We developed histological methods to increase precision in measuring oocyte size and, for the first time, quantify changes in oocyte composition during ovarian development in penaeids. Wild-caught female Metapenaeus dalliRacek, 1957 from the Swan-Canning Estuary, Perth, Western Australia were used as a model species to compare the novel method to traditional techniques. Morphological analysis showed that ovarian development in M. dalli occurs in five stages: immature, early maturing, late maturing, mature, and post spawning, which is consistent with other penaeids. Analysis of key morphometric parameters of length and Gonad Somatic Index (GSI) showed that GSI provided the strongest discriminators of ovarian development. Oogenesis was similar to qualitative descriptions of other penaeid prawns and most-closely related to previous descriptions of Metapenaeus affinis Milne Edwards, 1837. Comparisons between the novel perimeter tracing and traditional single linear methods for measuring oocyte dimensions showed that greater precision was achieved by tracing. This resulted in a 17-40% reduction in the confidence limits of the means for all cell types measured. A novel histological technique of examining oocyte composition was also developed. This technique allowed for the relationship between stages of ovarian development and proportion by volume of oocyte types to be determined. The difference in the proportions of cell types between each stage of ovarian development was found to be statistically significant, except between immature and post spawning females. The novel methods developed in this study provide new opportunities in the study of ovarian development in penaeids and possibly in other species.

The effects of temperature and salinity on the survival and development of larval Metapenaeus dalli were investigated in two experiments. First, the effects of four temperatures of 22.6, 25.8, 29.4 and 32.6°C on survival and development time were examined from the Nauplius VI to the Mysis I sub-stage. Survival was significantly lower at 32.6°C than at 22.6 and 25.8°C. Development times differed significantly across all temperatures, decreasing linearly with temperature from 161.5 h at 22.6°C to 74.8 h at 29.4°C then decreased slightly to 71.4 h at 32.6°C. Second, the combined effects of three temperatures (21.4, 26.5 and 29.7°C) and three salinities (30, 35 and 40%) on survival and development were quantified over a 48 h period from the Nauplius VI sub-stage. Only salinity was found to influence survival, with peak survival (77.7%) found to occur at the control salinity (*35%). Any increase or decrease in salinity from this value resulted in a decrease in survival, with the lowest salinity tested (30%) having a significantly negative effect on survival (58.4%) when compared to the control. Only temperature was found to influence the rate of development, with significant increases in development index values being recorded as temperature increased. The recommended conditions for optimal survival and development of M. dalli larvae as determined by this study are, therefore, 25.8°C and 35%.

This study determined environmental factors influencing the reproductive dynamics of a recreationally fished penaeid Metapenaeus dalli Racek in the Swan–Canning Estuary, south‐western Australia, during a restocking programme. Prawns were collected from nearshore (<2 m deep) and offshore waters (>2 m deep) every lunar month from October 2013 to March 2016. Reproduction occurred between November and March, when water temperature was >17°C, salinity >25 and stratification (bottom–surface salinity) <3. Densities of gravid M. dalli were highest in November of each year when 0+ females matured (19 mm; ~56% asymptotic length) and were highest in the Lower Canning Estuary. Individual fecundity ranged from 34,000 (18.1 mm carapace length [CL]) to 132,000 ova (27.1 mm CL). Egg production peaked in December/January and differed among years, being greatest in 2015/2016. These results suggest that closing fishing between November and December would protect breeding aggregations of M. dalli in inshore waters.

The six Naupliar, three Protozoea, three Mysis and first post-larval forms of the western school prawnMetapenaeus dalli Racek, 1957 were cultured in the laboratory. These stages were described in detail and compared to those of other metapenaeids. The ontogenetic development occurred in 12 days at 26°C, with both the growth rate and morphological patterns of development in M. dalli broadly following those recorded for other metapenaeids. Differences were found between M. dalli and other metapenaeids at corresponding stages of larval development, with these being the number, location and composition of individual setae and other minor spinal development.