Velmurugu Puvanendran

Foraging, growth and survival of Atlantic cod larvae reared in different light intensities and photoperiods

Abstract Studies have shown that most marine fish larvae are visual feeders and their feeding incidence increases with light intensity. Although laboratory studies on photoperiod showed variable results, evidence from the field suggest that larvae exposed to a continuous light may grow better than larvae exposed to reduced photoperiods. We set up experiments to investigate the foraging, growth and survival of Atlantic cod larvae ( Gadus morhua ; Grand Banks origin) at different light intensities and photoperiods. Behavioural observations were also carried out in an attempt to explain any differences in the performance of cod larvae under varying light intensities. Larval cod were reared at four light intensities (300, 600, 1200 and 2400 lx or 4.93, 10.96, 19.89 and 37.32 μE m −2 , respectively) and three photoperiods (24 L:0 D, 18 L:06 D and 12 L:12 D) from hatching to metamorphosis (42 days post-hatch; dph). Cod larvae grew and survived better in higher light intensity (2400 lx) and 24 L:0 D photoperiod. Examination of the foraging indicated that cod larvae reared in higher light intensity captured prey more efficiently than larvae reared in low light. Results also showed that the mortality rates of larval cod from 2400 lx and 24 h photoperiod were significantly lower than the larvae from other light intensity and photoperiod treatments until 28 dph. This indicates that photoperiod and light levels could be reduced beyond 28 dph.

Genetic variation in life-history reaction norms in a marine fish.

Neither the scale of adaptive variation nor the genetic basis for differential population responses to the environment is known for broadcast-spawning marine fishes. Using a common-garden experimental protocol, we document how larval growth, survival and their norms of reaction differ genetically among four populations of Atlantic cod (Gadus morhua). These traits, and their plastic responses to food and temperature, differed across spatial scales at which microsatellite DNA failed to detect population structure. Divergent survival reaction norms indicate that warm-water populations are more sensitive to changes in food, whereas cold-water populations are more sensitive to changes in temperature. Our results suggest that neither the direction nor the magnitude of demographic responses to environmental change need be the same among populations. Adaptive phenotypic plasticity, previously undocumented in marine fishes, can significantly influence the probability of recovery and persistence of collapsed populations by affecting their ability to respond to natural and anthropogenic environmental change.

Larviculture of Atlantic cod (Gadus morhua): progress, protocols and problems

Interest in the intensive culture of Atlantic cod has increased dramatically due to a reduced supply from the wild fishery, high market price and relative suitability of cod for culture. In spite of its many positive attributes for domestication, intensive culture has only been successful during the past 6 years. Large commercial efforts are currently underway in Norway, Scotland, Newfoundland, Canada and New Hampshire, USA. Cod are a geographically widespread species and because of this certain population differences in response to environmental factors, such as light and prey density exist. These differences must be taken into account when developing protocols for commercial production. Research in Newfoundland has focussed on determining optimal prey densities and light levels to use during larviculture. Using a prey density of 4000 prey/l and light intensities above 2000 lx, survival rates of over 40% from start-feeding to metamorphosis have been achieved. A comparison of production protocols used in Newfoundland to efforts in Norway is discussed.

Foraging, growth and survival of Atlantic cod larvae reared in different prey concentrations

Abstract Laboratory studies have shown that suboptimal prey concentrations during the first feeding usually result in slower growth and higher mortality. We investigated the growth, survival and foraging behaviour of Atlantic cod (Gadus morhua) larvae in different prey concentrations under laboratory conditions. Larvae were reared from hatching to metamorphosis (6 weeks post-hatch) on rotifers and/or Artemia nauplii at 250, 500, 1000, 2000, 4000, 8000 and 16,000 prey l−1. Once a week, standard length and myotome height were recorded and mortalities were monitored from day 15. Observations on feeding behaviour were recorded twice a week. Larvae reared at 4000–16,000 prey l−1 were significantly larger and had significantly higher condition indices than larvae from lower prey concentration (≤2000). Initially, specific growth rates (SGR) were significantly higher in larvae reared at higher prey concentrations (≥4000), but from 3 weeks post-hatch, no difference was found among treatments in SGR. Instantaneous mortality rates (Z) decreased in all treatments as the larvae grew. Survival was significantly lower for larvae reared at lower prey concentrations until week 3. Larvae reared at 250 and 500 prey l−1 did not survive beyond days 11 and 24, respectively. Survival of larvae was significantly higher at higher prey concentrations at weeks 2 and 6 post-hatch. Although survival of cod larvae at week 2 was similar among the three highest prey concentrations; survival at the end of the experiment (week 6) was higher, but not significantly, in the 4000 prey l−1 treatment than the other two treatments (8000 and 16,000 prey l−1). Swimming duration was significantly higher among larvae reared at lower prey concentrations. Larvae reared at higher prey concentrations (≥4000) showed higher orientation and captured success rates but lower attack rates than larvae reared at lower prey concentrations. Our results indicate that for intensive rearing of cod larvae, higher prey concentrations are required to sustain reasonable growth and survival than that have been reported for mesocosm studies.

Ocean Acidification Effects on Atlantic Cod Larval Survival and Recruitment to the Fished Population

How fisheries will be impacted by climate change is far from understood. While some fish populations may be able to escape global warming via range shifts, they cannot escape ocean acidification (OA), an inevitable consequence of the dissolution of anthropogenic carbon dioxide (CO2) emissions in marine waters. How ocean acidification affects population dynamics of commercially important fish species is critical for adapting management practices of exploited fish populations. Ocean acidification has been shown to impair fish larvae’s sensory abilities, affect the morphology of otoliths, cause tissue damage and cause behavioural changes. Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks.

Food ration requirements of 0+ yellowtail flounder Limanda ferruginea (Storer) juveniles

Abstract Several studies have shown that food ration can affect the growth of cultured fish. Determining the optimal food ration would help to achieve better growth and also provide direct economic benefits due to reduced food wastage, which would lead to commercial success. Therefore, we studied the effects of ration levels on growth performance of 0 + juvenile yellowtail flounder to determine the optimal food ration. Two experiments were conducted; the first experiment as a preliminary using ration levels of 1%, 2%, 4%, 6% body weight per day (% bw day −1 ) held at 7.0 °C with a stocking density of 0.95 kg m −2 (∼45% bottom coverage). Results of this preliminary experiment indicated that fish fed with 1% bw day −1 had significantly lower growth (weight, length, body depth and specific growth rates (SGR)) than those fed with 2%, 4% and 6% ration. However, fish fed with rations of 1% and 2% showed significantly lower gross food conversion ratios (GFCR) than fish fed with 4% and 6% rations. Survival was not significantly affected by different ration levels. Based on these preliminary results, we used ration levels of 1%, 1.5%, 2% and 3% for the main experiment. Fish were held at 10 °C with a stocking density of 1.45 kg m −2 (∼34% bottom coverage). Results indicated that fish fed with 1%, 1.5% and 2% bw day −1 had significantly lower growth than fish fed with 3% bw day −1 . GFCR was significantly different for all four rations. It was lower for 1% than 1.5%, 2% and 3% rations. Survival was not significantly different between any treatments. We discuss our results with emphasis on growth and economics (i.e., feed wastage) and stress the need to balance both components in a commercial operation.

Material properties of North Atlantic cod eggs and early-stage larvae and their influence on acoustic scattering

Chu, D., Wiebe, P. H., Copley, N. J., Lawson, G. L., and Puvanendran, V. 2003. Material properties of North Atlantic cod eggs and early-stage larvae and their influence on acoustic scattering. – ICES Journal of Marine Science, 60: 508–515. To study the acoustic signatures of Atlantic cod (Gadus morhua) at different biological stages from eggs to early-stage larvae (<37 days post-hatch), we conducted a series of experiments to estimate their sound-speed and density contrasts. A laboratory version of the ‘‘Acoustic Properties of Zooplankton’’ system was used. Sound speed was estimated by means of travel time between two transducers using a broadband-acoustic signal (� 300– 600 kHz). Density was estimated using a dual-density method in which two fluids of different densities were employed. It was found that the density contrasts of cod eggs and early-stage larvae were nearly all slightly less than unity (0.969–0.998), while the effective sound-speed contrasts were only slightly greater than unity (1.017–1.024) for eggs and yolk-sac stage larvae (<5 days post-hatch), and increased significantly ([1.130) for larvae older than 16 days. This change in sound-speed contrast reflected the transition of the swimbladder from an uninflated state to an inflated state. The regression relation between estimated target strength at 500 kHz and larval length in centimetres was found to be TS ¼ 176:1 log10L � 82:4 ðdBÞ. The inflation ratio of the swimbladder for early-stage larvae was an exponential function of time. The predicted period of time until full swimbladder inflation was 43.3 days.

Atlantic Cod Show a Highly Variable Sensitivity to Electric-Induced Spinal Injuries

Abstract Pulse trawling is the most promising alternative to conventional beam trawls targeting Sole Solea solea (also known as Solea vulgaris), but due to the electric fields created by electrotrawls spinal injuries are reported in gadoid round fishes such as Atlantic Cod Gadus morhua. This study aimed to investigate the variability in the occurrence of electric-induced spinal injuries in cod. Four groups of cod, each originating from a different wild or farmed stock, were exposed to the pulses used by electrotrawls targeting Sole. Effects were analyzed based on behavior, mortality, and lesions up to 14 d after exposure, and morphological characteristics such as size, somatic weight, muscularity, the number of vertebral bodies, and the vertebral mineral contents of animals were compared among different cohorts. Second, the influence of factors such as water temperature, electrode diameter, and pulse type and amplitude were tested. Electrode diameter and pulse amplitude showed a positive correlation with the intensity of the fishs reaction. However, the present experiments confirmed that cod also show variable vulnerability, with injury rates ranging from 0% to 70% after (almost) identical exposures near the electrode. This indicates that these injuries are not only determined by the pulse parameter settings but also by subtle, fish-specific factors. Although the absence of a sensitive group of cod did not enable the elucidation of the conclusive factor, the effect of physiological and morphological factors such as intervertebral ligaments and rearing conditions during early life merit further attention in future research.

Impact of Pulsed Direct Current on Embryos, Larvae, and Young Juveniles of Atlantic Cod and its Implications for Electrotrawling of Brown Shrimp

AbstractThe application of electrical pulses in fishing gear is considered a promising option to increase the sustainability of demersal trawl fisheries. In the electrotrawl fishery for brown shrimp Crangon crangon, an electrical field selectively induces a startle response in the shrimp. Other benthic organisms remain mainly on the seafloor and escape underneath a hovering trawl. Previous experiments have indicated that this pulse has no short-term major harmful effects on adult fish and invertebrates. However, the impact on young marine life stages is still unknown. Because brown shrimp are caught in shallow coastal zones and estuaries, which serve as important nurseries or spawning areas for a wide range of marine species, electrotrawling on these grounds could harm embryos, larvae, and juveniles. We carried out experiments with different developmental stages of Atlantic Cod Gadus morhua, which are considered vulnerable to electrical pulses. Three embryonic stages, four larval stages, and one juvenile ...

Effects of parental acclimation and energy limitation in response to high CO2 exposure in Atlantic cod

Ocean acidification (OA), the dissolution of excess anthropogenic carbon dioxide in ocean waters, is a potential stressor to many marine fish species. Whether species have the potential to acclimate and adapt to changes in the seawater carbonate chemistry is still largely unanswered. Simulation experiments across several generations are challenging for large commercially exploited species because of their long generation times. For Atlantic cod (Gadus morhua), we present first data on the effects of parental acclimation to elevated aquatic CO2 on larval survival, a fundamental parameter determining population recruitment. The parental generation in this study was exposed to either ambient or elevated aquatic CO2 levels simulating end-of-century OA levels (~1100 µatm CO2) for six weeks prior to spawning. Upon fully reciprocal exposure of the F1 generation, we quantified larval survival, combined with two larval feeding regimes in order to investigate the potential effect of energy limitation. We found a significant reduction in larval survival at elevated CO2 that was partly compensated by parental acclimation to the same CO2 exposure. Such compensation was only observed in the treatment with high food availability. This complex 3-way interaction indicates that surplus metabolic resources need to be available to allow a transgenerational alleviation response to ocean acidification.