Mass production and preservation of marine rotifer resting eggs.
Resting eggs of the marine rotifers Brachionus plicatilis (formerly called L-type) and B. rotundiformis (called S-type) were successfully mass-produced using a batch culture method (reviewed by Hagiwara, 1994). The numbers of resting eggs produced from 1 x 108 Tetraselmis cells were 1400 and 12 600 for B. plicatilis and B. rotundiformis, respectively. The efficiency of resting egg production is being improved by employing the semi-continuous culture method. Some semi-continuous cultures collapsed on the 15-20th day due to bacterial effects. The rotifer culture can be stabilized by placing filtration mats to remove organic material. Under these conditions a harvest of 8.1 x 102 resting eggs.d-1.g-1 (dry weight) Nannochloropsis oculata could be achieved, which is 3.0 times more efficient than that from batch cultures. Resting eggs of B. rotundiformis, however, were not mass produced after changing the culture water.
Resting eggs can be stored in seawater for more than 20 years under complete darkness. Hatchability of the eggs, however, decreased when stored with abundant organic substances. Resting eggs could be canned under 48-61KPa after lyophilization (-30C) without reducing their hatchability.
(Faculty of Fisheries, Nagasaki University, Bunkyo 1-14, Nagasaki 852, Japan)
Cost estimates of hatchery production of marine fish in Japan.
One hatchery belonging to the public sector (Azumacho Fish Seedling Center, AFSC) and one private hatchery (Mariculture Center of Kinki University, MCKU) were selected as typical examples for the production of fish seedlings in Japan. The former reported on the hatchery costs of four species produced in 1994: red seabream Pagrus major, tiger puffer Takifugu rubripes, flounder Paralichthys olivaceus and spotted parrot Hoplegnathus punctatus. The latter gave the prices of red seabream larvae produced during 1991 and 1994. The larvae costs of red seabream produced in AFSC and MCKU were 50-55 yen (Japanese 1 yen = US 1 cent) and 75-140 yen, respectively. The costs of the tiger puffer, flounder and spotted parrot produced in AFSC were 50-70 yen, 80-90 yen, and 135 yen, respectively. The prices of fish larvae were mainly depending on the numbers of seedlings produced in the hatcheries. In general, the prices of seedlings have gradually decreased from 1991 to 1994; this may be due to both overproduction and the economic situation in Japan.
(Faculty of Agriculture, Kinki University, Nara, 631 Japan)
A reappraisal of the potential of the sole, Solea solea (L.), for commercial cultivation.
Renewed interest in the farming of sole has been stimulated largely by a desire, if not a need, for the existing marine fish farming industry to diversify. Despite the extensive studies of the 1960s and 1970s, commercially viable techniques for this universally valuable species were not realised. The species proved relatively easy to rear through the larval stages but the juvenile stages performed poorly on formulated feeds, displaying low growth rates and an apparently high susceptibility to disease. Consequently, effort was directed to other species which did not present such difficulties.
Recent research, however, has demonstrated that these technical problems may not be as intractable as was once thought. This paper reviews the results of these studies, which have focused particularly on the problems of providing adequate nourishment to the larvae and juvenile stages. They have demonstrated: a) the ease with which larvae may be reared to the juvenile stages and a link between larval diet quality and juvenile performance; b) that the reputedly virulent disease, Black Patch Necrosis, may be associated with nutritional deprivation and that juveniles may be grown successfully without a sand substrate; c) that juveniles can attain a growth rate of about 4cm per month on natural prey; and d) that diets may be formulated which support survival rates in excess of 90% during weaning and subsequent growth rates approaching those on natural prey. The impact of this work on the prospects for developing commercially viable culture methods is discussed with reference to other important biological characteristics of the species, such as their response to crowding. It is concluded that there are no insuperable problems to the development of cultivation methods for the sole, but further work is required in certain critical areas before economic feasibility can be demonstrated unequivocally.
(Ministry of Agriculture, Fisheries and Food, Directorate of Fisheries Research, Fisheries Laboratory, Conwy, Gwynedd LL32 8UB, UK)
