Consumption, growth and evacuation in the Pacific cod, Gadus macrocephalus

Growth of Pacific cod was related to energy consumption (cal g⁻¹ day⁻¹) and was well described by linear equations. Maintenance ration was 11 and 12 cal g⁻¹ day⁻¹ at 4.5 and 6.5° C, respectively. Cod between 200 and 5000 g had similar growth rates when growth was expressed as a function of consumption (cal g⁻¹ day⁻¹). Laboratory consumption of food averaged 0.9 and 1.3% body weight per day at 4.5 and 6.5° C, respectively. At these temperatures growth was 0.34–0.38% body weight day⁻¹.
Maximum stomach volumes equated to approximately 4.7% of body weight with shrimp as prey. At this meal size Pacific cod did not feed the next day. A multiple meal evacuation experiment was used to verify the consumption estimates. A return-to-hunger estimate of the meal size evacuated was 1.5% body weight day⁻¹ at 6.5° C, similar to the 1.3% consumption estimate. For Pacific cod fed a single meal of 1% body weight the estimated instantaneous evacuation rate was 0.63 body weight day⁻¹ at 6.5° C. Meal size markedly affected the evacuation rate.
Measured consumption and growth rates are similar to those of Atlantic cod, Gadus morhua .     

Effect of ration size on growth and gross conversion efficiency of young lemon sharks, Negaprion brevirostris

Young lemon sharks, Negaprion brevirostris , were kept under controlled conditions in an aquarium and fed blue runner, Caranx crysos , at different ration levels. The relationship between feeding rate and growth rate was best described by a von Bertalanffy growth curve, which predicted a maximum growth rate of 140 kJ kg⁻¹ day⁻¹ (0·66% b.w. day⁻¹), a maintenance ration of 199 kJ kg⁻¹ day⁻¹ (1·06% b.w. day⁻¹), and losses due to starvation of -236kJ kg⁻¹ day⁻¹ (1·11% b.w. day⁻¹). The relationship between gross conversion efficiency ( K ₁) and feeding rate was also examined. K₁ ranged from - 64 to 25% and did not drop at high ration levels. Activity levels of both starved sharks and sharks fed at maintenance were not significantly different (0·2 body lengths s⁻¹). K ₁ values generated from both laboratory and field data suggest that young lemon sharks can convert food to new tissue as efficiently as teleosts.     

A PROPOSAL FOR A NEW RED ALGAL ORDER, THE THOREALES

Two abalone species: green Haliotis fulgens and yellow Halioti corrugata represent nearly 97% of the total production in the Mexican abalone fishery. It has been assumed that abalone feed on the kelp algae Macrocystis pyrifera. Regional hatcheries use this species as a main source of natural food. M. pyrifera does not occur at the southern limit of the distribution of abalone species along the Baja California Peninsula. In this study, growth rates of juveniles H. fulgens , 17.3 ± 2.2 mm shell length and 0.4 ± 0.2 g body weight, were evaluated. Juveniles were fed with common species in the benthic environments inhabited by abalone along the western coast of Baja California during 191 days. Three diets were based on algae: palm kelp, Eisenia arborea , giant kelp, M. pyrifera and Gelidium robustum , and one on seagrass, Phyllospadix torreyi. Shell length and body growth rates varied between 21.5 μm day⁻¹ and 2.2 mg day⁻¹ for E. arborea and between 45.9 μm day⁻¹ and 6.7 mg day⁻¹ for M. pyrifera. Higher specific growth rates (SGR) in length and weight were determined for M. pyrifera : 0.2% and 0.7% day⁻¹. Significant differences between values of juveniles fed M. pyrifera with the rest of the diets were found. The highest mortality (21%) was in juveniles fed the red algae G. robustum.     

Annual changes of bacterial mortality due to viruses and protists in an oligotrophic coastal environment (NW Mediterranean)

The impact of viruses and protists on bacterioplankton mortality was examined monthly during 2 years (May 2005–April 2007) in an oligotrophic coastal environment (NW Mediterranean Sea). We expected that in such type of system, (i) bacterial losses would be caused mainly by protists, and (ii) lysogeny would be an important type of virus–host interaction. During the study period, viruses and grazers together were responsible for 50.6 ± 40.1% day⁻¹ of bacterial standing stock losses (BSS) and 59.7 ± 44.0% day⁻¹ of bacterial production losses (BP). Over the first year (May 2005–April 2006), protists were the principal cause of bacterial mortality, removing 29.9 ± 20.4% day⁻¹ of BSS and 33.9 ± 24.3% day⁻¹ of BP, whereas viral lysis removed 13.5 ± 17.0% day⁻¹ of BSS and 12.3 ± 12.3% day⁻¹ of BP. During the second year (May 2006–April 2007), viruses caused comparable bacterial losses (29.2 ± 14.8% day⁻¹ of BSS and 40.9 ± 20.7% day⁻¹ of BP) to protists (28.6 ± 25.5% day⁻¹ of BSS and 32.4 ± 20.0% day⁻¹ of BP). In 37% of cases higher losses of BP due to viruses than due to protists were found. Lysogenic infection was detected in 11 of 24 samplings. Contrary to our expectations, lytic infections dominated over the two years, and viruses resulted to be a significant source of bacterial mortality in this oligotrophic site.     

Food intake and growth in the blue-spotted trevally, Caranx bucculentus Alleyne and Macleay 1877, with reference to predation on penaeid prawns

Blue-spotted trevally, Caranx bucculentus , were fed different rations of pilchard and prawn in order to investigate feeding and growth relationships. Maintenance rations at 25.5° C amounted to 3.7% B.W. day⁻¹ and 2.7% B.W. day⁻¹ for prawns and pilchards, respectively. Additional feeding experiments at 28.9° C yielded a maintenance ration of prawns of 3.8% B.W. day⁻¹, suggesting there is very little if any temperature effect on the feeding-growth relationship over the range studied. Fish fed twice or more each day consumed about 7.3 ± 1.4% B.W. day⁻¹.
Given the biomass of this trevally in Albatross Bay, Gulf of Carpentaria, and the contribution of prawns to its diet, we estimate consumption of commercial prawns at 25 ± 5 g.ha⁻¹ day⁻¹ or 11 g kg⁻¹ day⁻¹.     

Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid-May to mid-June. Tiny nymphs occurred from June to late August.
2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day⁻¹), very low from November to February (0.8% wet wt day⁻¹) and high until emergence (2.3% wet wt day⁻¹); short day length seemed to be the major factor reducing growth rate during winter.
3. Mortality was close to zero during winter and 1.4—1.7% day⁻¹during other seasons. Total mortality from egg to adult was 99.6%.
4. The annual production was about 9g wet wt m⁻² year⁻¹ and the annual P/ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m⁻² day⁻¹) and zero in February.     

Influence of different rations and water temperatures on the growth rates of shortfinned eels and longfinned eels

Juvenile (12–152 g) shortfinned eels Anguilla australis and longfinned eels A. dieffenbachia caught in New Zealand streams were fed squid mantle Nototodarus spp. 4 days per week in laboratory experiments. A linear multiple regression equation showed the amount of food eaten (0–2·7% w day⁻¹) explained 77·7% of the variation in specific growth rates (–0·60 to +1·07% w day⁻¹) among individual eels, while previous growth rates, water temperature (10·0–20·6°C), and eel weight (12–152 g) explained a further 5·6, 1·4 and 0·8%, respectively. Growth in length ranged from –0·3 to +0·9 mm day⁻¹. Eels which were starved and then given high rations grew substantially faster than expected. Once growth rates were adjusted for differences in ration and other factors, there were no significant differences in growth rates between species or individual fish. Growth of shortfinned eels fed maximum rations of commercial eel food depended on fish size and water temperatures and ceased below 9·0°C. Growth rates in the wild were substantially less than the maximum possible, after seasonal changes in water temperatures were taken into account, indicating that food supplies and not low water temperatures were controlling growth rates in the wild.     

Digestion rate, gut passage time and absorption efficiency in the Antarctic spiny plunderfish

The absolute gut evacuation rate (GER) (g day⁻¹) of Harpagifer antarcticus increased with increasing ration mass, fish mass only influenced the absolute GER at a daily ration level of 0·3% wet fish mass (approximately a maintenance ration). The relative GER (% of meal fed day⁻¹) was also affected differently by fish and ration mass depending on the relative ration level being fed; at rations of 0·7% wet fish mass or above the relative GER decreased with increasing fish or ration mass (in such a way that the absolute GER remained constant and unaffected by fish mass). At maintenance (0·3% wet fish mass) rations the relative GER was not affected by fish size or ration mass. Thus, there appears to be a ration threshold above which the digestion physiology alters. Mass-specific GER (% g fish⁻¹ day⁻¹) decreased with increasing fish mass. Within a set relative ration level (% wet fish mass) an increase in fish mass decreased the mass-specific GER. At a fixed ration mass, an increase in fish mass (i.e. a reduction in the ration expressed as % fish mass) resulted in a decrease in mass-specific GER. Gut evaluation time (GET) decreased and absorption efficiency (A) increased with increasing absolute GER. The effect of ration and fish mass on the absolute and relative GER followed the same pattern irrespective of the diet, however the A and GER (% day⁻¹ and g day⁻¹) were higher and the GET shorter when the fish were fed shelled krill rather than amphipods.     

Energy and ration requirements of juvenile Pacific halibut (Hippoglossus stenolepis) based on energy consumption and growth rates

Growth of captive juvenile Pacific halibut was linearly related to energy consumption (J g⁻¹ day⁻¹) at 4°C by the following equation: growth (% body weight (b.w.) day⁻¹)=0–007 (consumption J g⁻¹ day⁻¹)– 0.192; r² =0.81. Weight gain was independent of size for fish between 9 and 7000 g when growth was expressed as a function of consumption in J g⁻¹ day⁻¹. Maintenance ration determined in feeding–growth experiments averaged 27.4 J g⁻¹ day⁻¹ at 4–0°C. Small halibut ate significantly more food than large fish. Single meals following 2 day fasts averaged 4.1% b.w. for halibut under 100 g, 1.72% b.w. for 1.2 kg fish and 1.1% B.W. for 6.8 kg fish. Both large and small size categories of halibut tended to evacuate their meal in about 3 days even though small fish ate relatively larger meals. Minimum estimates for daily ration to achieve growth rates observed in the Gulf of Alaska were approximately 0.5 to 2.4% b.w. day⁻¹ depending on fish size and whether northern shrimp or yellowfin sole were their prey.     

Utilization of several plant proteins by gibel carp (Carassius auratus gibelio)

Six isonitrogenous (gross protein content 35%) and isoenergetic (gross energy content 17 kJ g⁻¹) diets were formulated to investigate the effects of inclusion of plant proteins on the gibel carp ( Carassius auratus gibelio L.). The plant proteins tested were: soybean cake (SBC), potato protein concentrate (PPC), peanut cake (PNC), cottonseed cake (CSC) and rapeseed cake (RSC). Fish meal (FM) was used as control. In each diet, 27% of the protein was supplied by fish meal, and the rest supplied by the plant protein tested. Each diet was fed to three groups of gibel carp for 8 weeks in a recirculation system. Specific growth rate (SGR) in fish fed the control diet was significantly higher than those in the other groups, and SGR in fish fed the PPC was significantly lower than in fish fed other plant proteins. There was no significant difference in SGR among the other groups. Feeding rates were ranked in the order: RSC > CSC > FM > PNC > SBC > PPC. Conversion efficiency was highest in groups fed FM, SBC and PNC, followed by groups fed CSC and RSC, and was lowest in the group fed PPC. The fish fed PPC showed lower protein retention than those fed FM and SBC. FM showed highest energy retention while PPC showed lowest. There was no significant relationship between SGR and intake of digestible protein (g g⁻¹ day⁻¹), digestible lysine (g g⁻¹ day⁻¹), digestible methionine (g g⁻¹ day⁻¹) or digestible total essential amino acids (g g⁻¹ day⁻¹), suggesting that the differences in SGR could not alone account for any of these variables.