<div><strong>Background:</strong> Temperature is one of the most important environmental factors affecting the survival, growth and metabolism of fish. The current study was aimed to study the effects of water temperature on the metabolic enzyme activities of juvenile <em>Siganus guttatus</em>.<br />
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<strong>Methods:</strong> The juveniles were domesticated at 28&plusmn;1&deg;C for two weeks and then the temperature was adjusted to the target temperature groups (31&deg;C, 27&deg;C, 23&deg;C and 19&deg;C) by the gradually increasing or decreasing temperature with the change rate of 2&deg;C per day. The experiment lasted for 70 d. At the end of the experiment, the fish were anesthetized and all the livers were dissected on ice plate and stored in the refrigerator at -80&deg;C for the determination of enzyme activity.<br />
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<strong>Result:&nbsp;</strong>The activities of glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT), hexokinase (HK) and pyruvate kinase (PK), lipoprotein lipase (LPL) and hepatic lipase (HL) tend to be increased with the reduction of temperature. The above enzymes activities in 19&deg;C group were highest. The activity of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH) and citrate synthase (CS) was lowest in 19&deg;C. These results suggests that 19&deg;C had exceeded the suitable temperature range for juvenile <em>S. guttatus</em>. At low temperature, S. guttatus mainly use fat for energy, but less anaerobic metabolism for energy.</div>


<p>Effects of Water Temperature on Activities of Metabolic Enzymes of Juvenile <em>Siganus guttatus</em></p>


<div>The effects of salinity, temperature and pH on the activity in the spermatozoa of Siganus guttatus were studied. Milt were collected from 8 wild mature males that came from a commercial hatchery. Sperm motility was measured with a VHS video-recorder and a video camera connected to a microscope. The results showed that most of the sperm were highly motile in 400-700 mM NaCl, the longest duration of sperm motility recorded in 600mM NaCl and the duration was 788.0&plusmn;16.9 s. Sperm was not motile when suspended at pH 4, sperm motility was observed at pH 5, there was a relatively higher percentage of motile sperm in solutions at pH 5-8 (above 80%), the duration was the longest and achieved (769.0&plusmn;19.8) s when pH was 8. The motility and duration increased within 10-25&ordm;C and decreased at the range of 25-40&ordm;C, the highest motility and the longest duration were all appeared at 25 &ordm;C, they were (91.0&plusmn;1.4) % and (725.0&plusmn;21.2) severally. Optimum salinity, temperature and pH for S.guttatus reproduction was 600mM NaCl, 25 &ordm;C and 8 respectively.</div>


<div>Effects of salinity, temperature and pH on the motility in <em>Siganus guttatus</em> spermatozoa</div>


<div style="text-align: justify;">The proximate composition and fatty acid profile of five tissues (head, skin, bones, muscle and liver) of juvenile Siganus guttatus fed with Enteromorpha prolifera were investigated. The results indicated that: (1) The content of protein and fat among these five tissues showed a significant differences (P&lt;0.05). The muscle has the highest content of protein and the lowest content of fat. (2) The highest content of fatty acid in SFA is 16:0 in all five tissues, the highest content of fatty acid in MUFA is18:1n-9c (cis) in skin, bones, muscle and liver, while the highest content of PUFA is DHA in muscle. Muscle contained the highest value of DHA and EPA, the total content was more than 100 times in bones. Muscle tissue is rich in many important polyunsaturated fatty acids such as EPA, DPA, DHA, ARA and ALA, which has better nutritional quality and immune and health function.</div>

Effects of Water Temperature on Activities of Metabolic Enzymes of Juvenile Siganus guttatus

Effects of salinity, temperature and pH on the motility in Siganus guttatus spermatozoa

Proximate composition and fatty acid profile in different tissues of juvenile Siganus guttatus fed with Enteromorpha prolifera