First account of a transient intersex in spotted scat, Scatophagus argus: a marine gonochoristic fish.

This study presents the first incidence of intersex associated with testis-ova in spotted scat (Scatophagus argus) reared in a controlled environment. The testis-ova is associated with the abnormal occurrence of primary oocytes (POs) in some male testis and is referred to as ectopic primary oocytes (Ecto-PO), whiles individuals with Ecto-PO are called "Ecto-PO gonad/individuals." We investigated gonads of 129 male spotted scat aged 4-12 and 18 months after hatch (mah) by histological studies for the presence of female sexual characteristics. A total of 20 out of 88 gonads representing 22.7% of male fish aged 6-12, or 15.5% of all male fish sampled, were found to have visible Ecto-PO. At least, the Ecto-PO had an average of 7 oocytes per gonadal section, indicating high severity. The Ecto-PO appears after sex differentiation and degenerates during sexual maturation. The Ecto-PO did not significantly influence the expression pattern of male and female sex-related genes performed using qPCR. Immunofluorescence of 42sp50 specifically stained the Ecto-PO without influence from the surrounding testicular tissues. In addition, temperature did not correlate with the proliferation of the Ecto-PO, but rather gonad developmental strategy. The results show that the naturally occurring Ecto-PO might not be detrimental to testis development and could be considered a frequent-high-level incidence of natural aberration. This study highlights the intricacy of fish sex differentiation and provides a new research chapter to ascertain the mystery behind the occurrence of Ecto-PO.

High Polymorphism in the Dmrt2a Gene Is Incompletely Sex-Linked in Spotted Scat, Scatophagus argus.

Unlike mammals and birds, many fishes have young sex chromosomes, providing excellent models to study sex chromosome differentiation at early stages. Previous studies showed that spotted scat possesses an XX-XY sex determination system. The X has a complete Dmrt3 copy (termed normal) and a truncated copy of Dmrt1 (called Dmrt1b), while the Y has the opposite (normal Dmrt1, which is male-specific, and a truncated Dmrt3 called Dmrt3△-Y). Dmrt1 is the candidate sex determination gene, while the differentiation of other sex-linked genes remains unknown. The spotted scat has proven to be a good model to study the evolution of sex chromosomes in vertebrates. Herein, we sequenced a neighbor gene of this family, Dmrt2, positioned farther from Dmrt1 and closer to Dmrt3 in the spotted scat, and analyzed its sequence variation and expression profiles. The physical locations of the three genes span across an estimated size of >40 kb. The open reading frames of Dmrt2a and its paralog Dmrt2b are 1578 bp and 1311 bp, encoding peptides of 525 and 436 amino acid residues, respectively. Dmrt2a is positioned close to Dmrt3 but farther from Dmrt1 on the same chromosome, while Dmrt2b is not. Sequence analysis revealed several mutations; insertions, and deletions (indels) on Dmrt2a non-coding regions and single-nucleotide polymorphisms (SNPs) on the Dmrt2a transcript. These indels and SNPs are sex-linked and showed high male heterogeneity but do not affect gene translation. The markers designed to span the mutation sites tested on four different populations showed varied concordance with the genetic sexes. Dmrt2a is transcribed solely in the gonads and gills, while Dmrt2b exists in the gonads, hypothalamus, gills, heart, and spleen. The Dmrt2a and Dmrt2b transcripts are profoundly expressed in the male gonads. Analyses of the transcriptome data from five other fish species (Hainan medaka (Oryzias curvinotus), silver sillago (Sillago sihama), Nile tilapia (Oreochromis niloticus), Hong Kong catfish (Clarias fuscus), and spot-fin porcupine fish (Diodon hystrix)) revealed testes-biased expression of Dmrt1 in all, similar to spotted scat. Additionally, the expression of Dmrt2a is higher in the testes than the ovaries in spotted scat and Hainan medaka. The Dmrt2a transcript was not altered in the coding regions as found in Dmrt1 and Dmrt3 in spotted scat. This could be due to the functional importance of Dmrt2a in development. Another possibility is that because Dmrt2a is positioned farther from Dmrt1 and the chromosome is still young, meaning it is only a matter of time before it differentiates. This study undeniably will aid in understanding the functional divergence of the sex-linked genes in fish.

Effects of probiotics on digestive enzymes of fish (finfish and shellfish); status and prospects: a mini review.

Digestive enzymes are found in the digestive tract of animals which assist in the breakdown of larger food molecules into more easily absorbed particles that can then be used by the body. The ability of fish to break down a diet is highly dependent on the availability of suitable digestive enzymes which mediate specific degradation pathways and on both the physical and chemical nature of food. Probiotics are known to produce helpful enzymes that aid in digestion and protect the gastrointestinal tract (GIT) of animals. When applied appropriately, probiotics improve intestinal microbial balance which also improves digestive enzyme activities, food absorption, and decrease pathogenic issues in the GIT. They work hand-in-hand with the digestive enzymes in the GIT of animals as supplements thereby improvings nutrition. This in turn leads to higher feed efficiency and growth as well as the prevention of antinutritional factors present in the ingredients, intestinal disorders, and pre-digestion. This review seeks to present summaries of the results of research findings on the application of probiotics on the activities of digestive enzymes including amylase, lipase, and protease. Further, this review points out gaps in available literature and suggests ideas that could be explored in further investigations to better understand and enhance the activities of these digestive enzymes to increase feed and nutrient utilization and the production of aquaculture species.

The Roles of Neuropeptide Y (Npy) and Peptide YY (Pyy) in Teleost Food Intake: A Mini Review.

Neuropeptide Y family (NPY) is a potent orexigenic peptide and pancreatic polypeptide family comprising neuropeptide Y (Npy), peptide YYa (Pyya), and peptide YYb (Pyyb), which was previously known as peptide Y (PY), and tetrapod pancreatic polypeptide (PP), but has not been exhaustively documented in fish. Nonetheless, Npy and Pyy to date have been the key focus of countless research studies categorizing their copious characteristics in the body, which, among other things, include the mechanism of feeding behavior, cortical neural activity, heart activity, and the regulation of emotions in teleost. In this review, we focused on the role of neuropeptide Y gene (Npy) and peptide YY gene (Pyy) in teleost food intake. Feeding is essential in fish to ensure growth and perpetuation, being indispensable in the aquaculture settings where growth is prioritized. Therefore, a better understanding of the roles of these genes in food intake in teleost could help determine their feeding regime, regulation, growth, and development, which will possibly be fundamental in fish culture.

Fish Feed Intake, Feeding Behavior, and the Physiological Response of Apelin to Fasting and Refeeding.

Feed is one of the most important external signals in fish that stimulates its feeding behavior and growth. The intake of feed is the main factor determining efficiency and cost, maximizing production efficiency in a fish farming firm. The physiological mechanism regulating food intake lies between an intricate connection linking central and peripheral signals that are unified in the hypothalamus consequently responding to the release of appetite-regulating genes that eventually induce or hinder appetite, such as apelin; a recently discovered peptide produced by several tissues with diverse physiological actions mediated by its receptor, such as feed regulation. Extrinsic factors have a great influence on food intake and feeding behavior in fish. Under these factors, feeding in fish is decontrolled and the appetite indicators in the brain do not function appropriately thus, in controlling conditions which result in the fluctuations in the expression of these appetite-relating genes, which in turn decrease food consumption. Here, we examine the research advancements in fish feeding behavior regarding dietary selection and preference and identify some key external influences on feed intake and feeding behavior. Also, we present summaries of the results of research findings on apelin as an appetite-regulating hormone in fish. We also identified gaps in knowledge and directions for future research to fully ascertain the functional importance of apelin in fish.