Presumably intestines will have a lot of bacteria, and hence also bacterial RNases to contend with and so there is more chance of degradation during the isolation process. The other tissues probably won't have this problem. No RNA sample should be at -20 (unless you use RNAlater). If you put in trizol but did not homogenize, it doesn't protect properly anyway (only RNA from the the outer cells of the tissue that are lysed will be protected).

Two things. 1) Whether it's intestines or just aquarium water, there is too much bacteria and stuff in the world, so you must clean the RNA quickly. 2) you may not have a severe problem

1. The solution to all good RNA extraction is kill (denature) and remove proteins quickly. The material stuck in your wells is not a good sign of purity. Sacrifice yield in favor of purity because dirty RNA is not much better than no RNA. Don't let tissues warm up. Grind frozen (-70/ dry ice) tissues, then go directly into the Trizol extraction. You may need to increase volume to improve the efficiency of extraction. Despite what many may tell you, clean RNA can last at room temperature for days, but don't assume that it will.

2. You have some signal at sizes greater than oligo-nucleotides (at least up to the first bright band), but your markers are fuzzy and I don't know the sizes. Do you know what your RNA should look like? Total RNA looks like a smear with intense bands of rRNA and others. You have too much RNA loaded on your gel. When you have the correct amount you will only see the rRNA bands and the smear will not be visible. Unless you take precautions, degradation will occur in that old gel buffer. Run the gel quickly, stain and document immediately. Use a 1% gel or little higher. If you see sharp bands your RNA is likely intact, but better extraction of protein in the future may be required for further experimentation.

To deal with possible RNAses, dissolve agarose in TAE/TBE buffer containing 2% Hypochlorite (v/v). That should inhibit RNases.