Social behaviors as welfare indicators in teleost fish

Animal welfare is a key issue not only for aquaculture industry and food production, but also for daily husbandry practices in research topics related to physiology in wild and farmed animals. In this context, teleost fish constitute interesting models to assess alternative welfare indicators because of their wide diversity in reproductive and social structures. Any framework for assessing teleost fish welfare needs to account for the physiological mechanisms involved in each species as a first step. A comprehensive approach should also take into account how these physiological and behavioral parameters can be altered by environmental enrichment considering the specific requirements in each case and identifying intrinsic biological characteristics of individual species. This review will show how cortisol and sex steroids regulate social behavior in teleost fish, and how different aspects of social behavior can be employed as welfare indicators according to specific characteristics in each case. This article will consider evidence in teleost fish, including cichlids, characids and cyprinids with different reproductive strategies and social structures (e.g., territorial social hierarchies or shoaling behavior). Neotropical species will be particularly emphasized. The main laboratory-based animal welfare indicators are cortisol, a classical stress hormone, together with sex steroids. Considering that the endocrine landscape is intrinsically related to social behavior, reproductive and agonistic behavioral traits such as aggression, anxiety and courtship are key elements to assess welfare under housing and culture conditions. This review highlights the importance of assessing physiological mechanisms and identifying behavioral characteristics in teleost fish, especially in Neotropical species, as a baseline to understand which environmental enrichment can improve animal welfare in each individual species.

Transcriptomes of testis and pituitary from male Nile tilapia (O. niloticus L.) in the context of social status

African cichlids are well established models for studying social hierarchies in teleosts and elucidating the effects social dominance has on gene expression. Ascension in the social hierarchy has been found to increase plasma levels of steroid hormones, follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) as well as gonadosomatic index (GSI). Furthermore, the expression of genes related to gonadotropins and steroidogenesis and signaling along the brain-pituitary-gonad axis (BPG-axis) is affected by changes of an animal’s social status. In this study, we use RNA-sequencing to obtain an in-depth look at the transcriptomes of testes and pituitaries from dominant and subordinate male Nile tilapia living in long-term stable social hierarchies. This allows us to draw conclusions about factors along the brain-pituitary-gonad axis that are involved in maintaining dominance over weeks or even months. We identify a number of genes that are differentially regulated between dominant and subordinate males and show that in high-ranking fish this subset of genes is generally upregulated. Genes differentially expressed between the two social groups comprise growth factors, related binding proteins and receptors, components of Wnt-, Tgfβ- and retinoic acid-signaling pathway, gonadotropin signaling and steroidogenesis pathways. The latter is backed up by elevated levels of 11-ketotestosterone, testosterone and estradiol in dominant males. Luteinizing hormone (Lh) is found in higher concentration in the plasma of long-term dominant males than in subordinate animals. Our results both strengthen the existing models and propose new candidates for functional studies to expand our understanding of social phenomena in teleost fish.

Endocrine and neuroendocrine regulation of social status in cichlid fishes

Position in a dominance hierarchy profoundly impacts group members' survival, health, and reproductive success. Thus, understanding the mechanisms that regulate or are associated with an individuals' social position is important. Across taxa, various endocrine and neuroendocrine signaling systems are implicated in the control of social rank. Cichlid fishes, with their often-limited resources of food, shelter, and mates that leads to competition, have provided important insights on the proximate and ultimate mechanisms related to establishment and maintenance of dominance hierarchies. Here we review the existing information on the relationships between endocrine (e.g., circulating hormones, gonadal and other tissue measures) and neuroendocrine (e.g., central neuropeptides, biogenic amines, steroids) systems and dominant and subordinate social rank in male cichlids. Much of the current literature is focused on only a few representative cichlids, particularly the African Astatotilapia burtoni, and several other African and Neotropical species. Many hormonal regulators show distinct differences at multiple biological levels between dominant and subordinate males, but generalizations are complicated by variations in experimental paradigms, methodological approaches, and in the reproductive and parental care strategies of the study species. Future studies that capitalize on the diversity of hierarchical structures among cichlids should provide insights towards better understanding the endocrine and neuroendocrine mechanisms contributing to social rank. Further, examination of this topic in cichlids will help reveal the selective pressures driving the evolution of endocrine-related phenotypic traits that may facilitate an individual's ability to acquire and maintain a specific social rank to improve survival and reproductive success.

Involvement of Transforming Growth Factor Beta Family Genes in Gonadal Differentiation in Japanese Eel, Anguilla japonica, According to Sex-Related Gene Expressions

The gonochoristic feature with environmental sex determination that occurs during the yellow stage in the eel provides an interesting model to investigate the mechanisms of gonadal development. We previously studied various sex-related genes during gonadal sex differentiation in Japanese eels. In the present study, the members of transforming growth factor beta (TGF-β) superfamily were investigated. Transcript levels of anti-Müllerian hormone, its receptor, gonadal soma-derived factor (amh, amhr2, and gsdf, respectively) measured by real-time polymerase chain reaction (qPCR) showed a strong sexual dimorphism. Transcripts were dominantly expressed in the testis, and their levels significantly increased with testicular differentiation. In contrast, the expressions of amh, amhr2, and gsdf transcripts were low in the ovary of E2-feminized female eels. In situ hybridization detected gsdf (but not amh) transcript signals in undifferentiated gonads. amh and gsdf signals were localized to Sertoli cells and had increased significantly with testicular differentiation. Weak gsdf and no amh signals were detected in early ovaries of E2-feminized female eels. Transcript levels of amh and gsdf (not amhr2) decreased during human chorionic gonadotropin (HCG)-induced spermatogenesis in males. This study suggests that amh, amhr2, and especially gsdf might be involved in the gene pathway regulating testicular differentiation of Japanese eels.

Sex Determination and Differentiation in Teleost: Roles of Genetics, Environment, and Brain

The fish reproductive system is a complex biological system. Nonetheless, reproductive organ development is conserved, which starts with sex determination and then sex differentiation. The sex of a teleost is determined and differentiated from bipotential primordium by genetics, environmental factors, or both. These two processes are species-specific. There are several prominent genes and environmental factors involved during sex determination and differentiation. At the cellular level, most of the sex-determining genes suppress the female pathway. For environmental factors, there are temperature, density, hypoxia, pH, and social interaction. Once the sexual fate is determined, sex differentiation takes over the gonadal developmental process. Environmental factors involve activation and suppression of various male and female pathways depending on the sexual fate. Alongside these factors, the role of the brain during sex determination and differentiation remains elusive. Nonetheless, GnRH III knockout has promoted a male sex-biased population, which shows brain involvement during sex determination. During sex differentiation, LH and FSH might not affect the gonadal differentiation, but are required for regulating sex differentiation. This review discusses the role of prominent genes, environmental factors, and the brain in sex determination and differentiation across a few teleost species.

Taste preferences and feeding behaviour in the facultative herbivorous fish, Nile tilapia Oreochromis niloticus

Taste preferences in fishes are known mainly for carnivorous species, whereas herbivorous consumers were rarely used in such studies. The main goal of the present study was to evaluate the taste preferences in the herbivorous African cichlid fish, Nile tilapia Oreochromis niloticus. In laboratory settings, the palatability of widely used taste substances (four taste substances that are considered to be sweet, sour, bitter and salty for humans - sucrose, citric acid, calcium chloride and sodium chloride; 21 free L-amino acids; 12 sugars and artificial sweetener Na-saccharin; 0.1-0.0001 M) was evaluated. In each trial, a standard agar pellet flavoured with a substance was offered for fish individually. The consumption of pellet, the number of grasps and the retention time before the pellet was finally ingested or rejected were registered. Overall, 21 of 38 substances were palatable, whereas other substances did not shift consumption of pellets in relation to blank pellets. Pellets containing citric acid, L-cysteine, L-norvaline, L-isoleucine, L-valine, Na-saccharin and D-sorbitol were consumed in >85% of trials. Taste attractiveness of amino acids was highly species-specific and was not associated with the trophic category of the 19 species compared. Moreover, it did not correlate with dietary quantitative requirements of Nile tilapia (r_s  = 0.27; P > 0.05). Palatability of sugars for O. niloticus and their sweetness for humans did not correlate as well (r_s  = 0.21; P > 0.05); nonetheless, Na-saccharin has the most attractive taste for both O. niloticus and humans. The most palatable amino acids lost their effect if the concentration was lowered to 0.01 M for L-cysteine and 0.001 M for L-norvaline (lower than 242.3 μg and 23.4 μg per a pellet, respectively). Single pellet grasp was characteristic of O. niloticus feeding behaviour (>95% of trials), and this pattern may be related to the social lifestyle of this species. Fish spent 4-8 s on average for orosensory evaluation of pellet edibility. The retention time correlated with the palatability of substances and was significantly longer in trials that ended up with pellet swallowing. It is suggested that prolonged orosensory evaluation of food before swallowing provides a reliable and accurate sensory evaluation, which, in turn, can reduce the probability that inadequate food will be consumed.

Effects of neuropeptide Y as a feed additive on stimulating the growth of tilapia (Oreochromis niloticus) fed low fish meal diets

Neuropeptide Y is known to stimulate food intake in fish. In this study, we investigated tilapia NPY (tNPY) both for its effects on the growth of tilapia (Oreochromis niloticus, GIFT) in low fish meal and for its thermal stability. Three diets were formulated containing 0, 3 and 10 % fish meal (NF, LF and HF). From these diets, six experimental diets were prepared by spraying either tNPY solution (0.3 μg/g feed) or distilled water (DW) onto the surface of formulated feeds (NF + DW, NF + tNPY, LF + DW, LF + tNPY, HF + DW and HF + tNPY). Tilapia were fed the six experimental diets for 8 weeks. Fish in the NF + tNPY, LF + tNPY and HF + tNPY groups showed increasing trends in the weight gain rate and specific growth rate compared to its corresponding control group. The feed coefficient of group HF + tNPY was significantly lower than that of the control group. The growth performance of the LF + tNPY approached that of the HF + DW group. The mRNA levels of npy in NF + tNPY were significantly higher than those in NF + DW. A field experiment in which tNPY was sprayed in feeds by the vacuum spray method with doses of 0, 0.2 and 0.4 μg/g feed was performed for three months, and the FBW of tilapia receiving tNPY at 0.2 and 0.4 μg/g feed was higher than that of the control group although not significantly. The bioactivity of tNPY was confirmed by its ability to reduce cAMP levels and activate the ERK1/2 pathway. These results demonstrated that tNPY could promote tilapia growth with oral administration low fish meal diets.

Amh dominant expression in Sertoli cells during the testicular differentiation and development stages in the olive flounder Paralichthys olivaceus

The olive flounder Paralichthys olivaceus, an important marine fish, shows gender differences in growth. The mechanism on its gonadal differentiation direction affected with exogenous factors still needs to be clarified. The anti-Müllerian hormone (amh) gene is involved in fish testicular differentiation and maintenance. The aim of this study was to investigate the expression of the flounder amh in tissues and the gonads. The quantitative expression analysis results showed that it was highly expressed in the testis, especially in the testis at stages I - IV (P < 0.05). Also, amh was detected in Sertoli cells surrounding spermatogonia and peripheral seminiferous lobule of the testis with in situ hybridization (ISH) and immunohistochemistry (IHC). During the differentiation period, the amh expression in the testis of the tamoxifen treatment group (100 ppm) was higher than that in the ovary of the 17β-estradiol (E2, 5 ppm) group, and the expression levels of amh during process of the male differentiation in the tamoxifen group were higher than those in the 17ɑ-methyltestosterone (MT, 5 ppm) group (P < 0.05). ISH results also exhibited that amh was expressed in the somatic cells that surrounded the germ cells of juvenile flounder similar to adult ones. Furthermore, the flounder gonads in the tamoxifen group maintained more germ cells and somatic cells than those in the MT group from 20 to 80 mm total length (TL). Especially, at 60 and 80 mm TL, the numbers of germ and somatic cells in the tamoxifen group were significantly higher than those in the MT group (P < 0.05). In summary, amh might initiate the process of testicular differentiation, and is involved in the early development and maintenance of testis.

An ex vivo Approach to Study Hormonal Control of Spermatogenesis in the Teleost Oreochromis niloticus

As the male reproductive organ, the main task of the testis is the production of fertile, haploid spermatozoa. This process, named spermatogenesis, starts with spermatogonial stem cells, which undergo a species-specific number of mitotic divisions until starting meiosis and further morphological maturation. The pituitary gonadotropins, luteinizing hormone, and follicle stimulating hormone, are indispensable for vertebrate spermatogenesis, but we are still far from fully understanding the complex regulatory networks involved in this process. Therefore, we developed an ex vivo testis cultivation system which allows evaluating the occurring changes in histology and gene expression. The experimental circulatory flow-through setup described in this work provides the possibility to study the function of the male tilapia gonads on a cellular and transcriptional level for at least 7 days. After 1 week of culture, tilapia testis slices kept their structure and all stages of spermatogenesis could be detected histologically. Without pituitary extract (tilPE) however, fibrotic structures appeared, whereas addition of tilPE preserved spermatogenic cysts and somatic interstitium completely. We could show that tilPE has a stimulatory effect on spermatogonia proliferation in our culture system. In the presence of tilPE or hCG, the gene expression of steroidogenesis related genes (cyp11b2 and stAR2) were notably increased. Other testicular genes like piwil1, amh, or dmrt1 were not expressed differentially in the presence or absence of gonadotropins or gonadotropin containing tilPE. We established a suitable system for studying tilapia spermatogenesis ex vivo with promise for future applications.

Vgll3 and the Hippo pathway are regulated in Sertoli cells upon entry and during puberty in Atlantic salmon testis

Vgll3 is linked to age at maturity in Atlantic salmon (Salmo salar). However, the molecular mechanisms involving Vgll3 in controlling timing of puberty as well as relevant tissue and cell types are currently unknown. Vgll3 and the associated Hippo pathway has been linked to reduced proliferation activity in different tissues. Analysis of gene expression reveals for the first time that vgll3 and several members of the Hippo pathway were down-regulated in salmon testis during onset of puberty and remained repressed in maturing testis. In the gonads, we found expression in Sertoli and granulosa cells in males and females, respectively. We hypothesize that vgll3 negatively regulates Sertoli cell proliferation in testis and therefore acts as an inhibitor of pubertal testis growth. Gonadal expression of vgll3 is located to somatic cells that are in direct contact with germ cells in both sexes, however our results indicate sex-biased regulation of vgll3 during puberty.

Steroids in teleost fishes: A functional point of view

Steroid hormones are involved in the regulation of a variety of processes like embryonic development, sex differentiation, metabolism, immune responses, circadian rhythms, stress response, and reproduction in vertebrates. Teleost fishes and humans show a remarkable conservation in many developmental and physiological aspects, including the endocrine system in general and the steroid hormone related processes in particular. This review provides an overview of the current knowledge about steroid hormone biosynthesis and the steroid hormone receptors in teleost fishes and compares the findings to the human system. The impact of the duplicated genome in teleost fishes on steroid hormone biosynthesis and perception is addressed. Additionally, important processes in fish physiology regulated by steroid hormones, which are most dissimilar to humans, are described. We also give a short overview on the influence of anthropogenic endocrine disrupting compounds on steroid hormone signaling and the resulting adverse physiological effects for teleost fishes. By this approach, we show that the steroidogenesis, hormone receptors, and function of the steroid hormones are reasonably well understood when summarizing the available data of all teleost species analyzed to date. However, on the level of a single species or a certain fish-specific aspect of physiology, further research is needed.

The role of Amh signaling in teleost fish--Multiple functions not restricted to the gonads

This review summarizes the important role of Anti-Müllerian hormone (Amh) during gonad development in fishes. This Tgfβ-domain bearing hormone was named after one of its known functions, the induction of the regression of Müllerian ducts in male mammalian embryos. Later in development it is involved in male and female gonad differentiation and extragonadal expression has been reported in mammals as well. Teleosts lack Müllerian ducts, but they have amh orthologous genes. amh expression is reported from 21 fish species and possible regulatory interactions with further factors like sex steroids and gonadotropic hormones are discussed. The gonadotropin Fsh inhibits amh expression in all fish species studied. Sex steroids show no consistent influence on amh expression. Amh is produced in male Sertoli cells and female granulosa cells and inhibits germ cell proliferation and differentiation as well as steroidogenesis in both sexes. Therefore, Amh might be a central player in gonad development and a target of gonadotropic Fsh. Furthermore, there is evidence that an Amh-type II receptor is involved in germ cell regulation. Amh and its corresponding type II receptor are also present in brain and pituitary, at least in some teleosts, indicating additional roles of Amh effects in the brain-pituitary-gonadal axis. Unraveling Amh signaling is important in stem cell research and for reproduction as well as for aquaculture and in environmental science.

Chemical communication in cichlids: A mini-review

The family Cichlidae is well-known for pair-formation, parental care, territoriality, elaborate courtship and social organization. Do cichlids use chemical communication to mediate any of these behaviours? Early studies suggest that parent cichlids can discriminate between conspecific and heterospecific wrigglers (but not eggs) using olfactory cues. Some species are able to discriminate between their own brood and other conspecific broods based on olfaction. The young recognise conspecific adults (although not necessarily their parents) through the odorants they release. In both scenarios, protection of the young from predation is the likely selective force. Some male cichlids use urinary pheromones during courtship and spawning to attract females and induce ovulation. Females--in their turn--may base their mate-choice in part on assessment of those self-same pheromones. The same pheromonal system may be involved in establishing and maintaining the social hierarchies in lek-breeding cichlids. Individual recognition is also mediated by chemical communication. Finally, there is ample behavioural evidence that cichlids--like ostariophysan fish--release alarm cues that alert conspecifics to predation danger. Although the effects of these cues may be similar (e.g., increased shelter use, tighter schooling), they are different substances which remain to be identified. Cichlids, then, use chemical communication associated with many different behaviours. However, given the diversity of cichlids, little is known about the mechanisms of chemical communication or the chemical identity of the cues involved. The aim of this mini-review is to persuade those working with cichlids to consider the involvement of chemical communication, and those working in chemical communication to consider using cichlids.

Dynamic expression of 11β-hydroxylase during testicular development, recrudescence and after hCG induction, in vivo and in vitro in catfish, Clarias batrachus

Cytochrome P450 11β-hydroxylase (11β-h), is involved in the production of 11-hydroxytestosterone, an immediate precursor for 11-ketotestosterone (11-KT), a potent androgen in teleosts. To understand the role of 11β-h in gonadal development, maturation, function and recrudescence in an annually reproducing teleost, the present study was conducted using Clarias batrachus. Four forms of 11β-h cDNA, regular type (2.253 kb), variant 1 (1.290 kb), variant 2 (1.223 kb) and variant 3 (1.978 kb) were identified from the testis of catfish which expressed ubiquitously with high levels in testis. 11β-h transcripts were detected as early as 0 days post hatch further, stage- and sex-dependent increase in the 11β-h transcripts were seen during gonadal differentiation/development. In addition, high expression of 11β-h (regular type) in pre-spawning phase was detected. Corroboratively, levels of 11-KT in serum and testicular tissue was high during pre-spawning and spawning phases, which might facilitate initiation and normal progression of spermatogenesis. The expression of 11β-h was high after human chorionic gonadotropin induction in vivo (all forms), and in vitro (regular type). Immunohistochemical and immunofluorescence localization showed the presence of 11β-h in Sertoli and interstitial/Leydig cells of the testis. These results suggest that 11β-h is involved in late stages of testicular development, together with the regulation of seasonal reproductive cycle in catfish.

Social regulation of reproduction in male cichlid fishes

Social interactions and relative positions within a dominance hierarchy have helped shape the evolution of reproduction in many animals. Since reproduction is crucial in all animals, and rank typically regulates access to reproductive opportunities, understanding the mechanisms that regulate socially-induced reproductive processes is extremely important. How does position in a dominance hierarchy impact an individual's reproductive behavior, morphology, and physiology? Teleost fishes, and cichlids in particular, are ideally-suited models for studying how social status influences reproduction on multiple levels of biological organization. Here I review the current knowledge on the reproductive behavioral and physiological consequences of relative position in a dominance hierarchy, with a particular focus on male cichlids. Dominant and subordinate social status is typically associated with distinct differences in activity along the entire hypothalamic-pituitary-gonadal axis. Further, when transitions in social status occur between subordinate and dominant individuals, there are plastic changes from whole-organism behavior to molecular-level gene expression modifications that occur quickly. These rapid changes in behavior and physiology have allowed cichlids the flexibility to adapt to and thrive in their often dynamic physical and social environments. Studies in cichlid fishes have, and will continue, to advance our understanding of how the social environment can modulate molecular, cellular, and behavioral outcomes relevant to reproductive success. Future studies that take advantage of the extreme diversity in mating systems, reproductive tactics, and parental care strategies within the cichlid group will help generate hypotheses and careful experimental tests on the mechanisms governing the social control of reproduction in many vertebrates.

Social dominance in tilapia is associated with gonadotroph hyperplasia

Tilapias are emerging as one of the most important fish in worldwide aquaculture and are also widely used as model fish in the study of reproduction and behavior. During the reproductive season, male tilapia are highly territorial and form spawning pits in which the dominant males court and spawn with available females. Non-territorial males stand a much lower chance of reproducing. Using transgenic tilapia in which follicle stimulating hormone (FSH) gonadotrophs were fluorescently labeled with enhanced green fluorescent protein (EGFP), we studied the effect of social dominance on the hormonal profile and pituitary cell populations in dominant and non-dominant males. Immunofluorescence studies showed that FSH-EGFP-transgenic fish reliably express EGFP in FSH-secreting cells. EGFP expression pattern differed from that of luteinizing hormone. Dominant males had larger gonads as well as higher levels of androgens and gonadotropins in the plasma. Pituitaries of dominant males exhibited higher gonadotropin content and gene expression. Flow cytometry revealed pituitary hyperplasia as well as FSH cell hyperplasia and increased granulation. Taken together, these findings suggest that gonadotroph hyperplasia as well as increased production by individual cells underlie the increased reproductive activity of dominant tilapia males.

Phenotypic characterization and in vitro propagation and transplantation of the Nile tilapia (Oreochromis niloticus) spermatogonial stem cells

In association with in vitro culture and transplantation, isolation of spermatogonial stem cells (SSCs) is an excellent approach for investigating spermatogonial physiology in vertebrates. However, in fish, the lack of SSC molecular markers represents a great limitation to identify/purify these cells, rendering it difficult to apply several valuable biotechnologies in fish-farming. Herein, we describe potential molecular markers, which served to phenotypically characterize, cultivate and transplant Nile tilapia SSCs. Immunolocalization revealed that Gfra1 is expressed exclusively in single type A undifferentiated spermatogonia (Aund, presumptive SSCs). Likewise, the expression of Nanos2 protein was observed in Aund cells. However, Nanos2-positive spermatogonia have also been identified in cysts with two to eight germ cells that encompass type A differentiated spermatogonia (Adiff). Moreover, we also established effective primary culture conditions that allowed the Nile tilapia spermatogonia to expand their population for at least one month while conserving their original undifferentiated (stemness) characteristics. The maintenance of Aund spermatogonial phenotype was demonstrated by the expression of early germ cell specific markers and, more convincingly, by their ability to colonize and develop in the busulfan-treated adult Nile tilapia recipient testes after germ cell transplantation. In addition to advancing our knowledge on the identity and physiology of fish SSCs, these findings provide the first step in establishing a system that will allow fish SSCs expansion in vitro, representing an important progress towards the development of new biotechnologies in aquaculture, including the possibility of producing transgenic fish.

Suppression effect of LHRH-A and hCG on Piwi expression in testis of Nile tilapia Oreochromis niloticus

Piwi proteins as constituent factors of the piRNA pathway are required for germline maintenance, meiosis and gonad development. Previous study showed hCG could regulate the Piwi expression in ovary of teleosts. In this study, we revealed effects of LHRH-A and hCG on Piwi expression in testis of tilapia using Real-time PCR and Western blot. Both in vivo and in vitro study suggest that LHRH-A and hCG significantly down-regulated Piwil-1 and Piwil-2 in mRNA or protein levels compared with controls. Meanwhile, tissue and cell distribution showed that Piwi proteins were mainly expressed in spermatocytes rather than mature sperms. These results indicated that HPG suppresses Piwis which may play a crucial role in testis differentiation and development.

Validation of reference genes for real-time PCR of reproductive system in the black tiger shrimp

Gene expression of reproductive system of the black tiger shrimp (Peneaus monodon) has been widely studied to address poor maturation problem in captivity. However, a systematic evaluation of reference genes in quantitative real-time PCR (qPCR) for P. monodon reproductive organs is lacking. In this study, the stability of four potential reference genes (18s rRNA, GAPDH, β-actin, and EF1-α) was examined in the reproductive tissues in various conditions using bioinformatic tools: NormFinder and geNorm. For NormFinder, EF1-α and GAPDH ranked first and second as the most stable genes in testis groups whereas GAPDH and EF1-α were for ovaries from wild-caught broodstock and domesticated groups. EF1-α and β-actin ranked first and second for the eyestalk ablated ovaries. For geNorm, EF1-α and GAPDH had the best stability in all testis and ovaries from domesticated groups whereas EF1-α and β-actin were the best for ovaries from wild-caught and eyestalk ablated groups. Moreover, the expression levels of two well-known reproductive genes, Dmc1 and Vitellogenin, were used to validate these reference genes. When normalized to EF1-α, the expected expression patterns were obtained in all cases. Therefore, this work suggests that EF1-α is more versatile as reference genes in qPCR analysis for reproductive system in P. monodon.