I felt that the fisheries, algaculture, marsh farming, and chinampas might need a little further explanation, since I largely glossed over them.
This largely relies upon the notion that we can use bodies of water as a "field" with nutrient levels, and also upon the food web notions discussed in the earlier food web and pests sections.
Fisheries, especially, need some more in-depth discussion. Apparently, the most ancient fisheries were actually created by some (hardcore) Chinese who found ways to trap carp (!) in pools as the flood waters in their major rivers receded. Strangely, they bred the carp to be smaller instead of training them to kill invaders, (their dungeon masters must not have shown up, either,) so they eventually created the harmless goldfish from the large, feared predators.
For dwarves, trapping fish in aquariums is... odd currently. You can trap fish, and they turn into fish items, and when released, they just sort of sit there and die. And rot. Not good.
What we could be doing, instead, is creating fisheries, constructed nets or grates or bars to allow certain sized creatures free passage, then flooded in pools and stocked with fish. Provided there is some basis for their food chain (like phytoplankton, which basically requires nothing more but exposure to sunlight and some nutrients in the water to support, or possibly magic-based xenophytoplankton that grow in caverns with no sunlight) depending on the trophic level of the particular fish, players should have the ability to create fairly simple food chains that support game fish in large quantities.
Food webs in the water tend to be much simpler than the food webs of terrestrial life forms, and ponds may form into true "food chains" where each species has only one prey species, and only three to five species in a stocked pond.
Considering all that I've already discussed, these fisheries would really only need the inclusion of many of the water-based equivalents of the food webs I have already discussed, plus an ability to build and designate fisheries, and an ability to designate areas for stocking with fish.
Algaculture is similar to a fishery, but actually even simpler. You just need nutrient-laden shallow water and sunlight, and "seeding" the water with some seaweed or lily pads. I highly doubt anything but an elf would really be into seaweed as a food source, but it's a very easy-to-grow (and extremely quick-growing) source of animal fodder, and potentially also fuel source for fires or reactions.
Although growing biofuels may be beyond dwarven tech, fast-growing seaweeds might at least be convertible into an alternate organic matter for charcoal, or failing that, fertilizer.
Chinampas are the closest thing the ancient world gets to hydroponics. Rather than irrigate a field by bringing water to the farm, they bring the farm to the water, and build artificial islands in the shallow end of a lake using netting to mitigate soil erosion. This is also a method that uses a fishery as a source of fertilizer instead of cattle manure. (It probably helps if humans dispose of waste well-diluted into that same water, as well...)
Technically speaking, this would require a greater "exception" and dedicated bit of coding to produce than other forms of farming, since it would mean that dwarves are building basically walls/floors of dirt that are built into the water, and letting the plant roots soak up water from below instead of more advanced irrigation systems, and drawing nutrients from nearby fisheries... excreting nutrients into the water. (Just muddying the top of a built stone wall isn't really the same, since there isn't really reason the stone wall will inherently absorb the nutrients of the surrounding water in the current model in the game.) The plants help make up the producer trophic level of the water, with some of the fish feeding off the roots that poke out of the soil-retaining nets, and the plants filtering out the impurities of the water for the fish, as well. (The fish probably still rely upon phytoplankton, however.)
Marsh and paddie farming are more complex, and need similar exception coding to allow them.
Marsh farming means that the water has to be kept at some low levels generally at all times, so the farm needs to be flooded, but sensitive to just how flooded it is.
Rice paddies, meanwhile, are only flooded when they hit a certain stage of the rice plant's growth, to cut off any chance for weeds to grow (with waterlily-like azola grown as a companion crop to cut off any further weed growth), and as such needs further exceptions to make a multi-stage growth system, where dwarves can be trusted to irrigate the paddies on their own. If using buckets or the irrigation pumps, this means purposefully dumping water beyond the saturation point until the area starts to flood, but only to a certain point, which requires more of that making sure the dwarves watch just how flooded the fields become.
Both of these would be related to the Water Management section's talk about how soil becomes saturated (and hence, is capable of absorbing a set amount of water, itself), and also involve dwarves being able to "know" when and how to keep adding water to the fields to make sure they are at the right water levels.
One more topic to discuss is the
concept of "Algal Blooms" and "Dead Zones". Although this only really become a true menace in the modern world with the invention of the Haber-Bosch Process, the cheapness of artificial nitrogen fertilizers and the perceived dire consequences of a failed harvest led most farmers to simply over-fertilize their fields to be safe, leading to an overwhelming bulk of their fertilizer (80-90%) simply washing off the land in the next rainstorm, rather than being taken up by the plants, themselves.
Aggressive fertilization could also hypothetically lead to an aquatic "pest" or even more dangerous outcome. Life in the sea is dependent upon nutrients from land reaching the water, and so tremendous fertilizer runoff leads to tremendous blooming of plankton to the point that they can even consume all the generally slim amounts of dissolved oxygen in the ocean, leading to "dead zones" where only sulfur-based life forms can live.
In a DF world, however, I might expect more magical and menacing reactions to a wasteful fertilization runoff, such as outright algae monsters rising from the depths to wreak revenge upon the dwarves.