Laurie J. Gage
Captive pinnipeds appear to have a disproportionally high incidence of chronic corneal problems when compared to the incidence of similar eye diseases in other captive mammalian species. Known or suspected causes include one or a combination of the following: trauma, periodic or persistent excessive chemical, oxidant, or noxious byproduct levels in the water, excessive UV light exposure, osmolality of the water, pathogens, and nutritional imbalances.
Common eye problems seen in pinnipeds are corneal edema, corneal opacities, chronic keratitis, blepharospasm, and cataracts. When trauma and infections can be ruled out, water quality is often to blame and checking the water quality records for chemical spikes or imbalances over the course of a year may help to identify the problem. When pinnipeds housed at a facility develop chronic eye problems, a thorough evaluation of oxidant levels, coliform counts, pool color, availability of shade, salinity, nutritional supplements, or exposure to pathogens is warranted.
Injury to the eyes can include a punctuate lesion to the cornea from a vibrissae or from a negative social interaction. Eye trauma may also occur from excessive debris, such as pine needles, in the water.
Excessive Chemicals, Oxidants, or Noxious Byproducts in the Water
Most modern filtration systems utilize oxidants such as chlorine, bromine, or ozone to control pathogen levels in the water. These chemicals should be measured daily and recorded. Total chlorine levels may spike on occasion, however if these spikes occur repeatedly, the chlorine or its byproducts could cause damage to the cornea. If the source water is municipal, levels of chlorine should routinely be measured out of the tap to ensure the chlorine levels going into the pool do not exceed 1-1.5 ppm. At several facilities municipal source water used for pinniped pools had over 3 ppm chlorine measured at certain times of the year. Optimally total chlorine levels in the water should not exceed 1 ppm. If the chlorine levels in the source water are too high, methods to dechlorinate should be employed before the water is placed in the animals' pools. Byproducts of disinfection, such as chloramines or trihalomethanes may also be irritating to the eye and screening for these compounds may be warranted. Ozone systems must have an efficient method to degas the water. Ozone is a powerful oxidant and there should be no measureable residual ozone in the animal pools.
While pinnipeds typically come from a bright and sunny environment, they are not adapted to dealing with bright, reflective surfaces when diving. Noting that clear water absorbs very little UVA light and UVA light is very effectively reflected by light blue or light green surfaces, it stands to reason that pinnipeds housed in pools painted with these reflective colors will be exposed to a higher ocular daily level of potentially damaging UVA light than their wild counterparts. Over time, this exposure could lead to cumulative oxidative damage to the cornea or the endothelial layer of the cornea.2
It appears there are more cases of corneal damage in pinnipeds housed in fresh water, however, there are some facilities utilizing fresh water (one with no chemical additives) where few eye problems are observed. The eyes of pinnipeds housed in saltwater systems seem better able to withstand occasional oxidative insults than those housed in fresh water systems. Saltwater pools are optimal for these marine mammals, however a well-managed fresh water system may be adequate.
Eye problems in pinnipeds may have fungal, bacterial or viral etiologies. Both bacterial and fungal etiologies have been diagnosed in captive pinnipeds with eye lesions. Because of the appearance of some corneal lesions, and ruling out other factors, herpesvirus has been suspected, but never proven to cause eye disease in some captive pinnipeds.
Free radicals produced from biological processes or in response to exogenous stimuli are controlled by various enzymes and antioxidants in the body. Antioxidants such as Vitamins E, A, or C, or other antioxidants may aid in mitigating oxidative damage to the cornea and other eye structures. Only the highest quality fish should be fed, it should be properly thawed, and fish stored in the freezer should be rotated to ensure freshness. Vitamins A, C, and E are unstable and over time levels in the fish tissues will decrease. Higher fat fish deteriorate faster than lower fat fish and are more prone to oxidation (or rancidity) and antioxidants such as Vitamin E are utilized during the breakdown process.1 A daily high quality vitamin supplement which includes antioxidants should be included in pinniped diets.
1. Crissey S. D., and S.B. Spencer. 1998. Handling of fish fed to fish eating animals: a manual of standard operating procedures. U.S. Department of Agriculture, Agricultural Research Service, National Agriculture Library http://www.nal.usda.gov/awic/pubs/fishhndl.htm.
2. Svobodova A., D. Walterova, and J. Vostalova. 2006. Ultraviolet light induced alteration to the skin. Biomed Pap Med Fac Univ Palaky Olomouc Czech Repub 150(1): 25-38.