Credit: Rodrigo Rivera González (Chile)
Introduction: The current photos illustrate parts of the artificial spawning of Chilean sea urchin using chemicals based on its effectiveness.
There are several physical, chemical and mechanical stimuli which could be used to induce the spawning of sea urchin and the release of gametes.
The procedures related to the photos are described as follows:
Spawning induction: Sea urchins are thoroughly washed using UV sterilized sea water to ensure taking off all epibionts (organisms living on the sea urchin). Each male or female is injected with a syringe via peristomal membrane to the celomic cavity, using 3 ml of potassium chloride (KCl) solution of 0.5 molar.
In order to receive the spawning products, the injected sea urchin are place individually over transparent beaker, with the aboral pore (genital pores) in contact with the filtered/UV treated seawater. Water temperature is maintained at 15 °C.
If the sea Urchins are ripe, the release of gametes will begin immediately after the injection, whereas the yellow-orange color for the gamete (ovules) would determine the female sea urchin while the whitish color will characterize the sperm of the sea urchin male.
While male sea urchin –once identified- will be immediately removed and temporarily maintained, female sea urchins are left for releasing their gametes for about 1 hour and never exceed 2 hours.
Eggs are washed with filtered and UV-treated seawater over 177-um sieves to clean eggs from dirt. The average egg size ranges from 120 – 130 um in diameters.
Because of the short longevity of the sperm (about 30 minutes), the sperm is obtained shortly before fertilization. It is recommended to select the best quality sperm –based on motility and number- via microscopic examination using Sedwegick and Neubauer chambers.
Fecundation (fertilization): Washed eggs are transferred into containers of 10-12 liters whereas about a million ovules are placed in 1-um filtered and UV-irradiated seawater and at 17 – 18 °C.
Fertilization is carried out by adding one ml of sperm solution with approx. 100×106 sperms to the mentioned ovules (1 million) which means a ratio of 100 sperms to each ovule. The sperm solution has 1 ml of concentrate of sperms obtained directly from the gonad of the sea urchins and diluted in a volume of 200 ml. The success of fertilization as well as embryonic development is determined through microscopic examination. After 30 minutes the fertilization, fertilized eggs (embryos) are poured out whereas one-half of the water is changed with fresh, 0.5 um-filtered and UV irradiated seawater at 17-18 °C.
Larval culture: After 24 hours post fertilization, the larvae which are are in gastrula stage, are siphoned from water surface as most of the larvae are swimming while dead/non fertilized eggs stay on the bottom. The larvae are transferred into 50-liter tanks and maintained at 18 °C for 24 hrs, with 1-um filtered and UV sterilized seawater whereas gentle aeration is provided. The larvae remain for a period until they reach the prisma stage. The larvae at this stage are transferred to 500-lt fiber-glass tanks which are supplied with 1-um filtered and UV-irradiated circulating seawater (18 °C). Aeration at the proper level is provided to maintain homogenous culture. The starting density during larval culture is 1.5 – 1.6 larvae/ml. During the larval culture period, periodic sampling for general well-being of the larvae is carried out. Moreover, density estimate is evaluated.
Larval feeding: The feeding is done twice/day directly to the culture tank. The common natural food used is made of a 1:1 mix of Chaetoceros gracilis and Isochrysis galbana. The concentrations of the natural food in the nursing water vary according to the stage of development as follows:
Larval stage Microalgae conc. (cell/ml)
4 arms 30,000
6 arms 40,000
8 arms 50,000
Note: We decided not to watermark the photos in order not to upset its clarity. However, we trust you will notify us if you wish to use a picture or more. This is expected and will be appreciated.