Variation of body condition and plasma energy substrates with life stage, sex, and season in wild-sampled nurse sharks Ginglymostoma cirratum

Proposal and Validation of a Body Condition Score System for the Evaluation of Energy Reserves in the Long-Snouted Seahorse Hippocampus reidi (Ginsburg, 1933)

Given the morphological conformation of seahorses, there are several difficulties associated with the evaluation of body reserves and physical condition. This study proposes the development and validation of a body condition scoring system (BCS) applicable to Hippocampus reidi. This study comprises two phases: first, the development of the BCS methodology, followed by its application to a group subjected to an experimental diet, which serves to validate our findings. Weight gain and biometric parameters of 31 seahorses were weekly monitored for a period of 90-150 days. Additionally, histological analysis of organs of the digestive and reproductive tract was carried out to characterize and validate the scoring system, as well as a skin lipid profile evaluation as a measure of lipid mobilization. It is proposed that animals should be evaluated for abdominal muscle coverage, thoracic narrowing, contrast between the dorsal and abdominal region and muscle coverage between dorsal rings. We found significant differences between size and accumulation of fat in the liver as well as the degree of development of the gonads in the animals evaluated. Better energy reserves and reproductive potential are therefore expected for animals with a higher BCS. Our BCS methodology presents itself as an alternative of high practicality, simplicity and low cost, being an innovative tool for the evaluation of energy reserves in Syngnathids.

Metal(loid) contamination in tiger sharks (Galeocerdo cuvier) from a remote oceanic island in the Equatorial Atlantic Ocean and potential impacts on physiological parameters

We investigated the relationship between blood metal(loid) concentrations and plasma levels of glucose, proteins, triglycerides, cholesterol, lactate, urea, and polyunsaturated fatty acids in tiger sharks (Galeocerdo cuvier) sampled off the Fernando de Noronha Archipelago, a remote oceanic marine protected area in the Equatorial Atlantic Ocean. Results revealed that Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn were detected in the whole blood of tiger sharks and no sexual differences in blood metal(loid) concentrations were observed. Females had higher concentrations of plasma proteins and docosahexaenoic acid. In females, all analyzed elements were positively correlated with each other, except As. Only As was positively correlated with triglycerides, suggesting a potential impact of As exposure on the nutritional condition of this species. The results presented herein reinforce that sharks, even from remote sites, are exposed to metal(loid)s and that such exposure might elicit physiological responses.

Influences of oxygen and temperature interaction on the antibacterial activity, antioxidant activity, serum biochemical indices, blood indices and growth performance of crucian carp

The well-being of fish used in aquaculture is of great interest. Oxygen and temperature are the main factors affecting the welfare of the crucian carp (carassius); however, there are few studies on the combined effects of these on the species. Therefore, this study investigated the impact of different temperatures (18 °C, 24 °C, 30 °C) and oxygen concentrations (2.1 mgL-1, 5.4 mgL-1, 9.3 mgL-1) on serum antibacterial activity, antioxidant activity, hematological parameters and growth performance of the crucian carp. The results showed that there were greater antibacterial properties under conditions of hypoxia at 18 °C (L18) and hyperoxia at 24 °C (H24). The activities of catalase, glutathione peroxidase and total superoxide dismutase were the highest at 24 °C under hypoxia and hyperoxia. In addition, the contents of glucose and total protein first increased and then decreased with the change of temperature; triglycerides were the lowest at 30 °C. The blood parameters of the carp were within a normal range at 24 °C; however, the growth rate was at its lowest under hypoxia treatment at 30 °C (L30). This study showed that high temperature impairs the antibacterial ability, antioxidant capacity and growth performance of the crucian carp, and high oxygen levels can alleviate these adverse reactions. This research provides a theoretical basis for subsequent aquaculture studies.

Serum Protein Electrophoresis Reference Intervals for Six Species of Wild-Sampled Sharks in South Florida

Serum proteins found in the blood have been used as diagnostic markers in both human and animal medicine. Evaluating proteins in the blood of sharks may be a valuable way to assess shark health. The purpose of this study was to perform serum protein electrophoresis from non-lethal blood samples of wild sharks and establish baseline values for six species off South Florida: blacknose (Carcharhinus acronotus), blacktip (C. limbatus), bull (C. leucas), lemon (Negaprion brevirostris), sandbar (C. plumbeus), and tiger shark (Galeocerdo cuvier). Two hundred and fifty-one serum samples were collected between 2015-2018 along with sex determination and morphometric measurements. Agarose gel analysis was performed using mammalian protein fraction delimits albumin, alpha 1-globulins, alpha 2-globulins, beta globulins, and gamma globulins alternatively defined as fractions 1-5. Reference electrophoretic profiles were established for each species, revealing the dominance of protein fractions 3 and 4. The fraction 3:4 ratio was determined for each shark and reference intervals for total solids, protein fractions, and fraction 3:4 ratio are reported for each species. There were no significant differences in total solids or protein fractions between males and females of any species. In both blacktip sharks and bull sharks, total solids were positively correlated with body size, but not in the other species evaluated. In blacknose sharks, the fraction 3:4 ratio was positively correlated with body condition. Results suggest that there may be differences in total solids values across dry and wet seasons for some species. Newly established reference intervals can now be utilized in future research to evaluate the health of captive sharks and to investigate the health status of individuals in the wild as well as relate health measures to environmental conditions.

Energetic consequences of resource use diversity in a marine carnivore

Understanding how intraspecific variation in the use of prey resources impacts energy metabolism has strong implications for predicting long-term fitness and is critical for predicting population-to-community level responses to environmental change. Here, we examine the energetic consequences of variable prey resource use in a widely distributed marine carnivore, juvenile sand tiger sharks (Carcharias taurus). We used carbon and nitrogen isotope analysis to identify three primary prey resource pools-demersal omnivores, pelagic forage, and benthic detritivores and estimated the proportional assimilation of each resource using Bayesian mixing models. We then quantified how the utilization of these resource pools impacted the concentrations of six plasma lipids and how this varied by ontogeny. Sharks exhibited variable reliance on two of three predominant prey resource pools: demersal omnivores and pelagic forage. Resource use variation was a strong predictor of energetic condition, whereby individuals more reliant upon pelagic forage exhibited higher blood plasma concentrations of very low-density lipoproteins, cholesterol, and triglycerides. These findings underscore how intraspecific variation in resource use may impact the energy metabolism of animals, and more broadly, that natural and anthropogenically driven fluctuations in prey resources could have longer term energetic consequences.

The role of context in elucidating drivers of animal movement

Despite its consequences for ecological processes and population dynamics, intra-specific variability is frequently overlooked in animal movement studies. Consequently, the necessary resolution to reveal drivers of individual movement decisions is often lost as animal movement data are aggregated to infer average or population patterns. Thus, an empirical understanding of why a given movement pattern occurs remains patchy for many taxa, especially in marine systems. Nonetheless, movement is often rationalized as being driven by basic life history requirements, such as acquiring energy (feeding), reproduction, predator-avoidance, and remaining in suitable environmental conditions. However, these life history requirements are central to every individual within a species and thus do not sufficiently account for the high intra-specific variability in movement behavior and hence fail to fully explain the occurrence of multiple movement strategies within a species. Animal movement appears highly context dependent as, for example, within the same location, the behavior of both resident and migratory individuals is driven by life history requirements, such as feeding or reproduction, however different movement strategies are utilized to fulfill them. A systematic taxa-wide approach that, instead of averaging population patterns, incorporates and utilizes intra-specific variability to enable predictions as to which movement patterns can be expected under a certain context, is needed. Here, we use intra-specific variability in elasmobranchs as a case study to introduce a stepwise approach for studying animal movement drivers that is based on a context-dependence framework. We examine relevant literature to illustrate how this context-focused approach can aid in reliably identifying drivers of a specific movement pattern. Ultimately, incorporating behavioral variability in the study of movement drivers can assist in making predictions about behavioral responses to environmental change, overcoming tagging biases, and establishing more efficient conservation measures.

Effects of urbanization on the nutritional ecology of a highly active coastal shark: Preliminary insights from trophic markers and body condition

The synergistic effects of coastal urbanization have dramatically impacted biological communities. Yet, few studies have investigated how urbanization can influence the diet quality and trophic ecology of coastal sharks. In a preliminary study, we examined for spatial variation in the nutritional ecology of a highly active marine predator, the blacktip (Carcharhinus limbatus) exposed to regional differences in coastal urbanization in southeast Florida. We used medium-term nutritional indicators (i.e., body condition and whole blood stable isotopes [δ¹⁵N and δ¹³C]) and short-term dietary markers (i.e., plasma fatty acid profiles) to test the hypothesis that blacktip sharks sampled within highly urbanized areas (hereafter, 'urban sharks') would exhibit higher body condition, but lower diet quality, compared to conspecifics sampled in areas exposed to relatively low levels of urbanization (hereafter, 'urban sharks'). Our initial results showed that urban blacktip sharks exhibited relatively higher body condition, blood δ¹⁵N levels, and percentages of saturated fatty acids compared to non-urban sharks. Collectively, these results suggest a possible positive alteration in the amount of food consumed by blacktip sharks in the study region and/or in the caloric value of their prey. We also found lower percentages of bacterial markers and higher values of dinoflagellate markers in urban sharks. Accordingly, we did not detect an expected reduction in diet quality (in terms of essential fatty acids) in this highly active species exposed to urbanization, as has been previously reported in a resident shark species (Ginglymostoma cirratum). Therefore, it is possible that lifestyle and feeding behavior influence the quality of food consumed by urban sharks. We suspect that impacts of urbanization are more pronounced in resident, sedentary and benthic species.

Unraveling Metabolite Provisioning to Offspring Through Parental Fluids: A Case Study of the Brazilian Guitarfish, Pseudobatos horkelii

Elasmobranchs have a very distinct metabolism, and many aspects related to the energetic dynamics of these animals remain poorly investigated. The reproductive period is particularly vulnerable for viviparous species, as part of the energy reserves of the parental biomass is reallocated for gamete production and embryo development. In this context, this study aimed to characterize parental metabolite provisioning to the offspring (both sperm and developing embryos) of the Brazilian Guitarfish, Pseudobatos horkelii, through glucose, β-hydroxybutyrate, triglycerides, and total cholesterol determinations in the uterine liquid (UL) and serum of pregnant females and in the seminal fluid (SF) and serum of males during the copulation period. No significant difference was observed for the analyzed markers between the UL and SF. Except for triglycerides, higher in female serum samples, all other energy markers were present at similar concentrations in the serum of both females and males. When comparing female UL and serum, significant differences were observed for triglycerides and total cholesterol. No differences were observed between SF and serum in males. The results indicate that all markers are being made available to offspring, possibly complementary to the yolk in the case of maternal liquid, and as an additional source for sperm mobilization required during egg fertilization in the case of the paternal fluid. Correlations between the markers in the parental matrices were also noted, compatible with the metabolic pathways activated during energy mobilization in vertebrates. Moreover, distinct marker predominance patterns were also noted for both UL and SF. Energy mobilization characterization directed to offspring through parental fluids aids in unraveling metabolic dynamics during the reproduction stage while also providing support for stress physiology studies to evaluate the indirect effects of parental allostatic overload in both sperm and developing embryos. Finally, energy mobilization assessments of parental fluids may also help elucidate how internal fertilization and viviparity evolved in this very distinct taxonomic group.

Initial Characterization of Male Southern Stingray (Hypanus americanus) Reproductive Parameters and Preliminary Investigation of Sperm Cryopreservation

Simple Summary

Understanding the reproductive biology of a species is critical for the development of biobanks and assisted reproductive techniques to aid in the genetic management of isolated populations. Male southern stingray (Hypanus americanus) reproductive examinations were opportunistically conducted in March and June. Semen and plasma were collected to characterize ejaculate parameters and to investigate the effect of plasma total testosterone on semen quality. Semen was used for preliminary sperm cryopreservation studies. Changes in semen quality were observed with changes in plasma testosterone concentrations and body conditions. Southern stingray spermatozoa were highly sensitive to cooling rates with slower rates, producing a higher post-thaw survival.

Abstract

This study investigated the reproductive biology and sperm cryopreservation of ex situ southern stingrays (Hypanus americanus) by semen collection and characterization and the development and validation of an enzyme-linked immunoassay for plasma total testosterone. Semen was collected in March and June using a manual massage technique, and the ejaculates were assessed for volume, pH, osmolarity, motility, status (0–5 scale: 0 = no forward progression, 5 = rapid linear progression) and total sperm count. Semen was extended in Hank’s elasmobranch ringer solution containing 10% DMSO, 10% glycerol or 5% glycerol with 5% N-methylformamide and cryopreserved using a conventional freezing method (~−50 °C/min) or a modified slow freezing method (~−3 °C/min). Body condition was scored from 1–5 and was noted to be low in March (1.93 ± 0.07) due to feeding practices and increased by June (2.93 ± 0.05) after dietary corrections were made. A concomitant increase (p < 0.05) in plasma total testosterone concentration and sperm motility was noted between March (8.0 ± 7.2 ng/mL, 5.71 ± 2.77%) and June (97.3 ± 11.3 ng/mL, 51.4 ± 14.3%). Samples cryopreserved using a modified slow freeze method (~−3 °C/min) had higher post-thaw motility and plasma membrane integrity than conventionally cryopreserved samples. Data indicate that southern stingray sperm morphometrics adheres to those of other elasmobranch species and that a slow cooling rate may be an avenue of research to improve southern stingray sperm survival during cryopreservation.