Incorporation of probiotic bacteria on larval culture of Macrobrachium amazonicum (Heller, 1862)

In this study, we evaluated the utilization of two probiotics incorporated into the water and in the diet in a larval culture system of Amazon River prawn. Autochthonous probiotic bacteria from the gut of wild juveniles of M. amazonicum juveniles and a commercial probiotic were tested and the following parameters were analyzed: survival, productivity, fresh weight, length, larval condition index (LCI) and larval stage index (LSI). The colonization of the larval gastrointestinal tract by probiotics took place when they were incorporated into diet, while probiotics in the water proved to be unsuccessful. The use of lactic acid bacteria had no significant effects (p>0.05) on survival, productivity, length, fresh weight, LSI and LCI, showing similar results in relation to the control group. However, we recommend the inclusion of probiotics into diet in larval culture of Amazon prawn since this method allowed bacterial gut colonization, which is important to evaluate the resistance to disease in further studies.

The influence of density on survival and larval development in the sea urchin Arbacia dufresnii (Echinodermata: Echinoidea)

Introduction: Density is one of the critical factors in echinoderm larvae for aquaculture purposes. Echinoplutei larvae are very sensitive to overcrowding. High culture density can lead to problems with bacteria or protozoa, decreasing survival and generating abnormal morphotypes. Objective: To evaluate the effect of culture density on survival and larval growth in the sea urchin Arbacia dufresnii. Methods: Two days after fertilization of A. dufresnii we we kept treatments at 1, 3, 5 and 10 larvae.ml-1, with three replicates each. We recorded survival and abnormal morphotypes periodically, as well as growth:somatic rod length, total length, and length of the post oral arms,. we applied generalized linear models. Results: Survival is dependent on density, time and replicates, and their interactions. Larval growth depended on density and time, also with interaction between the variables. The treatment of 5 larvae.ml-1 had the highest survival and larval condition. Conclusions: Larval culture of A. dufresnii had the best results at 5 larvae.ml-1.

Spatially variable larval histories may shape recruitment rates of a temperate reef fish

Several long-standing hypotheses purport variation in recruitment to be positively correlated with pelagic environmental conditions that enhance larval growth, survival, and/or delivery to recruitment sites. However, the relationship between recruitment intensity and larval environmental conditions (or more directly, larval condition) is difficult to evaluate and poorly known for most species. We evaluate this relationship for the reef fish Forsterygion lapillum that commonly inhabits rocky reefs throughout New Zealand. We quantified variation in recruitment of F. lapillum using a nested sampling design, and found that the largest source of variation was between 2 nearby regions (a semi-enclosed harbour and an adjacent open coast system). We estimated 'settler condition' as the composite of residual body mass and 2 measurements of larval growth (reconstructed from otolith microstructure) and found that recruitment intensity was positively correlated with settler condition for sites within the harbour, but negatively correlated with settler condition for sites on the open coast. Mean pelagic larval duration of recruits to the harbour was ̃3 d shorter than recruits to the open coast. These results suggest that larval experience and relationships between recruitment and settler condition are spatially variable. We speculate that (1) larval retention within a productive embayment facilitates a positive relationship between recruitment and settler condition while (2) dispersal through a less productive environment drives a negative relationship for replenishment on the open coast. These putative differences may have important implications for patterns of recruitment, the strength of post-settlement density-dependent interactions, and dynamics of local populations.

Spatially variable larval histories may shape recruitment rates of a temperate reef fish

Several long-standing hypotheses purport variation in recruitment to be positively correlated with pelagic environmental conditions that enhance larval growth, survival, and/or delivery to recruitment sites. However, the relationship between recruitment intensity and larval environmental conditions (or more directly, larval condition) is difficult to evaluate and poorly known for most species. We evaluate this relationship for the reef fish Forsterygion lapillum that commonly inhabits rocky reefs throughout New Zealand. We quantified variation in recruitment of F. lapillum using a nested sampling design, and found that the largest source of variation was between 2 nearby regions (a semi-enclosed harbour and an adjacent open coast system). We estimated 'settler condition' as the composite of residual body mass and 2 measurements of larval growth (reconstructed from otolith microstructure) and found that recruitment intensity was positively correlated with settler condition for sites within the harbour, but negatively correlated with settler condition for sites on the open coast. Mean pelagic larval duration of recruits to the harbour was ̃3 d shorter than recruits to the open coast. These results suggest that larval experience and relationships between recruitment and settler condition are spatially variable. We speculate that (1) larval retention within a productive embayment facilitates a positive relationship between recruitment and settler condition while (2) dispersal through a less productive environment drives a negative relationship for replenishment on the open coast. These putative differences may have important implications for patterns of recruitment, the strength of post-settlement density-dependent interactions, and dynamics of local populations.

Impacts of temperature and food availability on the condition of larval Arctic cod (Boreogadus saida) and walleye pollock (Gadus chalcogrammus)

The Arctic marine environment is rapidly changing with rising sea surface temperatures, declining sea ice habitat and projected increases in boreal species invasions. The success of resident Arctic fish will depend on both their thermal tolerance and their ability to cope with changing trophic interactions. Larval fish energetic condition is closely associated with mortality rates and therefore provides an indicator of overall well-being or fitness. In this study, we experimentally determined larval morphometric and lipid-based condition in an Arctic gadid (Arctic cod, Boreogadus saida) and a boreal gadid (walleye pollock, Gadus chalcogrammus) in response to different temperatures and food rations. Our results suggest that larval condition is highly sensitive to both factors but varies in a species- and ontogenetic-dependent manner. Results indicated that condition metrics based on length–weight relationships were not as sensitive as those based on lipid storage. Further, condition metrics changed with ontogeny and were best used within a developmental stage rather than across developmental stages. As expected, larval condition in first-feeding Arctic cod was higher at colder temperatures (2–5°C) than in the boreal gadid (5–12°C). However, at more developed larval stages the peak condition for Arctic cod was at warmer temperatures (7°C), while walleye pollock had the same thermal optimum as during earlier stages. Arctic cod were more sensitive to food ration at first feeding than walleye pollock, however; at later larval stages both species had a negative condition response to low food ration, especially at elevated temperatures (5 vs. 7°C). The lower thermal tolerance of Arctic cod, coupled with a higher sensitivity to food availability indicates that Arctic cod are particularly vulnerable to on-going environmental change. Arctic cod is a lipid-rich keystone species and therefore a reduction in their energetic condition during summer has the potential to affect the health of higher trophic levels throughout the Alaskan Arctic.

Combined effects of elevated pCO2, temperature, and starvation stress on larvae of a large tropical marine fish

Ocean acidification and other environmental changes pose an ecological challenge to marine organisms globally. Although the youngest life stages of these organism are likely to be most affected, a limited number of studies of larval fishes have investigated the effects of combined stressors. We conducted two experiments on larval cobia (Rachycentron canadum) raised under combinations of elevated pCO2 and increased temperature or starvation stress. Larvae responded to individual CO2, temperature, and rationing treatments, and there was a negative effect of elevated pCO2 on starvation resistance, but few synergistic effects of combined stressors. Elevated pCO2 (1700–2100 μatm pCO2) caused a transient but significant reduction in larval standard length (SL), growth rate, and development rate, while warmer temperature (32 vs. 27 °C) caused a consistent increase in SL, development rate, and swimming ability. Larval condition (RNA:DNA ratio) was unaffected by elevated pCO2 although larvae fed a 25% ration had significantly reduced SL, growth rate, and development rate. Under complete feeding cessation, larvae in elevated-pCO2 seawater demonstrated lower starvation resistance, indicating that acidification may increase starvation risk in a patchy marine environment. Overall, our results indicate that larval cobia are resistant to any major direct impact of combined elevated pCO2 and temperature or rationing stress.