Marine Fish Research Program

Recent and Ongoing Projects:

Team Fuiman	Khan Lab
Joan Holt lab	Nunez lab
Scott Holt lab	Thomas lab

Scales for Ontogenetic Progress and Biological Clocks:  This has been an ongoing theme in Team Fuiman because of its obvious importance to many other projects dealing with development in fishes, especially projects that attempt to compare species.  The problem is to quantify the developmental state of a fish in such a way that it can be compared the state of another individual of the same or different species.   Given the variety of developmental programs exhibited by fishes and the enormous range in developmental rates observed, this has been an especially challenging topic.   Nevertheless, we feel we have made some progress.

        Abstracts from recent meetings and publications: 

Larva 2000
Fuiman, Poling, & Higgs (Copeia 1998:602-611)
Fuiman & Higgs (pp. 225-249 in: Early life history and recruitment in fish populations)

Predation Mortality of Larval Fishes: Peril of the Unfit or the Unfortunate?: This collaboration with Jim Cowan (Dauphin Island Sea Lab, Alabama) is examining the question of whether predation mortality during early life is the result of chance encounters with predators or the predator evasion skills of the larvae. Laboratory assays measure survival skills of individual larvae to determine whether some individuals excel in several skills ("born athletes"). Laboratory results will be incorporated into an individual-based model and simulations will be performed to predict the survival of athletes and non-athletes. These predictions will then be tested in field mesocosm trials.

        Abstracts from recent meetings: 

1999 Fisheries Society of the British Isles
1999 Larval Fish Conference
1998 Larval Fish Conference - individual differences 

Evaluation of endocrine disrupting chemical effects across multiple levels of biological organization: integration of physiology, behavior, and population dynamics in fishes.:  This is a collaboration with Peter Thomas and Kenny Rose (Louisiana State University).  The aim of the proposed research is to estimate the impacts of several representative endocrine disrupting chemicals (EDCs) on Atlantic croaker (Micropogonias undulatus) populations in marine environments. The overall hypothesis that endocrinological, physiological, morphometric and behavioral biomarkers of reproductive and larva functions in individuals can be modeled to predict the effects of EDCs on croaker population dynamics will be examined by testing the following subhypothesis: (1) EDCs act during several critical reproductive and early life stages of croaker, (2) endocrinological, physiological, morphometric and behavioral responses are reliable predictors of EDC effects on these critical stages, (3) endpoints of critical reproductive and early life stages in individuals can be used to model population effects of EDCs. Specific objectives are to 1) determine the effects of the EDCs on biomarkers of gamete production and gonadal growth; 2) investigate the impacts of the representative EDCs on biomarkers of gamete maturation, fertilization success and larval survival; 3) assess the parental transfer of the EDCs to gametes and offspring; 4) determine the effects of parental exposure to the EDCs on ecological performance skills of larvae; 5) determine the influence of parental exposure to the EDCs on larva metabolism, growth, and development; 6) develop a suite of predictive computer models for scaling individual-level effects of EDCs to fish population response.  This integrative, multidisciplinary study involves collaborations between three groups of researchers with expertise in reproductive physiology, endocrine toxicology, bioaccumulation of EDCs by parents and offspring, development, functional morphology, behavioral ecology, and individual-based bridge modeling and population modeling.

Individual variability in growth rates of red drum (Sciaenops ocellatus) larvae- a potential cause and behavioral consequences: Assessment of particular traits that result in higher survival of individual larvae may be important for predicting the future of a particular cohort. Michael Smith is examining three such traits and their covariation: egg size, growth rate, and sensorimotor performance. Individual red drum are reared from eggs to measure variability in individual growth rates and potential covariation of growth rate with egg and hatchling size. Then laboratory trials are used to examine the ontogeny of sensorimotor performance and its covariation with individual growth rates and egg size. These performance trials will include measurement of routine swimming, burst responses to acoustic and visual stimuli, and escape behavior in the presence of a predator. Ontogeny and variability in sensorimotor performance of both field-collected and laboratory-reared red drum larvae are being studied.

1999 Larval Fish Conference

Biomarkers of larva fitness in croaker exposed to pesticides: This is a collaborative project with Peter Thomas' lab. Dan Sabath is following up Cindy Faulk’s thesis work using a collection of behavioral assays to determine whether parental exposure to a pesticide has ecologically significant sublethal effects on the larvae they produce. The assays measure foraging and antipredator behavior of Atlantic croaker larvae.

RNA:DNA ratio: Can it be more than a growth index?: RNA:DNA ratios have been used as an indicator of nutritional condition and recent growth of larval fishes.  Although it has been hypothesized that high RNA:DNA ratios could be correlated with decreased mortality under natural conditions, few attempts have been made to correlate this index with any functional (survival) benefit to individual larvae. Michael Smith, in collaboration with Sharon Herzka (Joan Holt’s lab), are examining relationships between RNA:DNA ratios and sensorimotor performance. Performance trials will include videotaping individual routine swimming and responses to visual and acoustic stimuli.

Effects of temperature and salinity on the interaction between red drum larvae and a piscine predator: Locomotor and physiological performance of both predator and prey may be influenced by differences in temperature and salinity, but the magnitude of the effects may differ for larvae and larger fishes. This project examines the responsiveness and response effectiveness of red drum larvae, and the capture success of larger pinfish under 12 combinations of temperature and salinity to determine relative importance of these two natural environmental variables to the predatory-prey interaction. 

Potential alarm pheromones in marine fishes: Most ostariophysian fishes (almost all freshwater) have behavioral alarm reactions to chemicals released from epidermal club cells of injured conspecifics. No marine ostariophysians have been tested for such responses. Michael Smith is recording activity levels of a marine ostariophysian, hardhead catfish (Arius felis), in the presence of conspecific skin-extract. Similar experiments are also being performed with the naked goby (Gobiosoma bosc) and darter goby (Gobionellus boleosoma).

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Larviculture and high density grow-out studies of marine species in closed systems aimed at developing a mariculture approach to the conservation of natural resources. 

1. Mariculture development throughout the world is hampered by the lack of reliable rearing systems and practical diets for the larvae. For example, high yields of red drum depend upon feeding the larvae live prey for one to several weeks. In order to reduce the requirement for live prey, feeding and nutrition studies here are focused on understanding the developing digestive system and nutrient requirements for larval sciaenids. The goal is to determine essential nutrients for larvae and the best means for supplying those nutrients. 

2. Role of microbial ecology in larval fish culture and nutrition has been investigated by Philippe Douillet. Initially the study aimed to develop a scheme for managing the composition of the microbial community in intensive, closed culture for red drum larvae. The second phase was to identify and culture beneficial microbes to add to the larva cultures. Currently we are exploring the possibility of using enzyme producing gut- bacteria to enhance the utilization of artificial diets. 

3. Culture of tropical reef fish and shrimp would function to conserve natural reef resources by offering alternatives to wild capture. Over the past we have successfully spawned seven reef species and reared the larvae of three: cubbyu (Equetus umbrosus), yellow-tail snapper (Ocyurus chrysurus) and a cleaner shrimp (Lysmata wurdemanni). Using the techniques we developed for rearing the larvae, together with micro-zooplankton culture it is possible that many coral reef species can be grown in culture. 

Biochemical measures of fish growth and condition to evaluate the condition or growth potential of lab cultured or natural populations of fish larvae. 

1. Several biochemical measures are under investigation including RNA-DNA ratio, lipids, and MPF (Mitosis Promoting Factor). The RNA-DNA ratio has been examined in larvae raised in the laboratory under various feeding, salinity and temperature conditions, and in natural population of red drum. The measure is a good indicator of recent history of feeding and perhaps temperature conditions. Studies by Claire Fernandez and others are investigating further the effect of temperature history on the RNA-DNA ratio. 

2. In a collaborative project with Mark Westerman, the usefulness of cyclin-dependent kinase activity, predominantly Mitosis Promoting Factor, in assessing how biological and environmental inputs affect growth of teleost larvae is being investigated. Classes of lipids (ie.. tags, steroles, etc.)vary depending on the nutritional state of larvae; this will be examined when we get access to an Iatroscan possibly later this year (automated thin layer chromatograph with a flame ionization detector). Both methods will be compared to the RNA-DNA ratio in larvae with different growth histories. 

Larval fish studies to determine the role of biological and physical factors in growth and survival of natural populations of estuarine dependent fishes. 

1. Overall the salinity tolerance of spotted seatrout is broad but we have shown that early life stages have reduced tolerance with 3 day old larvae being the most sensitive. Egg size varies inversely with salinity in natural spawning populations and the range of tolerance in pre-feeding larvae is directly related to spawning salinity. Furthermore changing the salinity on adults brought into the lab during the spawning season has detrimental effects on the development of eggs and larvae. Possible hypotheses to explain the data we have accumulated thus far are (1) long-term acclimation by adults to salinity regulates the pattern of salinity tolerance found in young larvae, (2) non-genetic, possible irreversible adaptation of the embryo or larva regulates salinity tolerance at the population level, or (3) stocks or populations of spotted seatrout are genetically adapted to the prevailing salinity regime of a bay system. 

2. In a collaborative study with S. Holt we are trying to identify critical periods during the transport of red drum and other sciaenids from spawning sites to estuarine nursery grounds. The role of physical factors and vertical positioning on transport of eggs and larvae through the Aransas Pass has been examined in several studies. We found that larval sciaenids could use modified tidal stream transport to reach estuarine nursery areas, by staying in near- bottom water in the pass on ebb tide and moving up on flood tide. Vertical movement was not associated with feeding since larvae feed only during daylight hours and flood and ebb cycles do not follow a strict diurnal pattern. The objectives of an ongoing study are to determine the temporal pattern of spawning, estimate density of larvae, and determine birthdate distribution of young fish that successfully recruit to the sea grass beds with the goal of quantifying physical and biological conditions that result in high survival. 

3. Studies by Jay Rooker and Andy Soto are examining how feeding, growth and condition of larvae in the sea grass beds are affected by habitat and competition. They will present their research at a brown bag seminar in the near future. 

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The central theme of research in Scott Holt's lab is fish ecology, with emphasis on larval and juvenile life history stages. Virtually all the studies are field oriented and are comparative, using "natural" experiments, rather than manipulative. 

Recent projects include: 

Studies of the temporal and spatial distribution of fish larvae in the Laguna Madre and the impact of the brown tide on those larvae. We have seen a dramatic decline in the density of all early-stage fish larvae (incl. spotted seatrout and black drum) in areas of high brown tide concentrations. Joan has lab data showing high mortality of eggs and nonfeeding larvae and reductions in feeding success of older larvae. Our field data reflect those impacts. 

Studies of the utilization of different seagrass habitats by larvae in the Laguna Madre. Jim Tolan recently completed a MS at TAMUCC looking at the occurrence of fish larvae and early juveniles in Halodule, Syringodium and adjacent bare bottom in the lower Laguna Madre. He found that highest densities of juveniles of most species was in Halodule with little difference between Syringodium and bare bottom. Early larval stages were found in all habitats but specific distributions varied by species. In general, early larvae of species which spawn in the open bay or inshore Gulf, (ie. spotted seatrout and red drum) were found primarily over unvegetated habitat whereas those species which spawn in structured habitat, especially those with demersal eggs (i.e., gobies and silversides), were more common over seagrasses. 

The primary focus of the rest of our research over the past 6-8 years has been the migration of fish larvae from offshore spawning grounds to estuarine nursery areas with emphasis on transport processes involved in ingress through the tidal inlet. Our focus has been on red drum but we have accumulated similar data for all other sciaenids in the collections and a few other species as well. Much of this research has been done in cooperation with Joan Holt and several of her students. 

We have looked at the temporal and spatial (both horizontal and vertical) distribution of larvae over several tidal cycles and found them most abundant in offshore water, as it pulses in and out of the estuary with each tidal cycle. Densities in estuarine water are only 10-20% of those in offshore water and those larvae are generally of the largest size classes we see in the plankton. The larvae change their vertical position in the water column such that they are concentrated near then bottom during the day and on ebb tide (especially those in estuarine water), and throughout (we think) the water column during the night and on flood tide. Flood tides are generally at night during red drum spawning time, complicating the tidal/diel migration pattern. Larvae also appear to be concentrated at the boundary of the tidal front separating estuarine water from offshore water. 

We examined the daily ingress of red drum larvae (and other sciaenids occurring in the same samples) over the entire spawning season. We found that the temporal occurrence of larvae was highly pulsed, with much higher densities of larvae occurring in 2-3 day pulses which were seen every 10-15 days over the immigration period. Preliminary analysis indicates that the pulses were correlated with wind events. Larvae of most other sciaenids occurring at the same time also showed the same pulsed occurrence, further strengthening the implication of physical control of the distribution pattern. Chris Drescher looked at RNA/DNA in these larvae for her thesis work (details are given in Joan Holt's section) 

These studies of larval immigration have extended to the nursery areas where we are looking at post-settlement processes. We have examined the spatial and temporal distribution of newly settled red drum larvae throughout the potential nursery area. The larvae were occasionally found in all sites examined but were much more abundant and persistent in some sites than others. We suspect the differences are driven largely by hydrodynamic processes and that issue is ripe for future research. Jay Rooker has looked at differences in condition and growth rates among sites and between seagrass habitats. Red drum larvae and early juveniles are much more abundant in Halodule than Thalassia seagrass but condition was not different between those habitats. Andy Soto is looking at food habitats of red drum and Atlantic croaker in those habitats. We are currently determining mortality rates of red drum larvae and early juveniles in those habitats but are still working on the data. A study of predation rates in both habitats in the works. 

In almost all of these studies we have used the analysis of otolith microstructure (ie growth rings) in some way. Our lab is set up to determine both annual age in adults and daily age of larvae. The primary information obtained is age of the individual fish which provides an estimate of overall growth rate and the hatch date of each larva. Jay Rooker has also used the width of the outer most rings to determine recent growth for comparison of habitats effects. We previously looked at pinfish growth rates between Halodule and Syringodium habitats in the Laguna (using overall growth rates) and found no difference in growth. Otolith analysis is also being used to determine growth rates of adult black drum in the Laguna Madre. 

Another line of research we are developing, but which has not yet culminated in a funded project, is the study of sounds made by spawning adult fishes, primarily sciaenids. We have the hydrophone and sound analysis software and have recorded spawning activity of several species. Interaction wit other worked in this field is encouraging and hopefully leading to funded research. 

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Demonstration of a progestin (20-beta-S) receptor on sperm membranes and its characterization in testes is one of the hot (cool!) projects in Thomas' lab. 20-beta-S is the maturation inducing steroid in sciaenids which has been shown to be involved in final oocyte maturation in Atlantic croaker and spotted seatrout. Regulation of the membrane receptor in testes and sperm membrane preparations is being investigated. Search is on to find a physiological function of the membrane receptor in the testis and on sperms. 

Charles Detweiler is currently working on hormonal regulation of sperm motility in Atlantic croaker and spotted seatrout. He is also investigating possible involvement of calcium channels in sperm motility in croaker. 

Todd Sperry has characterized androgen receptors in the brain and ovary of croaker. The ovarian androgen receptor(s) has different characteristics from those of the brain androgen receptor. Once these initial characterizations are completed we will begin to attempt to understand the physiological roles of multiple androgen receptors in Atlantic croaker. 

Karen Rogowski's project involves examining the role of prolactin and growth hormone in osmoregulation and reproduction of red drum and croaker. Her work includes isolation and purification of the two hormones from pituitary glands, raising of the antibodies to these hormones, and development and validation of radioimmunoassays for the measurement of these hormones. 

One of Yong Zhu's project is to determine physiological function(s) of somatolactin, a recently discovered hormone in fish. Somatolactin appears to be involved in adaptation of the fish to background and illuminations. A collaborative project with Prof. Katsumi Aida's group at the Tokyo University, is underway to construct red drum somatolactin cDNA library and to develop molecular probes for future studies on somatolactin gene expression. In addition, he is working on the purification of 20-beta-S membrane receptor from seatrout ovaries.

Izhar Khan is involved in the projects on multifactorial neuroendocrine control of gonadotropin secretion in Atlantic croaker. Role of the monoamine and amino acid neurotransmitters, neuropeptides, and gonadal steroids in the control of gonadotropin release from the pituitary is being investigated. Collaborative work with Prof. Yonathan Zohar's group at the Center of Marine Biotechnology, University of Maryland, Baltimore is in progress to develop molecular probes for the localization and quantification of gonadotropin-releasing hormone mRNAs in croaker brain. Development of a comprehensive marine fish model of neuroendocrine control of gonadotropin release provides the basic framework for our neuroendocrine toxicology program. 

Beth Hawkins has cloned and sequenced the estrogen and progesterone receptor genes. She has developed molecular probes to localize and quantify estrogen receptor mRNA by in situ hybridization. These molecular tools will help us understand the GnRH and estrogen receptor function in discrete brain areas that are involved in the control of reproduction in croaker. 

Interactions of environmental chemicals with the 20-beta-S membrane receptor. A variety of chemicals have been shown to bind to the membrane receptor. Attempts are being made to purify this receptor. A series of in vitro and in vivo experiments are planned to test whether the binding of the chemicals to this receptor can alter normal receptor functions including final oocyte maturation, ovulation and spawning success. 

Investigation of life history stages of croaker susceptible to environmental endocrine disruptors. This project proposes to study the mechanisms of reproductive impairment by a variety of chemicals including xenoestrogens and heavy metals during different stages of gonadal cycle as well as teratogenic effects of the chemicals due to parental exposure. 

Another major project in reproductive toxicology is on the interactions of xenoestrogens with androgen and other steroid receptors using croaker as a model species. 

Created: Fri Feb 23 15:05:51 CST 2001