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Age and growth of the Chinese fanray, Platyrhina sinensis, in the southern Taiwan Strait

This study presents the first age and growth estimates for the Chinese fanray (*Platyrhina sinensis*) in the southern Taiwan Strait based on 511 specimens, revealing sexual dimorphism in maximum size and growth rates, and providing essential life-history parameters for future population assessment and management.

Original authors: Yan Zhuang, Shuting Ke, Mingru Chen, Jiamei Xiao

Published 2026-09-21

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Yan Zhuang, Shuting Ke, Mingru Chen, Jiamei Xiao

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Deep in the warm, shallow waters of the southern Taiwan Strait, a flat, diamond-shaped ray glides over the sandy bottom. This is the Chinese fanray, a creature that has long been overlooked in the world of marine biology. For decades, scientists studying these rays in the region were likely looking at the wrong species entirely, confusing the Chinese fanray with a close relative that looks nearly identical. This mix-up meant that while we knew the Chinese fanray was listed as endangered on global conservation lists, we knew almost nothing about its life cycle in the specific waters where it is most abundant. To protect a species, managers need to know how fast it grows, how long it lives, and when it becomes old enough to reproduce. Without these basic facts, it is impossible to know if a fishery is taking too many fish or if the population can recover.

A team of researchers from Xiamen University and the Zhangzhou Institute of Surveying and Mapping set out to fill this gap. They did not go out to catch these rays themselves, which would have added to the pressure on an endangered population. Instead, they collected specimens that had already been caught by commercial fishing boats using bottom trawls. Over the course of a year, from August 2021 to October 2022, they gathered 511 of these rays from seafood markets and fishing ports in southern Fujian. The scientists were careful to confirm that every single specimen was indeed the Chinese fanray, using a specific physical trait: the presence of two or three rows of sharp, hooked spines running down the middle of the tail, a feature that distinguishes it from its look-alike cousin.

To figure out the age of these animals, the researchers turned to a method that works much like counting the rings on a tree. They removed small sections of the spine, cleaned them, and sliced them thinly to reveal a cross-section. Under a microscope, these slices showed a pattern of alternating light and dark bands. The dark bands are wide and opaque, while the light bands are narrow and translucent. By examining the edges of these bands on rays caught throughout the year, the team discovered a clear rhythm: the light bands form primarily during the winter months, from November to February, while the dark bands form the rest of the year. This confirmed that the rays lay down exactly one pair of these bands every year, allowing the scientists to count the years of a ray's life simply by counting the pairs of rings on its spine.

The results revealed a life history that is surprisingly fast-paced for a ray. The oldest male they found was eight years old, while the oldest female reached ten years. However, the population they sampled was dominated by young adults, with most rays being between two and four years old. The study showed that these rays grow quickly and reach sexual maturity very early. Males are ready to reproduce at just over two years of age, and females follow closely behind at roughly the same time. This early maturity is a crucial survival trait, but it also means the population is vulnerable if too many adults are removed before they can breed. The researchers found that females grow to a larger maximum size than males, reaching a total length of over 511 millimeters, while males top out around 435 millimeters.

Perhaps the most significant finding is that this study provides the first accurate biological data for the Chinese fanray under its correct scientific name. Previous studies from the region had likely been measuring the wrong species, leading to a distorted view of how this specific ray lives. The new data shows that while these rays live relatively short lives compared to some other marine animals, they grow rapidly and mature young. This information is now available to help fisheries managers in the region make informed decisions. By knowing exactly how fast these rays grow and when they start reproducing, authorities can set better rules to ensure that the local population remains healthy, turning a species that was once a mystery into one that can be effectively protected.

Technical Summary: Age and Growth of the Chinese Fanray (Platyrhina sinensis) in the Southern Taiwan Strait

Problem Statement
The Chinese fanray, Platyrhina sinensis, is classified as Endangered on the IUCN Red List, yet it remains absent from China's List of Wildlife under National Key Protection. While fishery surveys indicate local abundance in Dongshan Bay, southern Fujian, there is a critical lack of population-specific life-history data required for regional assessment and management. Previous studies reporting age and growth for P. sinensis were later found to have examined a different species, P. tangi, following a taxonomic revision by Iwatsuki et al. (2011). Consequently, no validated age and growth estimates exist for P. sinensis under its current taxonomic definition, hindering effective conservation and fisheries management strategies.

Methodology
The study analyzed 511 specimens (260 males, 251 females) incidentally caught by commercial bottom-trawl fisheries in the southern Taiwan Strait between August 2021 and October 2022. Specimens were identified using the revised diagnosis of Iwatsuki et al. (2011), distinguishing P. sinensis by the presence of two or three longitudinal rows of hooked thorns on the mid-dorsal tail.

Age Determination: Age was estimated from sagittal sections of vertebral centra (vertebrae 10–15). Samples were cleaned, embedded in epoxy resin, and sectioned to approximately 0.5 mm thickness.
Band Interpretation: Sections were examined under transmitted and reflected light. A band pair was defined as one translucent and one opaque band. The birth mark was identified as the first distinct mark distal to the focus, coinciding with an abrupt change in the corpus calcareum angle.
Precision Analysis: Three independent readers analyzed a subset of sections. Inter-reader precision was quantified using the Index of Average Percentage Error (IAPE) and Coefficient of Variation (CV).
Growth Modeling: The relationship between Total Length (TL) and Centrum Diameter (CD) was analyzed using linear, exponential, and power functions. Age and length data were fitted to von Bertalanffy, Gompertz, and Robertson growth functions. Model selection was based on Akaike's Information Criterion (AIC).
Maturity and Longevity: Ages at 50% sexual maturity ( $A_{50}$ ) were derived by substituting length-at-maturity estimates ( $L_{50}$ ) from a separate reproductive analysis (Ke 2023) into the fitted growth functions. Upper longevity bounds were estimated using an empirical equation incorporating the maximum observed age and the IAPE of the oldest 20% of specimens.

Key Results

Validation: The study confirmed that vertebral centra are a reliable structure for aging P. sinensis, with a strong linear relationship between TL and CD ( $R^2 = 0.8534$ ). Inter-reader precision was high, with an IAPE of 3.97% and a CV of 5.16%.
Band Deposition: Edge analysis indicated the annual deposition of one band pair. Translucent bands formed primarily from November to February, while opaque bands formed during the remainder of the year.
Age Composition: Observed ages ranged from 0 to 8 years for males (mean: 3.01 years) and 0 to 10 years for females (mean: 3.65 years). The population was dominated by individuals aged 2 to 4 years.
Growth Parameters: The von Bertalanffy growth function provided the best fit for both sexes.
- Males: Asymptotic length ( $L_\infty$ ) = 435.475 mm TL; Growth coefficient ( $k$ ) = 0.657 yr⁻¹.
- Females: Asymptotic length ( $L_\infty$ ) = 511.466 mm TL; Growth coefficient ( $k$ ) = 0.394 yr⁻¹.
- Females attained a larger maximum size but grew more slowly than males.
Maturity and Longevity: Estimated ages at 50% sexual maturity were 2.03 years for males and 2.17 years for females. The estimated upper longevity bounds were 11.51 years for males and 14.19 years for females.

Significance and Claims
The authors state that this study provides the first age and growth estimates for Platyrhina sinensis under its current taxonomic definition. The derived life-history parameters establish a biological baseline necessary for regional population assessments, ecological risk assessments, and fisheries management in the southern Taiwan Strait.

The paper characterizes P. sinensis as a relatively early-maturing and comparatively short-lived batoid, with maturity occurring near the lower limits of ranges observed in other batoid species. The authors note that while the study fills a significant data gap, the results should be interpreted as regional estimates. They highlight sampling limitations, specifically the underrepresentation of individuals between 140–250 mm TL and the scarcity of older, larger individuals, which may influence the precision of initial growth and longevity estimates. The study concludes that accurate species identification is essential for future monitoring to avoid the historical confusion between P. sinensis and P. tangi.

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