of pathogenic bacteria which may be associated with 

 these mortalities. In related work, the gonadal de- 

 velopment of the Manila clam, Venerupis japonica, 

 is being studied. Also, seed of this clam species is 

 being planted in commercial growing areas to deter- 

 mine the best annual planting density and minimum 

 length of time seed must be held in the hatchery to 

 give optimum yields to the clam grower. 



In a companion program, a prototype continuous 

 phytoplankton culture unit is being developed at the 

 University of Washington to provide nutritious, effi- 

 ciently grown feeds for the clam and oyster farm. 

 The prototype can produce at least 14 liters per day 

 of Mo HOC hr}' sis liitheri with a total yield of 2 x 10" 

 cells, consisting of 6. 8 gash-free dry weight, which is 

 22% protein. 



Clams 



A new hard clam culture method has been de- 

 veloped at the Virginia Institute of Marine Sciences. 

 The new method involves spreading shell, gravel, or 

 other material (aggregates) over the sand or mud 

 bottoms before planting the seed. This type of bot- 

 tom protects the young clams from their chief pre- 

 dator, the blue crab, and other predators, such as 

 other crabs, boring snails, bottom-dwelling fish, and 

 waterfowl. Other methods of protection tried in the 

 past included planting the young clams in screened 

 trays or boxes, within fenced enclosures, under 

 sheets of netting or hardware cloth, in saltwater 

 tanks, and intertidally. These techniques were unre- 

 liable and expensive, caused silting and slow growth, 

 and thus are unsuitable for commercial use. 



Other work on molluscs at the University of 

 Hawaii has included efforts to develop pond culture 

 of the Japanese littleneck clam which was intro- 

 duced to Hawaii, but whose natural populations are 

 declining. Research to date has identified proper 

 substrate as a key parameter with sand substratum 

 yielding normal growth. Spawning was achieved 

 through temperature elevation (30°-3I°C) and addi- 

 tion of sperm. 



Scallops 



The hatchery technicjues of conditioning, spawn- 

 ing, and rearing the bay scMop. Acqiiipcclen irrci- 

 (lidiis. have been developed at the Virginia Institute 

 of Marine Sciences. The scallop has been raised to 

 market size (5-6.5 cm) with the final growth phase 

 taking place in wooden, rectangular floats (2.1 m x 

 0.6 m X 15 cm) whose tops and bottoms are covered 



with fiber glass window screen or plastic netting. In 

 one experiment, the scallops were grovs n from 1.3 to 

 5.7 cm in a net enclosure directly on a relatively hard 

 mud-sand bottom. The total growth time from egg to 

 market size was 6-7 mo. Work is continuing to de- 

 termine optimum stocking densities and optimum 

 depth for holding the scallop floats and to develop 

 other methods for holding scallops from about 2.2 

 cm to market size. 



.\balone 



The culture of four commercially important 

 species of abalone is under study at the Scripps 

 Institution of Oceanography. University of Califor- 

 nia. Studies of spawning phenomena, early de- 

 velopment, settlement, growth of settled juveniles, 

 and hybridization are being conducted. Approxi- 

 mately 200, ()()() young red abalone, Haliot'ts nijes- 

 cens. were reared by the chief investigator in a com- 

 mercial venture. This resulted in the identification of 

 the problems being attacked in this research pro- 

 gram. Primary attention is being given to the influ- 

 ence of temperature on larval development and 

 juvenile growth, and to the behavioral problem of 

 substrate selection by settling larvae. Other efforts 

 are being devoted to determine the causes of larval 

 mortalities and to identify micropredators of newly 

 settle juveniles. 



Octopus and Limpets 



Two rather unusual species of molluscs are being 

 studied by University of Hawaii scientists. Work on 

 large limpets, which are in great demand for 

 Hawaiian luaus and which sell for as much as $70 per 

 gallon (6.000 yenVliter). is concentrating on the de- 

 velopment of an acceptable food source. Eggs have 

 been obtained from females and artificially fertilized 

 successfully with the females producing several 

 thousand eggs each. However, further ecological 

 work is necessary to ascertain conditions under 

 which the early larvae can be reared to acceptable 

 size. 



Research on the Day Octopus, another 

 specialized food that is highly prized in Hawaii, has 

 indicated a rapid growth rate with the animal reach- 

 ing the marketable size of 1 pound (0.45 kg) in about 3 

 mo and growing to 3-4 pounds (1.36-1.8 kg) in only 

 4-5 mo. Current efforts are directed toward the de- 

 velopment of an artificial food. Mating occurs read- 

 ily in captivity with the females producing an aver- 

 age of 500,000 eggs. Difficulty has been experienced 



4(i 



