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The swim bladder is important in maintaining neutral buoyancy. Abnormal buoyancy is a common presentation of ornamental fish (Wildgoose 2007a) with a number of etiologies that can be diagnosed using radiography or other imaging techniques. Positive buoyancy may be due to overinflating of the swim bladder (Figure 5.17), torsion (rare), or gas in the coelomic cavity or other coelomic organs. Negative buoyancy may be due the accumulation of fluid in the swim bladder, infection, neoplasia, or compression by enlarged coelomic organs, cystic kidneys or ovaries, or other coelomic masses. Swim bladder anatomy varies greatly among fish species and surgeons should be familiar with the anatomy of their patient (Zebedin and Ladich 2013). Some fish are physostomous (swim bladder is connected to the digestive tract), some are physoclistous (swim bladder inflation is regulated by a gas gland), and some fish do not have a swim bladder (e.g. elasmobranchs, mackerels, tunas, benthic fishes, and remoras) (McCune and Carlson 2004). Koi and goldfish have a bi‐compartmentalized swim bladder with the most cranial compartment being more rigid and a pneumatic duct connecting it to the caudal compartment (Muir Evans 1925), while some catfish species have multi‐compartmentalized swim bladders (Zebedin and Ladich 2013). Imaging both the patient and a normal conspecific helps identify swim bladder lesions whenever specific anatomy has not been described (Schwartz et al. 2002; Pees et al. 2010). Care should be taken to avoid trauma to and deflation of the swim bladder during a celiotomy.

Figure 5.17 Right lateral radiograph of a positively buoyant goldfish (Carassius auratus) presented with multiple gas (white arrows) and fluid‐filled (black arrows) structures connected to the swim bladder.

Source: Photo courtesy: Companion Avian and Exotic Pet Medicine Service, University of California, Davis.

In the case of swim bladder neoplasia or distension, surgical reduction of the swim bladder is indicated. This procedure has been termed pneumocystoplasty or complete pneumocystectomy depending on the volume of swim bladder reduction (Britt et al. 2002; Lewbart et al. 1995). Approach the swim bladder using a ventral coelomic midline incision (Lewbart et al. 1995; Britt et al. 2002) or a L‐shaped incision through the lateral coelomic wall (Harms and Wildgoose 2001). For pneumocystoplasty, locate and preserve the pneumatic duct and/or the gas gland that is a “rete mirabile” and partially surrounds the walls of the swim bladder and furnishes a rich supply of blood often located ventrally on the most cranial aspect of the swim bladder (Harms and Wildgoose 2001). Carefully dissect the swim bladder to avoid perforation and collapse (Harms and Wildgoose 2001). The wall of the swim bladder is very thin and delicate and achieving impermeability following formation of a tear may be very challenging. This can result in free coelomic gas, abnormal buoyancy, and communication between the digestive tract and the coelom in physiostomous fish, which may cause coelomitis. Depending on the size of the fish, place an encircling ligature (Harms and Wildgoose 2001) or a vascular clip (Hemoclip, Teleflex, Morrisville, NC) prior to excising the affected part of the swim bladder (Britt et al. 2002). Alternatively, a two‐layer inverting suture may be placed to close the swim bladder after excision of a section of this organ (Sladky and Clarke 2016). Negative buoyancy is a common complication immediately following pneumocystoplasty as the fish needs to adjust gas content of the swim bladder to accommodate the weight of a hemostatic clip or for decreased size of the swim bladder itself. This complication may persist for the remaining life of the fish if the resulting volume of the swim bladder is too small (Sladky and Clarke 2016). On the Internet, several hobbyists and websites have suggested ways to create custom‐made flotation harnesses for goldfish using chamois material, plastic airline tubing, and cork to allow locomotion in negatively buoyant fish.