Alternative Method of Removing Otoliths from Sturgeon

Summary

The goal of the protocol is to show an effective method to extract the otoliths from sturgeon carcasses.

Abstract

Extracting the otoliths (ear bones) from fish that have very thick skulls can be difficult and very time consuming. The common practice of making a transverse vertical incision on the top of the skull with a hand or electrical saw may damage the otolith if not performed correctly. Sturgeons (Acipenseridae) are one family in particular that have a very large and thick skull. A new laboratory method entering the brain cavity from the ventral side of the fish to expose the otoliths was easier than other otolith extraction methods found in the literature. Methods reviewed in the literature are designed for the field and are more efficient at processing large quantities of fish quickly. However, this new technique was designed to be more suited for a laboratory setting when time is not pressing and successful extraction from each specimen is critical. The success of finding and removing otoliths using this technique is very high and does not compromise the structure in any manner. This alternative technique is applicable to other similar fish species for extracting the otoliths.

Introduction

Sturgeon (Acipenseridae) populations throughout the world have been declining for over a century due to impacts including habitat loss, population fragmentation, and overfishing such that many populations are protected by state and federal laws^1,2. Management agencies throughout the USA and the world have identified sturgeon as a target species for restoration and recovery¹. Population characteristics (growth, recruitment, diet) of most sturgeon populations have been studied to better understand basic biology and life history characteristics¹. Due to the protected status of most sturgeon populations, age evaluation is difficul....

Protocol

Important Note: Due to the protected status of all species of sturgeon in the United States, permits to acquire and handle fish were obtained prior to laboratory procedure. All specimens were acquired from hatchery sources post mortem due to natural causes and disposed of following standard procedure.

1. Specimen Preparation

1. Before any incisions lay sturgeon carcass on its side and using a measuring tape to measure total length from the snout to the tip of the tail to the nearest 1 mm. (Figure 1A)
2. Weigh sturgeon carcass on a tared scale to the nearest 1 g. Evaluate carcass for any external tags or mark....

Results

The adult size of sturgeon across the world varies greatly but the location of the otoliths is consistent. The use of a sharp fillet knife was found to remove the soft tissue of the mouth easily shown in Figure 1D. An electric bone saw is the preferred tool for the lateral incision to expose the brain cavity in Figure 1E. However, attention to bisecting the midline of the skull is needed otherwise the otoliths may be crushed during this process. If this p.......

Discussion

The overview of an alternative method of extracting otoliths from sturgeon carcasses has been detailed. It is important to note that special attention is needed to the lateral incision placement on the midline of skull in order to bisect the skull evenly to ensure no harm to the otoliths during dissection. If the incision is not deep enough to completely bisect the skull it will be very difficult to expose the brain cavity where the location of the otoliths is clearly visible. With experience, the overall technique is re.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Measuring Board			Metric meter stick is preferred
Weighing scale
Filleting Knife
Scalpel
Forceps
Sample vials			25 ml scintillation vials work well