Monday, October 20, 2008

Answer to questions in class...

Do insects get fat?

Insects don’t get fat, and why they don’t may help our understanding of what has been described as the current human obesity epidemic.

The research team from Oxford’s Zoology Department, Texas A&M University, the University of Sydney and the University of Auckland conducted a series of experiments to find out whether caterpillars could adapt to extreme changes in their nutritional environment.

In their study ‘Evolving resistance to obesity in an insect’, published in the Proceedings of the National Academy of Science, they found that diamondback moth caterpillars evolved different physiological mechanisms related to fat metabolism. Which mechanism was used depended on whether the caterpillars were given carbohydrate-rich or carbohydrate-poor food. The researchers believe that caterpillars – and animals in general – can evolve metabolically to adjust to extreme nutritional environments.

The researchers studied the insects over eight generations. In one experiment, they fed caterpillars artificial diets that were rich in protein and low in carbohydrates; at other times the caterpillars received diets low in protein and high in carbohydrates. In a second experiment, caterpillars were allowed to eat freely one of two plants, an Arabidopsis mutant low in starch or an Arabidopsis mutant high in starch.

When the caterpillars were reared in carbohydrate-rich environments for multiple generations, they developed the ability to eat excess carbohydrate without adding fat to their bodies. On the other hand, those reared in carbohydrate-poor environments showed an ability to store ingested carbohydrates as fat. Also, after multiple generations on the low-starch plants, female moths preferred to lay their eggs on these same plants. The researchers explain that it is one of the first instances of a moth showing egg-laying behaviour that is tied to a plant’s nutritional chemistry.

The researchers believe moths from low-starch plans might avoid high-starch plants because they might make their offspring obese. Female moths reared on the high-starch plant for multiple generations showed no preference. The inference made by the researchers is that like insects, humans require carbohydrates and proteins, but that humans are not well adapted to diets containing extremely high levels of carbohydrates – a radically different diet to that of our ancestors. However, they say, lack of exercise might be another factor in why humans convert excess carbohydrate to fat.

Do goldfish grow to a certain size based on the size of their container?

All too often, we see this little sight on the cover of a package for a “bowl kit” at a pet store or in the bedroom of a child: a small goldfish, or group of goldfish, swimming around in circles in a little gallon or half gallon bowl. Many of us who have never kept fish before assume that the fish is fine and will live out its full life in this container… maybe a bit cramped as far as living space goes, but otherwise a healthy environment for a fish at a good price for the owner. However, ask any experienced breeder of goldfish or expert on the species, and you will hear a vastly different story.

You may be surprised that ALL goldfish (including the fancy varieties) will grow to a minimum of half a foot long (with comet and “common” varieties reaching close to a foot), and have life expectancies that rival many decades long. Some of the longest documented cases have been recorded by Chinese emperors, who have owned prized goldfish that lived over 40 years (sometimes outliving them!). The average lifespan, according to the Encyclopedia Brittanica, is 25 years in the wild, and I have seen firsthand or personally raised goldfish that exceeded 15 years easily in captivity. However, most goldfish lives are sadly shortened by well-meaning but misinformed owners, who kept them in bowls and believed they died of “natural causes” after a few short years.

Why are bowls all that bad, you may ask… as pet owners, we should have a higher standard than just having our pets barely survive for a short period of time to decorate the coffee table or entertain a child for a few days. Our pets are living creatures that depend on us for an environment that will at least provide the minimum requirements to keep them healthy. A bowl for a goldfish does not, for several reasons:

1) Goldfish produce more ammonia than other fish per unit mass because they are relatively inefficient eaters. This is a toxic product of fish waste decay (you may have noticed that goldfish cloud water faster than many other species) that will quickly pollute Goldie’s bowl and even frequent water changes will not be able to keep up with this. Not only will these wastes poison your fish directly, but they will stress them over time, reducing their natural immunity and making them more susceptible to disease. Smaller containers are inevitably more difficult to maintain balance in over time, and get dirtier faster, compounding this problem even more.

2) As mentioned, all varieties of goldfish grow to over six inches as adults (I’ve personally seen black moors and lionheads the size of small koi!). Some disreputable fish stores will try to convince you that they have different size varieties, but in truth, what this comes down to is age grades, since most fish are sold as juveniles. Chances are, if you buy a small goldfish, it will be a juvenile (grown specimens cost big $$!). If you see a goldfish that has been living in a container for more than a few years and it is only 2”, it is severely stunted! All fish give off pheromones, which limit their own growth in a closed environment, an adaptation that helps partition off limited natural resources in the wild.

3) Goldfish are a coldwater species, and thus evolved to need more oxygen than tropical fish (more gases can dissolve in cold water than the same volume of warmer water). No bowl or small container will provide enough, even with an airstone!

4) Most bowls do not allow room for a filter or apparatus to circulate water. Thus, the "good" bacteria which promote proper cycling can't really grow in a bowl to appreciable numbers, because they are mostly aerobic species. Toxins accumulate, making the situation, already bad, much worse. For these reasons, without even going into ethics or swimming room arguments, THE ONE INCH OF FISH PER GALLON GUIDELINE THAT APPLIES TO SMALL TROPICAL FISH DOES NOT APPLY TO GOLDFISH. In fact, the consensus among many experienced goldfish owners is that they need a MINIMUM 10 gallons per fish. This is actually just a bare minimum for smaller specimens (juveniles to young-adults, mostly), and full-grown adults really should be given even more. This idea may sound shocking to many new to the hobby, some which may have even been told that “bowls are fine” by pet store employees.

1 comment:

Lindsey said...

calley, you have the funny questions in class... but i love them! this was actually really funny and interesting to read. thanks for finding it chica