Uncoupling of Visual and Somatic Growth in the Rainbow Trout <i>Oncorhynchus mykiss</i>

Abstract

Hatchery reared juvenile rainbow trout of common parentage were reared on measured low or high rations, or fed ad libitum for 4.3 months to produce fish with different growth rates. Fish from the different groups differed in size by up to 40 and 290% for length and weight, respectively, by the end of the trial. Slow somatic growth was not accompanied by correspondingly slow growth of either the eyes, optic tectum or the cerebellum, suggesting that above a certain maintenance ration, growth of these parts of the CNS is strongly age-dependent. Retinal characteristics were also found to be age-dependent and not affected by the somatic growth rate of the fish. The corollary that age-dependent ocular growth should also be reflected in different relative eye sizes in fish with differential growth rates in the wild was tested by comparing fish of known age from lakes in which fish have markedly different growth profiles. Fish stocked from a single hatchery were recaptured from Lakes Okataina and Tarawera (rapid fish growth) and Lake Taharoa (slow fish growth) at times up to 5 years after release. As predicted, eye sizes of fish from Lakes Okataina and Tarawera were smaller for any given body size, than those of fish from Lake Taharoa. Absolute eye size was correlated with fish age, although there was some variation in eye size for any given age. Taken together, these results show that up to a certain level of food deprivation, growth of the eye is maintained at the expense, or in spite, of low somatic growth. However, there is a level of somatic growth below which ocular growth is affected.

Comparative morphometrics of two populations of <em>Mugil curema</em> (Pisces: Mugilidae) on the Atlantic and Mexican Pacific coasts

“…Montgomery et al (1997) showed with the Antarctic silverfish (Pleuragramma antarcticum) that eye growth and somatic growth are on separate trajectories, and the breaks in the relative eye diameter result from overwinter periods when somatic growth is static but the eye continues to grow. Similar results were found in the rainbow trout Oncorhynchus mykiss (Pankhurst and Montgomery, 1994). Moreover, carp pituitary extract together with a dopamine antagonist caused an increase in eye size and significant gonadal development in the female of Anguilla anguilla in wild and cultivated stocks (Muller et al, 2003).…”

The Chatham Islands endemic galaxiid: ANeochannamudfish (Teleostei: Galaxiidae)

“…3,4). Allometric growth in eye size (Pankhurst & Montgomery 1994) probably explains the comparatively large eye in the small specimens, and the difference in eye size between the larger and small Chathams fish.…”

Effects of chronic and periodic exposures to ammonia on the eye health in juvenile Atlantic halibut (Hippoglossus hippoglossus)

“…Pankhurst and Montgomery (1994) found that growth of the eye is maintained at the expense of low somatic growth during suboptimal rearing conditions that could help to explain the fact that no differences in cataract formation was seen albeit there were major ammonia-related growth differences. The unilateral eye changes indicate a mechanical causation compared to often bilateral nutritional-related changes (Waagbø et al 2010).…”