The captive spiny dogfish, Squalus acanthus, is commonly found in aquariums and in research settings. It is a valuable animal model and is used in several areas of biomedical research such as neurosciences, immunology, physiology and reproductive biology.2,5 Currently, most spiny dogfish are wild caught and like many other marine species, their populations are declining. Efficient utilization of this resource by researchers and industry is a necessity.
Several investigators at the Marine Biological Laboratory (MBL) use the spiny dogfish embryos as their study model. Embryos of approximately 9 cm are the most common size needed and must be harvested from pregnant females.3 In the past, females with enlarged abdomens were identified and possible embryos were dissected from these animals. Using this method, many of the embryos harvested were not of the correct size, thus wasting much life. Therefore, a major challenge was to develop a reliable, noninvasive method to determine pregnancy and embryo size before the female dogfish and its embryos were sacrificed.
Ultrasound has long been a standard technique for human, small and large domestic animals. Its applications are being explored by the aquaculture industry, processing plants and by research groups.2 Refinement of ultrasound techniques in aquatic animal medicine may help us solve commonly encountered research, medical and management problems. The normal echoanatomy of various fish has been established.1,4,6,7 However, different species vary in their shape, size and thickness which lead to intrinsic ultrasonographic differences between species.
The goal of this research was to describe the normal echoanatomy of the female spiny dogfish and determine if ultrasound can be used to assess pregnancies in ovoviviparous fish such as the dogfish.
In this study we used a portable Ausonics ultrasound to assess the echoanatomy of five wild caught female dogfish. They were kept in tanks at the Marine Biological Laboratory until our research was performed. The dogfish were immobilized by placing them in an ice bath for 10 minutes. The fish were measured and then placed in dorsal recumbency. Transverse and longitudinal scans of each studied organ were performed. Necropsies were performed in order to correlate the imaging findings to the normal anatomy of the dogfish.
In every animal, the heart, ovaries, follicles, liver, gallbladder, spleen, stomach, duodenum, spiral colon and rectal glands were identified and ultrasonographically characterized (size, shape, position and echogenicity). Determination of pregnancy and fetal anatomical measurements using ultrasound was accurate method of determining embryo size. Furthermore, the fetuses in the pregnant females were identified, counted and measured.
The use of ultrasound is an important method that not only provides an efficient, noninvasive technique of differentiating between all of the organs in the dogfish's body, but most importantly, determines if the animal is pregnant and the size/stage of embryo development. This noninvasive, accurate method can easily be used on a routine basis at the MBL thus eliminating the wasteful selection of animals.
The authors would like to thank the Marine Biological Laboratory for providing us with the spiny dogfish, Tufts University School of Veterinary Medicine for lending us the ultrasonographic equipment, Dr. Robert Gould, Dr. Teresa Salvina and Mr. Erik Peterson for their expertise and assistance during the course of this project.
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