Wild-caught Juveniles Research Articles

Recent insights into egg quality and larval vitality of the European eel Anguilla anguilla

To date, the eel industry still depends on wild-caught juveniles that are grown to marketable size. There is an urgent need to close the eel life cycle in captivity to make aquaculture independent of the natural population. With this artificial reproduction protocol, yolk-sac larvae can be produced but egg quality may be impaired. Low survival rates and high deformity rates are frequently observed during the first week after hatching. Over the past four years, we have conducted studies with the aim to optimize the artificial reproduction protocol, thereby focussing on increasing egg and larval quality. Weekly carp or salmon pituitary extract (PE) treatment was successfully replaced with recombinant gonadotropins (rGTHs) to mature female eels and produce larvae. 17α,20β-dihydroxy-4-pregnen-3-one (DHP) was replaced with upstream precursor progesterone (P) to induce the endogenous production of DHP by the female eel. DHP and P were found equally potent in inducing oocyte maturation and ovulation. The effects of antibiotics on larval survival and the occurrence of deformities were investigated. Antibiotic treatment increased survival and decreased the occurrence of deformities indicating bacterial infection as an important cause. A deformity determination key for young eel larvae has been developed that provides a framework of reference for larval deformities which will be instrumental with gaining insights on the reasons behind each larval deformity. These improvements of the artificial reproduction protocol and hatchery practices will contribute to the production of robust eel larvae that survive, grow and metamorphose into juveniles that will later be able to reproduce in captivity.

Testing assumptions underlying cabezon (Scorpaenichthys marmoratus) otolith microstructure analysis using wild-caught juveniles and opportunistic rearing of eggs and larvae.

Otolith microstructure analysis provides critical biological and ecological information about the early life history of fishes. This information is particularly important to interpret and predict population dynamics for socio-economically important fisheries species; nonetheless, several key assumptions underpin the use of otolith techniques. The authors validated the use of this analysis for cabezon (Scorpaenichthys marmoratus; Ayres, 1854), a long-lived, large-bodied cottid constituent of nearshore fisheries from Baja California, Mexico, to Alaska, USA. To test three critical assumptions, the authors coupled otolith and morphometric analyses from an opportunistic rearing study of cabezon eggs and larvae with a long-term time series of juvenile cabezon field collections. The authors confirmed the daily otolith increment deposition in laboratory-reared larvae, identified the timing of first otolith increment deposition and examined the relationship between otolith growth and somatic growth in field-collected juveniles, validating the use of otolith microstructure analysis in biological and ecological interpretations of early life-history traits for this species. The findings of this study also indicated that the absorption of yolk-sac reserves, and likely the transition to exogenous feeding, plays an important role in regulating otolith increment deposition. Finally, the authors found within-brood size-at-age variation, which may be an advantage for young fish in prey-limited environments.

Evolutionary divergence in phenotypic plasticity shapes brain size variation between coexisting sunfish ecotypes.

Mechanisms that generate brain size variation and the consequences of such variation on ecological performance are poorly understood in most natural animal populations. We use a reciprocal-transplant common garden experiment and foraging performance trials to test for brain size plasticity and the functional consequences of brain size variation in Pumpkinseed sunfish (Lepomis gibbosus) ecotypes that have diverged between nearshore littoral and offshore pelagic lake habitats. Different age-classes of wild-caught juveniles from both habitats were exposed for 6 months to treatments that mimicked littoral and pelagic foraging. Plastic responses in oral jaw size suggested that treatments mimicked natural habitat-specific foraging conditions. Plastic brain size responses to foraging manipulations differed between ecotypes, as only pelagic sourced fish showed brain size plasticity. Only pelagic juveniles under 1year-old expressed this plastic response, suggesting that plastic brain size responses decline with age and so may be irreversible. Finally, larger brain size was associated with enhanced foraging performance on live benthic but not pelagic prey, providing the first experimental evidence of a relationship between brain size and prey-specific foraging performance in fishes. The recent post-glacial origin of these ecotypes suggests that brain size plasticity can rapidly evolve and diverge in fish under contrasting ecological conditions.

Tetrodotoxin levels in lab-reared Rough-Skinned Newts (Taricha granulosa) after 3 years and comparison to wild-caught juveniles

The origin and biogenesis of tetrodotoxin (TTX) is one of the most interesting and perplexing questions remaining for TTX researchers. Newts can possess extreme quantities of TTX and are one of the most well-studied of all TTX-bearing organisms, yet seemingly conflicting results between studies on closely related species continues to generate debate. In this study, eggs from 12 female newts (Taricha granulosa) were reared in captivity and the metamorphosed juveniles were fed a TTX-free diet for 3 years. Using a non-lethal sampling technique, we collected skin samples from each individual each year. Wild-caught juveniles from the same population were also sampled for TTX. In lab-reared juveniles, mass increased rapidly, and after only 2 years individuals approached adult body mass. TTX levels increased slowly during the first two years and then jumped considerably in year three when fed a diet free of TTX. However, wild-caught juvenile newts of unknown age were more toxic than their lab-reared counterparts. These results, coupled with additional data on the long-term production and synthesis of TTX in adult newts suggest that TTX is unlikely to come through dietary acquisition, but rather newts may be able to synthesize their own toxin or acquire it from symbiotic bacteria.

Thermal tolerance of purple mud crab, Scylla tranquebarica (Fabricius, 1798), during egg incubation, larval rearing and juveniles’ production

Interest in the production of crustacean aquaculture has focussed primarily on mud crab species; however, mud crab production still relies on wild-caught juveniles due to the low production of viable seeds of mud crab. Thus, the aim of this study was to enhance mass propagation of purple mud crab seed by studying the relation of temperature on growth performance of the early life stage of purple mud crab. Several data such as survival, incubation duration and morphometric measurements were evaluated after temperature was exposed on the egg, larval and crablet stages. For the egg stage, high hatching success (78.95% and 75.00%) was noted within a limited temperature range (28°C and 30°C respectively). Also, significant increment of final egg diameter (0.33 ± 0.05 mm) after the berried crab incubated at 30℃. For larval stage, the highest survival rate was found when the larvae were reared at 30℃ and 31°C with 68.79 ± 2.69 and 66.98 ± 2.63% respectively. The largest morphometric measurements for megalopa (CW: 2.80 ± 0.15 mm) and C1 (CW: 2.86 ± 0.12 mm) were observed at 31℃. The yielded total juvenile at the end of the larval experiment indicated the highest production was obtained for temperature 31°C (1,095 ± 47.3 individuals) followed by 30°C (1,002 ± 84.7 individuals). For the crablet stage, the crablets were able to survive in a wide range of temperatures (26°C–32°C) with >95% survival; however, the temperature 26℃–29°C indicated larger morphometric measurements (CW: 6.24–6.39 mm). In brief, the optimal temperature for egg, larval and crablet stages was recommended within 28℃–30℃, 30℃–31℃ and 26℃–29℃ respectively.

Seasonal changes and endocrine regulation of gonadal development in hatchery-produced Pacific bluefin tuna Thunnus orientalis broodstock in sea cages

We examined the annual reproductive cycle of both female and male hatchery-produced Pacific bluefin tuna (PBT, Thunnus orientalis) broodstock at 3 years of age, including the associated changes in plasma levels of sex steroid hormones and the gene expression of key endocrine factors. The females progressed to vitellogenesis in April, and approximately 50% of the females were observed in late vitellogenesis between June and July at water temperatures between 24.1 °C and 29.0 °C. Approximately 90% of the males were in spermiation for at least 7 months between April and October, which included the period when vitellogenic females were present. Furthermore, the gonadosomatic index of both females and males peaked between June and July. These results indicate that the reproductive season of hatchery-produced PBT peaks between June and July, which is in agreement with the reproductive season reported for PBT broodstock originating from wild-caught juveniles. Furthermore, the percentage of hatchery-reared females that reached late vitellogenesis in the present study was higher than that in wild-caught captive-reared females reported in previous literature. Analysis of plasma sex steroid levels and gene expression profiles suggested that oocyte and ovarian development were associated with 17β-estradiol (E2) control, whereas spermatogonial differentiation towards meiosis seemed to be mediated by 11-ketotestosterone (11-KT). Furthermore, the production of E2 and 11-KT is likely regulated by luteinizing hormone and follicle-stimulating hormone, respectively, via their related receptors. The findings of this study are expected to contribute to improvements of technologies for obtaining fertilized eggs from hatchery-produced PBT broodstock.

Thermal sensitivity of juvenile rabbitfishes Siganus doliatus and S. lineatus (Siganidae): a key role for habitat?

The majority of our understanding of the effects of climate change on coral reef fishes are currently based on studies of small-bodied species such as damselfishes. By contrast, we know little about the potential impacts of ocean warming on larger species of herbivorous and detritivorous reef fish, despite them being a critical functional group and an essential source of food protein for millions of people. In addition, we know little of the role of habitat in determining species’ thermal sensitivity and the legitimacy of extrapolating thermal performance across closely-related species from different habitat types. Here we test the effect of exposure to increased water temperature during juvenile development on key physiological and behavioral traits of two species of rabbitfish typically associated with different habitats: Siganus doliatus (reef-associated) and S. lineatus (estuarine). Wild-caught juveniles were reared for 14 weeks at temperatures representing present-day ambient conditions (28.0 °C), late-summer ambient conditions (30.0 °C), or those projected on reefs under future global warming scenarios (31.5 °C). We then measured the somatic (growth, condition, immune response) and behavioral (feeding rate, latency to feed and activity level) traits of individuals within each treatment to determine the sensitivity of each species to elevated water temperatures. Overall, both species showed comparatively robust levels of thermal tolerance, based on previously-documented responses of small-bodied reef fishes. However, two very different patterns emerged. The reef-associated S. doliatus showed a greater physiological response to temperature, with negative effects on hepatosomatic condition and immune function observed in individuals exposed to the 31.5 °C treatment. By contrast, there were no negative physiological effects of temperature observed in S. lineatus and instead we recorded behavioral changes, with individuals at 30 °C and 31.5 °C displaying altered feeding behavior (increased feeding rate and decreased latency to feed). These distinct responses observed between congeners are likely due to their evolutionary history and flag the potential inaccuracies that could arise from extrapolating effects of ocean warming across even closely-related species adapted to different habitats.

Genetic variation among full-sib families and the effect of non-genetic factors on growth traits at harvest in Clarias magur (Hamilton, 1822)

Magur (Clarias magur) is an Indian catfish species with a good potential for aquaculture. The expansion of magur aquaculture is hindered because of low reproductive and survival rates. Furthermore, males need to be sacrificed to collect milt for artificial fertilization. At present, magur seed production mainly depends on the wild-caught juveniles and to a smaller extent, from broodfish whose genetic potential is unknown. The availability of high-quality seeds in a sustainable way can be ensured through the selective breeding program for magur. The knowledge of factors influencing growth traits and their genetic parameters is a pre-requisite for implementing a genetic selection program. The present study aimed to quantify the performance of C.magur reared in a two-year class and estimate their heritabilities at stocking and harvest and also to estimate the genetic and phenotypic correlations among them. The growth traits such as Body Weight (BW), Total Length (TL), Body Depth (BD), Head Width (HW), and Average Daily Gain (ADG) were recorded from 1413 animals belonging to 78 fullsib families produced by adopting single pair mating design, after one year of pond culture (traits at harvest). Genetic parameters were also estimated for body weight (BW0) and total length (TL0) measured from 2328 fish from 78 fullsib families at the time of stocking. Magur attained an average BW of 135 g and 24.5 cm TL after one year culture period. The heritabilities of BW, TL, and ADG were 0.44 ± 0.07, 0.32 ± 0.06, and 0.42 ± 0.07, respectively and may be biased upwardly due to the single pair mating design. Genetic correlations between harvest traits were all positive and varied in magnitude between traits (0.74 to 0.99). The results obtained from the current study indicate the presence of genetic variation in magur population for growth traits and selection based on genetic merit can produce improvement in these traits.

Comparative Anatomy and Histology Reveal the American Alligator (Alligator mississippiensis) Exhibits Regenerative Capacity of the Tail

Reptiles are the only amniotes that maintain the capacity to lose and regrow entire appendages. Among reptiles, tail regeneration has been extensively studied in Lepidosauria, the subclass that includes lizards, but this study presents the first anatomical and histological evidence of tail regeneration in an archosaur, the American alligator (Alligator mississippiensis). All animals were wild caught juveniles or sub‐adults with an average total body length of 133.4±29.2cm (n=3). Although the duration of tail regrowth is unknown, the average length of the regenerated tail was 15.7±7.3cm. The regenerated tail was externally distinct from the original tail. The scales were compacted and lacked organization as well as dorsal scutes. Gross dissection, radiographs, and magnetic resonance imaging revealed that the caudal vertebrae were replaced by a ventrally‐positioned, unsegmented endoskeleton. This contrasts with lepidosaurs, where the regenerated tail is radially organized around a central endoskeleton, but shares commonality with urodele amphibians that regrow a tail with a clear dorsal‐ventral axis. Immunohistochemistry confirmed that this alligator structure was composed of cartilage, which formed a hollow rod with foramina distributed along the proximal‐distal axis. Furthermore, in contrast to the original tail, the regenerated tail lacked skeletal muscle and instead featured adipose and fibrous connective tissue supplied by a dense network of newly established axons and blood vessels. Despite substantial regrowth of the tail, the deposition of extensive connective tissue is reminiscent of mammalian wound healing or fibrosis. Using Herovici’s stain, it was shown that the regenerated tail is composed of both type I and type III collagen fibers. The lack of muscle contrasts with the lepidosaurs, which regrow functional skeletal muscle groups, but shares similarities with regenerated limbs in Xenopus adult frogs, which have a cartilaginous endoskeleton surrounded by connective tissue, but lacking skeletal muscle. Overall, this study of regeneration in the alligator identifies a distinct pattern of regrowth with features in common with lepidosaurs, amphibia, and wound repair in mammals. Further analysis will help to shed light on the conservation of regeneration in amniote vertebrates.Support or Funding InformationThis work was funded by the College of Liberal Arts and Sciences at Arizona State University to KK.

Sex discrimination of cultured greater amberjack Seriola dumerili using steroid hormones

The aquaculture of greater amberjack Seriola dumerili is of considerable research interest worldwide. The larviculture methods employed to culture this species, however, are still under development, and the majority of farms still rely on wild-caught juveniles. One of the problems associated with the hatchery production of this species is the optimal selection of broodstock to ensure a stable supply of high-quality eggs. Specifically, no reliable low-stress sex-discrimination technique is currently available for selecting broodstock of this species. This study investigated the efficacy of a hormone-based sex-discrimination method in full-cycle cultured S. dumerili, ranging in age from 412 to 1150 days after hatching (DAH). Plasma concentrations of the female hormone 17β-estradiol (E2) and the male hormone 11-ketotestosterone (11-KT) were measured in both spawning and non-spawning seasons, and the optimal threshold levels for sex discrimination were estimated using a receiver operating characteristic curve. Sex discrimination using E2 produced several false positives in younger fish, and had an overall accuracy of 78.7%. However, sex discrimination using 11-KT had an accuracy of 96.7%, even in 412 DAH fish. This study demonstrated that sex discrimination using 11-KT is a reliable method for optimizing the sex ratio of S. dumerili broodstock, even before the broodstock mature.

Prevention of hypermelanosis by rearing Japanese flounder Paralichthys olivaceus in net-lined tanks

In artificially reared flatfish, especially the Japanese flounder Paralichthys olivaceus, pigmented skin (hypermelanosis) frequently appears on the fish’s blind side after normal metamorphosis. As no practical prevention method has yet been proposed, we examined the effectiveness of a loose net placed inside the rearing tank that covers the bottom and walls like a pouch. When juveniles (standard length [SL] 6 cm) were transferred to the net-lined tank (mesh size 4 mm) before the first appearance of hypermelanosis, the pigmented area after 2 months covered about 0.5% of the blind side; this is about 1/40th of the area covered by pigment in fish reared in an ordinary tank (20%). Although the initial appearance of pigmentation in the axilla area (the area covered by the pectoral fin) was not suppressed, utilization of a larger mesh size (12 mm) decreased the expansion of pigmentation in this area. Juveniles reared in the net-lined tank were about 5–15% smaller (SL) than those reared in the ordinary tank, but their body depth:SL ratio was closer to that of wild-caught juveniles. From the results of this study, we propose that net-lined rearing tanks with larger-sized mesh are a practical method of preventing hypermelanosis in Japanese flounder aquaculture systems.

Variability in Juvenile English Sole Condition Relative to Temperature and Trophic Dynamics Along an Oregon Estuarine Gradient

Many benthic fish and invertebrates, including the flatfish English sole (Parophrys vetulus), utilize estuaries as nursery habitat during their juvenile life stage. Regions within an estuary differ with respect to salinity, temperature, oxygen, and organic inputs, highlighting the complexity of nursery habitat and the need to assess multiple habitats within a single estuary. To determine the effect of variable estuarine habitat on juvenile English sole, we examined morphometric and energetic (lipid) condition, fatty acids, and stable isotopes (13C and 15N) of wild-caught juveniles from upriver and downriver habitats within the Yaquina Bay, Oregon estuary. Downriver-caught fish exhibited higher energetic condition, which may be attributed to cooler temperatures and the marine-sourced carbon that typified that region’s food web. Conversely, individuals from the upriver habitat exhibited higher morphometric condition. This may be due in part to the warmer temperatures upriver that have been observed to promote growth and suppress lipid storage in other marine species. Our findings highlight the important but variable contribution of both upriver and downriver habitats to English sole early life history.

Identification of Sox10-positive cells at the dorsal fin base of juvenile flounder that are correlated with blind-side skin ectopic pigmentation.

Flounder develop left-right asymmetric body color, with a dark ocular side and white blind side. However, ectopic pigmentation often occurs on the blind side when juveniles are reared in tanks. To examine the developmental mechanism underlying ectopic pigmentation, we first examined the pigmentation process on the blind side and the localization of chromatoblasts during spontaneous and regeneration-stimulated ectopic pigmentation. Wild-caught juveniles that had completed metamorphosis in a natural environment were reared in tanks, where they exhibited ectopic pigmentation on the blind side that was initiated at the base of the dorsal and anal fins, with chromatoblasts appearing at the edges of scales and melanophores spreading on the scale papilla beneath the epidermis. During tissue regeneration at the base of the dorsal fin in juvenile before ectopic pigmentation, melanophores and chromatoblasts newly appeared on regenerated blind-side skin, resulting in rapid pigmentation at the wounded site. During regeneration-stimulated pigmentation, gch2-positive chromatoblasts were detected only under the regenerated epidermis. Next, we found that Sox10-positive cells were localized in connective tissue at the base of the dorsal fin and that when connective tissue was labeled with DiO, DiO-labeled melanophores appeared in regenerated skin of the blind side after wounding. Therefore, we conclude that in flounder juveniles, Sox10-positive progenitors of pigment cell lineage reside at the base of the dorsal fin and start migrating to the blind-side skin in response to specific stimuli, resulting in ectopic pigmentation. Ectopic pigmentation in flounder could be a good model for examining the flexibility of pigment cell differentiation.

Captive broodstock development, breeding and seed production of Anthid fish (family: Serranidae) Marcia's anthias, Pseudanthias marcia in recirculation aquaculture system (RAS)

Marcia's anthias, Pseudanthias marcia Randall and Hoover, 1993, belonging to the subfamily Anthiinae (family: Serranidae) is a highly sought after marine ornamental fish mainly due to its vibrant pink shade. The present study reports the first successful captive brood stock development, spawning, and larval rearing of P. marcia. Brood stock was developed in a 5-ton recirculation aquaculture system (RAS) using 12 wild caught juveniles. After 6 months of rearing, the fish (8–9.5 cm size) started courtship behavior. Spawning occurred at 1900 to 2100 h. The eggs (mean size - 617.9 ± 14.9 μ) were transparent, pelagic, non-adhesive and with single oil globule. The eggs hatched out after an incubation period of about 14–16 h at a water temperature of 29 °C. Newly hatched larvae measured 1206.6 ± 100.02 μ in total average length and increased to 1852.9 ± 24.68 μ at 48 h post hatch (ph). Mouth opened at 48–50 h post hatch (ph) and measured 76 to 80 μ. Larval rearing trials were conducted using rotifer (L and S type), wild zooplankton, copepod nauplii, artemia nauplii and microparticulate diet. Primordial fin development started by the 10th day post-hatching (dph) (larval size ~2.9 mm) while the opercular and dorsal spines were fully formed by 15 dph (total length of the larva was 4.4 mm). Larvae metamorphosed to miniature adult shape by 32–34 dph and on 50 dph they reached the pink colored juvenile stage (42–43 mm) and at this stage, they were transferred to nursery rearing tank. Four treatments with different feed combination were tried and treatment III with wild copepod gave an average survival of 5.2 ± 1.07% and treatment IV with Parvocalanus crassirostris gave an average survival of 7.3 (±2.51) %.

Changes in body mass of postweaning juveniles of the edible dormouse,Glis glis (L.), in captivity

Edible dormice have to accumulate an adequate amount of body fat before hibernation. Because young dormice are born late in the season, they have a relatively short time for prehibernation fattening. The aim of our study was a) to determine what body mass juveniles reach prior to hibernation, and b) to examine patterns of mass gain in juvenile dormice with unlimited food supply. Dormice were kept in outdoor cages, fitted with wooden boxes and with the floor covered with soil suitable for hibernation. They were provided with water and fed ad libitum. They were weighed every 5-8 days. Of 34 juveniles (17 males and 17 females; 26 born in captivity and 8 caught in the wild), 22 began hibernation in underground cavities. The mean body mass of juveniles prior to hibernation was 89.7 $\pm$ 14.8 g. The mean daily mass gain was 0.82 g. The range of mass change varied from -4.00 to 5.71 g/day. Wild-caught juveniles most quickly gained mass during the first week in captivity with a mean rate of 4.54 g/day. We found that prior to hibernation body mass of juvenile dormice was lower than it was expected according to the literature. We show that fluctuations of body mass can be high, even in a short period of time.

Are antipredator behaviours of hatchery Salmo salar juveniles similar to wild juveniles?

This study explores how antipredator behaviour of juvenile Atlantic salmon Salmo salar developed during conventional hatchery rearing of eggs from wild brood stock, compared with the behaviour of wild-caught juveniles from the same population. Juveniles aged 1+ years were tested in two unfamiliar environments; in one S. salar were presented with simulated predator attacks and in the other they were given the opportunity to explore an open-field arena. No difference was found in their spontaneous escape responses or ventilation rate (reflex responses) after simulated predator attacks. Hatchery-reared juveniles were more risk-prone in their behaviours than wild-caught individuals. Hatchery juveniles stayed less time in association with shelter. In the open-field arena, hatchery juveniles were more active than wild juveniles. Hatchery juveniles were also immobile for less time and spent a shorter amount of time than wild juveniles in the fringe of the open-field arena. Salmo salar size had no effect on the observed behaviour. Overall, this study provides empirical evidence that one generation of hatchery rearing does not change reflex responses associated with threats, whereas antipredator behaviour, typically associated with prior experience, was less developed in hatchery-reared than in wild individuals.

Marine reserve creation and interactions between fisheries and capture‐based aquaculture: A bio‐economic model analysis

AbstractThe rapid growth of aquaculture affects wild fisheries in several ways. We present a bioeconomic model of the interaction between a commercial wild fishery and capture‐based aquaculture that depends on harvest of wild juveniles. We assume that aquaculture reduces the intrinsic growth rate of the wild fish stock due to wild caught juveniles used as seeds, influencing wild stock size and commercial harvest. This may increase the economic conflicts between fishers and farmers. Introducing a marine protected area is expected to reduce these conflicts. The model considers both open access and economically optimal management regimes outside the marine protected area using numerical simulation. The numerical results show that a marine protected area of a certain size may increase economic benefits of both fishers and farmers in the case of optimal management, and enhance wild catch outside the reserve when there is open access.

Juvenile social status predicts primary sex allocation in a sex changing fish

Both individual sex and population sex ratio can affect lifetime reproductive success. As a result, multiple mechanisms have evolved to regulate sexual phenotype, including adult sex change in fishes. While adult sex change is typically socially regulated, few studies focus on the non-chromosomal mechanisms regulating primary sex allocation. We investigated primary sex determination in the bluebanded goby (Lythrypnus dalli), a bidirectionally sex-changing fish. Of the studies investigating primary sex determination in species with adult sex change, this is the first to incorporate the roles of social status and size, key factors for determining adult sex allocation. For L. dalli, adult sex is regulated by social status: dominants are male; subordinates are female. In social groups of laboratory-reared juveniles, we demonstrate that status also predicts primary sex. Dominant juveniles developed male-typical genitalia, and their gonads contained significantly less ovarian tissue than subordinates, which developed female-typical genitalia. To better understand natural development, we quantified the distribution of juveniles and adults on the reef and analyzed genital papilla and gonad morphology in a sample of wild-caught juveniles. Juveniles were observed in various social environments, and most grouped with other juveniles and/or adults. The majority of field-caught juveniles had female-typical genitalia and bisexual, female-biased gonads. These data are consistent with a single mechanism that regulates sexual phenotype throughout life. Social status could first cause and then maintain through adulthood a female-biased population, allowing individuals to regulate sex based on local conditions, which is important for optimizing lifetime reproductive success.

Variations in hepatic biomarkers in American alligators (Alligator mississippiensis) from three sites in Florida, USA

Sub-individual biomarkers are sub-lethal biological responses commonly used in the assessment of wildlife exposure to environmental contaminants. In this study, we examined the activity of glutathione-s-transferase (GST) and lactate dehydrogenase (LDH), and metallothionein (MT) concentrations among captive-raised alligator hatchlings, wild-caught juveniles, and wild-caught adults. Juveniles and adults were collected from three locations in Florida (USA) with varying degrees of contamination (i.e. Lake Apopka (organochlorine polluted site), Merritt Island National Wildlife Refuge (NWR) (metal polluted site), and Lake Woodruff NWR (reference site)). We examined whether changes in the response of these three biomarkers were age and sex dependent or reflected site-specific variations of environmental contaminants. Juvenile alligators from Merritt Island NWR had higher MT concentrations and lower GST activity compared to those from the other two sites. This outcome was consistent with higher metal pollution at this location. Sexually dimorphic patterns of MT and GST (F > M) were observed in juvenile alligators from all sites, although this pattern was not observed in adults. GST activity was lower in captive-raised alligators from Lake Apopka and Merritt Island NWR as compared to animals from Lake Woodruff NWR, suggesting a possible developmental modulator at these sites. No clear patterns were observed in LDH activity. We concluded that GST and MT demonstrate age and sex specific patterns in the alligators inhabiting these study sites and that the observed variation among sites could be due to differences in contaminant exposure.

Resource selection by tuatara following translocation: a comparison of wild-caught and captive-reared juveniles

Animal reintroduction is an important tool for species conservation, but success rates can be low. Comparative studies can be used to identify factors that influence success during translocations. We studied the reintroduction of captive-reared and wild-caught juveniles of an iconic reptile, the tuatara Sphenodon punctatus, on the South Island of New Zealand. We followed juveniles from three treatment groups (wild-caught and from two outdoor head-start facilities, all of the same genetic stock) during the initial five months of the establishment phase. We compared resource selection at three scales: landscape, high-use areas, and retreat-sites. At the landscape scale, juvenile tuatara from all groups remained in forest habitats similar to those where they were released, which also had the highest night-time operative temperatures (theoretically equilibrated body temperatures); in high-use areas they chose to be close to cover; and for retreat-sites they selected burrows. Our results demonstrate that juvenile tuatara, irrespective of group, used similar resources, and suggest that either wild-caught or captive-reared juveniles could be used as founders for future translocations.