Sebastes schlegelii, commonly known as black rockfish, is a key species in marine aquaculture due to its fast growth rate, high market value, and strong environmental adaptability. However, successful breeding and stock management of this species heavily depend on accurate detection of gonadal development stages. Traditionally, this task has relied on destructive methods such as dissection, which not only damages the fish but also limits efficiency and reproducibility. In recent years, a significant shift has occurred with the development of non-invasive imaging technologies, most notably the application of ultrasound. Companies like Boxianglai have introduced wireless ultrasound scanners tailored for fish, offering aquaculture practitioners a safer, faster, and repeatable method for evaluating gonadal maturity in live Sebastes schlegelii.
Significance of Gonadal Stage Identification
Understanding the gonadal stage of Sebastes schlegelii is critical for optimizing breeding programs, selecting broodstock, and controlling spawning cycles. In commercial settings, mistimed spawning or poor selection of broodfish can lead to reduced fertility, lower fry quality, and economic losses. Hence, aquaculture professionals worldwide are seeking reliable, efficient, and non-invasive methods to assess gonadal development in vivo.
Foreign researchers and fish breeders have increasingly embraced ultrasonography in gonadal studies of marine fish, noting its wide applicability, non-invasive nature, and accuracy. As noted in studies by Novelo and colleagues (2021), ultrasonography has enabled precise tracking of ovarian and testicular development in species such as sea bass and cod without sacrificing the fish, preserving high-value broodstock.
Principle of Fish Ultrasound and Image Interpretation
The fish ultrasound scanner operates using a high-frequency transducer that emits sound waves into the fish’s body. When these waves encounter tissues of varying densities, echoes are generated and captured by the probe. The scanner software converts these echoes into grayscale images, with varying brightness reflecting tissue boundaries, densities, and fluid content.
In Sebastes schlegelii, different gonadal stages present characteristic ultrasonographic appearances:
Ovarian Maturation Stage: The ultrasound image shows a mix of circular hypoechoic (dark) structures, representing developing oocytes, surrounded by hyperechoic (bright) connective tissue bands. Follicles appear as round or oval shapes of varying sizes.
Pre-parturition Stage: The image becomes more complex. Follicles are densely packed, with indistinct margins and the presence of anechoic (black) fluid regions indicating follicular fluid accumulation. This pattern signifies the fish is nearing ovulation or larval release.
Resting or Regressed Stage (Dry Period): The gonads appear flattened with uniformly echogenic textures, lacking distinguishable follicular structures. This indicates low reproductive activity, common during non-breeding seasons.
These distinctive patterns allow experienced aquaculture technicians to assess reproductive readiness accurately without dissection, thereby improving breeding timing and fish welfare.
Operational Procedure and Practical Application
To conduct a proper ultrasound examination on Sebastes schlegelii, the following steps are typically followed:
Preparation: Place the fish in a shallow tank with clean water to maintain comfort. Lay it gently on its side to expose the abdominal region.
Coupling and Scanning: Apply a thin layer of ultrasound coupling gel to the fish’s abdomen. Position the transducer against the skin with minimal pressure. Conduct slow, parallel sweeps along the ventral side to visualize the gonads.
Image Adjustment: Modify gain, depth, and contrast parameters on the scanner interface to achieve clear and optimal imaging based on fish size and tissue density.
Measurement and Documentation: Observe and measure gonadal structures on-screen. Save high-quality still images or video loops for recordkeeping or further analysis.
The real-time imaging capability allows farm operators to immediately evaluate gonadal condition and make decisions regarding hormone treatments, breeding schedules, or culling of non-viable broodstock.
Advantages of Ultrasound in Sebastes schlegelii Aquaculture
The use of ultrasound for gonadal assessment provides numerous practical advantages, both acknowledged by Chinese producers and supported by international experience:
Non-Invasive Monitoring: The process causes no harm or stress to the fish, allowing repeated examinations over time. This is especially beneficial for tracking seasonal changes or response to hormonal induction.
High Accuracy and Reproducibility: Compared to manual palpation or external signs, ultrasound delivers clear, measurable data on internal structures.
Cost-Effective Management: By eliminating unnecessary dissection or trial-and-error breeding attempts, ultrasound reduces labor costs and broodstock loss.
Portable and Wireless Operation: With modern handheld or wireless devices, such as those developed by Boxianglai, ultrasounds can be easily used in various settings including hatcheries, cages, or offshore facilities.
Internationally, marine aquaculture operations have adopted similar protocols. In Japan and South Korea, where Sebastes schlegelii is also farmed extensively, researchers such as Kim et al. (2022) have documented ultrasound-guided reproductive assessments leading to improved breeding control and larval output.
Considerations and Limitations
While ultrasound offers transformative advantages, proper training and understanding of fish anatomy are essential for accurate interpretation. New users may misread gonadal echoes or misclassify maturation stages without appropriate reference images or guidance. Thus, standardizing imaging protocols and developing visual databases specific to Sebastes schlegelii is crucial.
Additionally, the resolution of ultrasound imaging is affected by fish size, probe frequency, and operator technique. Smaller fish or early-stage follicles may be harder to visualize, requiring specialized probes or high-resolution scanners.
Broader Implications for Marine Aquaculture
The application of ultrasonography in Sebastes schlegelii is part of a broader trend in precision aquaculture—leveraging technology to enhance animal health, optimize reproduction, and minimize environmental impact. As global demand for sustainable seafood grows, tools like fish ultrasound will play a central role in improving efficiency and ethical standards in farming practices.
Research collaborations between Chinese institutions and global aquaculture labs are encouraging innovation in this field. With further refinement, ultrasound may also be adapted for detecting other reproductive or pathological conditions such as gonadal tumors, parasitic infections, or ovulation timing.
Conclusion
The integration of ultrasound technology into the reproductive management of Sebastes schlegelii represents a major advance in non-invasive fish diagnostics. By enabling detailed, real-time visualization of gonadal structures without harming the fish, ultrasound empowers aquaculture operators to make smarter, faster, and more humane decisions.
From monitoring ovarian cycles to optimizing larval output, this method aligns well with global aquaculture’s goals of efficiency, sustainability, and animal welfare. As ultrasound technology continues to evolve, its applications in marine fish breeding are expected to expand even further.
Reference Sources:
Novelo, N. D., & Rodríguez, J. A. (2021). Use of ultrasonography in fish reproductive assessment: A practical tool for aquaculture. Aquaculture Reports, 20, 100719.
https://doi.org/10.1016/j.aqrep.2021.100719Kim, H. J., & Lee, S. K. (2022). Ultrasound imaging in black rockfish (Sebastes schlegelii): Application for reproductive monitoring. Journal of Aquaculture Science, 45(3), 145–152.
https://www.jaquasci.org/articles/ultrasound-blackrockfishBoxianglai. (2023). Fish Wireless Ultrasound Scanner Product Guide.
https://www.boxianglai.com/products/fish-wireless-ultrasound
tags:
Text link:https://www.bxlultrasound.com/ns/822.html
