Juvenile Horseshoe Crab Rearing Programme. Manual for rearing juvenile horseshoe crabs in secondary schools

Transcription

1 Juvenile Horseshoe Crab Rearing Programme Manual for rearing juvenile horseshoe crabs in secondary schools

2 A. Basic equipment for housing juvenile horseshoe crabs

3 Items glass tank (height: 6-10 ) A. Basic material Function to culture juvenile horseshoe crabs (water level: about 10 cm height, depending on the filter) seasalt air pump, air stone, air tubing to make artificial seawater (salinity: ; specific gravity: ) to supply oxygen (dissolved oxygen content: > 6.0 mg/l) heater, thermometer to keep temperature at about protein skimmer filter (with filter fibre/ sponge, activated carbon/ coral bone / bio-rings) bottom sand (small particle size is preferable) tubing clamps, tubing valves to remove organic compounds (e.g. horseshoe crabs excreta, including proteins, amino acids and fatty acids, particulates and detritus) physically from saline water by the process of form fractionation before they break down into nitrogenous water to filter water and maintain good water quality (filter fibre: for mechanical filtration; activated carbon: for removing odor and chemical filtration; coral bone / bio-rings: for biological filtration; sponge: for mechanical and biological filtration) to provide shelter for juvenile horseshoe crabs (about 2 cm depth) to control air supply and air flow

4 B. Before horsing juvenile horseshoe crabs

5 B. Before horsing juvenile horseshoe crabs 1. Clean the rearing equipment 2. Wash sand 3. Make artificial seawater 4. Install filtering material in the filter 5. Fix the apparatuses in the tank (including protein skimmer; filter; heater; thermometer; air pump, etc.) ** Please set the tank and the equipment, and run the system for one week, before the juvenile horseshoe crabs arrive**

6 Washing sand 1.Wash sand thoroughly with freshwater several times until the water is clear 2. Place a layer of bottom sand into the tank: cm depth

7 Making artificial seawater Salinity: 28 = specific gravity: ~ =28 g seasalt dissolves in 1 L (1 kg) freshwater e.g. Prepare 20 liters of 28 saline water 1. pour 20 L freshwater into a box/ a bucket 2. place a heater at about 25 in the water 3. weigh 560 g seasalt 4. pour the seasalt into the water 5. mix the solution with a submersible pump / an air stone overnight, until all seasalt dissolves in water ** If you want to keep the unused saline water, please keep the water aerated with an air stone or an submersible pump for 1-2 days **

8 Installing filtering material into the internal filter 1. Put a piece of fibre filter /sponge in the filter box (mechanical filtration) 2. Put a bag of filtering material, including coral bone / bio-rings/ activated carbon, in the filter box (biological filtration) 3. Bind the outlet of the filter with a piece of fibre filter to reduce water flow

9 Installing filtering material into the external filter (alternative) 1. Put a bag of filtering material, including coral bone / bio-rings/ activated carbon, in the filter box (biological filtration) 2. Put a piece of fibre filter /sponge in the inlet of the filter box, or on the top of the filtering material in the filter box (mechanical filtration) source: 3. Bind the inlet of the filter with a piece of net to prevent bottom sand from entering the system

10 Fixing the apparatuses in the tank Air supply 1. place an air pump on a place where is above the tank to prevent from water flowing back from the tank 2. connect an air stone to an air pump with air-tubing 3. turn on the air pump 4. adjust to optimal airflow with a tubing clamp / a tubing valve Heater 1. adjust a heater temperature to fix the heater in the tank covering water 3. switch on electricity supply Filter 1. pour saline water in the filter box (for external filter) 2. switch on electricity supply 3. adjust water flow rate Protein skimmer 1. connect an air wood to the air pump with air-tubing 2. turn on the air pump, the air wood produces air bubble 3. fix the protein skimmer in water at the level that water form is present

11 Protein skimmer Protein skimmer collection cup: collect organic matter in water Air wood: produce air bubble Air tubing: connect air wood to the air pump Water surface

12 Horseshoe crabs living environmental condition in the rearing tank Environmental parameter Optimal range Measuring instruments Temperature thermometer Salinity (specific gravity: ) Refractometer/ hydrometer ph 8 ph paper / ph meter Dissolved oxygen (D.O.) content > 6 mg/l D.O. meter

13 Refractometer Instruction of using refractometer: i. Take a small sample of water with a dropper, then place a few drops onto the prism glass surface, gently close the lid of the refractometer that water sample is evenly distributed onto the measuring surface; ii. Look through the eyepiece towards light source, turn the focus knob, until the numbers and the scale are clearly seen; iii. The intersection on the scale where black turns white measures the salinity. source:

14 Hydrometer Instruction of using hydrometer: i. Take a sample of water with a measuring cylinder; ii. Place the hydrometer into the measuring cylinder, until it floats ; iii. The point at which water surface touches the stem of the hydrometer measures the specific gravity of water. specific gravity: source:

15 C. Feeding juvenile horseshoe crabs

16 i. Food Horseshoe crabs (instar) Hatched brine shrimp nauplii 4 th instar 5 th instar 6 th instar 7 th instar or elder Frozen brine shrimp Chopped clam, shrimp or squid Brine shrimp: provide good nutritional value for juvenile horseshoe crabs

17 ii. Feeding juvenile horseshoe crabs 1. Collect juvenile horseshoe crabs with a small basket from the rearing tank ( Please stir up the sand to remove any accumulated waste in the sand at the same time) 2. Place the horseshoe crabs in a plastic container containing saline water and aerated with an air stone (Please be aware of the airflow) 3. Feed the horseshoe crabs for 1-3 hours in the plastic container (e.g. lunch time) 4. After feeding (e.g. after school), rinse the horseshoe crabs with clean saline water to remove uneaten food on their bodies 5. Place the horseshoe crabs back to the tank with a small basket

18 D. To-do list

19 D. To-do list Daily works 1, Measure and record the living conditions (salinity, temperature, ph) 2, Count no. of juvenile horseshoe crabs 3, Collect any molts and remove any dead horseshoe crabs 4, Feed juvenile horseshoe crabs (e.g. during lunch time, for 1 3 hours) 5, Replace freshwater, when water salinity is higher than 32 or water level does not cover the heater and the internal filter 6, Clean the equipment e.g. protein skimmer cup, filter, heater, the tank **During molting, juvenile horseshoe crabs do not eat, so you do not need to feed them** Reminder: i. Please remember to turn off the electric equipment before cleaning up the equipment; ii. Please do not expose the heater out of water

20 D. To-do list (Cont d) Weekly work (e.g. the end of the week) 1, Water: renew 2/3 of saline water in the tank ( ** please stir up the sand and remove the accumulated wastes during renewing water**) 2, Measure and record prosomal width & wet weight of juvenile horseshoe crabs prosomal width 3, Make new saline water 4, Renew half of the fibre filter, when it is dirty, and activated carbon Monthly work - Wash sand in the tank with old water (Please renew all saline water and sand in case of massive mortality of juvenile horseshoe crabs)

21 i. Daily works Measure & record the living conditions: i. Salinity (26 32 ) For refractometer: 1. Calibrate the refractometer with drops of freshwater: salinity = 0 2. Take a sample of water from the tank and measure the salinity; 3. Record the reading of salinity; 4. If the salinity reads too high, add small amount of freshwater in the tank to accordingly, when you are feeding the juvenile horseshoe crabs ii. Temperature (25 29 ) with a thermometer iii. ph values (> 7) with ph paper or a ph meter - ph < 7: please renew saline water in the tank

22 ii. Daily works Count no. of juvenile horseshoe crabs : 1. Collect any molts 2. Record no. of molts and the developmental stage of horseshoe crabs (** the characteristics of successfully molted horseshoe crabs: carapace colour: lighter carapace tissue: softer & more delicate) 3. Remove any dead horseshoe crabs (** If there are dead horseshoe crabs in the tank, please renew 2/3 of the water soon) Keep exuviae as specimen Store the molts in 70% alcohol in a sealed glass bottle After a period, take the molts out After drying, smear the molt with a thin layer of lacquer

23 iii. Daily works Check the health of juvenile horseshoe crabs Dead horseshoe crabs? Please check as the followings: 1. any horseshoe crabs flowing on the water surface? 2. any decolorized body tissue? 3. gills : white? move or not? swollen? 4. opisthosoma : move to protect itself or not? 5. horseshoe crab s body tissue in its molt during molting? Please keep the suspected dead horseshoe crabs separately in another plastic tank, in order to observe it for some days and avoid contamination in water decolorized body tissue body tissue in its molt *** Please DO NOT cut the little horseshoe crabs shell when they fail to molt, because they are delicate during molting and they may die eventually. white & swollen gills

24 Vernier Caliper iv. Weekly works Instruction of using Vernier Caliper: i. Main scale: the number on the main scale aligns with or falls to the left of the zero on the vernier scale; Main scale + vernier scale ii. Vernier scale: the line on the vernier scale aligns best with the line on the main scale; iii. Add readings of the main scale and vernier scale Source: en.wikipedia.org/wiki/vernier_caliper#vernier_caliper

25 E. Reminder Q: How can you keep little horseshoe crabs healthy during long holiday, e.g. Easter? Before holiday: 1. Please adjust the salinity of saline water to about 25 26, so that the salinity will not be over 32 when you come back school 2. Please renew 2/3 of saline water in the tank, and clean the equipment 3. If possible, please go to school to look after the juvenile horseshoe crabs every 2-3 day Please send your rearing record data sheet monthly to Vicky at or Billy at Please go to Juvenile Horseshoe Crab Rearing Programme facebook page, raise your questions and share your horseshoe crabs:

26 Reference Filtering material in the filter (Chinese) Agriculture, Fisheries and Conservation Department - Horseshoe crabs in Hong Kong (English) _mar_hor.html Agriculture, Fisheries and Conservation Department - Horseshoe crabs in Hong Kong (Chinese) mar_hor.html Gay, J. (2006). 完美水族箱 The Perfect Aquarium. 香港 : 萬里書店