ptot, PHCl, SO4 2-, AVS, Hgtot, and Hgpyrite in sediment cores collected throughout the bay were acquired. These profiles were then used to identify tracers of aquaculture activities and their impact on the redox zonation of the sediment. In addition, representative samples of fish food as well as farmed and wild salmon were analyzed to determine their Hg tot content as well as delta13C, delta15N, Corg, Corg:Ntot. / Our results show that, as by-products of salmon aquaculture (e.g., uneaten food, feces, antibiotics, and anti-fouling agents) accumulate in the sediments, their reactive organic carbon content increases and generate a greater oxygen demand. Subsequently, an upwards migration of the oxygen penetration depth and redox boundaries in the sediment column occurs, which is confirmed on the basis of the distribution of redoxsensitive phases (e.g., authigenic metal oxides and AVS) in the sediments. High resolution voltammetric microelectrode measurements show that the FeHCl and MnHCl distributions overestimate the oxygen penetration depth in the sediments. The total phosphorus distribution in the sediment record is shown to be a suitable tracer of marine aquaculture, reflecting the recent history of residual feed and fecal matter accumulation in the sediments. / Elevated mercury concentrations in sediments under fish pens are explained by its strong affinity for organic carbon. Although the source of additional Hg has yet to be resolved, as the organic carbon content of the sediments increases in response to the input from fish farming activities, so does the associated Hg. Mercury also partitions strongly to authigenic pyrite in the deeper sulfidic sediments. Of the few farmed Atlantic salmon analyzed, mercury levels were not elevated compared to the concentrations of mercury in the wild salmon captured in two rivers of the Canadian east coast.

Red drum (Sciaenops ocellata) from seven of the nine major embayments of the Texas Gulf Coast were electrophoretically analysed for genetic variability. Indices of genetic similarity and distance were derived, as well as estimates of genetic divergence between bays. Cluster analysis phenograms were developed, and possible causes for population structure were addressed. Forty presumptive loci were screened, of which 30 proved to be of value for genetic population analysis. Percent polymorphic loci and heterozygosity/locus/individual ranged from 6.7%-13.3% and 0.025-0.042 respectively. These values were lower than those reported in similar studies, including some dealing specifically with Sciaenidae, but remained within the range reported for teleosts in general. A total of thirteen tests of genetic similarity/distance were performed. Of these tests, no segregation below a genetic identity of 0.95 was detected in those samples large enough to statistically satisfy the analysis. Upon exclusion of the small samples, no differentiation below 0.97 was demonstrated. Contingency chi-square tests and F-Statistics found only extremely low levels of divergence. Indeed, none of the divergence indicated was significant in terms of distinction of subpopulations among bays. This lack of differentiation in spite of apparently low levels of interbay migration was explained as a function of the dichotomus life stages. While juveniles are geographically isolated, adults occupy the open waters of the Gulf of Mexico, and have yet to be thoroughly described from either a life history or reproductive strategy viewpoint. The indicated single stock of reproductively active red drum in the Gulf requires further investigation, in order to accurately determine migrational habits as well as breeding success. The implications for management of the fishery at present are to regulate the resource as a single stock; as well as institute a comprehensive physical and biochemical study for future policy formulation.

<p> Environmentally-derived elemental and isotopic ratios in the otoliths of anadromous river herring (alewife, <i>Alosa pseudoharengus,</i> and blueback herring, <i>A. aestivalis</i>) were used to distinguish among groups of fish at spatial scales ranging from sub-populations within a watershed to populations from throughout the species' ranges. These ratios were also used to understand early life migrations and habitat use within and among populations. Sub-populations within the Hudson River, NY were accurately distinguished (> 95%), and populations from the Hudson River and Long Island, NY were distinct from each other and outgroups at varying distances, but accurate classification was dependent on the inclusion of oxygen isotopic ratios. Populations from Maine to Florida showed strong separation based on otolith signatures excluding (&sim; 70%) and including (> 90%) oxygen isotopes. Reclassification accuracies improved for both models by including genetic results in a hierarchical assignment model. Though all natural tags were effective for stock discrimination, the accuracy varied depending on the markers included; while inclusion of oxygen isotopes resulted in the highest reclassification rates, accurate application requires intensive sampling because of high interannual variability. Genetic markers reduce the effects of interannual variation because they are generally stable over generations. </p><p> Variations in otolith chemistry across an otolith (i.e. the fish's life history) can provide information about movements among habitats and especially along salinity gradients. Juvenile alewife within the Hudson River, NY (a large watershed) moved among multiple freshwater habitats, and trends varied widely among individuals while in the Peconic River, NY (a small, coastal watershed) three distinct movement patterns were observed. Retrospective analysis of Hudson River adult otoliths showed that multiple nursery habitats contribute to the spawning stock. Throughout the coast, retrospective analysis of adult otoliths showed that juveniles used fresh waters, estuaries, or a combination of both as nursery habitats and migratory behavior varied among populations, and were correlated to the latitude of the watershed, the watershed area, the amount of accessible river kilometers, and the percentage of the watershed in urban use.</p>

<p>Aquatic food webs are comprised of complex spatial and temporal interactions within and among trophic levels. Human manipulations, such as construction of reservoirs, enhance uncertainties in our understanding of aquatic food web structure. Reservoirs are novel ecosystems which contain a unique composition of species. Species introductions into reservoirs may disrupt interactions within an already complex and poorly understood food web. In Scofield Reservoir in central Utah, a rapidly expanding population of Utah chub poses a detrimental threat to the blue-ribbon trout fishery. The Utah Division of Wildlife Resources has recently stocked cutthroat trout and tiger trout (a brown trout x brook trout hybrid) to potentially reduce Utah chub numbers as well as to enhance the sport fishery. I used standard fisheries techniques to describe food web interactions and to assess the potential for these piscivorous trout to control the expanding Utah chub population, as well as to determine sport fish performance and quantify diet overlap amongst top predators. Using bioenergetic modeling, I estimated very high rates of Utah chub consumption by cutthroat trout and tiger trout. These two species collectively display control of Utah chub, as the chub population is no longer exponentially increasing. Cutthroat trout and tiger trout are likely not food limited and convincingly exhibit high performance, as abundance of Utah chub is still extremely high. Both diet and stable isotope analysis showed significant overlap between these top piscivores in the reservoir, but also substantial overlap between cutthroat trout and rainbow trout with respect to Utah chub. Analysis of rainbow trout suggested this species is performing poorly; rainbow trout had extremely low catch rates and never switched to a piscivorous diet at larger sizes. Utah chub and rainbow trout had similar diet compositions, and thus rainbow trout may be competing (poorly) for food and space resources. This study contributes to our understanding of interspecific interactions among these unique assemblages of top predators in this artificial system. This research also provides knowledge to fisheries managers tasked with providing optimal sport fisheries in these artificial and dynamic systems, as well as expanding on our extremely limited knowledge of tiger trout ecology.

This thesis presents research on an alternative spatial-temporal method of fish stock assessment. We develop a simulation model of spatial-temporal stock analysis and compare its assessment with the common VPA/SPA method. In recent years, fisheries biologists have depended mainly on age structured aggregated sequential population analysis (SPA)/virtual population analysis (VPA) for stock assessment purposes. The VPA method is an aggregate model that consolidates all spatial and within-season temporal stock dynamics into a single total stock estimate. The proposed spatial-temporal method produces historical estimates of population size and fishing mortality rate by age and year. In this thesis, the abundance states of age-aggregated stock components are tracked in space over the course of each season using computer simulation. Data about fish stock spatial-temporal migration dynamics are used to estimate stock abundance in space and time over the course of a fishing season. The spatial-temporal assessment method is applied to the herring stock of the Scotia Fundy region of Atlantic Canada. The dynamics of the herring spawning groups are described and the simulation model is developed for a given season. The results suggest that disaggregated spatial-temporal estimates provide more information for in-season management of herring spawning groups than the traditional aggregate VPA approach.

The profitable rearing of the Atlantic salmon (Salmo salar L.) requires artificial diets high in carbohydrates or fats or both in order to avoid the high cost of protein feed; this practice is monitored by growth criteria such as animal length and body weight. The present study investigates the physiological state of hatchery-reared salmon smolts raised under cage culture conditions and fed a commercial pellet food of elevated carbohydrate content. Our results show metabolic disturbances that strongly suggest a diabetogenous situation: hyperglycemia, hypertriacylglycerolemia, some glucosuria and occasional ketonuria. Histopathological examination confirms the initial suggestion: significant reduction of the beta to alpha cell ratio in the islets of Langerhans, frequent alteration of the disposition of insular cells, hydropic changes in the B cells such as degranulation, vacuolization and nucleic pyknosis, evidence of hypertrophy and hyperplasia of B cells and pronounced neoformation of islet tissue. In addition, hyalinization of both the exocrine and the endocrine pancreas was observed as well as fibrosis, lipomatosis and microangiopathy of the exocrine acinar tissue and an increase in intrapancreatic nerve cell number. In conclusion, the smolts fed the pellet diet displayed a syndrome reminiscent of mammalian diabetes; a comparison is drawn between diabetes mellitus and the observed form of salmon diabetes. The study emphasizes the need to involve physiological criteria in the assessment of the suitability of artificial diets especially in the rearing of healthy salmon intended for restocking of natural environments.

The aim of this study, which is mainly osteological, is to clarify the status of the genera Cristivomer and Salvelinus. A morphometric and meristic study in conjunction with osteology was used to assess their phylogenetic relationships with other genera of Salmonidae. About 390 specimens of adult and adolescent fish and 268 eggs and fry were examined. Presently, seven genera are recognized in Salmonidae. The genus Cristivomer is separated from Salvelinus because of the shape of the supraethmoid, supramaxilla, subopercle, vomer, lingual plate, and caudal fin, and also the high number of pyloric caeca, presence of pearl organs, and breeding behaviour of the former. In the genus Salvelinus, S. alpinus (including various forms), S. malma, and S. fontinalis are distinguished. S. alpinus oquassa, previously known as S. marstoni, is considered a subspecies of S. alpinus. The two previously designated species S. oquassa and S. aureolus are synonymized with S. a. oquassa. S. timagamiensis is reduced to a sub-species of S. fontinalis. The genus Salmothymus is maintained. The genus Cristivomer is more generalized than Salvelinus. The species S. malma is intermediate between S. alpinus and S. fontinalis. For the first time a detailed osteological study of C. namaycush and several forms of Salvelinus is undertaken, and their relationships assessed.

No description available.