The Living Environment of Crayfish
Many netizens believe that since crayfish are often found in sewage ditches, this suggests they prefer dirty environments.Is this true?
Tang Jianqing, Director of the Aquaculture Department at Jiangsu Freshwater Fisheries Research Institute, explained that their experiments showed crayfish would choose corrosive food over fresh food at a ratio of 1:10 when both options were presented.
Are crayfish commonly caught in ditches?
June, July, and August mark the prime crayfish harvesting season in Dongting Lake. By late August, as lake temperatures drop, crayfish begin burrowing into the lake bottom or shores to hibernate until the following summer.By this time, lake-based fishing activities have slowed significantly, while river channel fishing becomes more prevalent. The tools for river channel fishing are simple: farmers typically only need a shovel for digging and a pair of gloves for catching crayfish. Farmers note that the water in these channels is very clean, similar to the habitats where eels and loaches thrive.The burrows dug by crayfish are usually between 1.5 and 2 meters deep. Combined with the cooler weather after autumn sets in, digging up crayfish in the ditches becomes quite laborious, yielding only about 6-7 pounds per day.
Surveys indicate: Due to the cooler weather, the suitable period for catching crayfish in ditches is very short. Moreover, it doesn't yield significant economic returns.Therefore, most crayfish currently sold in markets are sourced from lakes. How can one distinguish between crayfish dug from ditches and those caught in lakes? To illustrate the difference between lake crayfish and ditch crayfish, crayfish farmer Lao Gan compared the two.Crayfish raised in clean water tend to be larger. Lake crayfish have a lighter, redder hue, while ditch crayfish appear darker. Tip: Due to differences in growth environments, lake-produced crayfish are recommended for consumption. Lake crayfish are characterized by vibrant coloration, larger size, and a more balanced head-to-body ratio.
Currently, crayfish sold in China's market primarily originate from several lake regions including Dongting Lake, Poyang Lake, Honghu Lake, and Hongze Lake. Taking Dongting Lake as an example, peak-season daily output reaches approximately 30 tons, totaling around 3,600 tons over the four months of May, June, July, and August. Combined with other lake regions, the total peak-season production from these major sources is about 17,000 tons.This figure aligns closely with China's annual consumption of 20,000 tons of crayfish. Due to their high protein content and superior levels of trace elements like zinc, iodine, and selenium compared to other foods, coupled with their delicious taste, crayfish have gained immense popularity in many cities in recent years.In some areas, they've even sparked a "red craze" in summer dining. However, concerns exist because the water conditions in some crayfish production areas are far from ideal. During our investigation in the Dongting Lake region, we discovered a stone monument at the aquatic products trading market in Yuanjiang City bearing the warning: "Schistosomiasis present in this area. Take precautions when entering the water."Could crayfish surviving in such waters become hosts for schistosomiasis parasites? To investigate, we visited the Yuanjiang City Health and Epidemic Prevention Bureau. The director informed us that schistosomes only parasitize snails, and no evidence has been found of schistosomes in crayfish. However, experts confirm that crayfish are indeed intermediate hosts for lung flukes.
Are crayfish contaminated with excessive heavy metals? Heavy metal overload prevents molting and survival
In reality, crayfish are highly sensitive to heavy metals. In water bodies with excessive heavy metal levels, crayfish cannot successfully molt and will not survive.Heavy metals exhibit bioaccumulation properties, meaning organisms higher up the food chain accumulate greater concentrations. Crawfish feed on primary organisms like aquatic plants at the base of the food chain, resulting in low heavy metal accumulation. Under normal farming conditions, heavy metal residues do not exceed safety limits, according to a senior engineer at Hubei Provincial Fisheries Research Institute.