Study On The Energy Budget Of Young Girella Leonina

Fish bioenergetics is an important branch of bioenergetics. The model of fish bioenergetics is used to predict fish growth, ingestion, metabolism and excretion and has wide application in fishery management. The core part of this model is to study the quantitative relationships among various components of energy budget and the influence of ecological factors including temperature, salinity, weight and ingestion on these relationships, which is positive in recognizing the energy allocation mechanism of fish and thus providing reliable technical support for highly effective aquaculture.As an emerging cultured species in recent years, Girella leonina is now artificially cultivated in Taiwan, Fujian, Guangdong and along the southern coast of Zhejiang. However, the biological study on Girella leonina is very limited and the basic research data of this species is scarce. Therefore, it's quite necessary to enhance the basic research on this fish so as to improve the culture techniques, bring down the cost, raise the product quality and increase the effectiveness of resource utilization.The current thesis is based on experiments conducted in the Marine Bioengineering Laboratory of Ningbo University from Sep.2008 to Apr.2009. The dynamics of ingestion energy, growth energy and excretion energy was studied under lab rearing condition at a temperature of 18℃,22℃,26℃and 30℃, respectively, giving rise to the energy budget equation of Girella leonina yong at four temperatures. The changes of weight-losing rate, metabolic rate and excretory rate are recorded after fasting for 1d to 11d at 22℃, leading to the production of hunger-induced energy budget equation of Girella leonina yong. In addition, the ecological conversion efficiency, the biochemical composition of body and food digestion time is compared, respectively, among the above four temperatures, and the growth characteristics of cage-reared fish are traced and measured.The main content and conclusions of this study characterized by theoretical and technical breakthroughs are as follows:⑴The crude protein and crude fat content as a whole increases with the rise of temperature, so does the fish specific energy. The highest level of protein content is 20.09% within the 30℃group. The highest level of crude fat is 9.04% within the 26℃group, and the lowest is 7.27% within the 18℃group.⑵The average daily ingestion rate, weight increase rate, weight special increase rate, ecological conversion rate and special energy increase rate all go up with ascending temperature within the range of between 18℃to 26℃,and the values of the five parameters peak at 26℃, or 2.38%, 37.18%, 1.20%, 0.48% and 69.87%, respectively, 1.8 to 4.4 times the values reached at 18℃. Noticeably, the five parameters decline to different degrees at 30℃when the gross ingestion energy is increasing but the metabolic consumption is accelerating as well.⑶The protein content drops with extended starvation period. The metabolic rate declines moderately within 5 days post-fasting, plummets drastically after 5 days and becomes stabilized after 7days at 81.4% of standard level. The excretory rate decreases rapidly after 5 days to 50% of basic level. The protein content shows no remarkable changes in the 11 days following starvation, while the fat content declines significantly to 5.55%, which is the demonstration of a protein-saving mechanism of hungry yong. Based on this, the energy equation is established after starvation for 1d, 3d, 5d, 7d and 11d, respectively.⑷When the temperature stays between 18℃to 30℃, the digestion time of yong is reduced with the increase of temperature. The digestion time at 30℃is only a quarter of that at 18℃, or 443 min less. The digestion period is not affected by temperature.⑸The relationship between length and weight is described in the equation, W = 0.0407L 2.9702(R2 = 0.9866), according to Keys formula. The b value is 2.9702,or close to 3, illustrating Girella leonina is a equidistant-growing fish. The growing equations of weight and length are then built based on logistic equation(y = A /(1+Be-rt)) as follows: W = 435.661/(1+187.334e-0.00803t)(R = 0.954), L = 24.7894/(1+5.77593e-0.00401t)(R = 0.970).⑹The standard metabolic rate and the basic excretory rate are positively related to temperature within the range of between 18℃to 30℃. The standard metabolic rate is 0.304 mg/g·h, and the basic excretory rate is 0.0131mg/g·h at 30℃, 2 times and 2.9 times the value reached at 18℃, respectively. The relationship between the standard metabolic rate(Rs) and temperature(T) is characterized in the form of Rs= 0.0042T1.2259(R2 = 0.8458), while the relationship between the basic excretory rate (Ub) and temperature(T) is quantified with the equation Ub = 0.0008e0.0918T(R2 = 0.9226). As the temperature increases, the peak values of metabolic rate and excretory rate rise, the duration of the peaks decreases and the SDA gross increment goes up as well. The ingestion rate and metabolic rate are positively related to the peak of excretory rate, SDA duration and gross increment.⑺The energy supply from protein consumption of hungry yong increases steadily with temperature, contrary to the case in overeating yong where protein-derived energy is 1.4 to 3.9 times that produced by hungry yong. The lowest protein-derived energy proportion is 17.88% within the 26℃g roup,50% of that within the 18℃group, suggesting the yong preferentially selects fat as energy source and accumulates protein in preparation for the buildup of body.⑻The dynamic change of the metabolic energy and excretory energy is quantified accurately for the first time in the 24 hours following ingestion using enclosed continuous flow-through water, based on which the gross energy budget equation is established at four temperatures and the energy budget model of yong using temperature as variable is created. The proportion of growth energy increases from 18.44% at 18℃to 27.98% at 30℃, and the proportion of metabolic energy is 45.24%, or the lowest at 26℃and reach the highest level at 30℃. The assimilation equation indicates that at 26℃, the lowest proportion of metabolic energy expenditure is 62.9% and the highest proportion of growth energy expenditure is 37.1%. The equations are as follows: 18℃:100.00C = 18.44G + 65.46R + 4.08U + 12.01F 22℃:100.00C = 24.25G + 50.78R + 3.79U + 21.18F 26℃:100.00C = 26.69G + 45.24R + 3.72U + 24.36F 30℃:100.00C = 27.98G + 58.19R + 4.67U + 9.16F The energy budget equations could also be described featuring the assimilation energy: 18℃:100.00A =21.98G + 78.02R 22℃:100.00A =32.32G + 67.68 R 26℃:100.00A =37.10G + 62.90 R 30℃:100.00A =32.47G + 67.53R 100C=[ 18.616Ln(T) - 34.49]G + [0.4317 T2 - 21.405 T+ 311.35]R+ [0.0194 T2 - 0.8904 T + 13.86]U + [ -0.3806 T2 + 18.134 T - 191.71] FThe best growing temperature is 26℃, which is confirmed by comparisons of multiple parameters and energy budget equations. And the optimal temperature range is between 18℃to 30℃. The results also show that Girella leonina is a species with high metabolism consumption and slow growth rate.