Peter S. Davie

Physiological stress responses in big gamefish after capture: Observations on plasma chemistry and blood factors

The plasma electrolytes, Na+, K+, Ca2+, Cl- and osmolarities had high values in capture-stressed big gamefish. Blood metabolites measured after stress showed glucose and lactate elevations. The activity of the plasma enzymes alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, creatine kinase and lactate dehydrogenase suggested tissue disruptions following severe capture stress. Haematocrit values and methaemoglobin were high in capture-stressed gamefish. The plasma chemistry of resting and capture-stressed snapper (Chrysophrys auratus) was studied for comparison. Specific differences in plasma biochemistry appeared to be the result of different strategies of fish behaviour during capture.

10 Perfusion Methods for the Study of Gill Physiology

Publisher Summary This chapter discusses perfusion methods for the study of gill physiology. A large number of perfused gill preparations have been developed to study gill physiology. In general, isolated or in situ perfused gills allow to control or measure many variables concerning gill function. The control of perfusate composition, pressure, and flow and the exclusion of postbranchial circulation, together with an increased accuracy of measurements, are the principal advantages of perfusion methods. Perfused gill preparations fall into four main groups: isolated branchial arches, branchial baskets including all arches, heads, and whole bodies. Isolated branchial arches exclude tissues, such as the central nervous system, buccal and opercular epithelium, and pseudobranch, and represent truly isolated gills. The cost of isolation is the impairment of recurrent circulation, abnormal ventilation, and mechanical stresses. The lamellar blood channels of fish gills are perfused with blood under arterial pressure and in that sense bear a close resemblance to the capillaries of a glomerular kidney. Experiments designed to study branchial ion transport have also been conducted, primarily on intact animals.

Oxygen binding by the blood and hematological effects of capture stress in two big gamefish: Mako shark and striped marlin

Blood from capture-stressed striped marlin cannot be fully saturated with oxygen in the presence of lactic acid because of a substantial Root effect. Titration of blood to pH 7.6 at 25 degrees C gave an O2 affinity constant, P50 = 17 mmHg. The P50 was highly sensitive to pH showing a Bohr factor phi = delta log P50/delta pH = -0.74. Blood from capture-stressed mako sharks did not show either a Root effect or a significant Bohr effect (delta log P50/delta pH = +0.16). The O2-affinity constant, P50, was 10.6 mmHg at pH 7.6 and 25 degrees C. Hematological measurements following capture gave hematocrit values of 24.2 +/- 8.1% and 32.3 +/- 10.8% for marlin and mako respectively, and high concentrations of blood lactate in both species (15-16 mmol l-1). The O2 transport properties of the blood are discussed in relation to oxygen demand and capture stress.

The Physiology of Silvering in Anguillid Eels: Androgens and Control of Metamorphosis from the Yellow to Silver Stage

The onset of puberty heralds a significant change in the life of anguillid eels. The hypothalamo-hypophysial-gonadal axis is activated, and a suite of morphological, biochemical, and behavioral changes occurs in preparation for a long return migration to specific, but generally poorly known, oceanic spawning areas. These changes, collectively referred to as “silvering,” are dramatic enough to be recognized not simply as the development of secondary sexual characteristics but as components of a true metamorphosis (Petersen 1896; D’Ancona 1960; LecomteFinger 1990). The nature of these changes and the physiological mechanisms that mediate them form the subject matter of this chapter. The term silvering is used here to refer to the processes that transform an immature, feeding (yellow) eel into a maturing, migratory (silver) eel.

Heart Growth in Rainbow Trout in Response to Exogenous Testosterone and 17-α Methyltestosterone

Abstract This study was designed to quantify heart growth in trout with elevated plasma levels of testosterone or 17-α methyltestosterone. It arises from the observation that the heart of male trout doubles in mass in preparation for spawning and examines the relationship between plasma levels of male sex steroids and the observed heart growth. Using androgens implanted in vehicles of either cocoa butter or silicone rubber pellets, we have stimulated heart growth in immature male and female rainbow trout to achieve relative ventricle masses over 1.7 times those of controls within a 42-day period. Testosterone and 17-α methyltestosterone both induced growth of the heart relative to controls; 17-α methyltestosterone being about two times more potent in its anabolic effects on the heart.

Coronary vascular reactivity in the skate, Raja Nasuta

Abstract 1. Vasoactivity was examined in isolated vascular rings from the coronary arteries of the rough skate, Raja nasuta . 2. Adrenergic compounds produced contractions and relaxations, indicating a mixed population of α- and β-adrenoceptors, respectively. 3. Adenosine contracted vascular rings. ADP and ATP contracted vascular rings at concentrations below 0.1 mM and relaxed them at higher concentrations. 4. Similary, acetylcholine produced weak contractions at concentrations below 0.1 mM and strong relaxations at higher concentrations. Nitroglycerine also produced relaxations. 5. Nitroglycerine also produced relaxations. 6. The prostaglandin F 2α produced pronounced contractions. 7. Serotonin relaxed vascular rings. 8. Histamine, bradykinin and angiotensin II produced weak relaxations. 9. The responses of Raja nasuta are compared with the vascular reactivity previously reported for lar coronary artery in rainbow trout, Salmo gairdneri , and mako shark, Isurus oxyrinchus .

Myocardial oxygen consumption and mechanical efficiency of a perfused dogfish heart preparation

SummaryOxygen consumption of an in-pericardium heart preparation from the spiny dogfish (Squalus acanthias) was linearly related to cardiac power output. Basal oxygen consumption, predicted from the regression, was 0.127 μl · s-1 · g ventricle mass-1 and increased by 0.189 μl · s-1 · g ventricle mass-1 per milliwatt of power generated. From the relationship between cardiac power output and mechanical efficiency, mechanical efficiency was predicted to increase with cardiac power output to a maximum of 21 %. Mechanical efficiency was measured during volume loading and pressure loading at two power outputs (50% and 72% of maximum power output). At 50% of maximum power output, mechanical efficiency increased significantly by 2.87%, from 11.9±0.3% to 14.8±0.5% (n=7), when flow was halved and output pressure doubled to achieve the same power output. Similarly, at 72% of maximum power output, mechanical efficiency increased from 14.74±0.92% to 17.61±0.84% (n=6) when flow was halved and output pressure doubled to generate the same higher level of power output. The increased mechanical efficiency at higher output pressures is believed to result from cardiac myocytes working within a length range where they are able to generate the most tension during contraction and are most efficient. We speculate that the loss of mechanical efficiency associated with large changes in sarcomere length, when stroke volume is large, is a driving force behind the use of frequency as the principal means of increasing cardiac output as observed in more active fishes, birds and mammals.

Exhausting exercise in the hagfish, Eptatretus cirrhatus: the anaerobic potential and the appearance of lactic acid in the blood

Abstract 1. 1. Hagfish ( Eptatretus cirrhatus ) were able to sustain 30 min of forced swimming at ca 0.5 body lengths/sec without accumulating lactic acid in their tissues. 2. 2. When forced into extended bouts of burst swimming the muscles produced lactic acid, which entered the blood and caused a marked acidaemia. 3. 3. Enzyme activities in the myotome indicated a limited capacity for both anaerobic glycolysis and aerobic ATP production. 4. 4. There was no evidence for a preferential accumulation of lactic acid in the blood of the subcutaneous sinus rather than the central circulation. 5. 5. The animal can restore its acid-base balance before lactate is metabolised .

Size trends and population characteristics of striped marlin, Tetrapturus audax caught in the New Zealand recreational fishery

Abstract Size trends and population characteristics of striped marlin, Tetrapturus audax, caught in the New Zealand recreational fishery were evaluated using club records from the Bay of Islands Sword‐fish Club (BOISC) from 1925 to 2003 (n = 15 114) and biological samples from northern New Zealand collected from 1985 to 1994 (n = 684). Average weight (kg) ± SE of striped marlin declined 6–9 kg every 20 years between 1925 (124.2 ± 1.0 kg) and 2003 (100.1 kg ± 0.4). Weight (H14843 = 444.58, P < 0.001) and condition (H443 = 37.54, P < 0.001) increased significantly throughout the recreational fishing season (December‐May). No differences were observed in the lower jaw‐fork length (LJFL)‐weight (W) relationship between sexes or years but average weight of females (106.2 ±1.1 kg) was significantly greater than males (90.2 ±1.2 kg) from 1985 to 1994 (F684 = 88.37, P < 0.001). Negative allometric growth (W = 2E ‐08 LJFL2.88) was recorded for all striped marlin. Individual growth was modelled by fitting backcalculated LJFL to eight age classes derived from dorsal spine measurements (n = 94) using the von Bertalanffy growth equation (r2 = 0.96). The parameters estimated in the von Bertalanffy growth equation were asymptotic length (L ) = 3010 mm, annual growth rate (K) = 0.22, age (yr) at hypothetical length 0 (t0) = ‐0.04.

Reproductive biology and spatiotemporal patterns of spawning in striped marlin Kajikia audax

This study presents the first histology-based assessment of the reproductive dynamics of south-west Pacific striped marlin Kajikia audax. Maturity and reproductive status were assessed from histological sections of ovaries (n = 234) and testes (n = 243) of fish caught in commercial longline and recreational fisheries between 2006 and 2009. Spawning peaked in the Coral Sea during November and December at sea surface temperatures between 24.8 and 28.3° C. Lower jaw fork length (L(LJF)) at 50% maturity (L(LJF50)), a key variable for stock assessment, was estimated to be 2100 ± 102 mm (mean + s.e.) for females and 1668 ± 18 mm for males. Unlike large pelagic tunas Thunnus spp., the proportion of females increased with length and spawning fish formed multiple large-scale aggregations within a broad latitudinal band. This study provides a starting point for biological parameters needed for stock assessment and conservation of K. audax and introduces the multiple aggregation spawning concept as a reproductive mechanism to explain genetic heterogeneity observed in some highly migratory species.