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.
Reproductive Surgery
Determining the sex of fish through surgical incision into the coelomic cavity is performed routinely in some fish industries. Commercial sturgeon is sexed around three year of age to separate males for meat production and females for caviar production. Caviar collection itself may also be accomplished antemortem through a coelomic incision followed by closure of the body wall; this technique is employed in some commercial facilities to allow production by the same female during subsequent years. Sturgeon can be sexed using ultrasound eliminating the need for surgery (Colombo et al. 2004).
Ovariectomy has been performed in many piscine species (Stamper and Norton 2002; Lewisch et al. 2014). Indications for ovariectomy include contraception, persistent egg retention despite medical treatment, and gonadal tumors (Jafarey et al. 2015). Ovariectomy is rarely performed prophylactically in fish (Kizer and Novo 2003), with the exception of batoid species, i.e. rays and skates, kept in female‐only groups (Sladky and Clarke 2016) as this group structure may predispose rays to reproductive tract lesions. Rays with an oral disc ranging from 50 to 60 cm have been reported to have a better surgical outcome (Sladky and Clarke 2016). Ovariectomy should only be attempted in mature fish for contraceptive purposes, as gonads may be extremely difficult to locate in immature fish, resulting in gonadal tissue being left behind. It should be noted that some teleost species, such as the arowana, have a single ovary located on the left side of the coelom (Yanwirsal 2013). Some elasmobranchs have a single functional ovary (left ovary in rays and the right ovary and both oviducts in sharks) (Henningsen et al. 2004).
In teleosts, use a ventral approach to the coelomic cavity and locate the ovaries. Bluntly dissect from caudal to cranial with cotton‐tipped applicators or hemostats to locate the ovarian pedicle. Depending on the size of the fish, use a ligature, a hemostatic clip, or electrocautery to provide hemostasis. Transect the pedicle distal to the ligature and remove the ovaries (Figure 5.18). In some fish, the ovarian mass may be very friable and should be carefully handled with cotton‐tip applicators to avoid rupture. Leaving ovarian material in the coelomic cavity may result in coelomic inflammation; use a combination of irrigation and suction to avoid this complication (Sladky and Clarke 2016). In fish with egg retention, medical management (Ovaprim®, Syndel Laboratories Ltd., Nanaimo, Canada) should be attempted before surgical ovariectomy (Hill et al. 2009).
Figure 5.18 Ovariectomy in an Oranda goldfish (Carassius auratus): the head of the fish is toward the bottom of the picture and the caudal fin toward the top of the picture. A diseased ovary is been retracted with a stay suture.
Source: Photo courtesy: Companion Avian and Exotic Pet Medicine Service, University of California, Davis.
Use a dorsal paralumbar approach in batoid species. Make a craniocaudal longitudinal incision approximately 2 cm lateral to the dorsal lumbar muscles, on the side of the functional ovary (e.g. left side for cownose rays and stingrays). Use a #10 scalpel blade in large females, as the skin and body wall are very thick. Elevate and incise the coelomic membrane. Visualize the ovary (connected to the epigonal organ), ovarian pedicle, suspensory ligament, and cranial portion of the oviduct. Ligate the ovarian vessels with suture or a hemostatic clip. Dissect the caudal pole of the ovary from the epigonal organ and excise the ovary. Inspect the coelomic cavity to assess hemostasis. Close the peritoneum with 3‐0 polydioxanone or polyglyconate suture, then close the muscle and the skin in two layers (Sladky and Clarke 2016).
Ovarian and testicular tumors are frequent in koi and gonadectomy has been reported as curative in various fish species (Weisse et al. 2002; Lewisch et al. 2014). Some of these gonadal tumors become locally invasive in the coelomic cavity and surgical excision is not possible.
Cesarean section may be performed in ovoviviparous species with fry retention, or in viviparous species with dystocia. Surgery should be attempted before the dam is too debilitated. In teleosts,
