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This study was carried out to determine the effects of abrupt salinity change on osmoregulatory ability of the spottedtail goby Synechogobius ommaturus. 720 juvenile fish (65.3 ± 11.8 g) were transferred to 200 L tanks (with 40 juveniles in each tank), in which salinities were abruptly changed from 10 to 20, 30, 40, 50 and freshwater. Survival rate, serum osmolality, electrolytes (Na+, Cl−, and K+) and gill Na+/K+-ATPase (NKA) activity were assessed successively in 528 h. Results showed serum osmolality, ion concentrations and gill Na+/K+-ATPase activity increased significantly when fish were transferred to salinity 40 and 50 and all fish in these groups died by the end of the experiment. Serum osmolality, Na+, Cl− and K+ in fish transferred to a salinity of 20, 30 and freshwater were not affected and no mortality was detected. Compared with the control group, a significantly decrease of NKA activity happened in the freshwater group, but the activity in 20 and 30 groups was not affected significantly. The results indicated that S. ommaturus could adapt rapidly and maintain homeostasis in a wide range of salinities (from freshwater to salinity 30) and this species may be suitable for aquaculture in estuarine and coastal areas where rapid salinity fluctuations commonly occur. Keywords: Osmolality, Gill, Na+/K+-ATPase, Synechogobius ommaturus

Acute and chronic experiments were conducted to evaluate the effect of salinity on survival and growth of the juvenile Dark Sleeper Odontobutis potamophila. For the acute experiment, half-lethal concentrations (LC50) of salinity for the juvenile Dark Sleeper after exposures for 12, 24, 48, 72 and 96 h were determined. Mean survival time (MST) and half-survival time (ST50) at salinity of 32‰ were also recorded. For the chronic experiment, a 22-day trial focused on comparing the effects of different salinity levels (0, 2, 4, 6, 8, and 10‰) on survival rate and growth of the juvenile Dark Sleeper. Results revealed that the 96-h LC50 was 13.79‰ salinity. MST and ST50 at 32‰ were 35.4 min and 37.0 min, respectively. In the 22-d trial, survival rate and specific growth rate (SGR) decreased with salinity. Survival rate of groups in 8‰ and 10‰ salinity were significantly lower than that of other groups. The SGR for body length and body weight of the 10‰ group was significantly lower than that of the othe...

To determine the optimal condition of photoperiod for embryo development and larval culture of tawny puffer, Takifugu flavidus, the effects of photoperiod on egg hatching and the growth and survival of larvae from 3 to 23 d after hatching (dah) were assessed. The results show that photoperiodic responses varied with the developmental stage during the early development of tawny puffer. Photoperiod did not significantly affect the hatch rate, viability of 24 h post‐hatch larvae, and total mortality rate of tawny puffer embryos; however, it affected the incubation period, which significantly increased with increasing photoperiod from 6 to 24 h. The shortest incubation period was predicted to occur at 3.56 h day length from the quadratic relationship. However, photoperiod strongly affected the growth and survival of the tawny puffer larvae from 3 to 23 dah. Increasing the day length resulted in improvement of the larval growth and survival within the 0–12 h day length range; however, beyond the 12 h day length, a longer day length was not beneficial, and a 24 h continuous light had a negative effect on growth. From the quadratic relationships, the highest growth and survival rates were predicted to occur at 14.16 h and 17.74 h day length, respectively. Therefore, the optimal photoperiods for tawny puffer embryos and larvae were 3–6 and 12–18 h day length, respectively. The results of this study are useful in increasing the production of the species during incubation and larval culture.

Tawny puffer Takifugu flavidus is a species found in China considered to have potential for aquaculture. Experiments were conducted to determine the optimal temperature for its incubation and larval culture. Fertilized eggs collected from cultured broodstocks that were induced to ovulate with a [d-Ala6-Pro9-Net]-luteinizing hormone-releasing hormone analogue were inseminated. The effect of temperature (19, 20, 23, 26 and 29 °C) on the hatch rate, incubation period, viability of 24 h post-hatch larvae and total mortality rate was assessed. The effect of temperature (20, 23, 26 and 29 °C) on the growth and survival of larvae from 3 to 19 days after hatching (dah) was also assessed. The results showed that the optimal temperature for successful development of fertilized eggs ranged from 23 to 26 °C, and the highest hatch rate, the optimal viability of 24 h post-hatch larvae and the lowest total mortality rate were all predicted using quadratic equations. The relationship between temperature and the incubation period of tawny puffer eggs was determined using the effective degree-day model. The temperature at developmental zero (t0) was 11.34 °C, and the sum of effective degree-days (k) was 52.356. The survival rate of tawny puffer larvae at 20 °C was significantly lower than among 23, 26 and 29 °C, whereas the survival rate was not significantly different from that at 23, 26 and 29 °C. The larval growth rate increased rapidly as the temperature increased, showing a linear relationship in the range of temperatures investigated. The optimal temperature for larval culture ranged from 23 to 29 °C.

The effects of photoperiod, temperature, and salinity on growth and survival of obscure puffer Takifugu obscurus larvae were determined from 3 to 19 days after hatching (dah). The results showed that the optimal photoperiod for obscure puffer larvae was under continuous light conditions (24 h light:0 h dark). Increasing daylength resulted in improved larval growth and survival. Larvae cultured under total darkness grew very slowly and even negatively, and all died within 12 days (15 dah). The optimal and critical high temperatures for obscure puffer larvae were at 22–23 and 32 °C, respectively. The specific growth rates (SGR) of obscure puffer larvae increased with an increase in temperature from 20 to 29 °C, while no corresponding increase in SGR was observed for temperatures from 29 to 32 °C. Larval survival rate significantly decreased when the temperature increased from 23 to 32 °C, and there was a tendency for a low survival rate at 20 °C. A high salinity (25‰) resulted in reduced larval growth and survival probabilities. The highest survival and specific growth rates were both predicted to occur at 8‰ to 10‰ based on quadratic equations. High SGR (5.71–6.14% d − 1 ) and survival rates (> 90%) were found within a wide salinity range (0–20‰). The optimal and suitable salinity ranges of larviculture were 8–10‰ and 0–20‰, respectively. Therefore, obscure puffer larvae can feasibly be cultured in brackish water (0–20‰) existing in majority of coastal areas.

The respiratory rates of Tawny puffer Takifugu flavidus juvenile were measured at four temperatures (20, 23, 26 and 29 °C) and seven salinities (5, 10, 15, 20, 25, 30 and 35 g L−1). The results showed that both temperature and salinity significantly affected the oxygen consumption of tawny puffer juvenile. The oxygen consumption rate (OCR) increased significantly with an increase in the temperature from 20 to 29 °C. Over the entire experimental temperature range (20–29 °C), the Q10 value was 1.59, and the lowest Q10 value was found between 23 and 26 °C. The optimal temperature for the juvenile lies between 23 °C and 26 °C. The OCR at 25 g L−1 was the highest among all salinity treatments. The OCRs show a parabolic relationship with salinity (5–35 g L−1). From the quadratic relationship, the highest OCR was predicted to occur at 23.56 g L−1. The optimal salinity range for the juvenile is from 23 to 25 g L−1. The results of this study are useful towards facilitating an increase in the production of the species juvenile culture.

Tawny puffer Takifugu flavidus is a fish species that has aquaculture potential in China because of its high market value. To determine the optimal condition of salinity for embryo development and larval culture of the species, the effects of salinity (0‰, 5‰, 10‰, 15‰, 20‰, 25‰, 30‰, 35‰, 40‰, and 45‰) on egg hatching and the survival and growth of larvae at 3–23 days post-hatch (dph) were assessed. Embryonic hatching rates were above 70% at salinities of 5‰ to 45‰, and all embryos at 0‰ died 4 days after fertilization. Survival rates (> 75%) of larvae at 24 h post-hatch at salinities of 10‰ to 40‰ were significantly higher than that at salinities of 5‰ and 45‰. The highest hatching rates and lowest percentage of mortalities occurred at salinities of 10‰ to 20‰. Results suggest that the embryos can tolerate a wide range of salinity (10–40‰), and optimal range of salinity for embryo development is between 10‰ and 20‰. The time of egg hatching was not influenced by salinity. Larvae of tawny puffer continued to survive until Day 23 of post-hatch at salinities of 5‰ to 35‰, but all larvae died within 20 dph at 45‰. The highest survival rate occurred at salinities of 15‰ to 35‰, and the highest growth rate was found at salinities of 15‰ to 25‰. The results suggest that the optimal salinity for larval survival and growth is between 15‰ and 25‰.