Management methods for culturing planktonic larvae of sea cucumber
1. Density control Density control is crucial during the culture of larval planktonic larvae. Under hydrostatic conditions, ear-like larvae are generally distributed in the surface and upper layers of water, and the distribution is very uneven, and local water environment deterioration and lack of food are often caused due to excessive local density. If the density is too high, larvae tend to stick together, resulting in increased deformity, slow growth, and even large batch deaths. According to the long-term tests and the practice of nursery, the density of the ear larvae should be controlled within 1/ml, the most suitable density is about 0.5/ml, and the larval density should gradually decrease with the increase of individuals. Second, when the bait is fed at the beginning of the ear larval digestive tract has been formed and began feeding, appropriate feed should be fed in a timely manner. The bait is the material basis for the growth and development of larvae. Choosing the appropriate type of bait and determining a reasonable amount of feed is one of the determinants of the development of ear-like larvae. It can be seen that the selection of a suitable variety of feed and a reasonable amount of feed is crucial for the growth rate, survival rate and metamorphosis rate of juveniles. 1. Types of bait In the artificial breeding of sea cucumbers, there are many types of monocytes that can be used as bait for ear-like larvae, including Chaetoceros, Platymonas, D. salina, P. tricornutum, Z. nitida, L. nuclei Wait. The effect of various baits is not the same. Based on the relevant reports and experimental results, the most suitable bait for sea cucumber larvae is Dunaliella salina and Chaetoceros divers, which can be fed separately; Zhanjiang fork chlorella, single whit algae, and Isochrysis galbana can be fed in short term. Can not be fed alone for a long time, especially after the development of larvae to the middle ear larvae; Platymonasaurus, chlorella, micro-green algae, etc., in the ear larvae during the incubation period is not suitable for feeding, can only occasionally use when the feed is scarce. In addition, studies have shown that the effect of mixed feeding of different species of monocyanobacteria is better than that of feeding alone. Generally in the actual artificial nursery, the diatoms and Chaetoceros may be used as the main ingredient, and some other species of unicellular algae, such as Phaeodactylum tricornutum, Nitzschia closterium, and Xanthomonas oryzae, may be used together with feeding. At present, most of the nursery units use single-celled algae as the main bait for sea cucumber seedlings, and at the same time, many alternative feeds have been developed. At present, the substitute baits that have been developed mainly include photosynthetic bacteria, marine yeast, fresh bread yeast, and large-leaf algae crushing filtrates. 2. Feeding amount alone feeding 20,000 cells/ml in the early days of Chaetoceros, 25,000 cells/ml day to 30,000 cells/ml day in the middle ear larvae, 30,000 cells in the ear larvae /ml days or more. The above data only provide reference. In the specific practice of seedling raising, the actual feeding amount should be determined based on the larvae's density, food intake and other factors, and the feeding amount of the feed should be increased or decreased at any time according to the actual situation. Remember that the amount of feed should not be too large, so as not to eat too much larvae cause rot. 3. Feeding method The feeding method is appropriate for a small number of times, and the feeding is generally performed 4 to 6 times a day, and the quality of the bait is strictly checked to avoid feeding the aged bait that has been incubated for a long time. Protozoan infection is serious. The bait should not be fed. Third, inflating, agitating the pool to inflate or stir the pool on the one hand can increase the dissolved oxygen in the water, on the other hand can avoid the concentration of larvae and make it evenly distributed. Oxygen consumption of ear-like larvae is very low. Under normal density, when monomon algae are used as bait, generally, it will not cause low dissolved oxygen and affect larval development. However, in thunderstorms and hot weather or when feeding with substitute bait, there may be too low dissolved oxygen and hinder the development of larvae. Under hydrostatic conditions, the ear-like larvae of sea cucumber are mostly concentrated on the surface of the water body. As ear-like larvae are concentrated on the surface of water bodies, larvae often bind more than a dozen, dozens, or even more, resulting in a "clustering" phenomenon. In the most surface water near the pool wall, the larvae have a particularly serious phenomenon of "clustering", and sometimes they are even connected to each other in a shape of a strip. As a result, the ecological environment in which the auricular larvae are located is bound to deteriorate rapidly. The phenomenon that the larvae gather on the surface layer starts from the ear ear larvae and can continue until the late auricularia larvae. This phenomenon can cause a large number of ear larvae to die or stunted. Therefore, during the larval rearing period, in order to ensure sufficient dissolved oxygen and larvae can be evenly distributed throughout the pool, it is necessary to adopt aeration or pooling measures to promote the normal development of larvae. 1. Inflate the bottom area of ​​the cultivating tank, put a gas stone every 3 to 5 square meters, the gas volume can not be too large, micro-inflating method should be adopted, because the gas volume is too large, it is easy to lift the bottom of the pool of dirt , affecting the water quality, at the same time prone to bubble disease or bait-like larval rotting, resulting in the death of larvae. 2. Stirring the pool is also an effective measure to ensure that the water body is rich in dissolved oxygen and the larvae are evenly distributed. Stir at 1 hour per hour under normal density. Stir the water gently in the upper and middle layers of the pool to distribute the larvae evenly. This method is labor-intensive and easily damaged by larvae, so it is not suitable for large-scale production.