The ratio of RNA to DNA (RNA:DNA) in white muscle tissue of juvenile summer flounder (Paralichthys dentatus) and weakfish (Cynoscion regalis) was used as a proxy for recent growth rate in an estuarine nursery. Variability in RNA:DNA was examined relative to temporal changes in temperature and dissolved oxygen (DO). Initial laboratory experiments indicated (i) a strong positive relationship between RNA:DNA and growth rate, (ii) a rapid response of RNA:DNA to changes in feeding, and (iii) no effect of hypoxia on the relationship between RNA:DNA and growth rate (tested in weakfish only). Diel cycling DO occurred in the nursery throughout the summers of 2002 and 2003. Canonical correlation analysis of field data indicated a strong positive relationship between RNA:DNA and mean DO conditions prior to capture in both species. Correlations were weak or insignificant between stomach content mass (an index of feeding) and mean DO and between RNA:DNA and stomach content mass and DO variability. These results suggest a strong functional relationship between DO concentration and the growth rate of juvenile fishes in an estuarine nursery. Furthermore, growth rates of wild-caught fishes (estimated from RNA:DNA) appear to be more negatively impacted by diel cycling hypoxia than would be expected from published laboratory data. Résumé: Le rapport ARN sur ADN (ARN:ADN) dans le tissu du muscle blanc du cardeau d'été (Paralichthys dentatus) et de l'acoupa royal (Cynoscion regalis) a servi de mesure de remplacement du taux de croissance récent dans une nourricerie estuarienne. Nous avons examiné la variabilité d'ARN:ADN en fonction des changements temporels de température et d'oxygène dissous (DO). Des expériences initiales en laboratoire indiquent (i) une forte relation positive entre ARN:ADN et le taux de croissance, (ii) une réaction rapide de ARN:ADN aux changements d'alimentation et (iii) une absence d'effets de l'hypoxie sur la relation entre ARN:ADN et le taux de croissance (testée seulement chez l'acoupa royal). Il y a eu un cycle journalier de DO dans la nourricerie tout au cours des étés 2002 et 2003. Une analyse des corrélations canoniques des données de terrain montre une forte relation positive entre ARN:ADN et les conditions moyennes de DO avant la capture chez les deux espèces. Les corrélations sont faibles ou insignifiantes entre la masse du contenu stomacal (un indice alimentaire) et la valeur moyenne de DO et entre ARN:ADN et la masse du contenu stomacal et la variabilité de DO. Ces résultats indiquent une forte relation fonctionnelle entre les concentrations de DO et le taux de croissance des jeunes poissons dans une nourricerie estuarienne. De plus, les taux de croissance des poissons capturés en nature (estimés d'après ARN:ADN) semblent être affectés plus négativement par l'hypoxie cyclique journalière que ne le laissent prévoir les données de laboratoire de la littérature. [Traduit par la Rédaction]
This paper describes and evaluates a 50 mHz radio telemetry system for studying river movements of adult Atlantic salmon (Sdmo sular). In fresh water for most applications radio telemetry is preferable to ultrasonic telemetry, because the receiving element (antenna) can be above water, and radio signals are scarcely affected by turbulent, weedy or icecovered water. Within the range of 10-200 mHz higher frequencies are preferred, since the efficient antenna size is inversely proportional to frequency, and attenuation of signals is independent of frequency. Transmitters were cylindrical (6.5-9.6 cm long x 1.9 cm diam) with a 0.5 wavelength antenna trailing from one end. Each emitted pulsed signals on one of 20 crystal-controlled channels between 49.100 and 49.385 mHz. Transmitters were placed in the stomachs of salmon and the antenna trailed out the last gill slit. Receivers were portable 20-channel manual or automatic scan models, and antennas were 48 cm diam capacitor tuned loops. Some salmon regurgitated transmitters. Two salmon were recaptured and showed no ill effects from carrying transmitters for 32 and 42 days. Pulse rate had little effect on known transmitter life under natural conditions. Known tag life was variable, but averaged 70 days for transmitters with 1000 mah batteries. The range of transmission of transmitters to a receiving system in an airplane at 410 m altitude was about IOkm, and to a boat about 1 km. Range to a land vehicle was variable depending on obstructions. From the airplane transmitters can be located within a radius of about 50 m.
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