An epidemiological study of cataracts in seawater farmed Atlantic salmon Salmo salar

Abstract

Cataracts in farmed Atlantic salmon have been known for many years, but the aetiology and importance of the disease have not been clarified. A cross-sectional field study of 51 cages of Atlantic salmon at 49 randomly selected sea sites was performed during the summer of 1998. The target population was spring and autumn entry groups of the 1997 generation salmon. Approximately 15 fish from each cage, altogether 777 fish, were autopsied by the same person. Each eye of the fish was scored for cataracts on a scale from 0 to 4 using an otoscope lamp with magnification. The weight and length of each fish were measured. The prevalence of cataracts was 83% and 79% in spring entry groups and autumn entry groups, respectively. The overall mean cataract index (mean score of both eyes) was 1.23, being significantly higher in the spring entry groups (1.36) than the autumn entry groups (0.85). The final results in the spring entry groups showed that the fish groups with higher weight at sea transfer also had a higher cataract index at inspection. The risk of development of cataracts varied significantly among the offspring from the 5 strains represented in the study. Fish from sites located in 2 counties in the southern part of Norway had a significantly higher cataract index than fish farmed in the northernmost county in the study. For the autumn entry groups none of the explanatory variables was significant. In the spring entry groups a significant negative relationship was observed between the cataract score and the weight of the fish at the time of inspection (Pearson's r = -0.17), while the corresponding correlation for the autumn released groups was r = -0.10. Among the spring entry groups the average weight of the fish with the highest cataract score was estimated to about a third of the weight of the fish with no visible cataracts. KEY WORDS: Cataracts · Epidemiology · Atlantic salmon · Risk factors Resale or republication not permitted without written consent of the publisherDis Aquat Org 45: [229][230][231][232][233][234][235][236] 2001 (1) zinc deficiency (Ketola 1979, Barash et al. 1982, Richardson et al. 1985, (2) riboflavin deficiency (Poston et al. 1977, Hughes et al. 1981, Barash et al. 1982, (3) tryptophan deficiency (Poston & Rumsey 1983), (4) thiamine deficiency (Hughes 1985) and (5) methionine deficiency (Poston et al. 1977, Barash et al. 1982, Walton et al. 1982, Cowey et al. 1992. Other factors associated with cataract formation are rapid fluctuations in water temperature (Loewenstein & Bettelheim 1979, Bruno & Raynard 1994, Bjerkås & Bjørnestad 1999, rapid growth (Kincaid & Elrod 1991, fluctuations in the water salinity (Hargis 1991), triploid genetic constitution (Wall & Richards 1992), genetic identity (strain) (Kincaid & Elrod 1991), UV radiation (Cullen et al. 1993), cholinesterase inhibitors (Fraser et al. 1989) and electrolytic imbalance (Iwata et al. 1987).Cataracts in seawater farmed salmon have been noticed for many years, but the incidence apparently increased in the 1990s. On th...

Rapid growth causes abnormal vaterite formation in farmed fish otoliths

“…Aquaculture industries promote increasing individual growth (Thodesen and Gjedrem, 2006;Asche and Bjørndal, 2011) as it increases feed conversion efficiency, which in turn increases sustainability and economic efficiency (Cook et al, 2000). Rapid growth has previously been shown to increase the incidence of cataracts (Ersdal et al, 2001), but the present study is the first to show that it permanently deforms otoliths. If fish welfare is negatively impacted through impaired hearing (Reimer et al, 2016), the industry could reduce growth rates to prevent abnormal vaterite formation.…”

Quantitative genetic architecture of parasite-induced cataract in rainbow trout, Oncorhynchus mykiss

“…This has been reported to be the case in fish suffering from nonparasitic cataracts (Ersdal et al, 2001). Similarly, Seppä-nen et al (2008) showed a significant phenotypic relationship in landlocked Atlantic salmon, Salmo salar, between parasitism and individual growth (r ¼ À0.376, n ¼ 50 fish, Po0.01), such that fish with a higher parasite load and more severe cataracts suffered from reduced growth.…”

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Are fish immune systems really affected by parasites? an immunoecological study of common carp (Cyprinus carpio)

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