Aquaculture, or the practice of farming fish, is becoming increasingly common. So is the practice of entomophagy, or eating insects. These two areas should be of particular concern for animal advocates because the individuals involved are particularly small as well as harder to advocate for because they are perceived as dramatically more different than other animals.
While it's easy to make a comparison between a cat or a dog and a pig or a chicken, farmed fishes, and even more so, insects, are challenging victims to advocate for because they are so far outside most people's moral circles.
The results of this informal survey that I carried out shows that omnivores and vegans perceive farmed fishes and insects to have better welfare scores than other farmed animals, including beef cattle and dairy cows. This seems contrary to evidence (whereas beef and dairy cows might have net-positive welfare scores, based on subjective observation by animal welfare experts. See Norwood and Lusk, Compassion by the Pound, 2011 and Veganomics by Nick Cooney, 2013)
Based on this information, it seems that animal advocates should make sure to highlight factory farmed fishes in terms preventative dietary interventions. The rising popularity of insect farming should also be concerning and efforts should be made to prevent insects from being bred and killed for food. Additionally, for vegetarians and vegans who have environmentally-conscious circles, the topic of insect consumption could be a reasonable platform to raise awareness about insect sentience and the suffering of insects in the wild.
If vegetarians and vegans perceive farmed fishes and insects as being better or more ethical, then that sentiment could lend support to fairly suffering-intensive practices. Effective animal advocates should continue emphasizing anti-speciesism in their activism and continue to not rely too heavily on environmental or eco-centric arguments. To do otherwise would be to sacrifice short term gain or satisfaction instead of ideas which can help to reduce the most suffering.