Quivering movements to one side are also common, and like all the above signs usually results from local damage to spinal and peripheral nerves which control muscle action. Upon handling, the backbone may be obviously broken, and a grinding noise or 'crepitus' heard during movement of the tail. The fish can have an increased respiratory rate, will feed poorly and take on darker pigmentation. Many other fish in the stricken tank may appear perfectly normal. A recent history of electrical exposure is helpful, and a check of local weather records is of use to confirm thunder storm and electrical activity near your farm if you don't inspect facilities daily.
Dead fish feel abnormally limp.
Fractured spinal columns or severe compression of the vertebrae occurs due to violent contraction of the flank musculature. Palpation or X-ray photographs can be used to detect this, with the fractures usually evident below and just posterior to the dorsal fin. This is the centre of flexure of the tail, and the largest muscular forces are exerted here. Consequently, this is the common site for the vertebrae to break. Internally, there can be massive intramuscular hemorrhage close to the fracture, and numerous small haemorrhages may be spread throughout the body.