Zebrafish Anatomy and Physiology Quiz

Introduction

• Zebrafish (Danio rerio) a small freshwater fish, native to the Indian subcontinent, has become a valuable model organism in biomedical research.
• Zebrafish are small, freshwater fish with distinctive blue-purple stripes, typically reaching 3-4 cm in length.
• They exhibit complex behaviors like schooling and territoriality.
• High fecundity (females produce hundreds of eggs per spawning event), rapid development, and external fertilization make them ideal for genetic studies and large-scale screens.
• Zebrafish's transparent embryos, rapid development, genetic tractability, and physiological relevance to humans make them useful tools for studying various biological processes including developmental biology, neurobiology, genetics, drug discovery, and regenerative medicine.

Taxonomy and Systematics

• Zebrafish is a derived member of the genus Brachydanio, in the Cyprinidae family.
• It has a sister-group relationship with Danio aesculapii.
• Closely related to the genus Devario.
• Taxonomic classification highlights its position in the evolutionary tree of life and its relationship to other organisms.

Development

• Zebrafish life cycle begins with external fertilization.
• Female zebrafish release hundreds of eggs which are fertilized by male sperm.
• Fertilized eggs develop rapidly through blastula, gastrula, and eventually a neurula stages.
• Embryo hatches into a larval stage characterized by rapid organogenesis (heart, brain, sensory organs).
• Larvae feed on yolk reserves and transition to external feeding stage by 3-4 days post-fertilization, exhibiting pigmentation and fin development.
• Juvenile stage marks the transition from larval to adult morphology, exhibiting proliferation, and fin and pigmentation development.
• Juveniles reach sexual maturity within 3-4 months.
• Adult zebrafish are sexually mature and capable of spawning multiple times per week.

Embryonic Development

• Danio rerio, commonly known as zebrafish, typically reaches reproductive maturity in three months.
• Successful spawning necessitates the presence of a male to induce ovulation and egg release.
• Zebrafish are asynchronous spawners, meaning they can spawn frequently under optimal conditions like ample food and suitable water.

Spawning

• To stimulate spawning, researchers employ a tank with a sliding bottom insert that mimics a shallow riverbed.
• Zebrafish exhibit a preference for morning spawning, aligned with their circadian rhythms.

Anatomy and Physiology

• External Anatomy: Zebrafish has a streamlined, fusiform body shape allowing for efficient swimming. Specialized fins are designed for different functions: stabilizing and preventing rolling and propulsion.
• Skeletal System: The skeletal system provides structural support and protection for vital organs including the brain, supported by the cranial skeleton, and sensory organs. The vertebral column supports the spine, while fins have flexible bony structures.
• Nervous System: The nervous system includes the brain, spinal cord, and peripheral nerves. Five regions of the brain are responsible for various functions (memory, sensory processing, locomotion, homeostasis, and endocrine functions).
• Circulatory System: The circulatory system has two chambers, the atrium (collecting deoxygenated blood), and the ventricle (pumping blood to the gills for oxygenation), and the sinus venosus.
• Respiratory System: Zebrafish rely on gills for respiration, extracting oxygen and expelling carbon dioxide. Gill arches are maximized for efficient gas exchange through counter-current flow.
• Digestive System: Food is ingested, partially broken down in the mouth, transported to the stomach for enzymatic digestion and nutrient absorption in the intestine.
• Excretory System: Kidneys filter nitrogenous waste (like ammonia) from the blood while balancing water and ionic balance. Filtered waste exits through the urogenital pore.
• Reproductive System: Zebrafish are oviparous, with females producing eggs and males producing sperm. External fertilization occurs in the water.

Morphology

• Zebrafish have distinct morphology including body size, shape, coloration, eyes, mouth, fins, and axial skeleton.
• Adult size typically ranges from 4-5cm, though some individuals reach 6.5cm.
• Males are typically smaller and more slender than females.
• Males possess distinct markings on their anal fins.

Sensory Systems

• Well-developed sensory systems to interact with their environment, including large lateral eyes providing excellent vision.
• Olfactory organs detect chemical cues, essential for feeding, reproduction, and predator detection.
• Lateral line system detects water vibrations and pressure changes for navigation and social behavior.

Nervous System

• Highly specialized nervous system including brain, spinal cord, and peripheral nerves.
• Different regions of the brain are responsible for different functions such as memory, sensory processing, locomotion and other necessary body functions.
• Spinal cord connects the brain to the body and transmits motor and sensory signals.
• Peripheral nerves extend to muscles, fins, and sensory organs, enabling precise control and absolute responsiveness.

Endocrine System

• The endocrine system of zebrafish includes glands like the thyroid (regulates metabolism) and the pineal gland (influences circadian rhythms, seasonal behaviors, and other important body functions).
• Pituitary glands coordinate hormonal signals for growth, reproduction, and stress responses.

Immune System

• The zebrafish immune system includes innate and adaptive components.
• Thymus responsible for the development of T cells crucial for adaptive immunity.
• Thymus consists of a cortex (high T cell density) and medulla (more epithelial cells).

Metabolism and Aging

• Zebrafish regulate growth, metabolism
• Plays a role in aging processes.

Regenerative Processes

• Zebrafish have remarkable regenerative capacity, able to regenerate sections of their brains, hearts, and fins.
• Researchers study signaling channels and biological mechanisms to understand their regenerative processes.
• There is development of cell-based treatments for tissue regeneration.
• Stem cell transplants can also be used to encourage tissue regeneration and identify compounds that improve regeneration.

Synthesis

• Research on zebrafish will focus on neurodegenerative diseases, regenerative medicine, and cancer research over the next five years.
• Zebrafish embryos are used to investigate various pathological conditions like neurodegenerative disorders, tumor initiation/progression, metastasis, and potential therapeutic targets for tissue repair.
• Zebrafish can serve as a model organism to find possible anticancer medications and investigate cancer initiation and progression.
• Zebrafish offer an excellent platform for drug screening and examining the genetic basis of cancer.
• Scientists employ zebrafish for understanding the capacity and mechanisms of regeneration, such as the regeneration of tissue, and to find new therapeutic approaches for human tissue regeneration.

Genetics

• Zebrafish have high genetic homology with humans, with approximately 70% of human genes having analogs.
• 84% of human disease genes have counterparts in zebrafish making them a useful model organism.

Other relevant details

• The study summarises key genes/proteins in D. rerio development, and their human homologs.
• Important genes and processes are summarised.

Test your knowledge of zebrafish anatomy including their nervous, digestive, and immune systems. This quiz covers various components and functions related to the structure and physiology of zebrafish. Challenge yourself to match organs with their functions and understand how these fish adapt to their environments.