Juvenile Size Classes Research Articles

Oxidative responses in small juveniles of Colossoma macropomum anesthetized and sedated with Ocimum gratissimum L. essential oil.

This study evaluated the use of essential oil of Ocimum gratissimum (EOOG) for anesthesia and in transport of Colossoma macropomum. Experiment 1, Test 1, anesthesia induction and recovery times were determined using different EOOG concentrations (0, 20, 50, 100, 200, 300mg L-1), with two size classes: Juveniles I (0.86g) and Juveniles II (11.46g) (independent tests in a completely randomized design). Based on the results of Test 1, in Test 2 Juveniles II were exposed to EOOG concentrations: 0, 20, 100mg L-1. Tissue samples were collected immediately after induction and 1h post-recovery, to assess oxidative status variables. Experiment 2, Juveniles I (0.91g) and Juveniles II (14.76g) were submitted to transport in water with different concentrations of EOOG (0, 5, 10mg L-1) (independent tests in a completely randomized design). The effects on oxidative status variables were evaluated. Concentrations between 50 and 200mg L-1 EOOG can be indicated for Juveniles I, while concentrations between 50 and 100mg L-1 EOOG for Juveniles II. The concentration of 100mg L-1 EOOG was able to prevent oxidative damage in the liver. In Experiment 2, the concentrations of 5 and 10mg L-1 EOOG added to the transport water caused sedation for both studied size classes of juveniles and did not cause oscillations in water quality variables nor any mortality. The concentration of 10mg L-1 EOOG improved the oxidative status. It can be concluded that EOOG can be used for anesthesia and transport of C. macropomum.

Recent demographic survey of the Radiated Tortoise (Astrochelys radiata) in southwest Madagascar

Abstract.—Effective management strategies for at-risk chelonian populations require sound knowledge of populationdemographics. Previous research on the Critically Endangered Radiated Tortoise, Astrochelys radiata (Shaw 1802),revealed a trend of increasing male bias in the sex ratio and a concomitant decrease in the proportion of juveniles inLavavolo, southern Madagascar. This location is one of the few remaining sites with a high concentration of this speciesand was last studied ten years ago. The aim of our study was to provide an updated snapshot of Radiated Tortoisedemographics at Lavavolo, which, when combined with previous studies, will provide insight into changes over 20years (1999–2019). Additionally, we provide the first assessment on the impact of soil types (calcareous, ferruginous,and sandy) on the distribution of individuals across the site. We used mark-recapture data to determine the sex ratio,age structure, and distribution of size classes. Overall, the study site contained mostly adults (76.87%) with only afew juveniles (23.13%). Though the proportion of juveniles is low, it has increased over the last ten years. However,the sex ratio has become increasingly skewed towards males, 1.8:1. We did not find any significant difference in sexratios between soil types, but there were significant differences in the distribution of size classes, with the smallest sizeclass 0–8 cm most prevalent in sandy soil and the juvenile size class 17–24 cm most frequent in ferruginous soil. Mostjuvenile size classes were less common than expected on the calcareous soil. In general, populations located on calcareoussoil appear to be more vulnerable, potentially due to the long-term existence of poaching activities in this habitat.

Evidence of a compensatory response in invasive Rusty Crayfish (Faxonius rusticus) following intensive harvest removal from northern Lake Michigan fish spawning reefs.

The online version contains supplementary material available at 10.1007/s10530-023-03076-6.

Multi-decade catches of manta rays (Mobula alfredi, M. birostris) from South Africa reveal significant decline

Manta rays (Mobula alfredi and M. birostris) are poorly understood in South Africa, despite their ecological importance and charismatic appeal. This study analyzed a 41-year dataset from the KwaZulu-Natal bather protection program to investigate catch per unit effort between 1981-2021. We used Generalized Additive Models and the probability of encounter to assess annual and seasonal trends, as well as the effect of location and moon phases on catch rates. We also evaluated the size composition and demographics of caught manta rays using the same dataset. Our analysis revealed a significant decline in overall manta ray catches since the late 1990s (p<0.0001), with increased catch rates during summer, suggesting seasonal visitation to South African waters. We found that manta rays were caught at least once in all 46 netted beaches along the 350 km span of coastline, but with significantly more catches in the Central Area, between Anstey’s beach in the north and Mtwalume in the south. We also observed that moon phase had an effect on manta ray presence, with significantly more catches during spring tides at new and full moon phases. Over half of the caught individuals were juveniles, and a total of 841 individuals (52% of the total catch) belonged to the confirmed juvenile size class (1400-2500 mm disc width). We further found that a greater proportion (70%) of juveniles were caught in the southernmost sampled area, from Hibberdene in the north to Mzamba in the south. These findings highlight the importance of South African waters as a seasonal habitat for manta rays along the southern African coastline. The significant decline and spatial-temporal patterns we observed have critical implications for management and conservation efforts. Our study provides valuable baseline data for future research and underscores the need for continued monitoring and protection of these iconic marine species.

Using machine learning models to assess the population dynamic of the freshwater invasive snail Physa acuta Draparnaud, 1805 (Gastropoda: Physidae) in a tropical urban polluted streams-system

The poor understanding of the spread conditions and the geographical patterns of the exotic freshwater snail Physa acuta in sub-Saharan Africa urban streams makes it difficult to design and implement sustainable management tools, especially in deteriorating global and local environments. This study aimed to determine the ecological preferences and the major environmental variables associated with P. acuta abundance, occurrence and distribution in Douala urban streams-system using modelling approaches based on discriminant factor analysis, canonical Spearman correlation and random forest tree models. We inductively define four clusters for snail’s distribution along a geographical and upstream–downstream pollution gradient. Snail’s specimens were collected monthly over a 13-month period in two forest and ten urban sites using a long-handled net (30x30cm side, 400-µm mesh). Meanwhile, measurements of the physicochemical properties of water and streambed sediment were taken. In addition, ten metal contents were determined in P. acuta tissues to assess its ability of bioaccumulation of heavy metals. Results revealed that urban streams of Douala are adversely impaired, especially downstream of industrial effluents. Discriminant factor analysis and random forest regression trees model showed that dissolved oxygen, biochemical oxygen demand, alkalinity, salinity, pH, water depth, wetted width, zinc, iron, cadmium, encumbrance rate of the sediment and sediment types (high sandy mud, sandy mud and muddy sand) were the major environmental variables responsible for structuring P. acuta distribution. Abundances decline drastically following pollution gradient, with great decrease observed in juvenile size classes. High contents of metals were detected in P. acuta tissues, especially downstream of industrial effluents. This study highlights that P. acuta spread in Douala urban-streams system is structured by key environmental variables related to an upstream–downstream pollution gradient. Therefore management plans should emphasize on proper disposal ways of industrial wastes, and stakeholders should take responsible actions in water pollution control and implement the polluter-payer principle.

Settlement and recruitment of fish in mussel farms

. Fish are thought to settle and recruit to shellfish and seaweed farms; however, there is little published evidence to support this assumption. Shellfish and seaweed farms increase structural complexity and epibiota productivity, which may attract settling fish larvae. In this study, fish settlement and recruitment patterns into 2 aquaculture habitats, mussel-kelp co-culture and mussel farm monoculture, were compared to 2 adjacent natural habitats, soft-sediment seafloor and rocky reef, within a settlement season. Standard monitoring units for the recruitment of fish (SMURFs) were used, as they are a common and reliable method for measuring temporal and spatial variability in fish settlement and recruitment among habitat types. The communities of fish species settling and recruiting to both sets of aquaculture and natural habitats were equivalent. This was most likely due to the artificial 3D structure of the mussel farm habitats functioning in a similar manner to the structural complexity of a rocky reef habitat. Further, there was indication that for at least the most abundant fish species, Fosterygion lapillum, the 2 aquaculture habitats were of sufficient quality to support growth from settlement to juvenile size classes (i.e. in mussel monoculture habitat 65% were newly settled in December, and 86% were of juvenile size class by February). Overall, these findings provide foundational quantitative evidence of the interactions that fish have with mussel farms and increases the understanding of restorative opportunities for aquaculture operations.

Anesthesia with eugenol and menthol for Piaractus brachypomus (Cuvier, 1818): Induction and recovery times, ventilation frequency and hematological and biochemical responses

This work evaluated the use of eugenol and menthol as anesthesia for juvenile Piaractus brachypomus. Experiment I determined the times for anesthesia induction and recovery using different concentrations of eugenol and menthol (0, 25, 50, 75, 100 and 125 mg L−1), as well as their effects on ventilation frequency (VF) for two size classes: Juveniles I - 0.87 ± 0.20 g and Juveniles II - 17.14 ± 3.27 g for eugenol and Juveniles I - 0.83 ± 21 g and Juveniles II - 16.83 ± 2.78 g for menthol. Based on data from Experiment I, Experiment II evaluated the effects of 0, 25 (beyond the recommended times for induction and recovery) and 50 mg L−1 (within the recommended times for induction and recovery) of eugenol and menthol (independent tests) on hematological and biochemical parameters of fish measured at two blood collection times (1 h post-induction and 24 h post-recovery). Sixty juveniles weighing 16.92 ± 3.34 g and 60 juveniles weighing 18.49 ± 3.07 g were used to evaluate eugenol and menthol, respectively. Survival was 100% at 24 h after the end of Experiment I. Eugenol concentrations between 50 and 100 mg L−1 were able to induce deep anesthesia for both juvenile size classes, while menthol was able to induce deep anesthesia at concentrations between 25 and 100 mg L−1 for Juveniles I and between 50 and 125 mg L−1 for Juveniles II. The use of 50 mg L−1 of eugenol was able to reduce VF during recovery and prevent an increase in plasma glucose while having little influence on hematological and biochemical parameters after handling. The use of 50 mg L−1 of menthol also reduced VF during recovery and did not cause changes in blood parameters that would be harmful to fish physiology.

No evidence of selection against anomalous scute arrangements between juvenile and adult sea turtles in Florida.

Variations in the number and arrangement of scutes often are used for species identification in hard-shelled sea turtles. Despite the conserved nature of scute arrangements, anomalous arrangements have been noted in the literature for over a century, with anomalies linked to sub-optimal environmental conditions in the nest during development. Long-held assumptions suggest that anomalous scute arrangements are indicative of underlying physiological or morphological anomalies, with presumed long-term survival costs to the individual. Here, we examined a 25-year photo database of two species of sea turtle (Caretta caretta and Chelonia mydas) captured incidentally and non-selectively on the eastern coast of Florida. Our results suggest that C. mydas is substantially more variable with respect to the arrangement of carapacial scutes, while C. caretta had a relatively higher proportion of individuals with anomalous plastron scute arrangements. We also show evidence that (a) the forms and patterns of anomalous scutes are stable throughout growth; (b) there is limited evidence for selection against non-modal arrangements in the size classes that were examined; and (c) that their frequency has remained stable in juvenile cohorts from 1994 until present. These findings indicate that there may not be a survival cost associated with anomalous scute arrangements once the turtles reach juvenile size classes, and that variation in scute arrangements within populations is relatively common.

Where is the nursery for amphidromous nekton? Abundance and size comparisons of juvenile ayu among habitats and contexts

The use of estuarine and marine ecosystems by amphidromous fishes has not been thoroughly studied, especially with respect to habitat types. Here, abundance and size comparisons of juveniles of an amphidromous fish, ayu (Plecoglossus altivelis altivelis), were performed among four types of topographically distinct shallow, soft-bottom habitats across two different environmental contexts (marine and estuarine) through monthly seining along an estuary–ocean ecotone in southern Japan. Topography (open/enclosed and presence/absence of surf zone) and environmental parameters (water temperature and salinity) differed among the four habitats, i.e., riverine estuary, exposed beach, embayed beach, and lagoon estuary. The peak month of juvenile abundance also differed among habitats (riverine estuary in December, exposed beach in January, embayed beach and lagoon estuary in March), as did the mean standard length (riverine estuary < exposed beach < embayed beach < lagoon estuary), although the abundance at embayed beach was significantly greater than in the two estuaries, and almost all size classes of juveniles occurred at embayed beach. A likely explanation for these patterns is that juvenile ayu select coastal habitats as they develop swimming ability and that riverine estuary/exposed beach, embayed beach, and lagoon estuary function as a corridor, primary nursery, and possible foraging ground, respectively. These findings, coupled with implications from previous studies of habitat selection in coasts by anadromous fishes, highlight the importance of seascape-level analysis for elucidating the nursery functions of coastal habitats, even for diadromous nekton. Regional termsNorth-western Pacific, East Asia, Japan, Kyushu, Miyazaki Prefecture.

Seagrass (Zostera capensis) bed development as a predictor of size structured abundance for a ubiquitous estuary-dependent marine fish species

Episodic river flooding has the capacity to ‘reset’ estuaries and redirect these systems on a new path towards some sort of dynamic physical and biological equilibrium. A major river flood through the Kariega Estuary, South Africa, during 2012, provided an ideal opportunity to monitor the occupation of seagrass (Zostera capensis) beds by juveniles of the marine sparid Rhabdosargus holubi, post flood recovery. The estuary contained extensive dense submerged Z. capensis beds throughout the system prior to the flood, almost all of which was removed from the system as a result of the flood. Over the following four years there was a gradual recovery in the extent of cover of submerged Z. capensis beds, which by the end of 2015 had recovered to near the same levels of cover as the pre-flood conditions. In addition to the positive relationship between seagrass development and R. holubi abundance that was recorded, there was also a greater utilisation of this habitat type by the smaller (10–40 mm SL) compared to the larger (41–60 mm SL) juvenile size classes. This new finding emphasizes that occupation of particular estuarine nursery habitats by the juveniles of estuary-associated fish species may not necessarily be uniform and may change with age. The study also reinforces the changing nature of estuarine environments over time and highlights, once again, the importance of this habitat type for the most abundant estuary-dependent marine fish species on the African subcontinent.

Habitat use in different life and moulting stages of Callinectes sapidus (Decapoda, Portunidae) in South Brazilian estuarine and marine environments

AbstractThe blue crab Callinectes sapidus is an important ecological and commercial species. It plays a fundamental role in the structure and function of coastal benthic food webs, with global catches of ~74,357 tons. This is the most exploited portunid species in Brazil. However, few studies about the ecology and population dynamics of C. sapidus have been published. This study aimed to analyse the preferred areas for the spatial distribution of juveniles and moulting individuals of C. sapidus in shallow areas of the Patos Lagoon estuary and the adjacent marine reproductive area, and their relation to water and sediment characteristics. Juveniles and moulting individuals preferred the embayment of the upper estuary, where the sediments are finer, with higher contents of organic matter and the presence of submerged vegetation. There was also a temporal variability in the abundance of juvenile size classes, with two marked increments of smaller individuals: (1) in late spring and summer and (2) in winter, indicating two recruitment peaks. Unusual environmental conditions in the summer of the first year, with an increase of fine sediments and organic matter, combined with low salinities in the adjacent marine area, allowed recruitment of individuals there. We suggest better attention to the embayment around the Marinheiros Island (considered here as upper estuary) for management and protection measures due to the overlapping of recruitment preferences of the blue crab, pink shrimp and fish species in this area.

Habitat-dependent responses of terrestrial salamanders to wildfire in the short-term

Wildfire is an important natural disturbance event that promotes landscape heterogeneity and regulates many wildlife communities. The compounding effects of fire suppression and climate change have increased the frequency and severity of wildfire, but the responses of many organisms to wildfire is unknown. Landscape heterogeneity, specifically microhabitats, may mediate and buffer the effects of wildfire, and evaluating variable responses to wildfire given habitat is key to developing a more cohesive understanding of population responses. Terrestrial plethodontid salamanders are likely disproportionality affected by wildfire events because of their lungless anatomy and reliance on cool and moist habitats. Our knowledge of salamander responses to wildfire in the short-term is limited due to the inherent challenge of opportunistically studying post-wildfire events. We capitalized on a wildfire event in western North Carolina, USA to determine the short-term (6–18-month post-fire) habitat-mediated responses of salamanders to wildfire using body size measurement and repeated count surveys. We observed precipitous declines of the red-legged salamander, Plethodon shermani, in exposed upland forests, but no apparent negative effects in riparian forests 18-months post-fire relative to unburned sites. We also observed a loss of juvenile size classes in the upland burned forest with only the largest adult individuals remaining 18-months post-fire. There were no size class differences in the riparian forests. Our results suggest riparian forests may be buffered from the effects of wildfire because canopy cover, vegetation, and soil duff layer are retained following a wildfire event. Salamander populations inhabiting riparian forests may be at less risk of declining than those in exposed habitats. Our results underscore the need to assess wildfire effects in all habitat types to fully determine the effects of disturbance to populations.

An evaluation of body condition and morphometric relationships within southern California juvenile white sharks Carcharodon carcharias.

Length, mass and girth relationships are presented for 112 juvenile white sharks (JWS) Carcharodon carcharias caught in the Southern California Bight (SCB) nursery area between June 2008 and August 2017. No difference was found between male and female JWS length-mass relationships, but data suggest that JWS in the SCB gain more mass per unit length for the juvenile size classes compared with other C. carcharias populations. Condition-factor-to-liver-mass and condition-factor-to-liver-lipid-content relationships revealed that length and mass (i.e., condition factor) can be used as a non-invasive proxy for body condition for juveniles of this species. The parameters estimated in this study are key information for population assessments of juvenile C. carcharias in the north-east Pacific Ocean and will contribute to the conservation and management of this IUCN Red List Vulnerable species.

Feeding ecology of fishes associated with artificial reefs in the northwest Gulf of Mexico.

The feeding ecology of two reef fishes associated with artificial reefs in the northwest Gulf of Mexico (GoM) was examined using gut contents and natural stable isotopes. Reefs were divided into three regions (east, central, west) across an east to west gradient of increasing reef complexity and salinity. Gray triggerfish (Balistes capriscus) primarily consumed reef-associated prey (xanthid crabs, bivalves, barnacles) and pelagic gastropods, while red snapper (Lutjanus campechanus) diets were mainly comprised of non-reef prey (stomatopods, fishes, portunid crabs). Natural stable isotopes of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) were measured in consumer muscle tissue as well as potential primary producers. Gray triggerfish occupied a lower trophic position than red snapper, with lower δ13C and δ15N values across all size classes and regions, and generally higher δ34S values. Red snapper had a smaller range of stable isotope values and corrected standard ellipse areas across all size classes and regions, indicating a smaller isotopic niche. Contribution estimates of particulate organic matter (26 to 54%) and benthic microalgae (BMA, 47 to 74%) for both species were similar, with BMA contributions greater across all three size classes (juveniles, sub-adults, adults) of red snapper and all but the juvenile size class for gray triggerfish. Species gut contents and stable isotopes differed by region, with fishes consuming more crabs in the east region and more gastropods in the central and west regions. δ13C and δ15N values generally decreased from east to west, while δ34S increased across this gradient. Results highlight species-specific feeding differences associated with artificial reefs, where gray triggerfish may be more dependent on the reef structure for foraging opportunities. In addition, results offer further information on the integral role of BMA in primary production at nearshore artificial reefs.

Morphology and Histology of the Pirarucu (Arapaima gigas) Digestive Tract

The present study describes the morphology and histology of the digestive tract of juvenile pirarucu, which is a Neotropical fish species with great potential for aquaculture in the Amazon region. Three size classes of pirarucu juveniles from commercial fish farms were sampled for histological examination of the oesophagus, stomach, pyloric caeca, intestine and liver. The morphological and histological features of the pirarucu digestive tract are similar to other carnivorous teleosts and enable the species to ingest, store and digest large food items. Acidic and neutral mucins are secreted by the mucosa of the oesophagus, stomach, pyloric caeca and intestine to protect the mucosal epithelium and to lubricate and facilitate food passage along the digestive tract. Complex transverse folds are predominant in the intestinal mucosa and most likely contribute to optimization of the digestion and nutrient absorption processes, thereby offsetting the relatively short length of the intestine. The exocrine pancreas appears diffuse in the liver and mesentery around the pyloric region of the stomach, pyloric caeca and initial part of the intestine. The digestive tract morphology and thickness become increasingly developed with the size of pirarucu.

Abundance, population structure and harvesting selection of two palm species (Hyphaene coriacea and Phoenix reclinata) in Zitundo area, southern Mozambique

In southern Mozambique, the sap and leaves of the palms Hyphaene coriacea and Phoenix reclinata are harvested by local people as sources of traditional beverages, weaving, roofing, fencing and furniture material. The harvesting of these palm products may affect palm population structure, dynamics and viability. This work evaluates the abundance, population structure and harvesting selection of these two heavily harvested palm species. Hyphaene coriacea was more abundant, with a mean density of 601.5±455.9 stemsha−1 against the 251.9±527.3 stemsha−1 of Phoenix reclinata. Both species exhibited steeper negative slopes in the regression analyses of the size class distribution, indicating the presence of more individuals in smaller size classes. Although there was a dominance of shorter over taller size classes, limited recruitment was observed through low densities of seedling and juvenile size classes compared to the size class 1–50cm. The Simpson index of dominance, the permutation index, and the fluctuating quotients between the consecutive size classes showed a degree of instability in both populations. Hyphaene coriacea appears to be more resilient to tapping than Phoenix reclinata, evident in the higher rate of stem survival after tapping. Hyphaene coriacea is favored for tapping compared to Phoenix reclinata. Tappers exhibited positive selection for five out of the six Hyphaene coriacea size classes, against only one Phoenix reclinata size class. The most preferred size class to tap for both species was between 101cm and 150cm tall. The instability detected by the indices of population stability, the coincidence between the size classes with high numbers of dead stems and the most preferred and the low level of the sexual reproduction encountered in both population emphasizes the need for long-term monitoring as well as management measures that integrate the resource users, to ensure the long-term sustainability of these populations.

Interactive effects of nutrient availability and temperature on growth and survival of different size classes of Saccharina japonica (Laminariales, Phaeophyceae)

:In northern Japan, the production of Saccharina japonica exhibits marked annual fluctuation due to changes in seawater temperature and nutrient availability during winter and spring. To better understand this phenomenon, we examined the combined effects of temperature (5°C, 10°C, 15°C and 20°C) and nutrient availability (seawater enriched with 25% Provasoli's enriched seawater vs nonenriched seawater) on photosynthesis, growth and survival and nitrogen and chlorophyll a contents of juvenile sporophytes (2–3 cm) and larger size class sporophytes (100–150 cm) from southern Hokkaido. Both juvenile sporophytes and discs from 100–150-cm-class sporophytes cultured in enriched seawater showed significantly higher growth rates and photosynthetic activities than those cultured in nonenriched seawater. This difference likely was due to the significantly higher nitrogen and chlorophyll a contents of thalli grown in enriched seawater. Significant effects of temperature on growth and photosynthesis were also detected. A significant interaction between temperature and nutrient availability for relative growth rate (RGR) was detected. The positive effect of elevated nutrient availability on RGRs was magnified by an increase in temperature from 5°C to 15°C for juvenile sporophytes and from 5°C to 10°C for 100–150-cm-class sporophytes; whereas, the negative effect of elevated temperature from 10°C to 15°C on RGRs of 100–150-cm-class sporophytes was antagonised by a reduction in nutrient availability. In contrast to the 100% survival rate in enriched seawater, dead juvenile sporophytes and discs from 100–150-cm-class sporophytes were found at 15°C and 20°C in nonenriched seawater, and the survival rates decreased with increasing temperature. Therefore, the growth and survival of sporophytes of S. japonica are significantly affected by nutrient availability and temperature, which may lead to marked fluctuations in annual production.

Ecology of nonnative Siberian prawn (Palaemon modestus) in the lower Snake River, Washington, USA

We assessed the abundance, distribution, and ecology of the nonnative Siberian prawn Palaemon modestus in the lower Snake River, Washington, USA. Analysis of prawn passage abundance at three Snake River dams showed that populations are growing at exponential rates, especially at Little Goose Dam where over 464,000 prawns were collected in 2015. Monthly beam trawling during 2011–2013 provided information on prawn abundance and distribution in Lower Granite and Little Goose Reservoirs. Zero-inflated regression predicted that the probability of prawn presence increased with decreasing water velocity and increasing depth. Negative binomial models predicted higher catch rates of prawns in deeper water and in closer proximity to dams. Temporally, prawn densities decreased slightly in the summer, likely due to the mortality of older individuals, and then increased in autumn and winter with the emergence and recruitment of young of the year. Seasonal length frequencies showed that distinct juvenile and adult size classes exist throughout the year, suggesting prawns live from 1 to 2 years and may be able to reproduce multiple times during their life. Most juvenile prawns become reproductive adults in 1 year, and peak reproduction occurs from late July through October. Mean fecundity (189 eggs) and reproductive output (11.9 %) are similar to that in their native range. The current use of deep habitats by prawns likely makes them unavailable to most predators in the reservoirs. The distribution and role of Siberian prawns in the lower Snake River food web will probably continue to change as the population grows and warrants continued monitoring and investigation.

Effects of three cold weather event simulations on early life stages of Southern Flounder (Paralichthys lethostigma)

ABSTRACTTo determine the minimum age/size at which Southern Flounder, Paralichthys lethostigma, can safely be moved to outdoor rearing facilities in Texas, we examined survival of simulated temperature drops in two distinct life stages: premetamorphic larvae and two size classes of postmetamorphic juveniles (small = 9.8 ± 0.3 mm in TL; large = 19.7 ± 0.6 mm). Temperature was lowered by −0.33°C/h to 4°C, 7°C, or 10°C, held for 48 h and then raised at +0.33°C/h back to normal rearing temperature. Fish were monitored daily for survival. Larger postmetamorphic flounder had high survival for all temperature treatments (89%–100% survival), whereas both premetamorphic larvae and smaller postmetamorphic juveniles had low survival (<30%) for all temperature treatments.

High stocking density during larviculture and effect of size and diet on production of juvenile Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae)

Different stocking densities were investigated in larviculture and feeding of Lophiosilurus alexandri, as well as analyses of the effects on juveniles of two size-classes and two different commercial formulated diets. The first experiment was two-phased: (a) larvae stocked at densities of 60, 120, 180, 240, and 300 larvae L−1 fed with Artemia nauplii and reared for 15 days; (b) in phase 2, densities of 5, 10, 15, 30, and 40 juveniles L−1 were evaluated during feed training (20 days). Mean water temperature in both phases was 28°C. In the first phase of experiment 1, the different stocking densities did not affect fish growth or survival. In phase 2, growth was similar in all densities; however, survival was lower at higher densities. The increased density provided a rise in biomass and number of individuals produced in both phases. In the second experiment, two size-classes of feed-trained juveniles (30.22 ± 1.84 and 34.66 ± 2.41 mm) were given pellets of two different diameters (1.2 and 2.6 mm) for 20 days. The largest juveniles fed the 1.2 mm inert diet had higher final weights and lengths. Larviculture and feed training of L. alexandri can thus be performed successfully at high stocking densities of 300 larvae L−1 during the first 15 days of feeding, and at densities of up to 40 juveniles L−1 during the 20 days of feed training, respectively.