7.8 Clinical Presentations of Nutritional Malfunctions or Quality

Scoliosis

Scoliosis (lateral or sideways bending) was mentioned earlier in the ascorbic acid discussion. This condition is not the only external presentation related to ascorbic acid deficiency signs. Opercula may be shortened or deformed. Vitamin C is not the only etiology of spinal deformities but is a bona fide differential item. Scoliosis may confound the diagnosis and be accompanied by lordosis (downward) and kyphosis (upward) bending in a clinical condition called LKS. Spinal deformities in fry can often be associated with failure to inflate swim bladders. Fry and older fish without inflated swim bladders seldom grow efficiently and expend excess energy with feed prehension. Such multifactored presentations create a serious demand for investigation skills. This condition causes unwanted difficulty in processing fillets in large production operations, and the deformity is unacceptable in markets that rely on whole fish gutted (WFG) presentation. Most North Americans are unfamiliar with the WFG presentation in restaurants. It is widely accepted and mandatory in other parts of the world when fresh fish is on the menu.

Starvation

Starvation is a nutritional problem. Some caretakers will decrease food rations to a tank when water quality declines. The tactic can get real water quality results, but reducing feed can sometimes stunt rapidly growing fish, as in production nurseries. Great caution and good experience are needed to avoid such drastic measures. Drastic measures may also be needed where special nutrients become exhausted. Image 7.04 shows a “Lawnmower Blenny” tasked with cleaning the algae out of the aquarium.^[1]

When it finally completed the algae removal, it had eaten itself out of the house and home and into starvation. Caregivers can avoid this by matching the size of the task to the size of the animal in some cases or supplementing the diet with algae wafers or other additional sources of nutrition.

Issues caused by old feed

The old feed can be the cause of several nutritional deficiencies. Nutritional anemia related to folic acid deficiency can indicate old feed with heavy bacterial contamination. Nutritional gill disease indicates pantothenic acid deficiency from older stored/warehoused feed. This disease presents as hyperplasia on the edges of the gills. Some cases will have flared operculum indicating respiration insufficiency.

Pantothenic acid deficiency is the cause of Nutritional Gill Disease. Pantothenic acid is water soluble and a member of the B-vitamin group. The usual clinical signs include discoloration along the gill filaments’ trailing border and apparent lamella consolidation. The fish lose interest in feeding. Anemia can be a comorbidity. These changes often occur in confinement-reared fish, such as in hatcheries. This deficiency is seldom identified in feral populations because of the widespread natural nutrient sources.

The veterinary practitioner can bring a new set of eyes to the fish having the problem. Starting with something simple, check the feeding practices. One aspect of aquatic animal nutrition is the leaching of nutrients from the formulated feeds into pond or tank water. Leaching is dependent on dwelling time from feeding until ingestion. Water-soluble nutrients will be the most affected. Additionally, it stands to reason that smaller particles will lose water-soluble vitamins like pantothenic acid more rapidly than larger feed if consumption is delayed.

Old feed is the cause of many production maladies. An outdated feed can be the cause of poor production performance. Review feed room protocols to see if the new feed is rotated behind the previous feed when it arrives!

Tracking down the problem may lead to checking the feed formulation. Calcium pantothenate would be preferred in the formulation for its longer shelf life due to its chemical stability. Sodium pantothenate and free pantothenic are less preferred. Feed companies will check the batch of feed if the signs and history suggest a nutritional problem.

Nephrocalcinosis

Nephrocalcinosis is a “calcification” type lesion in the kidney. When first observed, it may suggest an infectious etiology that may be part of a differential diagnosis. The dietary cause is insufficient Mg in the diet. Others have suggested that using calcium carbonate instead of sodium bicarbonate in recirculating systems to buffer water may create the conditions described. The condition seldom becomes clinically evident. It can often be first noted in histology reports. ^[3]

Sunburn

Sunburn can be seen in fish kept in clear water that is too shallow or does not provide shade opportunities. The lesions can often mimic fungal lesions, which will be as opportunistic pathogens. The lesions will appear on the dorsum of the body around or close to the dorsal fin. The lesions may resemble the saddleback lesions often seen in Columnaris disease. There may be fungal hyphae present as the skin damage ages. Trout is likely to have this problem in clear spring water when the raceways are not shaded and water is on the short supply side for the number of fish held. Koi may also suffer in shallow unshaded ponds (See Image 7.05).^[4] Niacin is protective, but the shade is far more effective.

Aflatoxicosis

Aflatoxicosis is mold contamination, usually from the grain sourced for the feed ration. It comes with a heavy cost to production and marketing due to tumor formations. The aflatoxin develops primarily in poor growing conditions before the crop of grain is harvested. A wet growing season contributes to grain being harvested with higher levels of toxin. The clinical signs often ramp up in mortalities after a drop in production efficiency. Fish may not eat the ration if high in toxins. Necropsy will likely show many signs internally with enlarged liver and often many tumors throughout the visceral. As noted often in discussions around clinical signs, other diseases may look very similar to the gross appearance. In some situations, the only way even qualified veterinary practitioners determine the diagnosis may be laboratory sample submission to confirm a tentative etiology.

Hepatic steatosis

Fatty Infiltration of the Liver is the result in most cases of a formulated diet with too much fat content. The proper term for this condition is hepatic steatosis, meaning simply fatty liver in Latin. The livers become very light-colored and often enlarged (See Image 7.06).^[5]

Cataracts

Cataracts develop in fish with nutritional deficiencies and other causes. Nutrient deficiency to consider is Vitamin B12 or cyanocobalamin as well as methionine. Manganese and zinc deficiencies are also listed causes. Fish can lose most of their vision and be hindered in finding feed or avoiding predators. When the fish are familiar with their environment and have little threat of predation, they can utilize olfaction and sound to locate and obtain feed.

According to researchers at the University of Maine, cataracts occur in net pens rearing Atlantic cod (Gadus morhua), as shown in Image 7.07.^[6] Some recent studies show that histidine, one of the amino acids, may prevent cataract development during smoltification. The etiology is likely CO2 build-up in high-density net pens.^[7]