No abstract

A study was undertaken to measure the effects of conspecific density on the growth, mortality and deformity rate of yellowtail kingfish Seriola lalandi Valenciennes during the first feeding period. Newly hatched larvae were stocked in replicate tanks at initial densities of 40, 60 and 100 ind. l -1 until 30 d post-hatch (DPH). Live prey was administered at frequent intervals in an effort to maintain absolute prey density for all treatments. There was a negative relationship between conspecific density and mean individual length during the first half of the trial, which was attributed to food depletion between supplementary feedings at higher conspecific densities. The effect size (partial eta-squared) of conspecific density decreased considerably during the trial, to the point where the initial stocking density had no discernible effect on cohort growth or mortality rate. The apparent morphological deformity rate ranged from 17 to 32%, but did not differ between treatments. Jaw malformations were the most commonly observed deformity (12 to 30%). The weights of juveniles at the end of the trial were log-normally distributed, with some disproportionately large individuals skewing the weight distributions. There was substantial variation in mortality between and within treatments (74 to 97%), and the conspecific densities of each replicate at 30 DPH did not reflect the relative ordering of the initial treatments. Median individual weight was highly correlated with mortality and weight variance, and the positive skewness of populations decreased as mortality increased. Both trends indicated a strong population size-structuring mechanism. Given the controlled experimental conditions the size-structuring mechanism was not predation or cannibalism. Differential feeding success and an unidentified size-specific mortality agent are hypothesized to be the mechanisms by which mortality was able to strongly influence population size distributions. KEY WORDS: Cohort size distribution · Deformity rate · Growth variation · Juvenile mortalityResale or republication not permitted without written consent of the publisher Aquat Biol 11: 229-238, 2011 tail kingfish (Ebisu & Tachihara 1993, Chen et al. 2006, Moran 2007. Conspecific density is an important factor in moderating growth and survival, because it affects the intensity of competition for food and shelter and also the degree of aggression and cannibalism (Smith & Reay 1991, Hecht et al. 1996, Kotani et al. 2009). This is true both in the wild (Folkvord et al. 1994, Sakakura & Tsukamoto 1996, Smith & Fuiman 2003 and under the high-density conditions associated with aquaculture (Hecht & Pienaar 1993). The current study evaluated the effects of conspecific density on the mortality, growth and size distribution of yellowtail kingfish during the first feeding period.As is common for many marine fish species, considerable size heterogeneity develops during the first feeding phase in juvenile yellowtail kingfish, even in cohorts where the genetic parentage, age and la...