Common snook (Centropomus undecimalis) is a relatively new species for aquaculture; considered as a recreational species and not commercial. The aim of this study was to develop common snook larval rearing techniques for stock enhancement. Common snook culture has two main bottlenecks, broodstock management and larval culture. High mortality during the first 6 days is the main limitation for successful larval survival. Broodstock management of common snook is still developing and the only source of common snook eggs is from wild broodstock. Securing a regular supply during the natural spawning was essential to reach the main objective. Finding the optimal spawning sites, as well as optimal spawning time was achieved. Results showed Terra Ceia, Longboat and Cayo Costa to be the best sites for wild broodstock collection. The onset of spawning was triggered by a rise in water temperature. During the 4 years of this study spawning started at the end of May and finished in September. Total capture results and egg quality results, such as fertilization, hatching rate and lipid analysis, indicated June and July as the peak months during the spawning season. Common snook follow a lunar spawning cycle. Results showed that one to three days after the new and full moon were the peak spawning periods and therefore the best days to capture wild stock. Common snook egg lipid composition fits the general marine fish fatty acid composition with saturated fatty acids predominating. On the other hand, the omega 3, omega 6 (n-3/n-6) ratio was lower than the typical marine fish and arachidonic acid values were significantly higher than other marine species. This egg fatty acid profile will be helpful in the future to compare it with captive spawned eggs for egg quality purposes. Description of the common snook embryonic and larval development for the first 14 days was carried out. This has strengthened knowledge for this species’ development, and should provide a helpful tool to identify common snook embryos and larvae in the wild. Novel improvements to existing common snook larval culture protocols were implemented. Larval lipid analysis throughout development, and high mortality around day 6 post hatching, suggested that common snook larvae were dying of starvation. Gross morphological development and ultra-structure findings in the digestive and eye system development during the first three days indicated that day 2 post hatching larvae were capable of capturing and digesting food. Additionally, larval nutritional improvements were made, increasing the larval survival. The most significant ones were: finding a smaller and more nutritional prey (SS type rotifers and copepods), finding an optimal stocking and feeding density and the importance that green water technique has on larval survival. Overall, larval success was improved from a zero percent survival during the first 14 days to a 2% survival rate.

Advances in aquaculture technologies are being investigated to support the replenishment of local fisheries, develop marine food fish farming opportunities and to increase seafood production globally. In order to promote the expansion and development of aquaculture technologies required to raise new finfish species, a number of key bottlenecks restricting commercial-scale culture need to be addressed, including the ability to control fish reproduction in captivity and to produce high quality seeds. One candidate species for large-scale production, and the focus of this work, is common snook. Prized as a food fish in Mexico, Central and South America and as a popular game fish along the Gulf coast of the United States; common snook are economically important having both a high market value and recreational demand. Despite recent advances in captive spawning, a number of reproductive bottlenecks still need to be addressed such as lack of spontaneous spawning in captivity, poor fertilization rates and inconsistent production of high quality eggs and larvae. Therefore, the overall aim of this thesis was to better understand the reproductive biology of common snook in order to develop protocols to improve the reliability of captive spawning in closed recirculating aquaculture systems and the quality of eggs produced as a basis for commercial scale cultivation. First, this PhD project described oocyte development in common snook and validated a non-invasive method for assessing reproductive condition in wild and captive stocks (Chapter 2). This was done by using a tiered and adaptable staging scheme to compare the wet mount technique with histological preparations of ovarian biopsies. When compared with histology, the wet mount provided an immediate and precise method for determining whether female broodstock were candidates for hormonal induction. In fishery biology, an understanding of fish reproductive success and population reproductive potential is critical for designing and implementing effective fisheries management strategies. The wet mount technique provides a tool for non-lethal, low-cost determination of reproductive status in wild fish stocks. The next research chapter focused on spawning induction of captive snook populations. The first trial compared the effects of slow and regular release GnRHa implants whereas the second trial investigated the effects of GnRHa, alone or in combination with the dopamine antagonist, pimozide (PIM), on milt characteristics and plasma steroid levels in captive male common snook broodstock (Chapter 3). In an effort to better enable reliable control of reproduction under captive conditions, the annual plasma sex steroid profile of captive male and female broodstock maintained under natural photo-thermal conditions was also examined. When possible, milt samples were collected pre and post implantation; sperm density, sperm motility and spermatocrit were documented among individual males. The assigned treatments appeared to have no or little effects on milt production in male broodstock although plasma steroid levels were found to be significantly elevated in individuals treated with GnRHa in combination with the dopamine antagonist, pimozide. At the time this work was performed, no data on spawning dynamics, including individual spawning performance, had been reported for common snook in captivity. Mass spawning tanks are complex systems where fish are left to spawn naturally and fertilized eggs are collected with little or no control over the mating of the animals. Therefore, the third part of this thesis explored the potential of DNA profiling for monitoring mating outcomes in captive broodstock by employing eight microsatellite markers to detect and quantify individual parental contributions for 2,154 larvae obtained from the three broodstock tanks (Chapter 4). The panel of loci was generally robust and allowed unambiguous assignment of 89% of larvae to a single family. Overall, spawn contribution data 1) provided a confirmation of GnRHa treatment efficacy in female snook with a minimum stage of oogenesis (late secondary growth-SGl) required for successful spawning, 2) identified a potential impact of handling on maturation and spawning of captive broodstock and 3) confirmed that, through photothermal conditioning, captive broodstock can spawn over consecutive days and several times per year including outside of their natural spawning season. The exogenous cues that tropical species use to synchronize key life events like reproduction remain largely unstudied, therefore, my PhD project also investigated the influence of tidal cycle on reproductive activity in common snook (Chapter 5). Real-time quantitative RT-PCR assays were developed and validated to measure the temporal expression patterns of gonadotropin genes (fshβ and lhβ) during the reproductive cycle in males and females. These were evaluated in relation to sex steroid production, LH blood plasma levels, gonadal development and tidal cycle. The phylogenetic analysis of the deduced amino acid sequence of common snook for fshβ and lhβ revealed strong identity with other teleosts (75-90%). Additionally, the mRNA profiles of fshβ and lhβ in the pituitary of females displayed a clear pattern of expression concomitant with histological changes in oocyte development. Histological observations of gonads suggested a circa-tidal rhythm of follicular development. The findings, as a whole, provided new information supporting the role of tidal cycle on the entrainment of gametogenesis allowing for a better understanding of the environmental control of reproduction in common snook. Although the primary research emphasis in this PhD was on broodstock spawning and gamete quality, the final chapter focuses on larval ontogeny. The goal of this research was to gain improve understanding of the early life history characteristics of common snook in order to improve larval culture technologies. To do so, a combination of digital photography and histological techniques were used to document the embryonic and early larval development (0 to 14 days post hatch-DPH) of hatchery-reared individuals (Chapter 6). Larvae hatched 15 h after fertilization at 28°C, lacked pigmentation, had a rudimentary digestive tract and undeveloped visual system. Development was rapid and by 3 DPH larvae had almost doubled in length, the yolk sac was nearly exhausted, the mouth was open and eyes were pigmented with a well-structured retinal layer. The alimentary canal was differentiated into three distinct sections including the foregut, midgut and hindgut. Food was observed in the gut (rotifers) and structural epithelium organelles, such as the nucleus, mitochondria, and dark vesicles, were all present in high numbers. The swim bladder was formed and inflated. In summary, understanding early ontogenetic development in common snook can help provide information needed to address key bottlenecks seen in captive cultivation, such as the high incidence of larval mortality observed during the transition from endogenous to exogenous feeding. Overall, this doctoral work 1) validated molecular and endocrine analytical tools for future studies of common snook reproductive physiology, 2) provided a better understanding of both broodfish requirements in tank systems as well as the endocrine control of reproduction and spawning at the level of the brain-pituitary-gonadal axis, 3) increased our knowledge in genetic management of captive broodstock, in terms of parentage assignment and 4) offered new insight into wild population reproductive strategy as well as how reproduction is entrained through environmental cues and the pathways leading to oocyte recruitment and maturation. The new information presented here can be used to conserve wild snook stocks through production of farm raised individuals as a sustainable source of seafood and for fisheries enhancement.

With the majority of Earth’s population living in coastal areas, estuarine ecosystems have been particularly affected by anthropogenic disturbances. My dissertation research focused on three interrelated types of human disturbance that affect estuaries: Anthropogenic alteration of freshwater inflow, the introduction of invasive species, and habitat alteration. Using the LoxahatcheeRiver(Jupiter, FL) as a model system, my goal was to understand how these disturbances affect estuarine organisms, particularly fishes. One of the most ecologically harmful disturbances affecting estuaries is anthropogenic alteration of freshwater inflow (and resulting changes in salinity patterns). To identify effects of freshwater inflow on the behavior of an ecologically and economically important fish (common snook Centropomus undecimalis), I conducted a 19-month acoustic telemetry study. Common snook were more abundant and made more frequent upstream migrations during the wet season, but freshwater inflow did not appear to be the proximate cause for these behaviors. Increased estuarine salinity resulting from anthropogenic flow alteration may have facilitated the second type of disturbance that I address in this dissertation; the invasion of non-native Indo-Pacific lionfish into estuarine habitats. During the course of my dissertation research, I documented the first ever estuarine invasion by non-native lionfish. Using mark-recapture, I identified high site fidelity in lionfish, a trait that may aid future control efforts. The extremely low minimum salinity tolerance that I identified in lionfish appears to have allowed the species to colonize far upriver in estuaries with anthropogenically modified salinity patterns. Anthropogenic salinity alteration has also led to a severe degradation of oyster reef habitats in theLoxahatcheeRiver. As a foundation species, oysters provide food, shelter, and nursery habitat for a wide variety of estuarine organisms, including many ecologically and economically important fishes. Increasingly, degraded oyster reef habitats have been the focus of restoration efforts. I identified a relatively rapid (< 2 years) convergence between restored and natural oyster reef communities, and documented the importance of vertical relief in restoration success. My dissertation research is critical for the management and conservation of coastal rivers inFlorida, while more broadly informing restoration and management decisions in many other estuarine and coastal ecosystems.

Changes in global climate will likely increase climate variability. In turn, changes in climate variability have begun to alter the frequency, intensity, and timing of climate disturbances. Continued changes in the climate disturbance regime experienced by natural systems will undoubtedly affect ecological processes at every hierarchical scale. Thus, in order to predict the dynamics of ecological systems in the future, we must develop a more mechanistic understanding of how and in what ways climate disturbance affects natural systems. In South Florida, two climate disturbances recently affected the region, a severe cold spell in 2010, and a drought in 2011. Importantly, these disturbances affected an ecosystem of long-term, comprehensive, and persistent ecological study in the Shark River estuary in the Everglades National Park. The aims of my dissertation were to (1) assess the relative severity of these two climate disturbances, (2) identify effects of these disturbances on community structuring, (3) compare community change from the 2010 cold spell with community change from another extreme cold spell that affected sub-tropical China in 2008, (4) assess the effects of the drought on predator prey interactions in the Shark River and (5) apply a spatial approach to predicting population resistance to these events. My results show that the 2010 cold spell was the most severe cold event to affect the Shark River in the last 80 years, while the drought was the worst drought to occur in the last 10 years. The cold spell drove community change that was predictable based on the traits of component species, whereas community change was less predictable using trait-based approaches. When comparing community change from the extreme 2010 event in Florida with the event in China, I identified three consistencies related to community change from extreme cold events that occurred across both events that will help build generalized understanding of community resistance to increasingly extreme climate events in the future. From the trophic study, I found that the drought reduced prey for estuarine piscivores. Not only was prey biomass reduced, the drought drove a compositional shift in prey communities from fish to invertebrates, which are lower in calories. Last, I found that animal movement may create temporally dynamic resistance scenarios that should be accounted for when developing predictive models.

O robalo-flecha, Centropomus umdecimalis, e robalo-peva, Centropomus parallelus, sÃo duas spÃcies habitantes de ambientes estuarino e costeiro marinho ao longo das regiÃes Norte, Nordeste e Sudeste do Brasil portanto, com grande potencialidade para a maricultura. A estimaÃÃo dos parÃmetros de crescimento, objeto principal deste trabalho, fornecerà as informaÃÃes necessÃrias para se avaliar a relaÃÃo custo/benefÃcio na implantaÃÃo de projetos de cultivo, principalmente quanto à eficiÃncia alimentar sobre a taxa de crescimento registrada por populaÃÃes naturais. Os dados bÃsicos foram obtidos por amostragem dos desembarques de pescado no Mercado de SÃo Pedro (NiterÃi, Estado do Rio de Janeiro), efetuados pela frota comercial de barcos linheiros que atuam ao longo da costa de Cabo Frio (23 S). O material coletado consiste de 264 exemplares, sendo 130 de C. undecimalis e 134 de C. parallelus, no perÃodo entre junho de 1999 e junho de 2000. Destes foram retiradas escamas para os estudo da idade e crescimento, por meio da identificaÃÃo dos anÃis etÃrios e mediaÃÃo das zonas de crescimento. As amplitudes de variaÃÃo do comprimento total foram 33,1 â 78,9 cm (C. undecimalis), e 29,5 â 57,3 cm (C. parallelus). As premissas bÃsicas sobre proporcionalidade nos padrÃes de crescimento da escama e do peixe, e sobre a periodicidade na formaÃÃo dos anÃis etÃrios, foram avaliadas por meio da anÃlise de regressÃo e variaÃÃo mensal no Incremento Marginal, respectivamente. Os parÃmetros de crescimento, comprimento mÃximo teÃrico, coeficiente de crescimento, e idade inicial aparente, bem como o Ãndice de desempenho do crescimento, foram estimados. O coeficiente de mortalidade natural (M) foi tambÃm estimado para fazer parte da razÃo M/K. AnÃlises estatÃsticas foram empregadas para se comparar o padrÃo de crescimento entre as duas espÃcies (teste t) e a significÃncia da mudanÃa de idade em intervalos mensais (teste H, de Kruskal-Wallis). Os resultados obtidos estÃo resumidos nos seguintes itens: (a) Confirmou-se a premissa de proporcionalidade isomÃtrica entre os comprimentos do peixe e da escama; (b) as âdatas de aniversÃrioâ do robaloflecha e do robalo-peva correspondem aos perÃodos mensais de abril-junho e agosto-outubro, respectivamente; (c) os parÃmetros de idade e crescimento estimados para o robalo-flecha foram: L = 101, 1 cm, W = 11,4 kg, K = 0,112, t0 = - 2,59 ano, tmax = 29,3 anos e fâ = 3,058; (d) os parÃmetros de idade e crescimento estimados para o robalo-peva foram: L = 67,9, W = 3,6 kg, K = 0,187, t0 = - 2,48 ano, tmax = 18,6 anos e fâ = 2,936; (e) O robalo-peva atinge um menor tamanho mais tem taxa de crescimento mais rÃpida do que o robalo-flecha; (f) o coeficiente de mortalidade natural foi estimado como M = 0,259 (C. undecimalis) e M = 0,406 (C. parallelus), com os respectivos valores de M/K = 2,312 e M/K = 2,171, que classificam estas espÃcies como pertencentes ao 4 nÃvel trÃfico; (g) Os valores do coeficiente de desempenho (fâ) confirmam a adoÃÃo de uma estratÃgia de crescimento compatÃvel com espÃcies predadoras de mÃdio e grande portes. / The common snook, Centropomus umdecimalis, and the fat snook, Centropomus parallelus, are two species that dwell on estuarine and costal marine environments along the North, Northeast and South Brazil, hence with great potential for mariculture. The estimation of age and growth parameters, the primary objective of this paper, should supply the necessary information to evaluate the cost/benefit ratio for the development of marine fish farms, especially as to feeding efficiency in promoting the enhancement of growth rates in comparison to that of wild populations. The databank was obtained by means of sampling of the landings made at the SÃo Pedro fishmarket, in NiterÃi, Rio de Janeiro State, by the commercial fleet of liners which fish for pelagic resources off Cabo Frioâs coast (23oS) The collected material was comprised of 264 specimens, 130 of C. undecimalis and 134 of C. parallelus, in the period from June, 1999 through June, 2000. From a site below the pectoral fin scales were drawn for age and growth studies to be performed by means of the identification of age rings and measurement of growth bands. Total lengths of the sampled fish were in the range of 33.1 â 78.9 cm (C. undecimalis) and 29.5 â 57.3 cm (C. parallelus). The basic assumptions on the dependence of fish size on scale size, and the periodicity in age rings formation were investigated by regression equations and monthly variations in the scaleâs marginal increment, respectively. The parameters of the growth equation, namely asymptotic length, growth coefficient and theoretical age at birth, and growth performance index as well were estimated. The natural mortality coefficient (M) was calculated in order to make up the M/K ratio. Statistical analyses were used in order to compare the growth rate between common snook and fat snook through Studentâs t test, and to assess the significance of age changes between pairs of adjoining months through Kruskal-Wallisâ H test. The drawn results may be summarized as follows: (a) the assumption of a regression of scale length on fish length was met; (b) the âbirth datesâ of common snook and fat snook correspond with April-June and August-October monthly periods; (c) the age and growth parameters for common snook were: L = 101. 1 cm, W = 11.4 kg, K = 0.112, t0 = - 2.59 yr., tmax = 29.3 yr. and fâ = 3.058; (d) the age and growth parameters for fat snook were: L = 67.9, W = 3.6 kg, K = 0.187, t0 = - 2.48 yr., tmax = 18.6 yr. and fâ = 2.936; (e) the fat snook reaches a smaller size but grows quicker than the common snook; (f) the natural mortality coefficient was estimated at M = 0.259 (C. undecimalis) e M = 0.406 (C. parallelus), entailing respective values of M/K = 2.312 and M/K = 2.171, which classify those species into the fourth trophic level; (g) The growth performance indices indicate the adoption of a strategy consistent with that assumed by mean- and large-sized predatory species.