Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 19

The muscular system of fish has both red and white skeletal muscle. White (fast or twitch) muscle predominates and is important for anaerobic burst or sprint swimming (Roberts and Ellis 2012). Red (slow) muscle is associated with sustained aerobic swimming and has more blood supply; this muscle typically lies in a thin band under the skin along the lateral line and/or dorsal midline (Greek‐Walker and Pull 1975). Pelagic and more active fish have a higher proportion of red muscle (Greek‐Walker and Pull 1975). Drug pharmacokinetics are likely affected by muscle type although the impact is not well‐known. The scup (Stenotomus chrysops) has pink muscle, which has less myoglobin than red muscle, and icefish in the arctic family Channichthyidae have yellow muscle due to a lack of hemoglobin (Helfman et al. 2009).

Fish muscle and skin are generally inelastic; therefore, injection volume and depth are important considerations. Intramuscular medications are potentially more likely to cause injection site lesions than in other vertebrate classes and volumes should be small. Leakage from injection sites is also common both immediately and once fish begin to swim after injection, which is likely to alter pharmacokinetics (Figure A1.3) (Fredholm et al. 2016).

Figure A1.3 Leakage of drug with green marker following intramuscular injection in a Nile tilapia (Oreochromis niloticus).

Most fish are poikilothermic, with body temperature matching water temperature. A few bony fish species show regional endothermy, maintaining their body temperature above ambient, e.g. tunas (Thunnini), billfish (Istiophoridae), and one species of mackerel (Gasterochisma melampus). Endothermy is accomplished using retes in the brain, muscle, and viscera, and using red muscle located near the vertebral column. Endothermy improves digestion and nerve and muscle activity and is important for large predators chasing fast prey in colder waters (Block and Finnerty 1994).

Electrogeneration is possible from modified skeletal muscles in a variety of bony fish including freshwater elephantfish (Mormyridae), South American knifefish (Gymnotiformes), and electric catfish (Malapteruridae).