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5 Fish Surgery
Claire Vergneau‐Grosset and and E. Scott Weber, III
Surgeons working with fish should be familiar with their anatomy and physiology. Given that fish are the largest class of vertebrates, anatomic variability is common, and the surgeon should refer to species‐specific information, remembering that while many references are not veterinary based, they still provide critical information about anatomy and physiology (Harder 1975). In addition, there are an increasing number of articles describing normal and abnormal anatomic structures obtained with ultrasonography (Walsh et al. 1993; Raidal et al. 2006; Grant et al. 2013; Jafarey et al. 2015), radiography (Love and Lewbart 1997; Bakal et al. 1998; Govett et al. 2004; Schwarz et al. 2002), computed tomography (CT) (Figure 5.1a,b) (Pees et al. 2010; Carr et al. 2014; Schwarz et al. 2002), and magnetic resonance imaging (MRI) (Chanet et al. 2009). Ultrasound, CT, and MRI images may be obtained with the fish remaining in water (Pees et al. 2010).
Perioperative and Postoperative Surgical Management
Water
Thermoregulation, osmoregulation, and other water quality parameters must be maintained throughout surgery. Postoperatively, to reduce osmotic stress, add salt to the water at a concentration of 3–5 ppt for freshwater species. Increasing the water temperature to the higher temperature range of the species can hasten incision healing. It may be important to isolate the patient for improved monitoring depending on logistical and behavioral constraints. Because of the lower environmental temperatures, absorbable suture material will remain for a long period. Suture removal is usually not performed before three to four weeks and may take months in cold‐water species and careful examination of the wound margins to assess skin continuity is recommended prior to suture removal, typically after four to eight weeks in temperate species (Sladky and Clarke 2016).
Analgesia, Anesthesia, and Fluids
Various models have been used to investigate nociception, and nociceptive receptors are present in fish, predicating the importance to minimize noxious stimulations associated with fish surgery (Weber 2011a). The use of a perioperative opioid drug is currently recommended. Morphine 5 mg/kg intramuscularly (IM) has been proposed in koi (Cyprinus carpio) (Baker et al. 2013). Morphine at this dose caused temporary bouts of excitability and, if used, owners should be made aware of potential adverse effects (Baker et al. 2013). The pharmacokinetics of morphine have also been reported in goldfish (Carassius auratus) and salmon (Salmo salar) administered, respectively, 40 and 100 mg/kg IM and mean elimination half‐lives were 12.5–13.5 hours (Nordgreen et al. 2009). Nonsteroidal anti‐inflammatory drugs are used as part of multimodal analgesia in fish. Ketoprofen (Harms et al. 2005; Davis et al. 2006; Ward et al. 2012), carprofen (Mettam et al. 2011), and meloxicam (Larouche 2018; Fredholm et al. 2016) have been evaluated in fish. Adverse effects of other non steroidal anti‐inflammatory drugs have been reported and empirical use at high doses should be avoided (Schwaiger et al. 2004; Lovy et al. 2007). In‐depth reviews of fish anesthesia are available (Stoskopf and Posner 2014; Whiteside 2014). Perioperative fluids are chosen based on the plasma osmolarity of the species, ranging between 900 and 1500 mOsm/l in elasmobranchs (Hadfield et al. 2010).
Antibiotics
Only a few antibiotics are approved for specific species use in aquaculture, and these vary by country (Health Canada 2010; Tell et al. 2012). A growing number of pharmacokinetic studies evaluate therapeutic antibiotic use in ornamental fish (Nouws et al. 1988; Grondel et al. 1986; Lewbart et al. 1997; Yanong et al. 2011; Grosset et al. 2015).
Figure 5.1 (a) Positioning for a CT‐scan in an anesthetized koi (Cyprinus carpio) presented with an inability to close the mouth. The koi is kept anesthetized via a water‐circulating system over the gills and irrigation of the skin is provided with a syringe just before a very quick image‐acquisition period. Care should be taken to avoid any water leakage with the use of absorbing towels and foam. (b) Example of a CT‐scan of a koi (Cyprinus carpio) patient that presented for an inability to close the mouth: longitudinal section showing the ossicles (arrows), the globes (g), and opercular cavity (*).
Source: Photo courtesy: Companion Avian and Exotic Pet Medicine Service, University of California, Davis.
Surgical Table
Most fish surgeries are performed out of the water to facilitate visualization, tissue dissection, and suturing (Wildgoose 2000). Surgery tables adapted for fish should include a recirculating water system and a support element for the patient (Weber et al. 2009). The support element is typically made of nonabrasive material to preserve cutaneous mucus and should