Captive Conditions Research Articles

Environmental, individual and social traits of free-ranging raccoons influence performance in cognitive testing.

Cognitive abilities, such as learning and flexibility, are hypothesized to aid behavioral adaptation to urbanization. Although growing evidence suggests that cognition may indeed facilitate persistence in urban environments, we currently lack knowledge of the cognitive abilities of many urban taxa. Recent methodological advances, including radio frequency identification (RFID), have extended automated cognitive testing into the field but have yet to be applied to a diversity of taxa. Here, we used an RFID-enabled operant conditioning device to assess the habituation, learning and cognitive flexibility of a wild population of raccoons (Procyon lotor). We examined how several biological and behavioral traits influenced participation and performance in testing. We then compared the cognitive performance of wild raccoons tested in natural conditions with that of wild-caught raccoons tested in captivity from a previous study. In natural conditions, juvenile raccoons were more likely to habituate to the testing device, but performed worse in serial reversal learning, compared with adults. We also found that docile raccoons were more likely to learn how to operate the device in natural conditions, which suggests a relationship between emotional reactivity and cognitive ability in raccoons. Although raccoons in both captive and natural conditions demonstrated rapid associative learning and flexibility, raccoons in captive conditions generally performed better, likely owing to the heightened vigilance and social interference experienced by raccoons in natural conditions. Our results have important implications for future research on urban carnivores and cognition in field settings, as well as our understanding of behavioral adaptation to urbanization and coexistence with urban wildlife.

Conservation Biology and Reproduction in a Time of Developmental Plasticity.

The objective of this review is to ask whether, and how, principles in conservation biology may need to be revisited in light of new knowledge about the power of epigenetics to alter developmental pathways. Importantly, conservation breeding programmes, used widely by zoological parks and aquariums, may appear in some cases to reduce fitness by decreasing animals’ abilities to cope when confronted with the ‘wild side’ of their natural habitats. Would less comfortable captive conditions lead to the selection of individuals that, despite being adapted to life in a captive environment, be better able to thrive if relocated to a more natural environment? While threatened populations may benefit from advanced reproductive technologies, these may actually induce undesirable epigenetic changes. Thus, there may be inherent risks to the health and welfare of offspring (as is suspected in humans). Advanced breeding technologies, especially those that aim to regenerate the rarest species using stem cell reprogramming and artificial gametes, may also lead to unwanted epigenetic modifications. Current knowledge is still incomplete, and therefore ethical decisions about novel breeding methods remain controversial and difficult to resolve.

EFFECT OF AGRICULTURAL PESTICIDE (CYPERMETHRIN) ON Labeo rohita

The effect of cypermethrin pesticide on juvenile rohu (Labeo rohita) was determined in captive condition. Live and healthy rohu (average initial weight 21g) were exposed to five concentrations of Cypermethrin 0.63, 0.13, 0.025, 0.005, 0.001 ppm and one control group (no pesticide) with two replications for each treatment. The mean temperature and pH in the experimental tanks were 27.53±0.41ºC and 7.22±0.013 ppt, respectively. The highest growth recorded in control tank was 0.2g per week, where as nosignificant growths were found in 0.001 ppm and 0.005 ppm concentration. Rohu reared in the 0.13 ppm had the lowest growth. The median lethal concentration values were found at 0.025, 0.005 and 0.001 ppm for 9th, 17th and 20th day, respectively. Behavioral patterns were observed in both lethal 0.63, 0.13 ppm and sub lethal concentration 0.025 ppm. L. rohita in toxic media exhibited erratic and darting movements with imbalanced swimming activity, which might be due to the malfunctioning of neurotransmitters, followed by hyper and hypo opercula activity, loss of equilibrium and mucus secretion all over the body were observed

Observations on growth rate and allometry in the seasonal predatory killifish Nothobranchius ocellatus (Teleostei: Cyprinodontiformes).

During the course of a taxonomic study involving Nothobranchius ocellatus, a fast-growing seasonal killifish of predatory behaviour, important morphometric differences were observed between the original measurements of the lost holotype and the neotype and additional available material of the species. In a laboratory study, the total length (TL) of selected specimens was measured from hatching and, during the sub-adult to sexually mature young adult phase, from 37 to 84 days age, subjected to an additional suite of detailed morphometric measurements. Growth rate was relatively rapid and linear at 1.31.4 mm/day through the first phase to sexual maturity at 78 weeks, followed by a marked flattening of the growth curve with, from 14 weeks, rates of only about 1.0 mm/week in males and 0.6 mm/week in females. Under captive conditions, maximum TL for adult male specimens ranged from 101 to 116 mm and 88 to 102 mm for females. Analyses of the morphometric character measurements made during the 3784 day development phase showed allometric shape changes, primarily seen in body depth, head length and several other measures of head features, proportions of caudal peduncle, and length of fin bases. These changes are most prominently seen in males and changes in head proportions are important in relation to the predatory behaviour of the species. Morphometric differences between the immature holotype and the newly available material, including the neotype, are consistent with allometric shape variation, particularly in males of this species. Considering the seasonal life cycle common to all Nothobranchius species, and similar growth patterns, it is likely that allometric growth has broad relevance within the genus, suggesting it is a factor that should be taken into account in taxonomic endeavours, especially when the number of study specimens is limited.

Effects of Breeding Forest Musk Deer on Soil Bacterial Community Structure

Breeding captive forest musk deer is an important way to obtain musk resources, but it also causes changes in the ecological environment of the breeding site. This study compared the changes in soil bacterial communities inside and outside the captive breeding site and tried to find out its influencing factors. High-throughput sequencing analysis and other methods were used to analyze the changes in the bacterial community structure in the natural soil and forest surrounding the musk deer site after 4 years of captivity. The results showed that the main dominant phyla in the captive soil samples were Proteobacteria, Acidobacteria and Chloroflexi. In order, Sphingomonadales (8.7%), Acidobacteriales (9.9%) and Solibacterales (6.1%) were dominant in the captive soil, while Rhizobiales (11.3%) and Gaiellales (6.2%) were found in non-captive soil. The main soil-specific microorganisms under captive conditions were Burkholderiales, Pseudomonadales and Sphingomadales. These microorganisms mainly gather at the order level and can be used as indicator microorganisms. A canonical correspondence analysis (CCA) showed that the microbial diversity in captivity soil was significantly affected by the contents of organic matter, available phosphorus and total nitrogen. These results will provide a basis for the healthy breeding of animals and shed light on the protection of the ecological environment in the Bashan Mountains of Qinling.

Reproductive aspects of the dwarf cichlid Apistogramma agassizii under captive conditions

Apistogramma agassizii is a native fish from the Amazon basin, which is of great interest for fishkeeping and is supplied to the retail trade from extractivism. Knowledge about the reproductive characteristics of this fish is fundamental to successful breeding. Objective: This work aimed to study the behavior and reproductive performance of this species in white and black aquariums. A total of 16 pairs were used, 8 in each treatment. The system had water recirculation, with fresh and inert food supply. Result: The fish demonstrated parental care, more accentuated by the female and partial spawning. The same coloration pattern was observed in both treatments, with coloration intensifying only during spawning. The eggs were adhesive and U-shaped/oval. The females followed the larvae, even after they left the nests, and attacked the males when they approached the offspring. Males exhibited territorial behavior. No significant differences were observed for the following parameters studied: largest and smallest egg size, spawning weight, absolute fecundity, number of hatched larvae, and hatchability rate. Conclusion: This study found that the fish are prolific and show good reproductive rates in conditions of captivity; thus, they are suitable to rear for the ornamental fish trade.

Non-uniform metamorphosis underlies different development trajectories in hatchery-reared flathead grey mullet (Mugil cephalus)

The flathead grey mullet (Mugil cephalus) is at the focus of an intense domestication effort. However, despite significant advances, aquaculture of grey mullets is still based on capture of wild fingerlings in estuaries and stocking them into ponds. Such reliance on wild seed limits aquaculture production since it is highly seasonal, unpredictable, hinders genetic improvement programs and may negatively affect local capture fisheries. As captive breeding has been optimized for the species, to date, larval rearing remains the main challenge hindering the commercial production of captive-bred mullets. Here we set out to characterize larval development of grey mullets under captive conditions and to identify key developmental bottlenecks. By analyzing four larval batches from a commercial hatchery, we defined ten distinct developmental stages from hatching to the end of metamorphosis based on macroscopically observable morphological features. Using this developmental atlas to study development dynamics, we found that mullet larvae exhibit a biphasic growth profile with a 17-fold increase in growth rates at the onset of metamorphosis. Moreover, we found that within rearing batches, size variation almost doubles at metamorphosis, suggesting that the onset of metamorphosis is a critical step that increases variation by dictating different growth trajectories to early and late-metamorphosing larvae. By plotting the developmental stages against different morphometric parameters, we show here that age is a poor predictor of larval development due to large variations in development rates both within and between batches. We found that mullet larvae begin metamorphosis at a set size threshold of ~4.5 mm, however age at this threshold varies greatly even within batches. This age and size variance is further amplified by the aforementioned enhanced growth rates at metamorphosis and results in highly non-uniform fry, which complicate the rearing and weaning procedures. Understanding and treating the underlying causes for delayed metamorphosis are therefore considered important steps for the full domestication of the grey mullet.

American alligator (Alligator mississippiensis) weight gain in captivity and implications for captive reptile body condition.

The body condition of an animal is an indicator of health status and is dependent upon many factors, some of which can vary between wild and captive settings. Despite this, there have not been many studies on how captivity affects body condition relative to wild animal populations. This study explores the body condition of captive and wild American alligators (Alligator mississippiensis) because reptiles are frequently overlooked in studies of captive animal health and because alligators are well-represented in captivity. We collected body condition data from 209 captive alligators and 935 wild alligators throughout Florida and southeastern Georgia and compared the relationships between body condition and body length for each group. We found that captive alligators exhibited significantly higher body condition values as they aged, and that this result was driven by the difference between captive and wild males. Body condition values for captive juveniles did not differ from wild juveniles, but they differed when comparing adults. Our results suggest that factors such as diet and movement rates play major roles in determining alligator body condition and that body condition may be an important metric for monitoring captive alligator health, especially for older adult males.

Protein hydrolysate from cattle residues can be included in diets for Nile tilapia ( Oreochromis niloticus ) fingerlings

The study aimed to determine the optimal level of inclusion of protein hydrolysate from cattle residues in diets for Nile tilapia fingerlings. Nile tilapias with an average initial weight of 5 g were used, distributed in 15 net cages. The experiment was carried out for 42 days in a completely randomized design with five treatments (0.0%; 2.5%; 5.0%; 7.5% and 10.0% inclusion of protein hydrolysate) and three replications, with that 50 tilapia were stored in each net tank. After the experimental period, the fish were anaesthetized for blood collection and measurements of the parameters of zootechnical performance. Six animals from each experimental unit were euthanized for further bromatological evaluation of the carcass. The zootechnical performance data, the proximate chemical composition of the carcass and blood biochemical parameters were submitted to analysis of variance (α = 0.05), and the Tukey test (α = 0.05) was applied. There were no significant differences between treatments for the parameters of zootechnical performance and proximate chemical composition of the carcass (p > 0.05). As for blood parameters, a significant difference was detected between treatments in alkaline phosphatase activity, calcium and total protein (p < 0.05). The lower alkaline phosphatase activity determined in the treatments with protein hydrolysate indicates that this product can improve the physiological response of animals to the stress caused by production conditions in captivity. It is concluded that it is possible to include 10% of the protein hydrolysate in the rations without causing any type of damage to the performance, chemical composition of the carcass, or well-being of the fish.

Morphological detection and molecular characterization of Hepatozoon spp. from venomous terrestrial snakes in Iran

Hepatozoon spp. are blood protozoans that can infect snakes. Infections with these parasites are found in more than 200 snake species and are considered to be the most frequent hemogregarines in snakes. In this study, a total of 73 dead snakes in captivity conditions, belonging to six different species, which were collected between June 2018 to October 2020 from different parts of Iran, were examined for the presence of blood parasites with microscopy and molecular methods. DNA was extracted from the removed heart, and PCR was done with two pairs of primers targeting the 18S rRNA gene. By microscopy, Hepatozoon spp. were detected in the heart blood of 29 out of the 73 (39.72%) snakes. From these 29 positive samples, eight were found to be positive using the PCR method. This study aimed to report for the first time the molecular characteristics of Hepatozoon spp. infecting venomous terrestrial snakes in Iran.

Effect of environmental enrichment on Salvator merianae (Squamata: Teiidae) under captivity conditions.

Environmental enrichment seeks to improve the quality of care for animals in captivity through the constant generation of new sources of stimuli to simulate a complexand changing environment. Salvator merianae is a species of large lizard whose native distribution covers the subtropical and humid zones of southeastern South America.The study was carried out in the Experimental Lizard Hatchery belonging to the Facultad de Agronomía y Zootecnia from Universidad Nacional de Tucumán, UNT for its initials in Spanish. Two pens were used, a control group R1 (Enclosure 1) and an experimental group R2 (Enclosure 2), where data were taken ithout enrichment (R2 W/O-E) and with enrichment (R2 WE). An ethogram was used to record the different behaviors that were then grouped into eight categories to evaluate how animals spend their time. Behaviors were recorded on video, the applied technique was the focal animal sampling with instantaneous recording, the extracted data were ex-ported into individual spreadsheets. The Landau index was calculated to determine the existence of hierarchies. The data suggest that the modification of the enclosure conditions has the capacity to alter the behavioral profiles. Only a few behavioral categories showed significant differences. No significant differences were found, in the frequency of the behavioral categories, between males and females. There was a decrease in the frequency of reproductive behavior in males in R2. There was anon-linear hierarchy among the individuals. A ecrease in the chases was observedamong individuals in R2.

Long-term memory in frog-eating bats

Long-term memory has clear advantages for animals but also has neurological and behavioral costs1-3. Encoding memories is metabolically expensive1. Older memories can interfere with retrieval of more recent memories3, prolong decision-making and reduce cognitive flexibility2,3. Given these opposing selection pressures, understanding how long memories last can shed light on how memory enhances or constrains animals' abilities to exploit their niches. Although testing memory retention in wild animals is difficult, it is important because captive conditions do not reflect the complex cognitive demands of wild environments, and long-term captivity changes the brain4 (Data S1A). Here, we trained wild-caught frog-eating bats (Trachops cirrhosus) to find prey by flying to a novel acoustic cue. After they learned the rewarded sound, we released them back into the wild, and then re-captured some of them one to four years later. When re-tested, all eight 'experienced' bats that previously learned the novel prey sounds flew to those sounds within seconds, whereas 17 naïve bats tested with the same sounds showed weak responses. Experienced bats also showed behavior indicating generalization of memories between novel sounds and rewards over time. The frog-eating bat's remarkably long memory indicates that an ability to remember rarely encountered prey may be advantageous for this predator and suggests hitherto unknown cognitive abilities in bats.

Suspended Structures Reduce Variability of Group Risk-Taking Responses of Dicentrarchus labrax Juvenile Reared in Tanks

Structural enrichment is considered a useful tool to improve the welfare conditions of captive fish by deliberately increasing the physical heterogeneity and complexity of captivity environments. However, the potential effects of structural enrichment on the stress response at the group level and on social interactions have not been well studied yet. In this study, we demonstrate that suspended vertical structures (U-shaped ropes) can reduce behavioural variability among fish groups (tank level) of European seabass (Dicentrarchus labrax) juveniles. Differences in behavioural responses during group risk-taking tests (e.g., number of passes per fish) between treatments were detected, and these responses in seabass in enriched captive conditions were more homogeneous among tanks compared to fish from non-enriched tanks. These results suggest a positive effect of the structural enrichment on social stabilisation and response to stressful events at the tank level in seabass. However, further research is still needed to improve the knowledge of the potential effects of structural enrichment on fish welfare and aquaculture management, considering different enrichment designs, intensities, and strategies according to farming conditions, biological needs, and preferences of the fish species and life-stage reared in captivity.

Endocranial volume increases across captive generations in the endangered Mexican wolf

Endangered animals in captivity may display reduced brain sizes due to captive conditions and limited genetic diversity. Captive diets, for example, may differ in nutrition and texture, altering cranial musculature and alleviating constraints on cranial shape development. Changes in brain size are associated with biological fitness, which may limit reintroduction success. Little is known about how changes in brain size progress in highly managed carnivoran populations and whether such traits are retained among reintroduced populations. Here, we measured the endocranial volume of preserved Mexican wolf skulls across captive generations and between captive, wild, and reintroduced populations and assessed endocranial volume dependence on inbreeding and cranial musculature. Endocranial volume increased across captive generations. However, we did not detect a difference among captive, wild, and reintroduced groups, perhaps due to the variability across captive generations. We did not find a relationship between endocranial volume and either inbreeding or cranial musculature, although the captive population displayed an increase in the cross-sectional area of the masseter muscle. We hypothesize that the increase in endocranial volume observed across captive generations may be related to the high-quality nutrition provided in captivity.

Successful Culture of Pelagia noctiluca (Cnidaria: Scyphozoa) Over Time: A Continuous Supply of the Holoplanktonic Jellyfish for Research and Industrial Applications

The scyphozoan Pelagia noctiluca has potential value for research and a wide variety of industrial applications. However, its holoplanktonic life cycle makes it difficult to maintain a permanent stock in aquaculture, unlike the continuous supply of newly-released ephyrae from jellyfish species with a benthic life stage. We investigated optimal feeding conditions for the captive breeding of P. noctiluca, monitoring total body diameter, morphological development, survival rate, and instantaneous growth rate. Diets of different items encapsulated in gelatin or non-motile prey were not suitable for successful growth of the early stages (ephyra and metaephyra), whereas rotifers were a sufficient food source for healthy growth. Fertilized eggs from sexually-mature jellyfish were obtained at 84.5 ± 2.1 and 87.0 ± 9.9 days post-fecundation in the presence and absence of gelatinous prey (Aurelia sp.), respectively. In contrast with the general consensus, we demonstrate that the incorporation of medusivorous prey was not essential for proper growth and closure of P. noctiluca life cycle. Instead, we recommend the inclusion of white shrimps (Acetes sp.) for the formation and maturation of gonads and production of eggs. Instantaneous growth rates (57.0% d-1), the highest reported to date for this species in captive conditions, were higher during the early stages. A third generation of cultured P. noctiluca was obtained for the first time (169 – 179 experimental days), demonstrating the durability of the culture, providing permanent stock and halving the production time of mature individuals compared to previous studies. Finally, we validated the use of captive-bred specimens through quantification of the hemolytic area after the sting process using the tentacle skin blood agarose assay methodology.

Childhood in Captivity: Bioarchaeological Evidence from a Late Colonial Sugar Plantation in Central Peru

Children and childhood have emerged as important topics for understanding the history of African slavery in the Americas. In historical archaeology, analyses of subadult skeletal remains have provided valuable information about the biological and social conditions of captivity, yet children are infrequently the primary subjects of study in African diaspora bioarchaeology. Recent bioarchaeological research at Hacienda La Quebrada, a late colonial sugar plantation in central Peru, brings new data to bear on these subjects. Excavations at the cemetery for the plantation's enslaved African and Afro-descendant population recovered 158 subadults ranging from newborns to 20 years old, who represented 64% of the burial sample. Paleodemographic data and skeletal indicators of stress indicate that enslaved children were disproportionately affected by the conditions of life at Hacienda La Quebrada, particularly because of insufficient diets and susceptibility to infection and disease. Although these results are specific to the context of plantation slavery in Peru's coastal sugar economy, they contribute new information about the history of African slavery in Peru and about the study of childhood in conditions of captivity and colonialism in the Spanish Americas more broadly.

Gut microbiota of ring-tailed lemurs (Lemur catta) vary across natural and captive populations and correlate with environmental microbiota

BackgroundInter-population variation in host-associated microbiota reflects differences in the hosts’ environments, but this characterization is typically based on studies comparing few populations. The diversity of natural habitats and captivity conditions occupied by any given host species has not been captured in these comparisons. Moreover, intraspecific variation in gut microbiota, generally attributed to diet, may also stem from differential acquisition of environmental microbes—an understudied mechanism by which host microbiomes are directly shaped by environmental microbes. To more comprehensively characterize gut microbiota in an ecologically flexible host, the ring-tailed lemur (Lemur catta; n = 209), while also investigating the role of environmental acquisition, we used 16S rRNA sequencing of lemur gut and soil microbiota sampled from up to 13 settings, eight in the wilderness of Madagascar and five in captivity in Madagascar or the U.S. Based on matched fecal and soil samples, we used microbial source tracking to examine covariation between the two types of consortia.ResultsThe diversity of lemur gut microbes varied markedly within and between settings. Microbial diversity was not consistently greater in wild than in captive lemurs, indicating that this metric is not necessarily an indicator of host habitat or environmental condition. Variation in microbial composition was inconsistent both with a single, representative gut community for wild conspecifics and with a universal ‘signal of captivity’ that homogenizes the gut consortia of captive animals. Despite the similar, commercial diets of captive lemurs on both continents, lemur gut microbiomes within Madagascar were compositionally most similar, suggesting that non-dietary factors govern some of the variability. In particular, soil microbial communities varied across geographic locations, with the few samples from different continents being the most distinct, and there was significant and context-specific covariation between gut and soil microbiota.ConclusionsAs one of the broadest, single-species investigations of primate microbiota, our study highlights that gut consortia are sensitive to multiple scales of environmental differences. This finding begs a reevaluation of the simple ‘captive vs. wild’ dichotomy. Beyond the important implications for animal care, health, and conservation, our finding that environmental acquisition may mediate aspects of host-associated consortia further expands the framework for how host-associated and environmental microbes interact across different microbial landscapes.

Pigs in a pit: An unusual find of ritual suid exploitation in an Early Islamic context at the site of Tel Yavne, Israel

A shallow, human dug pit dated to the Early Islamic period (Area C3, 9th-10th century CE) and containing solely pig remains (Sus scrofa/S. s. domesticus) was discovered in an ongoing large scale excavation in Tel Yavne, Israel. Evidence of the intentional disposal or interment of the pig remains in the pit raises questions regarding the reasons for this peculiar occurrence at a time that the southern Levant was subject to the rule of Islamic law and dietary prohibitions. While it is known that non-Muslim communities continued to flourish in the region during the Early Islamic period (Fischer and Taxel 2007, and see the historical references therein), direct evidence of pig exploitation at this time has not been extensively documented. Our results indicate that at least seven suids, most of them domesticated and a few of feral/wild individuals, were slaughtered and rapidly deposited together inside the pit, in a one-time event. A comparison of the remains from the pit with other suid remains from the site, dated to the late Byzantine-Early Islamic period (7th-10th century CE), shows the pit to be a strikingly dense concentration of pig remains and reveals a unique techonomic pattern of the dominance of maxilla over mandibles. Pig husbandry at the site was generally based on culling of young animals (piglets), a pattern typical of dense urban sites, while many of the animals in the pit displayed abnormal molar tooth wear, suggesting consumption of abrasive food and teeth defects indicating stressful captivity conditions. We refer to archaeological and historical data in an attempt to reconstruct a scenario explaining the suid pit.

Seasonal Changes of Growth, Immune Parameters and Liver Function in Wild Chinese Sturgeons Under Indoor Conditions: Implication for Artificial Rearing.

Seasonality has a significant effect on the physiology of fish, especially the effect of water temperature changes. In the present study, the growth, innate immune parameters and liver function indices of two rescued wild adult Chinese sturgeons under captive conditions were monitored for 1 year. The results showed that the total annual weight loss rate of the male was −4.58% and the total weight gain rate of the female was 24.12%, in which the weight of both individuals registered highly significant differences in summer, fall and winter (p < 0.01). The male Chinese sturgeon also exhibited negative specific growth rates (−0.1 to −0.8%) during spring to fall, whereas positive specific growth rates, ranging from 0.03 to 0.11%, were recorded in the female. Seasonality also affected the innate immune parameters of the two Chinese sturgeons, in which leukocytes had been increasing since spring and C-reactive protein (CRP) content was significantly higher (p < 0.05) in summer than fall in both individuals. The CRP level of the male Chinese sturgeon showed a significant increase from fall to winter (p < 0.05), suggesting that it may have contracted infection or inflammation during this study period. With the analysis of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), transaminase (AST:ALT) ratio, alkaline phosphatase, albumin to globulin ratio and triglycerides, it was found that the liver function of the captive Chinese sturgeons was adversely affected along seasonal changes, with the highest degree of liver impairment in winter. In combining observations from growth performance and changes in innate immune and liver function parameters, the present findings deduced that the male Chinese sturgeon under study was more susceptible to seasonal changes than the female. For better indoor culture of adult Chinese sturgeons, monitoring of hematological parameters to detect early signs of inflammation and liver function abnormality should be conducted with routine veterinary care during prolonged captivity.

The effects of Synthetic gonadotropin releasing hormone analogue (S-GnRHa) on artificial propagation of spotted scat, Scatophagus argus (Linnaeus, 1766)

Spotted scat Scatophagus argus is an important brackishwater species predominantly inhabited in south-west coast of Bangladesh. The aim of this study was to develop a hormonal induced reproduction protocol of farm-domesticated S. argus along with larvae rearing techniques. Synthetic gonadotropin releasing hormone analogue (S-GnRHa) was injected at the dose of 60:30 μg/kg BW (Female: Male). In female fish 20% of the total dose was applied as priming dose and 12 hours later 80% as resolving dose. The latency period ranged from 32 to 36 h was determined by observing the time between first injection and ovulation. However, after achieving full oocyte maturation and ovulation, eggs were collected by stripping and fertilization was carried out using pooled sperm from male. The mean ovulation, buoyancy, fertilization and hatching rate were found 70±1.8; 68±7.7; 40±2.3% and 53±5.2% respectively. Over the embryonic development following stages were witnessed in embryos: meroblastic cleavage (2-cell), blastula, gastrula and pharyngula. Maximum embryos hatched within 19 hr post fertilization at 28±2.0°C temperature and 28±2.0 ppt salinity. In this study, we dispense the first information on the reproduction of spotted scat in captive condition using S-GnRHa and the optimal dose limit and larval rearing techniques are established. Further studies are warranted to develop the larvae into juvenile stage under variable environmental conditions to increase the fertilization, hatching rate and survival of embryos.