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A look at gill cover deformities in aquaculture peer-reviewed research

“…skeletal deformities are one of the most significant biological and recurrent problems affecting worldwide finfish aquaculture.” Ortiz-Delgado et al. 2014

When an animal is 100% dependent on human inputs and care, things can go wrong. Things do go wrong.

Some of the issues that aquaculture has struggled with include deformed spines, jaws, heads, gills, fins and, short opercula (gill covers). Some studies report that in the early days of European fish farming, opercula deformity rates were as high as 80% (as cited in Ortiz-Delgado et al. 2014).

The operculum is actually 4 bony plates held together with collagen and other tissues. One study found two types of operculum deformity: a) one or both of the two largest bony plates were actually folded back into the gill opening or b) one or more of the bony plates were either completely missing or under-developed (Ortiz-Delgado et al. 2014).

I looked for research that explores causes of operculum deformity. Here’s what I found:

  1. Vitamin C deficiency. In salmonids (trout and salmon), tilapia and milkfish, gilthead sea bream. Vitamin C deficiency can cause shortened opercula and abnormal support cartilage in the gills of salmonids (Halver et al. 1975 and Soliman et al. 1986, Hilomen-Garcia 1997, Merchie et al. 1997 as cited in Darias et al. 2011).
“Many of these vitamin C-deficient signs can be attributed to the impaired collagen and support cartilage formation in most tissues.” Darias et al. 2011

    1. Dietary unsaturated fatty acids deficiency. Milkfish fed a diet rich in unsaturated fatty acids had reduced opercular deformity, 17% vs. 33% in the control group (Gapasin and Duray 2001).
  1. Temperature of egg incubation. High temperature during incubation and early development leads to increased incidence of shortened opercula (Jobling 2010).
  1. Physical trauma such as damage on netting, excessive water movement in the tank (Galeotti et al 2000 as cited in Ortiz-Delgado et al. 2014).
  1. Not genetic. Triploid salmon had a higher incidence of shortened opercula than genetically normal fish in an aquaculture setting (Sadler et al. 2001). But triploid fish have three sets of chromosomes instead of the normal two. They are bred to be sterile so aquaculture escapees can’t breed with wild fish. This is not relevant because wild cutthroat are not triploid. Inbreeding in captive rainbow trout has been implicated to spinal deformity but wild populations don’t exhibit this inbreeding depression-linked susceptibility to deformity (see for e.g. Evans and Neff 2009). I found nothing linking operculum deformity to genetics. Branson and Turnbull (2008) conclude that environment and diet, not genetics, are the most likely explanations for shortened opercula in farmed fish.

Because aquaculture tries to provide the best water quality for fish rearing, there’s no data here on pollution effects. Pollution doesn’t apply. But what these studies do tell us is that *ANYTHING* that sabotages bone or collagen development is a possible culprit. It could be dietary, it could be physical, it could be environmental.

So back to the wild, to the westslope cutthroat trout of the Elk River.

I think we can take physical trauma off the table as a possible culprit. It’s unlikely they suffer from physical damage caused by excessive water flow during larval development or rubbing up against net pens. Catch and release fishing is physically traumatic, but not in a chronic wearing-the-operculum-down kind of way. And by the time they’re big enough to catch much of the critical gill cover development has already occurred.

I think we can also take genetics off the table. There’s just no convincing evidence of genetic influence in either wild or non-triploid farmed fish. Egg incubation temperature is also an unlikely culprit. (Although with climate change it may become an issue in future.)

Elk River cutthroats are, however, exposed at critical stages of development to what’s in the food.

This and my previous review of gill cover deformity in wild fish leaves us with two likely perps: Food. And water pollution.

Next: What’s in the water anyway? I’m going to start sharing some of my audio interviews with scientists because it’s time to break out of the journals and talk to people with expert knowledge.

Do you have questions about fish or the waters of the Elk you’d like to ask a scientist? Email or message me and I’ll find an independent scientist who can answer. I’d like to hear from you!

Literature Cited

Branson, E.J., T. Turnbull. 2008. Welfare and Deformities in Fish. Fish Welfare. pp 207.

Darias, M.J., D. Mazurias, G. Koumoundouros, C.L. Cahu and J.L. Zambonino-Infante. 2011. Overview of vitamin D and C requirements in fish and their influence on the skeletal system. Aquaculture. 315, 49-60.

Evans, M.L. and B.D. Neff. 2009. Non-additive genetic effects contribute to larval spinal deformity in two populations of Chinook salmon (Onchoryhnchus tshawytscha). Aquaculture 296:169-173.

Gapasin, R.S.J. and M.N. Duray. 2001. Effects of DHA-enriched live food on growth, survival and incidence of opercular deformities in milkfish (Chanos chanos). Aquaculture 193, 49-63. As cited in Cahu, C., J. Zambonino Infante and T. Takeuchi. 2004. Nutritional components affecting skeletal development in fish larvae. Aquaculture. 227(1-4): 254-258.

Galeotti, M., P. Beraldo, S. de Dominis, L D’Angelo et al. 2000. A preliminary histological and ultrastructural study of opercular anomolies in gilthead sea bream larvae (Sparus aurata) juveniles. Fish Physiol Biochem 22:151-157. Abstract only.

Halver, J.E., R.R. Smith, B.M. Tolbert and E.M. Baker. 1975. Utilization of ascorbic acid in fish. Ann. N.Y. Acad. Sci. 258: 81-102. Abstract only.

Hilomen-Garcia, G. . (1997). Morphological abnormalities in hatchery-bred milkfish (Chanos chanos Forsskal) fry and juveniles. Aquaculture, 152(1–4), 155-166. Abstract only.

Jobling, M. 2010. The Rearing Environment. Finfish Aquaculture Diversification. N. R. Le François, M. Jobling, C. Carter, eds. CAB International. pp. 52.

Loizides, M., A.N. Georgiou, S. Somarkis, P.E. Witten and G. Koumoundouros. 2013. A new type of lordosis and vertebral body compression in Gilthead seabream (Sparus aurata Linnaeus, 1758): aetiology, anatomy and consequences for survival. J Fish Dis, doi:10.111/jfd.12189 as cited in Ortiz-Delgado et al.

Merchie, G., P. Lavens and P. Sorgeloos. 1997. Optimization of dietary vitamin C in fish and crustacean larvae: a review. Aquaculture 155, 165-181.

Ortiz-Delgado, J. B., I. Fernández, C. Sarasquete and E. Gisbert. 2014. Normal and histopathological organization of the opercular bone and vertebrae in gilthead sea bream Sparus aurata. Aquatic Biology. 21:67-84.

Sadler, J., P.M. Pankhurst, H.R. King. 2001. High prevalences of skeletal deformity and reduced gill surface area in triploid Atlantic salmon (Salmo salar L.). Aquaculture. 198(3-4):369-386. Abstract only.

Soliman, A.K., K. Jauncey and R.J. Roberts. 1986. The effect of varying forms of ascorbic acid on the nutrition of juvenile tilapia (Oreochromis niloticus). Aquaculture 52, 1-10. Abstract only.

Photograph of a westslope cutthroat trout with missing gill cover, courtesy of Paul Samycia