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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, incise the coelomic cavity on ventral midline from the anus caudally to the pelvic symphysis cranially and locate the pouches internally on each side of the coelom. Place stay sutures in the gravid pouch and elevate it from the rest of the coelom. Make an incision with scissors where the tail of a fry is visible and exteriorize the fry through the incision. Other fry in the same pouch can be gently manually expressed through the same incision. Close each incubation pouch with a simple continuous pattern or a continuous inverting pattern using absorbable suture. If possible, remove air trapped in the incubation pouches prior to closure of the coelom, otherwise, the fish may be positively buoyant postoperatively.

In batoids species, position the fish in ventral recumbency and make a longitudinal incision 2 cm lateral to the lumbar muscles, similar to the approach used for ovariectomy. Enter the coelomic cavity after elevating the peritoneum. Locate the uterus and incise its wall, paying attention not to contaminate the coelomic cavity with uterine contents including the embryonic histotroph. After removing the young from the uterus and handing it to a team dedicated to young recovery, close the uterus in two layers with a continuous inverting suture pattern using monofilament suture. Lavage the coelomic cavity before routine closure (Sladky and Clarke 2016).