Ostraciidae, The Family of Adorable Fish

By Monique White

 

In November of 2022, I snorkelled for the first time, on the Great Barrier Reef. What struck me was the diversity in colour and shape of the creatures living underwater. I then decided to learn how to scuba dive, and was still fascinated with the diversity of the fish, and other animals underwater. I have come to adore the fish that belong to the family Ostraciidae. One thing I find particularly interesting about the boxfish is the change in appearance as they age (Figure 1), and the difference between genders (Figure 2). Other fish in this family include the cowfish and trunkfish.

Boxfish are given this name as they have a body shape that is akin to a box (Figure 2). The box-like shape comes from the fusion of bony plates, making up the carapace which protects the back of the animal. They have evolved to have the carapace by positively selecting the genes shown to contribute to the formation of bone and keratinization of scales, such as acsl4a, casr, keap1a, and tbx (Wei et al. 2023). The somewhat unconventional shape is a trade-off between speed and maneuverability (Van Wassenbergh, 2015). The box shape increases the drag and resistance of the fish in the water, reducing their speed. As they cannot quickly flee from predators, the species in the Ostraciidae family have developed other strategies to evade predation.

Figure 2a. Male Spotted Boxfish (Ostracion meleagris), taken by Monique White (Gili Islands, Indonesia).

Figure 2b. Female Spotted Boxfish (Ostracion meleagris), taken by Sophia Schmalzer (Gili Islands, Indonesia)

They employ a molecular defence by secreting the neurotoxin, ostracitoxin, under stress (Thomson, 1964). Ostracitoxin is highly toxic to marine fishes and aggregates the red blood cells (erythrocytes) of fish (Thomson, 1964; Thomson, 1969). The exact mechanism of how Ostracitoxin is synthesised is unknown, however, the study by Wei et al. highlighted genes that are upregulated in the yellow boxfish (2023). The genes of interest included transmembrane proteins, ATP-binding cassettes, apolipoprotein and vesicle trafficking genes. ATP-binding cassettes are important as they facilitate the transport of substrates into or out of the cytoplasm. (Locher, 2009).

Another interesting fish in the Ostraciidae family is the cowfish. They get their name due to the structures above their eyes that are akin to cow horns (Figure 3). Studies have even been conducted on the structure of the horns, including the compressibility, density and composition (Wen et al. 2014).

Figure 3. Longhorn Cowfish (Lactoria comuta) hunting for food at 7m off Gili Air. Taken by Monique White.

Final Remarks

I hope you begin to adore this family of fish as I do. I think there is a lot we still don’t understand about marine organisms, and I hope one day we may have some answers too. As I come from a background of biochemistry, my curiosity sparks when I see morphological changes in species, whether it is due to age or gender. I wonder how this is regulated on a molecular level, are pigments regulated by sex chromosomes? Or by stretching skin? For this, I couldn’t find an answer in my preliminary research.

But this is a reminder to stay curious, and enjoy nature while we still can.

 

References

Locher., K. (2009). Structure and mechanism of ATP-binding cassette transporters. Philos Trans R Soc Lond B Biol Sci. doi: https://doi.org/10.1098/rstb.2008.0125

Thomson, D. A. (1964). Ostracitoxin: An Ichthyotoxic Stress Secretion of the Boxfish, Ostracion lentiginosus. Science, 146(3641), 244–245. http://www.jstor.org/stable/1713828

Thomson, D. A. (1969). Toxic Stress Secretions of the Boxfish Ostracion meleagris Shaw. Copeia, 1969(2), 335–352. https://doi.org/10.2307/1442084

Van Wassenbergh, S., van Manen, K., Marcroft, T. A., Alfaro, M. E., & Stamhuis, E. J. (2015). Boxfish swimming paradox resolved: forces by the flow of water around the body promote manoeuvrability. Journal of the Royal Society, Interface, 12(103), 20141146. https://doi.org/10.1098/rsif.2014.1146

Wei, S., Zhou, W., Fan, H., Zhang, Z., Guo, W., Peng, Z., & Wei, F. (2023). Chromosome-level genome assembly of the yellow boxfish (Ostracion cubicus) provides insights into the evolution of bone plates and ostracitoxin secretion. Frontiers in Marine Science. https://doi.org/10.3389/fmars.2023.1170704

Winterbottom, R., & Tyler, J. C. (1983). Phylogenetic Relationships of Aracanin Genera of Boxfishes (Ostraciidae: Tetraodontiformes). Copeia, 1983(4), 902–917. https://doi.org/10.2307/1445092

Yang, W., Nguyen, V., Porter, M., Meyers, M., & McKittrick, J. (2014). STRUCTURAL CHARACTERIZATION AND COMPRESSIVE BEHAVIOR OF THE BOXFISH HORN. Advances in Bioceramics and Biotechnologies II. doi:10.1002/ 9781118771587.ch10