Comprehensive Prevention and Control Techniques for Soft-Shelled Turtle Gill Gland Inflammation

Since the intensification of soft-shelled turtle farming, because research on turtle diseases has lagged behind production, various hidden disease risks have remained latent. Among them, the most harmful and also the most difficult to treat, turtle gill gland inflammation, has gradually become prevalent in recent years. At the farm where the author works, the annual losses caused by this disease account for about 50% of total losses. This disease repeatedly occurs in broodstock turtles and adult turtles, and has now developed to affect the entire production process.

1 Main symptoms and pathogens

This disease is mainly characterized by systemic edema and pale plastron. Most have intact body surfaces, with very few showing symptoms such as scabies or skin rot. Some male soft-shelled turtles have exposed genitalia; some float on the water surface, and when caught they immediately dive into the water, then float up again shortly after, and soon die. There are also a few hemorrhagic-type cases that struggle ceaselessly when placed in a tray, bleed from the mouth and nose, and die shortly after. These soft-shelled turtles all share a common characteristic, namely that their body condition is relatively good, thick and not thin. Upon dissection and observation, the intestines are empty, mostly milky white. The gill glands are pale white and eroded, with secretions, and the liver is earth-yellow or light gray.

This disease has no obvious seasonal prevalence during the greenhouse farming stage, occurring throughout the entire farming process, only slightly more common during the juvenile and adult turtle stages. Under normal-temperature farming, broodstock turtles are mostly affected in May and June, and there are also more cases in September and October when post-partum conditioning is poor.

At present, there is still no accurate conclusion regarding soft-shelled turtle gill gland inflammation. However, those engaged in production and research have basically reached a consensus, namely that it is very likely viral. Current reports classify it into three types, namely the hemorrhagic type, the mixed type, and the blood-loss type. According to the author's observations, the most convincing and representative symptomatic type should be the blood-loss type. Because most diseases such as enteritis, hemorrhage, and goiter share identical or similar symptoms with one or two of these types, it is very difficult to make a preliminary diagnosis based on these symptoms from sensory observation alone. In addition, in production practice, the author has found that for hemorrhagic-type related diseases, broad-spectrum antibacterial drugs with strong sensitivity can achieve obvious therapeutic effects. However, for diseases with symptoms such as edema and pale plastron, there is nothing that can be done, with many sporadic or small-batch deaths. Only after adopting comprehensive diagnosis and treatment was basic control achieved.

2 Analysis of causes

Analyzing according to the conditions for disease occurrence and transmission, it comes down to pathogens, susceptibility, and an environment suitable for transmission. The interaction of these three leads to the occurrence of disease. Regarding turtle diseases themselves, various pathogenic microorganisms exist in their living environment. When water quality is good and the soft-shelled turtle's resistance is strong, they mostly remain in a latent state. Once water quality deteriorates, the soft-shelled turtle's body surface or internal systems are damaged, and for other reasons (such as bite wounds, various stresses, etc.), these pathogenic microorganisms become activated, their virulence increases, and their numbers grow, causing the soft-shelled turtle to become ill. In current intensive farming, due to cost considerations, water changes are infrequent, and in particular some ecological conditions completely fail to meet the physiological needs of soft-shelled turtles, causing disease resistance to decline. The all-concrete greenhouse structure is a case in point. As for soft-shelled turtle gill gland inflammation itself, the direct cause is pathogenic microorganisms. But it must go through certain pathways to trigger disease. According to the author's observations, greenhouse soft-shelled turtles with fresh water quality, good body condition, and good routine preventive work rarely become ill; on the contrary, those with foul-smelling water and thin, weak bodies often become ill. In addition, broodstock turtles raised at normal temperatures or soft-shelled turtles undergoing environmental changes are also more susceptible to this disease. The author believes that in these cases, illness is mainly caused by weak body condition after overwintering and the influence of various stress factors in the environment. Therefore, the author believes that comprehensive prevention and control should be implemented against various causes for this disease.

3 Comprehensive prevention and control techniques

3.1 Reform the farming model, changing from sand-based farming to sand-free farming. In production practice, the author found that soft-shelled turtles raised without sand rarely become ill under the same conditions, and the soft-shelled turtles grow well with robust body condition. This may be related to better water quality maintenance.

3.2 Improve farming environmental conditions. For heated farming, use light-transmitting greenhouses as much as possible, introduce aquatic plants to purify water quality, strengthen indoor air circulation, etc., so that environmental conditions become more rationalized and meet as many physiological needs of the soft-shelled turtle as possible. Especially on sunny days, stronger light has a certain inhibitory and killing effect on pathogenic microorganisms (especially viruses); at the same time, a dry environment is more beneficial to soft-shelled turtles. For this reason, the outer film should be rinsed frequently, and indoor aeration should minimize air leakage to keep the interior dry.

3.3 Strengthen water quality regulation and control, specifically:

①Increase oxygen, increase aerator power, extend aeration time, avoid excessive accumulation of organic matter that deteriorates water quality. This point should be given special attention in production management.

②Cultivate aquatic organisms, making full use of the organisms themselves to decompose organic matter and purify water quality. At the beginning, species should be introduced and cultivated, and during production, moderate water changes should be made to maintain the relative balance and stability of the biological community.

③Use water quality disinfectants and improvers scientifically and reasonably according to water quality conditions. Routinely rotating quicklime and bleaching powder (or other disinfectants such as PV-I, etc.) about every 7 days can achieve relatively satisfactory results.

3.4 Regular drug prevention and treatment

Due to the particularity of soft-shelled turtle gill gland inflammation itself, prevention and treatment methods and medication differ from other diseases. First, it is a viral disease, and its onset has no pattern; sometimes deaths occur while medication is being administered. Second, the incubation period is long; for example, broodstock turtles that contract the disease in the first year will only show obvious signs in the spring and summer of the following year. Therefore, prevention and treatment of this disease must be symptomatic, timely, and effective. In production practice, the author achieved relatively good results according to this principle, reducing the incidence of this disease from the original 50% (of total incidence) to 10%, and it can be very clearly controlled within a certain treatment course. Specifically: for affected ponds, first drain about two-thirds of the old water, add new water, and increase aeration; at the same time, splash decocted liquid from various Chinese herbs such as Isatis root (banlangen) and plantain herb into the pond at a certain concentration. At the same time, add moroxydine. Depending on the condition, it can be used two to three times consecutively. While splashing the drugs, add Isatis root and other liquids as well as moroxydine, ciprofloxacin, and other drugs to the feed. Increase the proportion of live fresh animal material in the feed, generally feeding for about 10 days each time, and depending on the situation, continue feeding for one treatment course. Ponds with unaffected soft-shelled turtles are also fed medication for prevention. Routinely feeding one treatment course per month can achieve relatively good preventive effects.

In addition, while preventing and treating this disease, the author also found that diseases such as scabies and red plastron, which previously occurred more frequently, were significantly reduced. Soft-shelled turtle growth was also better. This may be related to the prescription containing both antiviral and antibacterial components. Moreover, the Chinese herbs themselves have multiple effects including antibacterial, antiviral, and conditioning.