Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 173

The prior diet of a fish (e.g. seafood, pellets, soaked flake) can often be made into a slurry or gruel for tube feeding. It is essential that gruel be well‐blended and smooth, so heads, spines, fins, skin, and/or shells usually need to be removed prior to using a blender. Commercial tube‐feeding formulas may also be useful (e.g. Oxbow® Carnivore Care, Mazuri® Shark/Ray gel). The gruel or formula, or a mixture, should be blended with water or an electrolyte solution so that it is just thin enough to pass through a syringe and appropriately sized tube. It should not be any more dilute, as this will reduce the caloric concentration. A good starting point is a 60:40 ratio of food to water. This ratio can be adjusted based on the resulting gruel consistency and thickness. The volume for tube feeding will often start at 0.5–1% of fish body weight and increase to 2–3% as necessary.

Tube feeding can be performed under manual or chemical restraint. For small fish, red rubber tubes, avian tracheal tubes, or IV catheters can be used. Luer‐lock syringes are useful as they hold the tubing more securely than Luer‐slip syringes. For large fish (e.g. >10 kg), small or large animal gastric tubes are useful. The tubing should be cut to an appropriate length by approximating the length from the mouth to the middle of the pectoral fins (the approximate location of many fish stomachs). Beveling the leading edge of the tube and filing any rough edges may reduce the risk of trauma.

It is usually best to fill the syringe immediately before feeding to reduce the risk of clogging. Air pockets should be removed prior to feeding. Most fish are easiest to gavage in ventral recumbency, while small elasmobranchs are often easiest to gavage in dorsal recumbency and large sharks may be easiest in slight lateral recumbency. If a gag is needed, PVC tubes and syringe cases work well. The tube should be gently inserted through the mouth along the midline into the esophagus. If the tube is not centered correctly, it will emerge from one of the gill openings or the spiracle. If this happens, the tube should be retracted and replaced along the midline. It is normal to feel the pharyngeal teeth when placing a gastric tube in a bony fish. Once the resistance changes or the predetermined length has been reached, gentle pressure can be used to deliver the mixture into the stomach. Once the appropriate volume has been provided, or if any regurgitation is seen, the tube should be removed. Fish should be monitored for any subsequent regurgitation as this is common. If the syringe or tubing becomes clogged, it is usually best to remove the gavage tube and try again with a new setup. Serious problems such as gastrointestinal rupture or accidental administration into the swim bladder in physostomous fish are rare but can occur, so suitable restraint and gentle pressure are important.

When tube feeding is needed, it often needs to be repeated regularly to keep an individual on a positive nutritional plane. The frequency will depend upon the condition of the fish, its sensitivity to handing stress, practicalities of regular handling, and the animal's natural feeding periodicity. Gastrostomy tubes could be used to reduce handling requirements in some species, with one report in a green moray eel (Gymnothorax funebris) (Kizer 2005). Food should continue to be offered to the fish during tube feeding to encourage free feeding.