Carbon, nitrogen and caloric content of eggs, larvae, and juveniles of the walleye pollock, Theragra chalcogramma

Measurements of dry weight (wt), carbon (C), nitrogen (N) and calories were made on walleye pollock eggs (0.24 mg, 35.3% C, 8.3% N, and 4.6 kcal g⁻¹ dry wt), larvae (0.16 g, 42.9% C, 11.1% N and 5.1 kcal g⁻¹ dry wt) and juveniles (22.4 g, 47.2% C, 9.0% N and 5.6 kcal g⁻¹ dry wt). For juvenile fish (9–360 g wet wt) the measured values were related to dry weight and Fulton's condition factor index (CFI) by regression models. The CFI was a better predictor of body composition than dry weight. As CFI improved from a minimum starvation level of 0.42 to a maximum of 1.16, body caloric content, percentage C, and the C/N ratio increased (kcal g⁻¹ dry wt = 4.4 CFI + 1.7, percentage carbon = 49.7 CFI^0.5, C/N ratio = 5.0 CFI + 0.9), while percentage N and percentage ash decreased (percentage N =−3.5 CFI + 12.1; percentage ash = 9.1 CFI^−1.4). The results of this study suggest that seasonal C, N and caloric content of young pollock can be estimated from measurements of Fulton's condition factor index.     

Seasonal changes in organic composition and caloric content of an Arctic marine amphipod, Onisimus (= Boeckosimus) affinis H.J. Hansen

Protein, lipid, carbohydrate, chitin, ash, and caloric energy contents of the Arctic marine benthic amphipod Onisimus (= Boeckosimus) affinis H.J. Hansen were determined at intervals over two and one half years. The lipid content exhibited the most pronounced seasonal change, from a minimum of about 14–17% of dry wt to a maximum of 25–27% of dry wt. An increase in lipid content in the spring coincided with the reproductive period of the species. Lipid and caloric content decreased during the summer to levels that were maintained through the winter, indicating that the animals do not store significant nutritional reserves for use during the winter. The dry weight proportions of other components were: protein 27.7–38.3%; carbohydrate 1.8–4.0%; chitin 7.8–8.2%; ash 21.3–27.2%. Caloric content varied between 3.29 and 4.18 cal/mg dry wt.     

Chemical composition and caloric content of egg and zoea of the hermit crabeupagurus bernhardus

Summary 1. Chemical composition and caloric content of egg and zoea of the hermit crabEupagurus bernhardus have been determined and the cumulative efficiencies of yolk utilization calculated.2. The cumulative efficiencies of yolk utilization for different constituents were 70.0%, 55.3%, 79.4% or 35.0% for dry weight, caloric content, protein or fat.3. Since the efficiencies with which the different constituents of yolk utilized vary, the chemical composition of the developing eggs undergoes considerable changes. While fat and caloric content showed remarkable decreases, water, ash and protein contents of the eggs increased.4. Of 0.0722 cal expended on metabolic processes of the embryo, only 28.4% was drawn from the oxidation of protein, while fat contributed as much as 66.6%.5. Considerable quantities of inorganic salts (0.77µg/egg) are absorbed from the sea-water by the developing egg.

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Chemische Zusammensetzung und Kaloriengehalt von Ei und Zoea des EinsiedlerkrebsesEupagurus bernhardus

Kurzfassung Im Laufe der vollständigen Eientwicklung findet eine Zunahme von Wasser um 31,5%, Asche um 5,7%, Eiweiß um 8,8% und Nicht-Eiweiß-Stickstoff um 0,2% statt. In der gleichen Zeit sinkt der Fettgehalt von 29,5% auf 14,8% und der Energiegehalt von 6292 auf 5282 cal/g organischer Substanz. Der Kumulativ-Nutzeffekt der Entwicklung von einem Ei zur Zoea-Larve beträgt 70,0%, 55,3%, 79,4% bzw. 35,0% bezogen auf Trockengewicht, Kaloriengehalt, Eiweiß bzw. Fett. Von den 0,0722 cal, die sich auf den Stoffwechsel der gesamten Entwicklung eines Eies beziehen, werden nur 28,4% aus Eiweiß gewonnen; 66,6% werden durch Oxydation von Fett beigetragen.

     

Biometrical relationships, energy content and biochemical composition of Neomysis mercedis from Lake Washington

Morphometric relationships, caloric content and biochemical composition of Neomysis mercedis were determined for freshly caught mysids. Strong positive correlations between telson length, carapace length, dry weight, energy content and total length are described by the equations: Ln (Dry weight) = –5.02 + 2.57^* Ln (Total Length), Telson Length = 0.13^* Total Length, and Energy (Calories) = –37.13 + 4.85^* Mean Total Length. Energy (4.92 cal mg^–1 AFDFW), ash (8.61% dry weight) and total Kjeldahl nitrogen (10.6% dry weight) content are comparable to values reported for other species. A comparison of the length-weight relationship for N. mercedis with similar equations published previously for other mysid species indicated that the predicted mean dry weight at any particular length varied among species.     

Effects of grazing on the quantity and quality of freshwater Aufwuchs

Qualitative and quantitative measures of the Aufwuchs (scum flora) on artificial substrates in situ were used to evaluate the effects of grazing by freshwater pulmonate snails in a shallow pond in southeastern Michigan. Grazer densities of 216 snails/m² marked reduced standing crop so that after 45 days grazed substrata had 6.46 mg dry weight, 604 µg C and 4.18 µg chlorophyll a as compared to controls with 30.62 mg dry weight, 3699 µg C and 6.29 µg chlorophyll a, all on a per dm² basis.Grazing did not change carbon per mg dry matter but caused significant increases in both µg chlorophyll a (control, 0.206; and grazed, 0.649 µg chlorophyll a/mg dry weight, P < 0.01) and nitrogen (control, 8.3; and grazed, 24.2 µg N/mg dry weight, P < 0.001) after 45 days. Both abundance and diversity of the attached community was reduced by grazing from 24 taxa and 80,889 individuals/cm² on control to 8 taxa and 501 individuals/cm² on grazed substrates. Mean productivity of the Aufwuchs was significantly (P < 0.001) reduced by grazing from 76.3 µg C/(dm²·day) on control to 17.7 µg C/(dm²·day) on grazed substrata.Snails were very efficient at clearing smooth surfaces of living cells, detritus, and particulate inorganic matter. There was little evidence of selectivity except for an apparent inability to remove some of the smallest cells (e.g. Cocconeis sp.) probably for mechanical reasons.     

Effects of carbon concentration and carbon-to-nitrogen ratio on growth, conidiation, spore germination and efficacy of the potential bioherbicide Colletotrichum coccodes

The effect of carbon concentration and carbon-to-nitrogen ratio (C:N) as well as their interaction on Colletotrichum coccodes growth and sporulation in submerged flask culture were evaluated. When C:N ratios were held constant, both mycelial dry biomass and spore yield increased with increasing carbon concentration. The specific spore yields (spore yield g⁻¹ carbon), however, were not significantly different for the same C:N ratio in most cases. The highest spore yields (1.3 × 10⁸ spores per ml) were obtained from media containing 20 g per liter carbon with C:N ratios ranging from 5:1 to 10:1. When the C:N ratio was greater than 15:1, spore yields were significantly decreased with increasing C:N ratios. High carbon concentration (20 g L⁻¹) combined with high C:N ratios (above 15:1) reduced both mycelial growth and sporulation, and increased spore matrix production. Spores produced in medium containing 10 g L⁻¹ carbon with C:N ratios from 10:1 to 15:1 had 90% germination on potato dextrose agar after 12 h and caused extensive shoot dry weight reduction on the target weed, velvetleaf. These results suggest that C:N ratios from 10:1 to 15:1 are optimal for C. coccodes spore production. Received 9 December 1997/ Accepted in revised form 22 May 1998     

Optimum growth conditions and light utilization efficiency of Spirulina platensis (= Arthrospira fusiformis) (Cyanophyta) from Lake Chitu, Ethiopia

Spirulina platensis (= Arthrospira fusiformis) was isolated from Lake Chitu, a saline, alkaline lake in Ethiopia, where it forms an almost unialgal population. Optimum growth conditions were studied in a turbidostat. Cultures grown in modified Zarrouk's medium and exposed to a range of light intensities (20–500 µmol photons m^–2s^–1) showed a maximum specific growth rate (µ_max) of 1.78 d^–1. Quantum yield for growth (µ) was 3.8% at the optimum light for growth of 330 µmol photons m^–2s^–1, and ranged from 2.8 to 9.4%. With increase in irradiance, the chlorophyll a concentration decreased, and the carotenoids/chlorophyll a ratio increased by a factor of 2.4. The phosphorus to carbon ratio (P/C) showed some variation, while the nitrogen to carbon ratio (N/C) remained relatively constant, thus causing fluctuations in the N:P ratio (7–11) of cells. An optimum N:P ratio of about 7 was attained in cells growing at the optimum light for growth. Results from the continuous culture experiments agreed well with maximum values of photosynthetic efficiency given in the literature for natural populations of S. platensis in the soda lakes of East Africa, Lake Arenguade (Ethiopia), and Lake Simbi (Kenya).     

The biochemical composition and calorie density of the walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> in the Sea of Okhotsk

In tissues of the walleye pollock Theragra chalcogramma the dry matter content averages 18.5%. The lipid content of the raw material is 0.7%, the protein content is 15.3%, carbohydrates are 0.6%, and ash is 1.3%. The average calorie density is 940 cal/g wet weight and 5080 cal/g dry weight. The dry matter content of gonads varies within 14.9–28.0% in females and 14.5–17.0% in males. The lipid content of the raw material is 0.9–3.0% in females and 1.3–1.8% in males; the protein content is 10.2–21.5% and 10.7–13.4%, respectively. The calorie density of female gonads is 702–1537 cal/g wet weight and 4426–5482 cal/g dry weight; for the male gonads it is 760–960 cal/g wet weight and 4952–5641 cal/g dry weight. The dry matter content of the liver varies within 42.2–62.2% for females and 34.4–62.4 for males. The lipid content of the raw material is 25.6–44.5% for females and 16.6–41.3% for males; the protein content is 6.3–9.8% and 8.1–12.3%, respectively. The calorie density of the liver in females varies within 2918–4601 cal/g wet weight and 6370–7395 cal/g dry weight; in males it is 2291–4357 cal/g wet weight and 6392–7492 cal/g dry weight. The minimum calorie density of the liver is observed in juvenile pollock: 963 cal/g wet weight and 2045 cal/g dry weight. The dry-matter content of feces in different size groups varies within 15.0–18.4%. Values of the average lipid content of raw material range from 1.1 to 1.6%; the protein content is from 1.8 to 3.8% and carbohydrates are from 0.9 to 1.4%. The calorie density of feces from variously-sized walleye pollock varies within a narrow range, from 308 to 362 cal/g wet weight. The energy equivalent ranges, depending on body size, from 259 to 2377 cal. The share of energy concentrated in the somatic (muscle) tissue of variously-sized walleye pollock during ontogenesis constitutes 56.5–93.9%; in female gonads it is 0.9–26.6%; in male gonads it is 0.4–7.3%, in the female liver it is 7.9–27.2%, and in the male liver it is 5.7–26.9%. The amount of energy (cal), concentrated in the female liver and gonads is on average 1.5 and 3 times as high as that in the male liver and gonads, respectively. The maximum total energy loss (15–30%) in mature walleye pollock of various-sizes occurs in the spawning period, during the transition from the maturity stage 5 to stage 6. The total amount of energy accumulated during the lifecycle from small juveniles (<17 cm) to very large individuals (>60 cm) averages 1964 kcal for females and 1465 kcal for males. The difference in the amount of energy is explained by the fact that oogenesis requires more energy than spermatogenesis.     

Variation in the carbon content of two Asplanchna species

The rotifers of the genus Asplanchna were sampled four times during the summer from eight lakes of different types. The mean individual carbon content in the population varied between 0.15–0.66 µg C ind.^-1 (n = 21) for A. priodonta and 1.0–1.6 µg C ind.^-1 (n = 3) for A. herricki. The carbon content and the size of A. priodonta varied considerably between the populations of both different lakes and dates.The carbon level of both Asplanchna species (sample mean 0.2–1% of wet weight) was considerably lower than is generally found for rotifers. Much of the variation of carbon level could be explained by an inverse relationship with wet weight. The high variation in the carbon content of individuals suggests that Asplanch population may adapt their mean body size to fit prevailing environmental conditions.     

Nutritional composition of edible Hawaiian seaweeds

Fresh seaweeds, both wild and cultivated,are commonly eaten as food in the HawaiianIslands. Before Western contact, limu (seaweed) was a regular part of thediet, and is thought to have contributedvitamins and essential mineral nutrientsnot found in other staple food items. Twenty-two species of edible Hawaiianmacroalgae (6 Chlorophyta, 4 Phaeophyta, 12Rhodophyta) were analyzed for protein,lipid, carbohydrate, ash, caloric, mineraland vitamin content. Halymeniaformosa and Porphyra vietnamensisranked highest in total protein contentamong the species analyzed. Most speciescontained less than 5% crude lipid,although two Dictyota species hadover 16% crude lipid based on dry weight. Soluble carbohydrates ranged from 4.5 to39.9% dry weight. Ash values ranged from22.4% to 64.2%. Dictyotasandvicensis and Monostromaoxyspermum had caloric content each over3000 cal g^-1 ash-free dry weight. Allspecies contained measurable quantities of11 essential mineral elements. The majorityof Hawaiian seaweeds tested contained-carotene (vitamin A), and Enteromorpha flexuosa contained thehighest amount of vitamin C (3 mg g^-1).     

Developmental patterns of larval growth in the edible spider crab, Maja brachydactyla (Decapoda: Majidae)

The large edible spider crab Maja brachydactyla Balss, 1922, an overexploited coastal fishery resource in Galicia (NW Spain), is considered as a potential aquaculture candidate. Patterns of its larval growth were studied under controlled laboratory conditions (constant 18 ± 1 °C; 36‰ salinity; photoperiod ca. 12:12 h; lipid-enriched Artemia metanauplii provided as food). From hatching through complete larval development and metamorphosis to the first juvenile crab instar, changes in carapace size, dry weight (DW), ash content, elemental composition (carbon, hydrogen, nitrogen; CHN), and proximate biochemical composition (total proteins, lipids, carbohydrates; Pr, L, Ch) were measured in successive stages (zoea I, II, megalopa, crab I). Body size may be described as a linear function of the number of molting cycles, whereas the amounts of DW, CHN, Pr, L, and Ch per individual increased exponentially (3 to 9 fold). The highest growth rates were observed in L, C and H, the lowest in DW, Pr and N. As a consequence of these patterns, the C:N mass ratio as well as the fractions of L, C and H (in % of DW) increased significantly, while those of Pr and N decreased from 26% to 16% of DW. Throughout development, however, Pr remained the principal biochemical component of total DW. Positive correlations between biochemical and CHN data allow for estimates of Pr from N and of L from C values per individual. The patterns of larval growth observed in M. brachydactyla are, in general, similar to those previously described for other brachyuran crabs with a planktotrophic mode of larval development.     

Zur chemischen Zusammensetzung der CtenophorePleurobrachia pileus in der Kieler Bucht

The chemical composition of the ctenophorePleurobrachia pileus was investigated in March, May and July 1981 in Kiel Bight, western Baltic. The results of all determinations yielded low values compared with other zooplankton groups. Dry weight made up 1.95 to 2.28% wet weight with a minimum occurring in may. Ash-free dry weight amounted to 28–37% of the dry weight but exhibited a maximum in May. Carbon and nitrogen analyses yielded amounts of between 2.6–4.7% of the dry weight and 0.5–1.0% of the dry weight, respectively. Both elements reached lowest levels in May. Proteins reached a minimum in May, too, and values ranged between 2.5 and 5.1% of the dry weight. However, lipids as well as carbohydrates exhibited highest values in May and ranged from 0.8 to 1.6% and 0.8–1.1% of the dry weight, respectively. The C∶N values increased between March and July from 3.7∶1 to 6.7∶1, indicating a decline in protein content. To relate the biochemical compounds to organic matter I used three different approaches: (1) On the basis of ashfree dry weight, carbohydrates remained constant whereas lipids increased from March to July. A minimum of proteins occurred in May. The three compounds made up only 14–22% of ash-free dry weight. (2) Organic matter approximately equals organic carbon content multiplied by 2. Proteins, lipids and carbohydrates summed up reached 61–100% of this reference value and the seasonal course of these compounds changed in a drastic way: proteins decreased, whereas lipids as well as carbohydrates showed a relative maximum in May. (3) Finally, the carbon content of each biochemical compound was calculated in relation to total carbon content measured via C/N analysis. On this basis, 63–105% of total carbon were recovered, and the course of seasonal changes agreed with that of the second approach. A comparison of these three approaches suggests that comparative calculations based on carbon measurements are more valid than those based on ash-free dry weight. The results show that seasonal changes in the amount of organic matter and the biochemical composition occurred. Dry weight was lowest in May, which could be due to the low salinity environment recorded at that time and the corresponding low salt content of the tissue. The observed relative maxima of lipids and carbohydrates in May may be explained by good food conditions since high zooplankton densities are characteristic for this month in Kiel Bight.      

Trockengewicht und Kaloriengehalt sich entwickelnder Heringseier

Dry weight and caloric content of eggs from spring spawning western Baltic Sea herrings have been determined employing the bomb calorimetry technique. Water temperature throughout incubation was kept at 8.0°±0.2° C. Average dry weight and caloric content values of one pist fertilized egg are 0.170 mg (0.124 mg without chorion) and 0.748 cal (without chorion), respectively. The caloric content per egg decreases progressively during the incubation period (Fig. 2). The same holds for the dry substance of the egg (Fig. 1). Energy extraction efficiency related to dry weight is 67.8%, the efficiency related to dry organic substance 70.4%, and the caloric efficiency 63.7%.     

Chemische Zusammensetzung und Biomasseparameter der OhrenqualleAurelia aurita

During summer 1982 and 1983, measurements on the chemical composition and biomass parameters ofAurelia aurita from Kiel Fjord, Western Baltic, were made. The relationships between size vs. wet weight and wet weight vs. carbon content were determined. Dry weight accounted for less than 2% of wet weight in both years. Carbon, nitrogen and phosphorus content of whole medusae were 51–52, 14 and 1.4 mg/g dry weight (dw) respectively. The C:N ratio (by weight) was about 3.7 and the C:N:P-ratio (by atoms) was determined to be 94:22:1. Proteins and carbohydrates made up 59 and 29 mg/g dw. Lipids were estimated to be 19 mg/g dw. Using these data, it was possible to calculate the caloric content of the medusae to be about 0.55 cal/mg dw. In summer 1982, the organic content of different tissues (gonad, oral arm, umbrella) in unfertilized and fertilized females was studied. In unfertilized females, the gonads exhibited the highest values, the umbrella had the lowest values and the values of oral arm tissue were intermediate. However, in fertilized females the oral arm tissue was enriched, whereas the gonads were impoverished; both types of tissues exhibited very similar values. This pattern can be explained by the transfer of fertilized eggs from the gonads into the brood pouches of the oral arms.     

Dry weight and chemical composition (CHN) in relation to population density of cultivatedTisbe holothuriae (Copepoda,Harpacticoida)

The harpacticoid copepodTisbe holothuriae was cultivated at different densities in a running-water system. Dry weight and chemical composition (CHN) of both females and egg-sacs have been determined. Dry weight decreased significantly with increasing density from 3,48 to 1.94μg in egg-sacs, and from 10.80 to 6.58μg in females. Increasing density in both egg-sacs and females results in decrease of carbon, nitrogen and hydrogen contents, expressed as a percentage of dry weight of egg-sacs and females, respectively. Carbon decreases from 52.56 to 50.57% (egg-sacs) and 45.80 to 39.95% (⧫), nitrogen from 12.63 to 11.94% and 10.72 to 9.73% and hydrogen from 9.08 to 7.78% and 7.47 to 6.17%. The dry weight and elemental compositions of the egg-sacs varied in accordance with that of the females, however, a higher percentage of elemental content was observed in egg-sacs. The energy equivalents were calculated from the carbon content. This indicates that more energy was transferred from the maternal body into egg-sacs. The ratio of carbon to nitrogen did not show any marked variations; no clear relation appeared between C:N and density, indicating a relatively constant chemical composition in both females and egg-sacs.     

Ammonia-nitrogen excretion in Daphnia pulex

Ammonia-nitrogen excretion rates were measured in natural summer and cultured populations of Daphnia pulex from Silver Lake, Clay County, Minnesota, USA during 1973. The mean rate of ammonia-nitrogen excretion for the summer populations was 0.20 µg N animal^–1 day^–1 or 5.11 µg N mg^–1 dry body weight day^–1 (N = 80) measured at 15°, 20°, and 25°C. These rates appear to be temperature and weight dependent, but they are probably affected by factors other than temperature and dry body weight. Ammonia-nitrogen excretion rates of Daphnia pulex cultured on Chlamydomonas reinhardi yielded the following relationship with temperature: Log₁₀E = (0.061) T 1.773, where E is µg N animal^–1 day^–1 and T is temperature °C. The ammonia-nitrogen excretion on a mg^–1 dry body weight day^–1 basis was related to temperature according to the following similar expression Log₁₀E = (0.043) T + 0.153, where E is µg N mg^–1 dry body weight day^–1, and T is temperature °C. The length-weight relationship of Daphnia pulex for the summer populations (N = 1583) was log₁₀W = (0.526) Log₁₀L + 1.357, where W is weight in µg and L is length in mm.     

Protein, lipid and caloric contents of bluntnose minnow, Pimephales notatus Rafinesque, during growth at different temperatures

Changes in the relative proportions of protein, lipid, water and caloric contents of bluntnose minnow growing at various temperatures (15, 25, 30° C) were investigated by application of the allometry equation, y=ax^b . Fish grew significantly faster at 25° C (closest to optimum), more slowly at 30° C and most slowly at 15° C. Protein, as a percentage of body wet weight, tended to increase with fish size at all temperatures ( b > 1.000), whereas in juveniles (<0.7 g) it decreased ( b < 1.000). However, with the exception of the 15° C group, protein as a percentage of body dry weight, decreased in all groups ( b < 1.000). Temperature appeared to modify the body composition of bluntnose minnows, e.g. decreasing temperature led to significantly enhanced protein content during growth. Lipid (%) and caloric content (cal g⁻¹) increased with increasing fish weight ( b > 1). The slower growing fish (15°, 30° C) deposited significantly more lipid (and had higher caloric contents) than those growing most rapidly (at 25° C). Water content (%) decreased with increasing body weight in all groups. Despite intergroup growth rate differences, all groups showed evidence of a tendency to follow similar trends in b values for body constituents and caloric content (except for protein v. body dry weight for the 15° C group). This suggests a general conservativeness of body composition in bluntnose minnow. The correlations between body constituents, caloric content and body weight were high ( r ²>0.9) so that estimates of body composition can be obtained from body weight for all temperature groups.     

Growth patterns,chemical composition and oxygen consumption in early juvenileHyas araneus (Decapoda: Majidae) reared in the laboratory

Early (instar I and II) juveniles of the spider crabHyas araneus were reared under constant conditions (12 °C, 32‰S) in the laboratory, and their growth, biochemical composition, and respiration were studied. Every second day, dry weight (W), ash-free dry weight (AFW), and contents of ash, organic and inorganic carbon (C), nitrogen (N), hydrogen (H), protein, chitin, lipid, and carbohydrates were measured, as well as oxygen consumption. Changes in the absolute amounts of W. AFW, and C, N, and H during the moulting cycle are described with various regression equations as functions of age within a given instar. These patterns of growth differ in part from those that have been observed during previous studies in larval stages of the same and some other decapod species, possibly indicating different growth strategies in larvae and juveniles. There were clear periodic changes in ash (% of W) and inorganic C (as % of total C), with initially very low and then steeply increasing values in postmoult, a maximum in intermoult, and decreasing figures during the premoult phase of each moulting cycle. Similar patterns were observed in the chitin fraction, reaching a maximum of 16% of W (31% of AFW). Ash, inorganic C, and chitin represent the major components of the exoskeleton and hence, changes in their amounts are associated with the formation and loss of cuticle material. Consequently, a high percentage of mineral matter was lost with the exuvia (76% of the late premoult [LPM] ash content, 74% of inorganic C), but relatively small fractions of LPM organic matter (15% of AFW, 11% of organic C, 5–6% of N and H). These cyclic changes in the cuticle caused an inverse pattern of variation in the percentage values (% of W) of AFW, organic C, N, H, and biochemical constituents other than chitin. When these measures of living biomass were related to, exclusively, the organic body fraction (AFM), much less variation was found during individual moulting cycles, with values of about 43–52% in organic C, 9–10% in N, 6–9% H, 31–49% of AFW in protein, 3–10% in lipid, and <1% in carbohydrates. All these constituents showed, on the average, a decreasing tendency during the first two crab instars, whereas N remained fairly constant. It cannot be explained at present, what other elements and biochemical compounds, respectively, might replace these decreasing components of AFW. Decreasing tendencies during juvenile growth were observed also in the organic C/N and in the lipid/protein weight ratios, both indicating that the proportion of lipid decreased at a higher rate than that of protein. Changes were observed also in the composition of inorganic matter, with significantly lower inorganic C in early postmoult (2–4% of ash) than in later stages of the moult cycle (about 9%). This reflected probably an increase in the degree of calcification, i.e. in the calcium carbonate content of the exoskeleton. As a fraction of total C, inorganic C reached maximum values of 17 and 20% in the crab I and II instars, respectively. The energy content of juvenile spider crabs was estimated independently from organic C and biochemical constituents, with a significant correlation between these values. However, the former estimates of energy were, on the average, significantly lower than the latter (slope of the regression ≠1). Since organic C should be a reliable integrator of organic substances, but the sum of protein, lipid, chitin, and carbohydrates amounted to only 60–91% of AFW, it is concluded that the observed discrepancy between these two estimates of energy was caused by energy from biochemical constituents that had not been determined in our analyses. Thus, energy values obtained from these biochemical fractions alone may underestimate the actual amount of organic matter and energy. Respiration per individual in juvenile spider crabs was higher than that in larval stages of the same species (previous studies), but their W-specific values of oxygen consumption (QO₂) were lower than in conspecific larvae (0.6–2μg O₂·[mg W]⁻¹). QO₂ showed a consistent periodic pattern in relation to the moult cycle: maximum values in early postmoult, followed by a rapid decrease, and constant values in the intermoult and premoult phases. This variation is interpreted as an effect mainly of cyclic changes in the amounts of cuticle materials which are metabolically inactive. From growth and respiration values (both expressed in units of organic C), net growth efficiency, K₂, values may be calculated. In contrast to previous findings in larval stages, K₂ showed an increasing trend during growth of the first two juvenile instars ofH. araneus.     

Caloric content of larvae of the brine shrimpArtemia salina

Summary 1. Caloric contents ofArtemia salina nauplii and larvae have been determined by employing a combustion calorimetry. Freshly hatched nauplii contain on an average 5953 cal/g organic substance; the respective value for 7-day-old (2 mm long) larvae is 5854 cal/g.2. The effect of starvation on the caloric contents was investigated. After a 72 hour starvation period, nauplii contain 5430 cal/g organic substance, 2 mm long larvae 5115 cal/g.3. The ash contents (expressed as % of body dry weight) ofArtemia larvae increase as a function of the length of the starvation period.4. After determining the weight of the nauplii, the caloric content of a single nauplius was calculated after different periods of starvation. It ranges from 0.00924 cal per freshly hatched nauplius to 0.00459 cal per nauplius starved for 96 hours.

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Kaloriengehalt von Larven des SalinenkrebsesArtemia salina

Kurzfassung Der Energiegehalt frisch geschlüpfter Nauplien (5953 cal/g organische Substanz) und 2 mm langer Larven (Metanauplius IV, 5854 cal/g organische Substanz) vonArtemia salina Leach wurde mit einem Parr 1412 Bombenkalorimeter ermittelt. Ferner wurde der Einfluß verschieden langer Hungerperioden auf den Kaloriengehalt dieser Tiere untersucht. Nach 72stündigem Hungern wurden für die Nauplien 5430 cal/g organische Substanz und für die 2 mm langen Larven 5115 cal/g organische Substanz ermittelt. Der Aschegehalt der Tiere stieg mit zunehmender Dauer der Hungerperiode. Anhand des Gewichts der geschlüpften und hungernden Nauplien wurde der Kaloriengehalt einzelner Tiere bestimmt: er reicht von 0,00924 cal pro Tier (gerade geschlüpfter Nauplius) bis 0,00459 cal pro Tier (Nauplius, 96 Stunden ohne Futter).

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Dedicated to Professor Dr.Friedrich Krüger on his 65^th birthday, August 18, 1967.     

Changes in carbon and nitrogen content during decomposition of three macrophytes in freshwater and marine environments

Three species of aquatic plants were analyzed for their ash, organic carbon and nitrogen content both fresh and after decomposition using the mesh bag method Chara contraria A. Br. ex Kütz in a small freshwater pond and Lemna minor L. in a shallow swamp were examined over a 70 day period of in situ decomposition. Fucus vesiculosus L. was examined over a 63 day period of decomposition in a rocky shore and a salt marsh environment.During decomposition Chara showed a decrease in carbon and an increase in nitrogen content while Lemna increased in carbon and decreased in nitrogen, all on an ash-free dry weight basis. Although the C : N ratio of Chara was high initially and that of Lemna relatively low, after decomposition the C : N ratio for the remains of the two plants was nearly the same. Fucus decomposing in the salt marsh showed no significant change in carbon but increased in nitrogen content while that at the rocky shore decreased in carbon and increased in nitrogen content. Much of the loss in total dry weight in the first few hours of submergence could be attributed to solubilization of ash and of some high C : N ratio organic material. Consistent and significant differences in the C : N ratio of decomposing Fucus at the two marine sites may be attributable to the nature of the decomposer organisms that inhabit these environments. The accumulation of a high proportion of autotrophic microbial biomass (such as purple sulfur bacteria) in the structural carbohydrates of the salt marsh Fucus may have caused these differences.This study suggests that initial differences in nutritional value of aquatic macrophytes diminish during decomposition and that the ultimate C : N ratio attained may be more dependent on the nature of the decomposer organisms present than on the nature of the organic material undergoing decomposition.