David T. Morehead

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.

Influences of dietary n-3 long-chain PUFA on body concentrations of 20 : 5n-3, 22 : 5n-3, and 22 : 6n-3 in the larvae of a marine teleost fish from Australian waters, the striped trumpeter (Latris lineata)

We determined the effect of dietary long-chain (≥C20) PUFA (LC-PUFA), 20∶5n−3 and 22∶6n−3, on larval striped trumpeter (Latris lineata) biochemistry through early development and during live feeding with rotifers (Brachionus plicatilis). Rotifers were enriched using seven experimental emulsions formulated with increasing concentrations of n−3 LC-PUFA, mainly 20∶5n−3 and 22∶6n−3. Enriched rotifer n−3 LC-PUFA concentrations ranged from 10–30 mg/g dry matter. Enriched rotifers were fed to striped trumpeter larvae from 5 to 18 d post-hatch (dph) in a short-term experiment to minimize gross deficiency symptoms such as poor survival that could confound results. No relationships were observed between larval growth or survival with dietary n−3 LC-PUFA at 18 dph. The larval FA profiles generally reflected those of the rotifer diet, and significant positive regressions were observed between most dietary and larval FA at 10, 14, and 18 dph. The major exception observed was an inverse relationship between dietary and larval 22∶5n−3. The presence of 22∶5n−3 in elevated amounts when dietary 22∶5n−3. The presence of 22∶5n−3 in elevated amounts when dietary 22∶6n−3 was depressed suggests that elongation of 20∶5n−3 may be occurring in an attempt to raise body concentrations of 22∶6n−3. We hypothesize that accumulation of 22∶5n−3 might be an early indicator of 22∶6n−3 deficiency in larval fish that precedes a reduction in growth or survival. A possible role of 22∶5n−3 as a biochemical surrogate for 22∶6n−3 is discussed.