I am certainly not an expert of Portfolios for stock photography but I do think that all is fine with your portfolio. Mostly time is the biggest thing, Being patient and photos that are approved will sell.
Personally, I love your "baby Boy" and Tank Farm" photographs. Zoo shots look a little undersaturated for my liking, I love to see more bright colours in the animals and bright grass or backgrounds.
I think your images are sellable. Maybe you just need to add more keywords to direct people to your images. I try to think of all aspects my images can take, besides just what I took it for. Ideas can come from expressions.
Like this image:
I would add these key words: facial, grab, claw, hand, take, give, scare, playful, laugh, laughter, suprise, shocked, health, healthy, skin, fair, fare, sunscreen, sunny, outside....
Sometimes I will take one word, like "grab" and go to dictionary.com. I will look in the thesaruse for other words that mean the same thing.
Your images are fine, just find more ways to bring traffic your way.
and in home studio.
Associates Art Degree in Photography and Multi...
English is not my language so it is difficult for me to write but I will try.I have one recommendation for pictures with child. Take not only picture of baby but something more - baby and food, baby and toy, baby and mother, baby and other children, baby with dog or cat, baby in bath, in baby-coach,in car.... Every this theme you can take in many variants. Example: baby and food - baby likes food, baby doesn´t want food, baby is traying to eat by itself or mother is feeding baby..... you will find next ideas. It makes no difference when you are taking pictures with this young lady - try to take pictures with woman reading a book, shopping, sleeping, cooking, running .... Designers need very often concrete images. Sorry for my english, I hope you understand me :-)
You've got some good shots in there __ you just need many more of them. It takes time to learn what makes a good stock image but there's an awful lot of assistance on here just by checking out the top sellers stuff, etc. Sort other photographers' portfolios by 'downloads descending' to see what the buyers are after.
I note that most of your subjects are fairly central in the frame too __ you might want to read up on The Rule of Thirds too for compositional tips.