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Courtesy of the Aquaculture Program Research Report from HSWRI:

Physical abnormalities, also known as malformations, can commonly affect cultured finfish and are widely varied and typically occur in the embryonic or early juvenile stages of development. Many variables are known to cause malformations including nutrition, handling, and water temperature, currents and quality. The majority of malformations in juvenile fish appear to impact bone development, particularly those comprising the head region. HSWRI recently formalized a Quality Assessment and Control Program (QA/QC) that hatchery workers use to consistently identify and remove malformed fish so that only the highest quality fish are released into the ocean and their post-release survival is not impaired. This procedural document is being coupled with complementary research designed to minimize malformations among all species cultured at HSWRI.

Several methods are available to examine the bones in fish (e.g. radiographs, computed tomography); however their successful application varies with fish size and degree of bone development. One method successfully used on small fish (i.e., <100g) is to clear the tissue and muscles and stain the cartilage and bones (Figure 5). Commonly referred to as clearing and staining, this method immerses the fish in multiple chemical baths during a month long process that yields a “see-through” fish with red and blue colored cartilage and bone. There are many variations on this method and each species of fish reacts differently to the chemical process so it becomes somewhat of an art form to achieve a good specimen.

HSWRI research assistant Genevieve Rich has been working through this process with 50 day old white seabass to determine what works best for this species. As the malformation assessment continues at HSWRI, viewing these cleared and stained specimens will assist in our identification of the bones that are malformed. Understanding when and where these malformations occur during the culture process is an important element in helping to control or eliminate the factors that may cause them.