It's a damned shame we've effectively killed off all life in the oceans...

" The group consuming the fish oil gained 5 to 10 percent less weight and 15 to 25 percent less fat over the course of the experiment."
Percentages--how to say little in a portentous way. Did all the mice gain weight, just the fishy mice gained less? If so, maybe this isn't such a great diet.

You're also getting a hotter ass, as compared to control diet-fed mice:
From the abstract (bottom): "In this study, we investigated the effect of fish oil intake on energy metabolism. Fish oil intake reduced body weight gain and fat accumulation, while increasing oxygen consumption and rectal temperature, as compared to control diet-fed mice. Furthermore, fish oil intake induced UCP1 expression in both of BAT and WAT, and activated the SNS. Combined, our data indicate that fish oil intake enhances energy utilization by inducing UCP1 in both BAT and WAT, and could thereby prevent obesity and related metabolic disorders.

Another example of idiot intelligence. The primary driver of lipogenesis is the hormone insulin. The primary driver of insulin are carbohydrates. So long as we keep promoting our idiotic "healthy high carb" diet which has driven the whole country to illnes, we will never be able to control obesity or any of its cousins (metabolic illness)

@AGO Wrong
Carbs are what we live off of. Carbs feed the body, give you energy, and help the brain function. You need carbs. You need carbs and fiber. Excess carbs pass through you if you have enough fiber. High meat diets and protein diets are what makes you fat and lead to heart disease.
You don't have to eat fish, or fish oil to get Omega 3 or Omega 6 fatty acids. You can get that from Flax Seed and Chia Seeds. You can also get it from Algae which is where the fish get it. Fish contain heavy metals, and fish oil is usually from unhealthy sources and is often old and ineffective as it sits on the shelf to long. Omega 3 is one of those things that breaks down and goes bad quickly.

Healthy body composition centers around a healthy gut microbiome.

Fish oil to prevent obesity? How about learning to eat/cook fresh produce instead of boxed junk? Culture shift is needed, not these miracle products.

Will taking fish oil capsules work and if so how many grams a day.

I took fish oil capsules a few years back, on the advice of my doctor (for boosting "good" cholesterol). I had to quit after a few days because, well, my bathroom smelled as if a shark had exploded in it. Yuck. Went right through me, apparently.
I substituted flax seed and it did help the cholesterol, but did nothing to aid in my weight loss (I just try to eat plenty of fiber, fresh vegetables/fruits, grains and so on). I wonder if the source of Omega 3 makes any difference, or if I just have to tweak my diet a bit.
It's hard to "get it right".

The primary flaw in this claim is that it is extrapolated from mice to humans.
Genomic responses in mice don't mimic human inflammatory diseases. (There's a great paper about it here: http://www.pnas.org/content/110/9/3507.abstract)
One of the things you should always be weary of are articles in which drugs/substances/experiments worked on one type of animal, mice, and the claims behind them are extrapolated to humans.
https://www.quora.com/What-are-examples-of-drugs-that... - this is a great example.
Lastly, be weary of anything about fish oil. The strength of claims around fish oil are fundamentally weak and most likely off by a few standard deviations.
http://www.webmd.com/heart-disease/news/20130508/fish-oil-supplements-dont-protect-against-heart-trouble-study