Ian Laing

Interactive effect of diet and temperature on the growth of juvenile clams

Abstract Small juveniles (0.3–3 mg live weight) of three clam species, Tapes semidecussata Reeve, T. decussata L., and Mercenaria mercenaria L., were fed eight single-species algal diets at a range of temperatures. Nutritional value of the algae tested was in the order: Isochrysis aff galbana (T. ISO) = Skeletonema costatum > Chaetoceros calcitrans = Chroomonas salina = Thalassiosira pseudonana > Tetraselmis suecica > Phaeodactylum tricornutum > Chlamydomonas coccoides , when the same weight of these species was given in the diet to each clam species. Reasons for differences in nutritional value are discussed with reference to the biochemical content of the algae and the relative growth efficiency of the animals. Respiration rate, food cell clearance rate, and growth (as increase in organic weight) of M. mercenaria and T. semidecussata increased with temperature from 10 to 25 °C. Growth rates decreased at > 25 °C. T. decussata showed only a slightly increased growth response at > 15 °C.

Relative growth and growth efficiency of Ostrea edulis L. spat fed various algal diets

Abstract Recently settled spat of Ostrea edulis L. were grown in upwelling tubes in 50-l recirculation systems. Five different marine microalgae species were fed singly and in various mixtures. Greatest growth was with Chaetoceros calcitrans as a single-species diet. Nutritional value of the other single-species diets was in the order Chroomonas salina > Isochrysis galbana > Skeletonema costatum > Tetraselmis suecica. Of the mixtures tested 30% C. calcitrans 70% T. suecica , 50% C. calcitrans 50% S. costatum and 50% T. suecica 50% S. costatum supported growth equivalent to the C. calcitrans-fed control. Percentage composition of the mixtures was based on the organic weight of the cells. Possible reasons for the different nutritional values of the algae investigated are discussed. The size (live weight)-specific total organic content was higher and food cell clearance lower for spat given diets which promoted greater growth rates. Decreased food cell clearance was associated with lower metabolic energy expenditure. Net and gross growth efficiency were greater with higher food value diets. Growth potential of the spat was dependent on the amount of lipid reserves in the larvae at the time of settlement as well as on post-larval diet. Faster growing spat accumulated greater lipid reserves, which were, in turn, associated with relatively higher growth rates when spat were transferred to the sea.

Preliminary observations on the nutritional value of ‘Tahiti Isochrysis’ to bivalve larvae

Abstract The tropical flagellate, Isochrysis aff. galbana (Clone T-ISO), and the small, centric diatom, Chaetoceros calcitrans (Paulsen) Takano were fed singly and in mixture to larvae of the Pacific oyster, Crassostrea gigas , the mangrove oyster, Crassostrea rhizophorae , the American hard-shell clam, Mercenaria mercenaria and the Manila clam, Tapes semidecussata . Trials started at the Dveliger stage and continued until larvae were about to metamorphose. C. calcitrans supported good growth of each of these bivalves but T-ISO was only good for the clams. T-ISO seemed deficient in at least one nutritionally important component to Crassostrea spp. larvae which led to growth retardation beyond 6-day-old veligers. Enhanced growth effects were observed in all of the bivalves, except for M. mercenaria , in response to the mixed diet. Results are compared with previous published data of the food value of Isochrysis galbana Parke where some evidence suggests a similar deficiency to that in T-ISO for Crassostrea larvae. Polyunsaturated fatty acid composition of the algae tested is considered.

Nutritional value of dried algae diets for larvae of Manila clam (Tapes philippinarum)

Spray-dried Nannochloris sp. and Tetraselmis suecica were fed to larvae of the Manila clam (Tapes philippinarum) . These dried diets supported growth equal to, or greater than, their live algal counter-parts, but less than a control diet, a mixture of two algae species of known high nutritional value (Chaetocems calcitrans and T-ISO). Larvae were grown through to metamorphosis on the dried Nannochloris sp. diet in 21 days, compared with 8–11 days with the control diet. Using dried Nannochloris , it was shown that T. philippinarum larvae do not have an essential requirement for long-chain (20 and 22C) polyunsaturated fatty acids, but are able to synthesize them from shorter chain (18C) fatty acids present in the diet. The higher total carbohydrate content of the dried algae was reflected in the larvae feeding on this diet.

Nutritional value of spray-dried Tetraselmis suecica for juvenile bivalves

Juvenile bivalves of five commercially important species (Tapes philippinarum, T. decussata, Mercenaria mercenaria, Crassostrea gigas and Ostrea edulis) were fed a spray-dried preparation of Tetraselmis suecica. Growth and carbohydrate content of the juveniles were measured and compared with animals fed live T. suecica, a live diatom (Chaetoceros calcitrans), or a mixture of these two algae. Dry weight growth rate and carbohydrate content were similar for juveniles fed dried or live T. suecica. Growth rate was less and carbohydrate content greater than those for animals fed C. calcitrans or the mixed live diet. Food cell consumption rates of the various diets were compared. In most cases, the weight of each diet eaten was similar for each bivalve species. Preliminary observations on the effect of supplementing the dried diet with live algae show that a mixture containing 20% C. calcitrans gave improved growth.

Comparative tolerance of small juvenile palourdes (Tapes decussatus L.) and Manila clams (Tapes philippinarum Adams & Reeve) to low temperature

Abstract Small (3.24–31.70 mg dry weight) juvenile clams of a native British species (palourde. Tapes decussatus L., 3 size groups) and an introduced species (Manila clam, Tapes philippinarum Adams & Reeve, 4 size groups) were maintained either unfed or with low algae rations at 3 °C, 6 °C and 9 °C for up to 11 wk. The various size groups responded in a similar way within each experimental treatment. At 9 °C, all the juveniles survived for 11 wk. Unfed clams utilised biochemical reserves and lost weight and condition during this period. Increases in weight, reserves and condition in fed juveniles were greater in Manila clams than in palourdes. At 6 °C, all Manila clam juveniles survived and fed animals showed a small increase in growth and condition. All palourdes and unfed Manila clams lost weight and condition and the mortality of palourdes was 24–46% after 11 wk. At 3 °C, the majority (>88%) of juveniles of both species survived short (3 wk) periods without food. All juveniles utilised reserves and lost weight and condition, with a greater decline in palourdes. High mortalities (>50%) of all palourdes and unfed Manila clams occurred after 3 wk. At all temperatures, a greater proportion of carbohydrate than lipid was used as an energy reserve. Total lipid content and the proportion of polyunsaturated fatty acids (PUFAs) in the neutral lipids increased in treatments in which juveniles grew and decreased where a loss of organic weight was observed. In both clam species the proportion of (n-6) fatty acids, principally 20:4 (n-6), in the phospholipids appeared to indicate a response to stress; juveniles in treatments in which total organic weight decreased contained proportionally more than juveniles which grew. Food cell consumption rates were lower at lower temperatures and at each temperature were higher in Manila clams than in palourdes. Respiration rates increased with temperature only in fed Manila clams. In unfed palourdes respiration rates were higher at 3 °C than at 6 °C and 9 °C. Results are discussed with respect to recruitment and distribution of these clams in relation to winter survival of small juveniles.

The use of artificial diets in rearing bivalve spat

Abstract Spat of five species of commercially cultivated bivalve molluscs were reared in 50-l recirculating sea water systems. They were held in one of three feeding regimes: a live algal diet, a microencapsulated artificial diet, and not fed. Dry weight growth rates of oyster and clam spat fed the artificial diet were up to 54% and 64%, respectively, of the rates with the algal diet. Unfed spat showed almost no growth. Substitution of the microencapsulated diet with 40% and 15% by weight of algae for oysters and clams, respectively, gave growth similar to that with the algal control diet.

Effect of food supply on oyster spatfall

Abstract The amount, concentration and type of algae diet supplied to larvae of the European oyster ( Ostrea edulis L.) and the Pacific oyster ( Crassostrea gigas Thunberg) prior to and during spatfall (setting) were varied. Both oyster species gave lower spatfalls when feeding was discontinued immediately prior to settlement. In comparison with control larvae, that were fed a normal diet throughout, 47.7% (range 19–78%) of O. edulis set if the larvae had grown to 295–325 μm (mean shell length) before feeding was stopped but 8.8% (3–16%) if they had only grown to 275–295 μm. Mean spatfall of C. gigas was 10.6% (2–20%) compared with fed controls and, in contrast with O. edulis , was not related to size of larvae, in the range 262–312 μm, at the time that feeding was withheld. The proportionally greater spatfall from larger larvae was related to higher lipid reserves in these larvae, compared with smaller larvae of this species and all C. gigas larvae. O. edulis spat which set in the absence of food contained less lipid and initially grew more slowly than spat which set from fed larvae. Between 95 and 100% of the larvae of both oyster species survived without food for 2 days, but only 20–30% after 6 days. Subsequent spatfall on resumption of feeding was lower than in controls that were fed throughout. This was related to loss in organic weight of surviving unfed larvae of 0.32–0.79 μg over 6 days (15–25% of initial weight when feeding was stopped). This loss was sustained by preferential utilisation of lipid reserves in O. edulis (53–61% of organic weight lost) and protein in C. gigas (about 70% of organic weight lost) during the unfed period. The food requirements for maximum spatfall were estimated as 0.4 μg (organic weight of algae) · larva −1 · day −1 for O. edulis and 0.6 μg · larva −1 · day −1 for C. gigas . With this amount of food per larva available, spatfall at a food concentration as low as 0.035 mg (organic weight of algae) · 1 −1 was similar to that at the control concentration of 1.0 mg ·1 −1 . Spatfall was also affected by the nutritional value of the food species supplied during settlement. Algae species known to support slower growth rates of bivalves gave lower spatfalls.

The physiology and biochemistry of diploid and triploid Manila clam (Tapes philippinarum Adams & Reeve) larvae and juveniles

Abstract Triploidy was induced in fertilised eggs of the Manila clam [Tapes philippinarum (Adams and Reeve)] at meiosis II. Growth rate, survival, food consumption, respiration rate and biochemical content of separate ploidy classes containing diploid or mainly (> 60%) triploid larvae and juveniles reared in the hatchery were compared and found to be similar. Newly formed D-larvae were 88–95 μm in length and became pediveligers after 15–17 days, when they had grown to 200–220 μm. Juveniles grew from 0.03 mg (mean dry weight) to 15 mg in 7 wk. Larval food consumption was described by the equation C= 0.577 × LW0.587 (where C = organic weight of food cells consumed (μg·d−1) and LW = organic weight of larvae (μg). Juveniles consumed 0.76 μg·d−1 of food per μg organic weight. Lipid and carbohydrate reserves increased during larval growth to 17.5 and 7.5% of organic content, respectively. Lipid reserves were utilised during metamorphosis. In the juveniles, reserves remained constant at about 11% (lipid) and 7% (carbohydrate). The relationship between dry weight (W, mg) and oxygen consumption (R, μg·d−1) of individual clams was described by R = 15.07 × W0.638. Energy budgets for larval and juvenile Manila clams were calculated. Assimilation efficiency was high in the larvae (> 80%), and net growth efficiency increased with size and declining activity of the clams. The physiological and biochemical attributes of the clams were similar to those reported for other bivalve mollusc species. The results are discussed in relation to the apparent absence of recruitment of Manila clams in UK coastal waters.

The influence of salinity on the production of two commercially important unicellular marine algae

Abstract During 1975 and 1976 it was found that lower growth and therefore productivity from 20 l semi-continuous cultures of Isochrysis galbana Parke and Tetraselmis suecica (Kylin) Butch. was related to an increase in salinity from 31 to 36‰ of the natural sea water used in medium preparation. This effect was removed in 1977 by lowering salinity to 25‰ prior to medium preparation. Small-scale trials with Isochrysis in 1977 showed that growth was improved when the salinity was reduced to 28‰. Optimal salinity ranges for growth in medium prepared from artificial sea water were found to be 15–25‰ for Isochrysis and 25–30‰ for Tetraselmis.