Environmental effects on feed utilization

Both external and internal factors affect the response of fish to variations in dietary quantity and quality. An attempt is made to review major, recent studies on the series of intermediate steps (intake, digestion, metabolism, excretion and retention) involved in the global response of fish to environmental changes. Among these external factors, greater attention is however devoted to those that are the most important natural effectors within the aquatic environment: temperature, ambient oxygen and salinity. The changes brought about by a change in temperature at different levels of nutrient utilization have been studied to a great extent in the recent past. As temperature affects in the first instance, the voluntary food intake, a discussion on current nutrient requirement data should preferably be dealt with in absolute terms. While critical levels of oxygen below which growth is hindered are sufficiently defined for many species, precise data on the direct effects of oxygen deficiency on nutrient utilization are still fragmentory. With regard to salinity, a distinction between stenohaline and euryhaline species and a knowledge of the physiological mechanisms corresponding to their life cycles are required before attempting comparative analyses. Within euryhaline species, best performances are noted at salinities isotonic to the internal medium. Despite accumulating evidence on the effects of cyclical phenomena, the chronobiological approach to fish culture remains practically unexplored.     

Evolutionary implications of two rainbow trout growth hormone genes

The primary structures of two rainbow trout growth hormone mRNAs (GH1 and GH2) have been deduced by direct sequencing of their respective cDNA clones and portions of the mRNA. Both GH1 and GH2 mRNA contain open reading frames comprised of 630 nucleotides and encode 210 amino acid residues of which 11 are variant. The translated regions of both mRNA are flanked by a short but rather conserved 5′-end, and a relatively long but highly diverged 3′-end. The differences at translated and 3′-untranslated regions suggest that the GH1 and GH2 mRNA originate from different loci. The GH1 and GH2 mRNA are likely transcribed from two distinct loci which were duplicated during tetraploidization of salmonid genome between 50 to 100 million years ago. The GH2 gene has been isolated and sequenced from a rainbow trout genomic library. This gene spans a region of approximately 4 kilobases. The trout GH gene is comprised of 6 exons and 5 introns, in contrast to 5 exons and 4 introns in mammals. The additional intron in the trout gene interrupts the translated regions that are analogous to the last exon of the mammalian counterpart. The alleged internally repeating sequences in mammalian GH, prolactin (Pr1) and placental lactogen (PL) are not observed in the predicted polypeptide sequence of trout GH. In addition, direct repeats that flank exons I, III and V of mammalian GH, Pr1 and PL genes are absent in trout gene. These findings indicate that the rainbow trout GH gene structure does not support the current hypothesis that internally repeated regions in GH, Pr1 and PL arose from a small primordial gene.     

Life history and ecology of the glowbelly <Emphasis Type="Italic">Acropoma japonicum</Emphasis> in the Uwa Sea,Japan

ABSTRACT:   The life history and ecology of the glowbelly Acropoma japonicum a commercially important fishery resource, were investigated in the Uwa Sea, Japan. Newly settled juveniles (0⁺) appeared at the end of the breeding season and reached maturity in the next season, i.e. when they became yearlings (1⁺). The yearlings made a gametic effort comparable to that of older fish. During the breeding season, the somatic conditions were more deteriorated for males than for females. That the deterioration of male somatic conditions was not attributable to a sexual difference in energy gain from feeding suggests that the males incurred higher energetic costs of reproduction despite their relatively low gonadosomatic indices. Such an energy depletion may increase the mortality risk, resulting in female-biased sex ratios in the older age classes. Most of the 1⁺ fish disappeared in winter following their first breeding. For A. japonicum , the observed precocity and short life span is notable because it is a higher consumer that is generally expected to show later maturation and longer life. As possible explanations for their disappearances, predation and postbreeding emaciation were less likely. While fishing is one of the most influential factors, the possibility of age-specific migration toward deeper waters remains to be examined.     

Growth and nutrient utilization of Murray cod Maccullochella peelii peelii (Mitchell) fingerlings fed diets with varying levels of soybean meal and blood meal

Abstract The Australian native freshwater fish Murray cod, Maccullochella peelii pellii (Mitchell), currently supports a fledgling inland aquaculture industry, which is thought to have considerable growth potential. The aim of this study was to evaluate the suitability of two alternate protein sources [blood meal (BM) and defatted soybean meal (SBM)] as substitutes for fish meal at various levels of inclusion in diets for juvenile Murray cod. The growth performance of juvenile Murray cod in response to nine isonitrogenous and isocalorific diets (50% protein, 14% lipid, 20.2 kJ g^?1) consisting of a control diet in which protein was supplied from fish meal, and test diets in which the fish meal protein was substituted at levels of 8%, 16%, 24%, and 32% with BM or SBM was evaluated from a 70‐day growth experiment. The per cent apparent dry matter (% ADC_dm) and percentage protein digestibility (% ADC_p) of the test diets were also determined using Cr₂O₃ as a marker. Survival in all the SBM dietary treatments was high but that of fish on the BM dietary treatments was significantly (P < 0.05) lower than in all the other dietary treatments. Specific growth rate (% day^?1) of Murray cod fed SBM incorporated diets ranged from 1.63 ±  0.06 to 1.78 ±  0.10 and even at the highest level tested (32% of the dietary protein from SBM) was not significantly different (P > 0.05) from the fish fed the control diet (1.65 ±  0.09). Feed conversion ratios of the SBM dietary treatments ranged from 1.36 ±  0.08 to 1.45 ±  0.07. The protein efficiency ratios and protein conversion efficiencies of Murray cod in the soybean meal treatments were also good and for a majority of the SBM diets were better than those for the control diet. Per cent ADC_dm and ADC_p of the SBM diets tested ranged from 70.6 ±  1.46 to 72.3 ±  1.81% and 88.6 ±  0.57 to 90.3 ±  0.17%, respectively, and was not significantly different (P > 0.05) from the control diet (% ADC_dm 74.3 ±  1.63; % ADC_p 91.3 ±  0.55). The reasons for significantly poor survival and growth of Murray cod reared on BM incorporated diets, and relatively poor digestibility of these diets are discussed. The study shows that for Murray cod diets in which fish meal protein is substituted up to 32% performance or carcass composition is not compromised.     

Digestive protease activities and free amino acids in white muscle as indicators for feed conversion efficiency and growth rate in Atlantic salmon (Salmo salar L.)

The aim of the present experiment was to screen several biochemical indices in fish and their interrelations in order to select variables for future studies of growth rate and feed conversion. Several parameters [trypsin activity, chymotrypsin activity, free amino acids (FAA) in plasma and white muscle, and RNA and RNA/protein ratio in the white muscle] were measured together with specific growth rate (SGR), feed intake and feed conversion efficiency (FCE) in four groups of diploid or triploid Atlantic salmon (Salmo salar L.) reared under different light regimes. SGR was measured on individually tagged fish, whereas feed intake and feed conversion was estimated on tank basis. A principal component analysis (PCA) explained 80.6% of the variance in the data, using all measured parameters, regardless of ploidy and light regime. Muscle free hydroxyproline showed the highest correlation, alone explaining 55% of SGR variability. The SGR also significantly correlated with trypsin activity (r=0.34), the activity ratio of trypsin to chymotrypsin (T/C) (r=0.39), plasma essential FAA (EAA) (r=0.39), plasma total FAA (TFAA) (r=0.37), the ratio of essential to non-essential FAA (EAA/NEAA) in the white muscle (r=–0.45), muscle RNA (r=–0.45) and RNA/protein ratio (r=–0.41). Tank FCE correlated positively (r=0.97) with SGR, T/C ratio and muscle free hydroxyproline, and negatively (r=–0.90) with muscle EAA/NEAA. The groups reared under continuous light (LL) regime showed significantly higher SGR than simulated natural photoperiod (SNP) groups, and with an apparently higher FCE. A higher growth rate was associated with either a higher consumption rate and/or a higher feed utilization. A negative correlation between muscle RNA concentration and SGR may indicate that increased growth rate under LL regime was not caused by an increased protein deposition rate.     

Changes in myoglobin content and proximate compositions of the dorsal ordinary muscles of full-cycle cultured Pacific bluefin tuna Thunnus orientalis (Temminck et Schlegel) with body size

We investigated the changes in myoglobin (Mb) content and proximate compositions of the cephalad parts of the dorsal ordinary muscles (Ce‐DOM) of full‐cycle cultured (FC) Pacific bluefin tuna [body length: 42.6–115.4 cm, body weight (BW): 1.7–38.4 kg, killed from July 2004 to October 2005]. The Mb content of Ce‐DOM increased (P<0.01) until a BW of 7.0 kg was reached. However, the Mb content of Ce‐DOM had a wide variety above a BW of 7.0 kg. On the other hand, the moisture, protein and ash contents of Ce‐DOM of FC tuna decreased (P<0.05 and 0.01) with an increase in BW. However, the lipid content of Ce‐DOM increased gradually above about a BW of 20.0 kg. Furthermore, the Mb content in protein of the Ce‐DOM of FC tuna increased with an increase in BW. These results indicated that the increase in Mb content of Ce‐DOM of FC tuna was not related to changes in proximate composition between a BW of 1.7 and 38.4 kg.     

The effect of feeding three anabolic steroids in different combinations on the growth,food conversion efficiency and protein and nucleic acid levels of liver,kidney, brain and muscle of mirror carp (Cyprinus carpio)

A study on the effect of three different anabolic-androgenic steroids on the growth, food conversion efficiency and nucleic acid contents of liver, kidney, brain and muscle of carp,Cyprinus carpio was undertaken. The three steroids, methyltestosterone (MT), ethylestrenol (EE) and oxandrolone (ON), were fed in different combinations at final concentrations of 5 or 6 mg/kg diet for 60 days. No effect on the growth was observed in any of the experimental groups. A decrease in the specific growth rate (11–21%) and food conversion efficiency (20–29%) was noted. Feeding of drugs increased the cranio-somatic and reno-somatic index in all except one group. Hepatosomatic (ON+MT) and viscero-somatic (ON+MT; EE+MT+ON) indices decreased. Protein increased and RNA/DNA decreased in only one group while a decrease in protein/DNA was observed in the liver of all experimental groups. RNA/DNA increased and protein/RNA decreased only in one group while no effect was seen in protein and protein/DNA contents in any of the treated kidneys. Proteins, protein/RNA and protein/DNA decreased in certain groups in brain tissue. In muscle, no effect was seen in proteins or protein/DNA. Protein/RNA decreased in all but one group while RNA/DNA was higher only in the group fed all the three steroids together.     

Evaluation of Cassia fistula meal as a replacement for soybean meal in practical diets of Oreochromis niloticus fingerlings

This study was undertaken to determine the replacement value of Cassia fistula seed meal (CFM) for soybean meal (SBM) in practical diets of Oreochromis niloticus fingerlings. Five practical diets (350 g kg^?1 crude protein) containing 0 g kg^?1 (control), 170 g kg^?1 (diet II), 340 g kg^?1 (diet III), 509 g kg^?1 (diet IV) and 670 g kg^?1 (diet V) substitution levels of CFM for SBM were formulated and fed to triplicate groups of O. niloticus fingerlings (mean initial weight of 10.22 ± 0.03 g) for 70 days. Fish mortality increased linearly with increase in inclusion levels of CFM in the diet. Growth and diet utilization efficiency were depressed in fish fed diets containing CFM at varying inclusion levels. Feed conversion ratio, specific growth rate and protein efficiency ratio of O. niloticus fed on diet containing 170 g kg^?1 substitution level of CFM were similar (P > 0.05) to the control diet. Digestibility of the different diets decreased with increase in inclusion levels of CFM. Fish fed diet containing 670 g kg^?1 CFM had significantly lower carcass protein. However, no significant differences were observed in carcass protein and lipid contents between fish fed the control diets and diet containing 170 g kg^?1 CFM. The most efficient diet in terms of cost per unit weight gain of fish was obtained in 170 g kg^?1 CFM dietary substitution.     

The effects of long-day photoperiod on growth, body composition and skin colour in immature gilthead sea bream (Sparus aurata L.)

Immature gilthead sea bream (Sparus aurata L.) with a mean initial weight of 25.6 g were reared over 11 months to market size under different photoperiods: 16L:8D; 24L:0D and a control. Differences in final mean weight were significant between the three treatments (P<0.001): 16L:8D, 465.0 g; 24L:0D, 445.9 g; control, 402.6 g. Fish from the 24L:0D consumed most while 16L:8D fish converted it most efficiently. The lipid content of fillets was lower (P<0.05) for the 24L:0D (5.37±0.16 g 100 g^?1 of fillet) than for the control (6.02±0.12 g), and the moisture content lower for the control than for either treatment groups. Skin luminosity (L^*) was directly related to the number of hours of light exposure.     

Does the aerobic capacity of fish muscle change with growth rates?

To ascertain whether growth rate modifies the oxidative capacity of fish white muscle, we examined the effects of individual growth rate on the activities of four mitochondrial enzymes in white muscle of the fast growing Atlantic cod,Gadus morhua. Growth rates were individually monitored in cod held at three acclimation temperatures during experiments repeated in four seasons. The size dependence of citrate synthase (CS), cytochrome C oxidase (CCO) and β-hydroxyacyl CoA dehydrogenase (HOAD) activities was established using wild cod ranging from 115 to 17,350 g. Given their negative allometry, CS and CCO activities in the experimental cod were corrected to those expected for a 1.2 kg animal. HOAD activities did not change with size. The specific activities of CCO and CS were positively correlated with growth rate. However, for both enzymes, season explained more of the variability than growth rate or temperature. Season was the only factor to significantly affect the activity of HOAD, while temperature and season interacted to determine glutamate dehydrogenase activity. CS activity was positively correlated with the initial condition of the cod, which differed among the seasons. The other enzymes did not show this relationship. The independent changes of these enzymes suggest that mitochondria undergo qualitative modifications with changes in growth rate, season and size. Although growth rate and the activities of CCO and CS are positively correlated, the activity of the mitochondrial enzymes is more affected by size, physical condition and season.