By Abigail Lynch

The holidays are over.  No more cookies; no more egg nog; no more latke and fruitcake.  No more holiday goodies, well, unless you count the extra pudge that I’m carrying around as a result of that deliciously festive fudge…

Without fail, this time of year makes many of us turn to New Year’s Resolutions of better eating habits, weight loss, and improved exercise regimes.  We want to shed our post-holiday pounds but have you ever wondered if fish can get fat as well?

The short answer is yes.  Depending on diet, fish can have varying levels of fat deposits and some fish can be chubbier than others.

In nature, overweight fish are uncommon because fish generally live in food limited environments.  They eat when they have access to food because their next meal may not be for quite some time.  Fish will store fat deposits to prepare for long periods of fasting.  In fact, certain salmon runs are renowned for their decadent flavor which is the a result of higher fat stores, provisions intended to last through long migration routes to their spawning areas.

Most examples of obesity in fish are documented in aquaculture and aquarium settings.  For farmed fish, lipids can be stored in subcutaneous fat, in muscle, and visceral fat; there is a delicate balance in dietary lipid content to optimize the final product for the consumer.  High-fat diets can result in higher weight gain than medium-fat diets, but if that gain is mainly in the form of visible fat deposits, that may not be ideal for market (Refstie et al. 2001).  Excessive lipid deposition can also be commonly associated with clinical disorders, such as abdominal distention syndrome (bloat; Lie 2008),  in aquacultured fish like trout (Noga 2011).

For aquarium fish, overfeeding can result in obesity (Livengood and Chapman 2007).  Remember that pet fish have evolved as wild fish so they are programmed to “clean their plates,” and eat anything and everything to which they have access.  That being said, most abdominal swelling in aquarium fish is not excess fat but rather caused by infection (Noga 2011).  So, don’t necessarily attribute any rapid change in girth of your pet fish to mere gluttony.

That fact that fish can gain fat may actually help humans with obesity-related illnesses in the future.  Zebrafish (Danio rerio) have been found to have similar processes of lipid metabolism to humans and are used as a model organism for lipid-related diseases and diet-induced obesity (e.g., Chu et al. 2012; Song and Cone 2007; Zang et al. 2014).

While Zebrafish may not be able to help me from getting heavier at the holidays, scientific studies using them as model organisms can help address important human health related issues, such as examining new diabetes drug treatment options.