among which the same type of farms had mixed species farmingand polyculture of yellow catfish (Table 4). Mixed species farmingof yellow catfish occurs when a farmer produces yellow catfish andother freshwater fish in different ponds on the same farm. Poly-culture is when yellow catfish are raised with other species in thesame pond. Fish farmers in Zhejiang province had a higher propor-tion of culture combinations, with 61% practicing monoculture and39% farming polyculture or mixed species. White carp (Erythrocul-ter ilishaeformis) was the species usually stocked with yellow catfishin polyculture operations. Black carp (Mylopharyngodon piceus) andyellow catfish (Pelteobagrus fulvidraco) were cultured in differentponds from yellow catfish farms in category II farms in ZhejiangProvince (Table 4). However, in Guangdong province, most farmers(97%) kept yellow catfish in monoculture on the same farm, andonly 3% of farmers practiced mixed-species farming and there wasnegligible yield information for the different species in polyculture.3.2.2. Feed brand choices, feed usage, and crude protein inputTwo different types of domestic fish feed companies (local andnon-local) supply farms. We differentiated them based on produc-tion scales and marketing strategies. Interestingly, 88% of farmersin Guangdong chose non-local companies, while in Zhejiang almostequal percentages of farmers chose non-local (57%) and local com-panies (43%). Most category I farms in Guangdong chose non-localcompanies, while among farms in the same category in Zhejiang,the number of farms choosing non-local feed companies was 1.5times greater than those choosing local feed companies.In this study, the feed input for yellow catfish farms in Guang-dong was 44.95 t per hectare, while for farms in Zhejiang it was22.59 t per hectare (Table 5). Crude protein usage in the 2 provincesshowed a similar difference. Farms in Guangdong had an overallhigher estimated apparent feed conversion ratio (AFCR) (Table 5).The average AFCRs of farms in Guangdong: 1.83 for category I, and1.55 for catergory II. In contrast, there was no apparent variation ofAFCRs among different types of farms in Zhejiang.3.3. Returns and costs analysis3.3.1. Capital requirements and costsCosts varied among different types of farms in the 2 provinces;for example, total fixed costs ranged from 4.6% to 10.1%, and totalvariable costs ranged from 90.2% to 95.3% (Table 7). Extreme valuesof the cost components were found in category II farms in Guang-dong and category III farms in Zhejiang. Farmers in Guangdonginvested less short-term capital than those in Zhejiang while, incontrast, the amount of medium- and long-term capital invested inGuangdong was higher than in Zhejiang.3.3.1.1. Total fixed cost. Medium- and long-term capital in Guang-dong (USD 2492) was about 2-fold higher than in Zhejiang (USD1401) (Table 6). Farmers in Zhejiang invested 91.1% of theirmedium- and long-term capital on oxygenators (Table 6), whilemachinery investments by farmers in Guangdong included otheraquaculture equipment, i.e. diesel generators, harvest nets, feedmixers, and water pumps.Differences in total fixed cost components, particularly land rentpercentages, existed among farms in the 2 provinces (Table 6),while the overall percentage of land cost of farms in Guangdong was50% higher than in Zhejiang. Farmers in Zhejiang reported reducedproduction costs by not investing in aquaculture equipment, suchas harvest nets, feed mixers, and water pumps. Furthermore, thepercentage differences of depreciation of medium- and long-termcapital between the 2 provinces were directly related to totalmedium- and long-term capital investments. Farmers in Cate-gories I and II in Guangdong reported larger investments in aquaticmachinery than farms in the same categories in Zhejiang.3.3.1.2. Total variable cost. Total variable cost as a percentage oftotal cost was 94.8% in Zhejiang and 91.4% in Guangdong (Table 7).Compared with medium- and long-term capital requirements, theshort-term capital requirement was responsible for the majority oftotal costs, 90.7% in Guangdong and 93.5% in Zhejiang. Among allcomponents of total short-term capital of farms in both provinces,