Patricia M. Pankhurst

Structure and function of the vertebrate magnetic sense

Some vertebrates can navigate over long distances using the Earths magnetic field, but the sensory system that they use to do so has remained a mystery. Here we describe the key components of a magnetic sense underpinning this navigational ability in a single species, the rainbow trout ( Oncorhynchus mykiss). We report behavioural and electrophysiological responses to magnetic fields and identify an area in the nose of the trout where candidate magnetoreceptor cells are located. We have tracked the sensory pathway from these newly identified candidate magnetoreceptor cells to the brain and associated the system with a learned response to magnetic fields.

High prevalence of skeletal deformity and reduced gill surface area in triploid Atlantic salmon (Salmo salar L.)

Abstract The prevalence of skeletal deformity throughout the development of different populations (all-female triploid, mixed-sex triploid, all-female diploid and mixed-sex diploid) of Tasmanian Atlantic salmon (Salmo salar L.) was determined to elucidate the possible effects of ploidy or sex status on the incidence of deformity. Populations were produced and maintained under commercial conditions in freshwater until individuals had attained a wet weight of approximately 80 g, at which time each population was divided and either retained in freshwater (FW smolt) or transferred to seawater (SW smolt), where fish were held for a further 2 months. Whole fish were sampled throughout this period from hatching (470° days post-fertilisation). The prevalence of skeletal deformities was significantly higher in triploid populations. Jaw deformity, including lower jaw deformity syndrome (LJD), occurred in up to 2% of triploid fry, 7% of triploid FW smolt, 14% of triploid SW smolt and 1% of diploid FW smolt. The prevalence of LJD was highest in triploid FW smolt. Short opercula were observed in up to 22% of triploids and 16.6% of diploids. Up to 60% of triploids and 4% of diploids suffered from the absence of primary gill filaments (gill filament deformity syndrome (GFD)) during FW development prior to SW transfer, then, up to 50% of triploid FW smolt and 60% of triploid SW smolt suffered from GFD. There was no significant difference in the sex ratio of each deformity type. An index of gill surface area (GSA) was significantly reduced in normal triploids and triploids afflicted with GFD, compared to diploid counterparts. It is likely that the reduction of GSA affects an individuals capacity for metabolic gas exchange under vigorous exercise or suboptimal environmental conditions.

Effect of photoperiod on growth and survival of snapper Pagrus auratus larvae

Abstract Experiments were done in 100-l recirculation tanks to determine the effects of photoperiod on (1) first-feeding and (2) post-swimbladder inflated snapper, Pagrus auratus, larvae. In Experiment 1, feeding onset, growth, initial swimbladder inflation, and tail flexion were assessed at five photoperiod treatments (0L:24D, 6L:18D, 12L:12D, 18L:6D, and 24L:0D) in larvae from 3 to 15 days after hatching (dah). Growth and development of first-feeding larvae increased with increasing photoperiod duration in the 12L:12D to 24L:0D treatments. Larvae did not start feeding in 0L:24D and onset of feeding was delayed by up to 3 days in 6L:18D. All larvae held in 0L:24D and 6L:18D died within 6 or 9 dah, respectively. Initial swimbladder inflation was best (80–100%) in an intermediate photoperiod of 12L:12D at 9 dah. By 15 dah, although the percentage of larvae with inflated swimbladders had increased in all treatments, swimbladder inflation in 12L:12D was 1.3 and 2.0 times greater than that of larvae in 18L:6D and 24L:0D, respectively. In the second experiment, growth and survival of snapper after the initial swimbladder inflation period (11–32 dah) were assessed at three photoperiod treatments (12L:12D, 18L:6D, and 24L:0D). Growth was greatest in 18L:6D in which wet weights (16.3±0.5 mg; mean±S.E.) and dry weights (2.8±0.1 mg; mean±S.E.) of larvae were approximately 1.3 and 1.9 times heavier than the larvae held in 24L:0D and 12L:12D, respectively. Survival of snapper larvae to 32 dah was not significantly different between the three photoperiod treatments, but power of the experiment to detect effects on survival was small due to large variability within treatments. Further research is needed to determine optimal photoperiods for the survival of the snapper larvae. Because of the potential for large larval mortality, if initial swimbladder inflation is not achieved, the optimal photoperiod for the period from feeding onset to swimbladder inflation (3–15 dah) was deemed to be 12L:12D, whereas on the basis of growth parameters that were measured (total length, wet and dry weights), 18L:6D was determined to be the optimal photoperiod for the culture of snapper from the post-swimbladder window to metamorphosis (11–32 dah).

Jaw development and malformation in cultured striped trumpeter Latris lineata

Intensive culture of striped trumpeter (Latris lineata) has resulted in a high incidence of jaw malformation in juveniles. In this study, cranial and jaw development in striped trumpeter was described in cultured larvae reared in greenwater on rotifers and Artemia. Jaw malformation was only evident in post-flexion larvae greater than the standard length of 10 mm and was characterised by an open jaw in which the maxilla and premaxilla were aligned dorso-ventrally, and the anterior hyoid arch elements were in an abnormal ventral position. X-radiography of the heads of juvenile and adult cultured striped trumpeter revealed ventro-lateral distortion of the jaw elements in comparison with wild-caught fish. The possible role of physical environmental factors and nutrition during culture are discussed in relation to jaw malformation in this and other species.

Effects of photoperiod and light intensity on initial swim bladder inflation, growth and post-inflation viability in cultured striped trumpeter (Latris lineata) larvae

Transient physostomes often fail to complete initial swim bladder inflation in culture and display reduced survival and growth. Three experiments were conducted in replicate 200-l tanks to determine the effects of photoperiod and light intensity on initial swim bladder inflation, postinflation viability (surviving larvae with inflated swim bladders) and growth in striped trumpeter (Latris lineata) larvae. Both photoperiod and light intensity were found to affect initial swim bladder inflation, growth, survival and post-inflation viability of striped trumpeter larvae. Higher initial swim bladder inflation was promoted by providing a dark-phase before and during initial swim bladder inflation. Swim-up behaviour where larvae gulped air at the water surface to fill their swim bladder was predominantly observed during the dark-phase. In Experiment 1, a 12L:12D photoperiod was inferior to either a 18L:6D or 24L:0D photoperiod for larval growth. In Experiment 2, initial swim bladder inflation was higher in larvae reared under a light intensity of 4 Amol s 1 m 2 compared to 40 Amol s 1 m 2. From Experiment 3, a 18L:6D photoperiod provided higher post-inflation viability than either 24L:0D, or a photoperiod combination of 24L:0D from stocking, changing to 21L:3D at the onset of initial swim bladder inflation. However, different optimal photoperiods for initial swim bladder inflation (18L:6D) and survival (24L:0D) lowered post-inflation viability in

Blood oxygen transport, rheology and haematological responses to confinement stress in diploid and triploid Atlantic salmon, Salmo salar.

Abstract Diploid and triploid all-female Atlantic salmon (Salmo salar) smolts were challenged with 2.5 h of confinement stress in aerated seawater. Subsequent stress responses were quantified by plasma cortisol, glucose, and lactate, and by the haematological parameters haematocrit (Hct), red blood cell count (RBCC), mean cell volume (MCV), blood haemoglobin concentration (Hb), mean cell haemoglobin (MCH), mean cell haemoglobin concentration (MCHC), total protein and erythrocyte adenosine triphosphate (ATP). The magnitude of stress responses was similar between diploid and triploid smolts. Triploid smolts displayed a higher MCH, but lower Hb than diploid smolts. The blood oxygen affinity of diploid and triploid fish was similar at 15°C over the pH range 6.76–7.99 and the isohaemoglobin components were identical. The enlarged triploid erythrocytes showed reduced shear-dependence on blood viscosity at constant Hct and are therefore unlikely to contribute to greater peripheral vascular resistance. The results show that despite having fewer, larger erythrocytes, triploids have very similar oxygen carrying capacity and haematological response to stress as diploids. This suggests that the higher farm mortality reported for triploids in response to stress is not generated by their failure to show respiratory homeostasis in the face of stress.

Swim bladder malformation in hatchery-reared striped trumpeter Latris lineata (Latridae)

Abstract Swim bladder malformation is common in both larvae and later life stages of cultured striped trumpeter Latris lineata. This study used histology and gross morphology of whole larvae to describe the progression of abnormal development that proceeded initial liquid dilation of the primordial swim bladder. In addition, radiography was used to compare swim bladder morphology of cultured juveniles with wild-caught specimens. The histomorphology of the swim bladder prior to lumenal dilation was typical of transient physostome larvae reported in the literature. A distinct swim bladder lumen present in larvae between 5.2–5.7 mm standard length (SL) was assumed to be liquid dilated and coincided with mouth opening. Initial gaseous inflation was first apparent when larvae attained 5.7–6.2 mm SL, after the resorption of the yolk sac and oil globule and the onset of first feeding (

Feeding behaviour of greenback flounder larvae, Rhombosolea tapirina (Günther) with differing exposure histories to live prey

Abstract This study examined the feeding performance of cultured larvae of the greenback flounder Rhombosolea tapirina , using the live feed organisms, Brachionus plicatilis and Artemia sp., to determine the primary sensory modality involved in feeding, and the effect of previous exposure to prey on subsequent prey selection. The proportion of larvae that fed on rotifers in the light (400–700 nm daylight fluorescent tubes — light intensity of 5–6 μmol s −1 m −2 ), increased significantly from 66% to 96% from day 12 to day 27 post-hatching, respectively. In comparison, the proportion of larvae that fed on rotifers in total darkness, never exceeded 5% during the same period. This indicates that greenback flounder larvae are primarily dependent upon vision to feed. Prior feeding experience of greenback flounder larvae with either rotifers only (R-treatment) or a mixed diet of Artemia and rotifers (A&R-treatment) significantly affected subsequent prey selection when larvae were offered a mixed diet of Artemia and rotifers. It did not, however, affect the temporal onset of selection of the novel prey species ( Artemia ) by R-treatment larvae. Therefore, the differences in prey selection by larvae, with or without prior exposure to Artemia prey, were not due to the inability of larvae to handle and ingest a novel prey species, but they reflect positive selection for familiar prey. The latter indicates a learned component in the feeding behaviour of fish larvae. This has implications for the timing of the introduction of new live prey species during intensive culture of marine fish larvae.

Jaw malformation in cultured yellowtail kingfish (Seriola lalandi) larvae

Abstract Several jaw malformations are common in cultured finfish larvae. Hatchery‐reared yellowtail kingfish (Seriola lalandi) larvae were cleared and stained to examine cartilage and bone structure of the jaw. One malformation, characterised by a lowered hyoid arch, was present in kingfish larvae on days 4 and 8 post‐hatching, but not on day 12. A different malformation was present in larvae on day 16, typified by abnormal positioning of the lower jaw and hyoid arch, and breakage of the Meckel’ s cartilage. Evidence of jaw malformations as early as day 4 suggests that broodstock nutrition may be a factor in the jaw malformation of kingfish larvae, but other potential causes are environmental factors in culture and larval nutrition.

Effects of temperature on initial swim bladder inflation and related development in cultured striped trumpeter (Latris lineata) larvae

Abstract Many physoclist fish have physostomous larvae, initially inflating the swim bladder by ingesting air at the water surface during a brief, finite period. Failed initial swim bladder inflation has been predominantly linked to abiotic factors and larvae which fail to complete initial swim bladder inflation exhibit reduced survival and growth. This study investigates the effects of temperature on initial swim bladder inflation, survival and post-inflation viability (surviving larvae with inflated swim bladders) in striped trumpeter ( Latris lineata ) larvae. Growth, developmental stages and stage-specific larval size are examined in relation to initial swim bladder inflation. Larvae were reared at 12, 14, 16 or 18 °C (Experiment 1) or at 15, 17, 19 or 21 °C (Experiment 2) from day 1 posthatching in replicated 200-l tanks. Initial swim bladder inflation was significantly affected by temperature, with highest initial swim bladder inflation at 14 °C (67.8±5.9% S.E., n =3) to 16 °C (71.1±4.8%) and 15 °C (72.2±1.1%) to 17 °C (76.6±12.0%) in Experiments 1 and 2, respectively. Survival was also significantly influenced by temperature, with the highest survival at 16 °C (31.2±4.9%) to 18 °C (30.6±4.0%) in Experiment 1, and 17 °C (12.4±2.4%) to 19 °C (9.6±2.8%) in Experiment 2. In both experiments, the highest post-inflation viability occurred through a combination of maximum initial swim bladder inflation and survival, at 16 °C (21.3±2.1%) and 17 °C (9.5±1.8%) in Experiments 1 and 2, respectively. Reduced post-inflation viability at 18 and 19 °C was due to decreased initial swim bladder inflation, not survival. The reverse trend was apparent at lower temperatures where survival was significantly lower at 14 and 15 °C, but initial swim bladder inflation remained high. Overlapping optimal temperature ranges for survival and swim bladder inflation narrowed the thermal optima for post-inflation viability to 16–17 °C. Mean size of larvae at initial swim bladder inflation decreased at higher temperatures. Larger larval size at initial swim bladder inflation was positively correlated to increased initial swim bladder inflation at termination in both Experiment 1 ( r =0.780) and Experiment 2 ( r =0.866). It is suggested that this relationship is a key mode of influence of temperature on initial swim bladder inflation.